. ..

C()

(/N

ITIH

PS

YC

HO

LOG

Y 1

8,86 (1986)

0010

-028

5/86

$7.

50C

o"yr

i~hl

~ 1

9II~

hy

Aca

dem

ic P

re...

Inc,

All

ri~h

.. or

r."

rodu

clio

n in

any

ror

m r

e""r

yed.

MC

CLE

LLA

ND

AN

D E

LMA

N

Cm

"'I'1

?i.f

!-M

elltm

U"i,

'er,f

;/Y

the

abili

ty to

trad

e cu

es o

ff a

gain

st e

ach

othe

r in

pho

nem

e id

entif

icat

ion.

At t

hew

ord

leve

l. th

e m

odel

cap

ture

s Ih

e m

a.io

r po

sitiv

e fe

atur

e of

Mar

slen

-Wils

on

CO

HO

RT

mod

el o

f spe

ech

perc

eptio

n. in

that

it s

how

s im

med

iate

sen

sitiv

ity to

info

rmat

ion

favo

ring

one

wor

d or

set

of w

ords

ove

r ot

hers

. At t

he s

ame

time,

itov

erco

mes

a d

iffi

culty

with

the

CO

HO

RT

mod

el: i

t can

rec

over

fro

m u

nder

spec

-, i

fica

lion

or m

ispr

onun

ciat

ion

of a

wor

d's

begi

nnin

g. T

RA

CE

II

also

use

s le

xica

lin

form

atio

n to

seg

men

t a s

trea

m o

f sp

eech

into

a s

eque

nce

of w

ords

and

to f

ind

wor

d be

ginn

ings

and

end

ings

, and

it s

imul

ates

a n

umbe

r of

rec

ent f

indi

ngs

rela

ted

to th

ese

poin

ts. T

he T

RA

CE

mod

el h

as s

ome

limita

tions

, but

we

belie

ve it

is a

step

tow

ard

a ps

ycho

logi

cally

and

com

puta

tiona

lly a

dequ

ate

mod

el o

f th

e pr

oces

sof speech perception. ~

1986

Aca

dem

ic P

re..,

Inc,

The

TR

AC

E M

odel

of S

peec

h P

erce

ptio

n

JAM

ES

L. M

CC

LELL

AN

D

AN

DC

onsi

der

the

perc

eptio

n of

the

phon

eme

/g/ i

n th

e se

nten

ce "

She

re-

ceiv

ed a

val

uabl

e gi

ft; "

The

re a

re a

larg

e nu

mbe

r of

cue

s in

this

sen

tenc

eto

the

iden

tity

of th

is p

hone

me,

Fir

st, t

here

are

the

acou

stic

cue

s to

the

iden

tity

of th

e /g

/ its

elf,

Sec

ond.

the

othe

r ph

onem

es in

the

sam

e w

ord

prov

ide

anot

her

sour

ce o

f cu

es. f

or if

we

know

the'

res

t of t

he p

hone

mes

in th

is w

ord.

ther

e ar

e on

ly a

few

pho

nem

es th

at c

an f

orm

a w

ord

with

, them, Third. the semantic and syntactic context further constrain the

poss

ible

wor

ds w

hich

mig

ht o

ccur

. and

thus

lint

it st

ill f

urth

er th

e po

ssib

lein

terp

reta

Jion

of

the

firs

t pho

nem

e in

"gi

ft,

The

re is

am

ple

evid

ence

that

all

of th

ese

diffe

rent

sou

rces

of i

nfor

-m

atio

n ar

e us

ed in

rec

ogni

zing

wor

ds a

nd th

e ph

onem

es th

ey c

onta

in,

In~

eed.

as

Col

e an

d R

udni

cky (1983) have recently noted. these basic

fact

s w

ere

desc

ribed

in e

arly

.exp

erim

ents

by

Bag

ley

(190

0) o

ver

80 y

ears

ago,

Col

e an

d R

udni

cky

poin

t out

that

rec

ent w

ork

(whi

ch w

e c~

msi

der

in d

etai

l bel

ow)

has

adde

d cl

arity

and

det

ail t

o th

ese

basi

c fi

ndin

gs b

utha

s no

t lea

d to

a th

eore

tical

syn

thes

is th

at p

rovi

des

a sa

tisfa

ctor

y ac

coun

tof

thes

e an

d m

any

othe

r ba

sic

aspe

cts

of s

peec

h pe

rcep

tion,

In th

is p

aper

. we

desc

ribe

a m

Ode

l who

se p

rim

ary

purp

ose

is to

acc

ount

for

the

inte

grat

ion

of m

ultip

le s

ourc

es o

f in

form

atio

n. o

r co

nstr

aint

, in

spee

ch p

erce

ptio

n, T

he m

odel

is c

onst

ruct

ed w

ithin

a f

ram

ewor

k w

hich

appe

ars

to b

eid

eal f

or th

e ex

ploi

tatio

n of

sim

',lta

neou

s. a

nd o

ften

mut

ual,

cons

trai

nts.

Thi

s fr

amew

ork

is th

e in

tera

ctiv

e ac

tivat

ion

fram

ewor

k(M

cCle

lland

& R

umel

hart

. 198

1; R

umel

hart

& M

cCle

lland

. 1981. 1982),

Thi

s ap

proa

ch g

rew

out

of

a nu

mbe

r of

ear

lier

idea

s. s

ome

com

ing

firs

tfr

om r

esea

rch

on s

poke

n la

ngua

ge r

ecog

nitio

n (M

arsl

en-W

ilson

& W

elsh

.19

78; M

orto

n. 1

969;

Red

dy. 1

976) and others arising from m

ore

gene

ral

cons

ider

atio

ns o

f in

tera

ctiv

e pa

ralle

l pro

cess

ing

(And

erso

n. 1

977;

Gro

ss-

berg

. 197

8; M

cCle

lland

. 197

9),

Acc

ordi

ng to

the

inte

ract

ive-

activ

atio

n ap

proa

ch. i

nfor

mat

ion

pro-

cess

ing

take

s pl

ace

thro

ugh

the

exci

tato

ry a

nd in

hibi

tory

inte

ract

ions

amon

g a

larg

e nu

mbe

r of

pro

cess

ing

elem

ents

cal

led

units

, Eac

h un

it is

a ve

ry s

impl

e pr

oces

sing

dev

ice,

It s

tand

s fo

r a

hypo

thes

is a

bout

the

inpu

t bei

ng p

roce

ssed

. The

act

ivat

ion

of a

uni

t is

mon

oton

ical

ly r

elat

ed

,. q, ~

JEF

FR

EY

L. E

LMA

N

U"i

t'er.fi/y of C(/l((omi(/. Stili Dif!1!O

We

desc

ribe

a m

odel

cal

led

the

TR

AC

E m

odel

of

spee

ch p

erce

ptio

n. T

he m

odel

is b

ased

on

the

prin

cipl

es o

f in

tera

ctiv

e ac

tivat

ion.

Inf

orm

atio

n pr

oces

sing

take

spl

ace

thro

ugh

the

e xci

tato

ry a

nd in

hibi

tory

inte

ract

ions

of

a la

rge

num

ber

ofsimple processing u

rtits

, eac

h w

orki

ng c

ontin

uous

ly to

upd

ate

its o

wn

activ

atio

non

the

basi

s of

the

activ

atio

ns o

f ot

her

units

to w

hich

it is

con

nect

ed. T

he m

odel

is c

alle

d th

e T

RA

CE

mod

el b

ecau

se th

e ne

twor

k of

uni

ts f

orm

s a

dyna

mic

pro

-cessing structure called "the Trace."

whi

ch s

erve

s at

onc

e as

the

perc

eptu

alpr

oces

sing

mec

hani

~m

and

as

the

syst

ems

wor

king

mem

ory.

The

mod

el is

in-

stan

tiate

d in

two

sim

ulat

ion

prog

ram

s. T

RA

CE

I, d

escr

ibed

in d

etai

l els

ewhe

re,

deals with short seg~ents orreal speech. and suggests a m

echa

nism

for

cop

ing

with

the

fact

that

the

cues

to th

e id

entit

y, o

f pho

nem

es v

ary

as a

fun

ctio

n of

cont

ext.

TR

AC

E II

_th

e fo

cus

of th

is a

rtic

le, s

imul

ates

a la

rge

num

ber

of e

mpi

rica

lfin

ding

s on

the

perc

:ept

ion

of p

hone

mes

and

wor

ds a

nd o

n th

e in

tera

ctio

ns o

fph

onem

e ;m

d w

ord

perc

eptio

n. A

t the

pho

nem

e le

vel,

TR

AC

E I

I si

mul

ates

the

innu

ence

of l

exic

al j

nfor

mat

ion

on th

e id

entif

icat

ion

of p

hone

mes

and

acc

ount

sfor Ihe fact that le

xic:

ial e

ffect

s ar

e fo

und

unde

r ce

rtai

n co

nditi

ons

but n

ot o

ther

s.T

he m

odel

als

o sh

ows

how

kno

wle

dge

of p

hono

logi

cal c

onst

rain

ts c

an b

e em

-bo

died

in p

artic

ular

lexi

cal i

tem

s bu

t can

stil

l be

used

to in

nuen

ce p

roce

ssin

g of

nove

l. no

nwor

d ul

lera

nces

. The

mod

el a

lso

exhi

bits

cat

egor

ical

per

cept

ion

and

The

wor

k re

port

ed h

ere

was

sup

port

ed in

par

t by

a co

ntrd

ct fr

om th

e O

ffice

of N

aval

Research CN-

tKK

II4-

!l2-

'13741. in part by a grant from the National Science Foundation

IHN

S-79

-240

621.

and

in p

art b

y a

.Res

earc

h Sc

ient

ists

Car

eer

Dev

elop

men

t Aw

ard

to th

efi

rst a

utho

r fr

om th

e N

atjo

nalln

stitu

te o

f M

enta

l Hea

lth (

5-K

OI-MHOO3851. We thank

Dr.

Joan

ne M

iller

for

a ve

ry u

5efu

l dis

cuss

ion

whi

ch in

spire

d us

to w

rite

this

art

icle

in it

s pr

esen

tfo

rm. D

avid

Pis

oni w

as e

~tre

mel

y he

lpfu

l in

mak

ing

us d

eal m

ore

fully

with

sev

eral

impo

rtan

tis

sues

, and

in .I

erlin

g us

to a

larg

e nu

mbe

r of

use

ful p

aper

s in

the

liter

atur

e, W

e al

so th

ank

Dav

id R

umel

hart

for

use~

ul d

iscu

ssio

ns d

urin

g th

e de

velo

pmen

t of t

he b

asic

arc

hite

ctur

e of

TR

AC

E a

nd E

ileen

Con

way

, Mar

k Jo

hnso

n. D

ave

Pare

, and

pod

ul S

mith

for

thei

r as

sist

ance

in p

rogr

amin

g an

d gr

aphi

cs. S

end

requ

esls

for

rep

rint

s to

Jam

es L

McC

lella

nd. D

epar

tmen

tof

I)sy

chol

ogy.

Car

negi

e..'.

Mel

lon

Uni

vers

ity. S

chen

ley

Par

k. P

illsb

urgh

, PA

152

13.

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

to th

e st

reng

th o

f th

e hy

poth

esis

for

whi

ch th

e un

it st

ands

, Con

stra

ints

amon

g hy

poth

eses

are

rep

rese

nted

by

conn

ectio

ns. U

nUs

whi

ch a

re m

u-tu

ally

con

sist

ent a

re m

utua

lly e

xcita

tory

, and

uni

ts th

at a

re m

utua

lly in

-co

nsis

tent

are

mut

ually

inhi

bito

ry. T

hus,

the

unit

for

/g/ h

as m

utua

llyex

cita

tory

con

nect

ions

with

uni

ts f

or w

ords

con

tain

ing

/g/,

and

has

mu-

tual

ly in

hibi

tory

con

nect

ions

with

uni

ts f

or o

ther

pho

nem

es, W

hen

the

activ

atio

n of

a u

nit e

xcee

ds s

ome

thre

shol

d ac

tivat

ion

valu

e, it

beg

ins

toinfluence the

activ

atio

n of

oth

er u

nits

via

its

outg

oing

con

nect

ions

; the

stre

ngth

of

th~s

e si

gnal

s de

pend

s on

the

degr

ee o

f th

e se

nder

s ac

tivat

ion,

The

sta

te o

f the

sys

tem

at a

giv

en p

oint

in ti

me represents the current

stat

us o

f the

var

ious

pos

sibl

e hy

poth

eses

abo

ut th

e in

put;

info

rmat

ion

proc

essi

ng a

mou

nts

to th

e ev

olut

ion

of th

at s

tate

, ove

r tim

e, T

hrou

ghou

tthe course

of

proc

essi

ng, e

ach

unit

is c

ontin

ually

rec

eivi

ng in

put f

rom

othe

r un

its, c

ontin

ually

upd

atin

g its

act

ivat

ion

on th

e ba

sis

of th

ese

inpu

ts,

and,

if it

is o

ver

thre

shol

d, i

t is

cont

inua

lly s

endi

ng e

xcita

tory

and

inhi

b-ito

ry s

igna

ls to

oth

er u

nits

. Thi

s " i

nter

activ

e-ac

tivat

ion

" ,p

roce

ss a

llow

sea

ch h

ypot

he~

is b

oth

to c

onst

rain

and

be

cons

trai

ned

by o

ther

mut

ually

cons

iste

nt o

r in

cons

iste

nt h

ypot

hese

s,

Cri

teri

ll lI

nd C

olls

tmill

ts O

il M

odel

Dev

elop

men

t

The

re a

re g

ener

ally

two

kind

s of

mod

els

of th

e sp

eech

per

cept

ion

pro-

cess

, One

kin

d of

mod

el, w

hich

gro

ws

out o

f speech engineering and

artif

ical

inte

llige

nce,

atte

mpt

s to

pro

vide

a m

achi

ne s

olut

ion

to th

epr

oble

m o

f s~

eech

rec

ogni

tion,

Exa

mpl

es o

f th

is k

ind

of m

odel

are

HE

AR

SA

Y (

Erm

an &

Les

ser,

198

0; R

eddy

, Erm

an, F

enne

ll. &

Nee

ly,

1973

) H

WIM

(Wol

f &

Woo

ds, 1

978)

, HA

RPY

(L

ower

re, 1

976)

, and

LA

FS/S

CR

IBE

R (

Kla

tt, 1

980)

, A s

econ

d ki

nd o

f m

odel

, gro

win

g ou

t of

expe

rimen

tal ~

sych

olog

y, a

ttem

pts

to a

ccou

nt fo

r as

pect

s of

psy

chol

og-

ical

dat

a on

the

perc

eptio

n of

spe

ech.

Exa

mpl

es o

f th

is c

lass

of

mod

els

incl

ude

Mar

sl~

n-W

ilson

s C

OH

OR

T M

odel

(M

arsl

en- W

ilson

& T

yler

,19

80; M

arsl

en~

Wils

on &

Wel

sh, 1

978;

Nus

baum

& S

iow

iacz

ek, 1

982)

;M

assa

ros

feat

ure

inte

grat

ion

mod

el (

Mas

saro

, 198

1; M

assa

ro &

Ode

n,I

980a

, 198

0b; O

den

& M

assa

ro, 1

978)

; Col

e an

d Ja

kim

ik' s

(1978, 1980)

mod

el o

f au

dito

ry w

ord

proc

essi

ng, a

nd th

e m

odel

of

audi

tory

and

pho

-ne

tic m

emor

y es

pous

ed b

y Fu

jisak

i and

Kaw

ashi

ma

(196

8) a

nd P

ison

i(1973, 1975).

Eac

h ap

proa

ch h

onor

s a

diff

eren

t cri

teri

on f

or s

ucce

ss. M

achi

nemodels are ju4ged in terms of actual performance in

rec

ogni

zing

rea

lsp

eech

. Psy

chol

ogic

al m

odel

s ar

e ju

dged

in te

rms

of th

eir

abili

ty to

ac-

coun

t for

det

ails

of

hum

an p

erfo

rman

ce in

spe

ech

reco

gniti

on, W

e ca

llthese two criteria

ompi

llllti

mw

i an

d pj

iych

olog

;cal

ad

equa

cy.

In e

xten

ding

the

inte

ract

ive

activ

atio

n ap

proa

ch to

spe

ech

perc

eptio

n,w

e ha

d es

sent

ially

two

ques

tions

: Firs

t, co

uld

the

inte

ract

ive-

activ

atio

n

appr

oach

con

trib

ute

tow

ard

the

deve

lopm

ent o

f a c

ompu

tatio

nally

suf

fi-ci

ent f

ram

ewor

k fo

r sp

eech

per

cept

ion?

Sec

ond

, cou

ld it

acc

ount

for

wha

tis

kno

wn

abou

t the

psy

chol

ogy

of s

peec

h pe

rcep

tion?

In

shor

t, w

e w

ante

dto

kno

w, w

as th

e ap

proa

ch f

ruitf

ul, b

oth

on c

ompu

tatio

nal a

nd p

sych

o-lo

gica

l gro

unds

.T

wo

fact

s im

med

iate

ly b

ecam

e ap

pare

nt. F

irst

, spo

ken

lang

uage

intr

o-du

ces

man

y ch

alle

nges

that

mak

e it

far

from

cle

ar h

ow w

ell t

he in

tera

c-tiv

e-ac

tivat

ion

appr

oach

will

ser

ve w

hen

exte

nded

fro

m p

rint

to s

peec

h.Se

cond

, the

app

roac

h its

elf i

s to

o br

oad

to p

rovi

de a

con

cret

e m

odel

,w

ithou

t fur

ther

ass

umpt

ions

, Her

e w

e re

view

sev

eral

fac

ts a

bout

spe

ech

that

pla

yed

a ro

le in

sha

ping

the

spec

ific

ass

umpt

ions

em

bodi

ed in

TR

AC

E.

Som

e Im

port

ant F

acts

abo

ut S

peec

h

Our

inte

ntio

n he

re is

not

to p

rovi

de a

n ex

tens

ive

surv

ey o

f th

e na

ture

of s

peec

h an

d its

per

cept

ion,

but

rat

her

to p

oint

to s

ever

al fu

ndam

enta

las

pect

s of

spe

ech

that

hav

e pl

ayed

impo

rtan

t rol

es in

the

deve

lopm

ent

of th

e m

odel

we

desc

ribe

'her

e, A

ver

y us

eful

dis

cuss

ion

of s

ever

al o

fth

ese

poin

ts is

ava

ilabl

e in

Kla

tt (1

980)

.T

empo

ral n

atur

e of

the

speec'h stimulus,

It d

oes

not,

of c

ours

e, ta

ke a

scie

ntis

t to

obse

rve

one

fund

amen

tal d

iffe

renc

e be

twee

n sp

eech

and

prin

t: sp

eech

is a

sig

nal w

hich

is e

xten

ded

in ti

me,

whe

reas

pri

nt is

. ast

imul

us w

hich

is e

xten

ded

in s

pace

, The

seq

uent

ial n

atur

e of

spe

ech

pose

s pr

oble

ms

for

a m

odel

er, i

n th

at to

acc

ount

for

con

text

eff

ects

, one

need

s to

kee

p a

reco

rd o

f the

con

text

, It w

ould

be

a si

mpl

e m

atte

r to

proc

ess

spee

ch if

eac

h su

cces

sive

por

tion

of th

e sp

eech

inpu

t wer

e pr

o-ce

ssed

inde

pend

ently

of

all o

f th

e ot

hers

, but

in f

act,

this

is c

lear

ly ri

otth

e ca

se. T

he p

rese

nce

of c

onte

xt e

ffec

ts in

spe

ech

perc

eptio

n re

quir

esa

mec

hani

sm th

at k

eeps

som

e re

cord

of

that

con

text

, in

a fo

rm th

at a

llow

sit

to in

flue

nce

th~

inte

rpre

tatio

n of

sub

sequ

ent i

nput

.A

fur

ther

poi

nt, a

nd o

ne th

at h

as b

een

muc

h ne

glec

ted

in c

erta

in. m

odel

s, is

that

it is

not

onl

y pr

ior

cont

ext b

ut a

lso

subs

eque

nt c

onte

xtth

at in

flue

nces

per

cept

ion,

(T

his

and

rela

ted

poin

ts h

ave

rece

ntly

bee

nm

ade

by G

rosj

ean

& G

ee, 1

984;

Sal

asoo

& P

ison

i, 19

85; a

nd T

hom

pson

,19

84).

For

exa

mpl

e, G

anon

g (1

980)

rep

orte

d th

at th

e id

entif

icat

ion of a

sylla

ble-

initi

al s

peec

h so

und

that

was

con

stru

cted

to b

e be

twee

n /g

I an

d/k

/ was

;ptlu

ence

d by

whe

ther

the

rest

of t

he s

ylla

ble

was

Iisl

(as

inki

ss)

or /l

ftl (

as in

"gi

ft" )

, Suc

h' "

righ

t con

text

eft

ects" (Thompson,

1984) indicate that the pe

rcep

tion

of w

hat c

omes

in n

ow b

oth

infl

uenc

esan

d is

infl

uenc

ed b

y th

e pe

rcep

tion

of w

hat c

omes

in la

ter.

Thi

s fa

cisu

gges

ts th

at th

e re

cord

of

wha

t has

alr

eady

bee

n pr

esen

ted

cann

ot n

otbe

a s

tatic

rep

rese

ntat

ion

, but

sho

uld

rem

ain

in a

mal

leab

le f

orm

. sub

ject

to a

ltera

tion

as a

res

ult o

f inf

luen

ces

aris

ing

from

sub

sequ

ent c

on/e

x!.

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

::.-

LL

I

LL

I0:

:

:.....

..

wor

d se

gmen

tatio

n (B

ond

& G

arne

s, 1

980)

. and

cer

tain

seg

men

tatio

nde

cisi

ons

are

easi

ly in

flue

nced

by

cont

extu

al f

acto

rs (

Col

e &

Jak

iinik

.19

80),

Thu

s. it

is c

lear

that

wor

d re

cogn

ition

can

not c

ount

on

an a

ccur

ate

segm

enta

tion

of th

e ph

onem

e st

ream

into

sep

arat

e w

ord

units

. and

m

any

case

s su

ch a

seg

men

tatio

n w

ould

per

forc

e ex

clud

e fr

om o

ne o

f th

ew

ords

a s

hare

d se

gmen

t tha

t is

doin

g do

uble

dut

y in

eac

h of

two

succ

es-

sive

wor

ds, .

CO

fltex

t-se

miti

t'ity

of m

e.f,

A

thir

d m

ajor

fac

t abo

ut s

peec

h is

that

the

cues

for

a p

artic

ular

uni

t var

y co

nsid

erab

ly w

ith th

e co

ntex

t in

whi

chth

ey o

ccur

. For

exa

mpl

e, th

e tr

ansi

tion oftht second formant carries a

great deal of information about the identity of the stop consonant

Ibl

Fig,

I. b

ut th

at f

orm

ant w

ould

look

qui

te d

iffe

rent

had

the

sylla

ble

been

big"

or "

bog" instead of "

bag.

" T

hus

the

cont

ext .

in w

hich

a p

hone

me

occu

rs r

estr

uctu

res

the

cues

to th

e id

entit

y of

that

pho

nem

e (L

iber

man

,19

70).

The

ext

ent o

f th

e re

stru

ctur

ing

depe

..ds

on th

e un

it se

lect

ed a

ndon

the

part

icul

ar c

ue in

volv

ed. B

ut th

e pr

oble

m is

ubi

quito

us in

spe

ech,

Not

onl

y ar

e th

e cu

es f

or e

ach

phon

eme

dram

atic

ally

aff

ecte

d by

prec

edin

g an

d fo

llow

ing

cont

ext.

they

are

als

o al

tere

d by

. mor

e gl

obal

fact

ors

such

as

rate

of

spee

ch (

Mill

er. 1

981)

. by

mor

phol

ogic

al a

nd p

ro-

sodi

c fa

ctor

s su

ch a

s po

sitio

n in

wor

d an

d in

the

stre

ss c

onto

ur o

f th

eut

tera

nce.

and

by

char

acte

rist

ics

of th

e sp

eake

r su

ch a

s si

ze a

nd s

hape

of th

e vo

cal t

ract

. fun

dam

enta

l fre

quen

cy o

f th

e sp

eaki

ng v

oice

. and

dialectical variations (see Klatt, 1980. an

d R

epp

& L

iber

man

. 1984. for

disc

ussi

ons)

, .A

num

ber

of d

iffe

rent

app

roac

hes

to th

e pr

oble

m h

ave

been

trie

d by

diff

eren

t inv

estig

ator

s. O

ne a

ppro

ach

is to

try

to find relatively invar-

iant

-generally relational-

feat

ures

(e.

g.. S

teve

ns &

Blu

mst

ein.

198

1),

Ano

ther

appr

oach

has

bee

n to

red

efin

e th

e un

it so

that

it e

ncom

pass

esth

e co

ntex

t and

ther

efor

e be

com

es m

ore

inva

rian

t (Fu

jimur

a &

Lov

ins.

1982

; Kla

tt. 1

980;

Wic

kelg

ren,

196

9), W

hile

thes

e ar

e bo

th s

ensi

ble

and

usef

ul a

ppro

ache

s, th

e fi

rst h

as n

ot y

et s

ucce

eded

in e

stab

lishi

ng a

suf

-fi

cien

tly in

vari

ant s

et o

f cu

es, a

nd th

e se

cond

may

alle

viat

e bu

t doe

s no

tel

imin

ate

the

prob

lem

; eve

n un

its s

uch

as d

emis

ylla

bles

(F

ujim

ura

&L

ovin

s, .1

982)

, con

text

-sen

sitiv

e al

loph

ones

(W

icke

lgre

n, 1

969)

. or

even

who

le w

ords

(K

latt,

198

0) a

re s

till i

nflu

ence

d by

con

text

. We

have

cho

sen

to f

ocus

inst

ead

on a

thir

d po

ssib

ility

: tha

t the

per

cept

ual s

yste

m u

ses

info

rmat

ion

from

the

cont

ext i

n w

hich

an

utte

ranc

e oc

curs

to a

lter

con-

nect

ions

, the

reby

eff

ectiv

ely

allo

win

g th

e co

ntex

t to

retu

ne th

e pe

rcep

tual

mec

hani

sm o

n th

e fly

.Noise and indeterminacy

in

the speech signal.

To

com

poun

d al

l the

prob

lem

s al

lude

d to

abo

ve, t

here

is th

e ad

ditio

nal f

act t

hat s

peec

h is

ofte

ilpe

rcei

ved

unde

r le

ss th

an id

eal c

ircum

stan

ces.

Whi

le a

slo

w a

nd c

aref

ulsp

eake

r in

a q

uiet

roo

m m

ay p

rodu

ce s

uffic

ient

cue

s to

allo

w c

orre

ct

Lack

(~

r hOllllc!a/";es alld te

mpo

/"al

OI'C

'r/ap

. A

sec

ond

fund

amen

tal p

oint

abou

t spe

ech

.is th

at th

e cu

es to

successive units of speech frequently

over

lap

in ti

me.

The

pro

blem

is p

artic

ular

ly s

ever

e at

the

phon

eme

leve

l. A glance at a schematic speech spectrogram (Liberman. 19

70; F

ig. I

)cl

earl

y ill

ustr

ates

this

pro

blem

. The

re o

are

no s

epar

able

pac

kets

of i

nfor

-m

atio

n in

the

spec

trog

ram

like

the

sepa

rate

fea

ture

bun

dles

that

mak

e up

letlt

~rs

in p

rinte

d w

ords

,B

ecau

se o

f th

e ov

erla

p of

suc

cess

ive

phon

emes

. it i

s di

ffic

ult a

nd. w

ebelieve. counterproductive to try to divide the speech st

ream

up

into

sepa

rate

pho

nem

e un

its in

adv

ance

of

iden

tifyi

ng th

e un

its. A

num

ber

ofot

her

rese

arch

ers

(e.g., Fowler, 1984: Klatt, 1980) have m

ade

muc

h th

esa

me

poin

t. A

sup

erio

r ap

proa

ch s

eem

s to

be

to a

llow

the

phon

eme

ide;

n-

tific

atio

n pr

oces

s to

dam

ine

the

spee

ch s

trea

m fo

r ch

arac

teris

tic p

at-

tern

s. w

ithou

t fir

st s

egm

entin

g th

e st

ream

into

sep

arat

e u!

1its

,

The

pro

blem

of

over

lap

is le

ss s

ever

e fo

r w

ords

than

for

pho

nem

es.

but i

t doe

s no

t go

away

com

plet

e.ly

, In

rapi

d sp

eech

. wor

ds r

un in

to e

ach

othe

r. a

nd th

ere

are

no p

ause

s be

twe~

n w

ords

in r

unni

ng s

peec

h, T

o be

sure

. the

re a

re o

ften

cues

that

sig

nal t

he lo

catio

ns o

f bou

ndar

ies

betw

een

words-stop consona

hts

are

gene

rally

asp

irate

d at

the

begi

nnin

gs o

fst

ress

ed w

ords

in E

nglis

h. a

nd w

ord

initi

al v

owel

s ar

e ge

nera

lly p

rece

ded,

by g

lotta

l sto

ps. f

or e

xam

ple.

The

se c

ues

have

bee

n st

udie

d by

a n

umbe

rof

inve

stig

ator

s. p

artic

tllar

ly L

ehis

te (

e,g,. Lehiste, 1960, 1964) an

d N

ak-

atan

i and

col

labo

rato

rs, N

akat

ani a

nd D

ukes

(197

7) .

dem

onst

rate

d th

atpe

rcei

vers

exp

loit

som

e of

thes

e cu

es b

ut f

ound

that

cer

tain

utte

ranc

esdo

not

pro

vide

suf

fici

ent c

ues

to w

ord

boun

dari

es to

per

mit

relia

ble

per-

cept

ion

of th

e in

tend

ed u

ttera

nce,

Spe

ech

erro

rs o

ften

invo

lve

erro

rs o

f

TIM

EFI

G, I

, A ~

chcm

alic

spc

clrn

gram

ror

the ~yJlab'e "

bag,

" indicating the overtap or the

inro

rmat

ion

~pe

ciry

ing

the

diffe

rent

pho

nem

es. R

eprin

ted

with

per

mis

sion

rro

m L

iber

man

1197

01,

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

perc

eptio

n of

all

of th

e ph

onem

es in

an

utte

ranc

e w

ithou

t the

aid

of l

exic

alor

oth

er h

ighe

r le

vel c

onst

rain

ts, t

hese

con

ditio

ns d

o no

t alw

ays

obta

in,

People can correctly perceive speech under quite impoverished condi-

tions

, if

it is

sem

antic

ally

coh

eren

t and

syn

tact

ical

ly w

ell f

orm

ed (

G,

Mill

er, H

eise

, & L

icht

en, 1

951)

, Thi

s m

eans

that

the

spee

ch m

echa

nism

sm

ust b

e ab

le to

fun

ctio

n, e

ven

with

a h

ighl

y de

grad

ed s

timul

us, I

n pa

r-tic

ular

, as

Tho

mps

on (

1984

), N

orri

s (1

982)

, and

Gro

sjea

n an

d G

ee (

1984

)ha

ve p

oint

edou

t, th

e m

echa

nism

s of

spe

ech

perc

eptio

n ca

nnot

cou

nt o

nac

cura

te in

form

atio

n ab

out a

ny p

art o

f a

wor

d, A

s w

e sh

all s

ee, t

his

fact

pose

s a

serio

us p

robl

em fo

r on

e of

the

best

cur

rent

psy

chol

ogic

al m

odel

sof

the

proc

ess

of s

poke

n w

ord recognition (Marslen-Wilson & Welsh,

1978

),M

any

of th

e ch

arac

teri

stic

s th

at w

e ha

ve r

evie

wed

dif

fere

ntia

te s

peec

hfrom print-

at le

ast,

from

ver

y hi

gh q

ualit

y pr

int o

n w

hite

pap

er-b

utit

wou

ld b

e a:

mis

take

to th

ink

that

sim

ilar

prob

lem

s ar

e no

t enc

ount

ered

in o

ther

dom

ains

. Cer

tain

ly, t

he s

eque

ntia

l nat

ure

of s

poke

n in

put s

ets

. speech apart from vi

sion

, in

whi

ch th

ere

can

be s

ome

degr

ee o

f si

mul

-ta

neity

of p

erce

ptio

n, H

owev

er, t

he p

robl

ems

of il

l-defined boundaries,

cont

ext s

ells

itivi

ty o

f cu

es, a

nd n

oise

and

inde

term

inac

y ar

e ce

ntra

lpr

oble

ms

in v

isio

n ju

st a

s m

uch

as th

ey a

re in

spe

ech

(cf.

Bal

lard

, Hin

ton,

an

d S

ejno

wsk

i, 19

83; B

arro

w &

Ten

enba

um, 1

978; Marr, 19

82),

Thu

s,th

ough

the

mod

el w

e pr

esen

t her

e is

foc

usse

d on

spe

ech

perc

eptio

n, w

ew

ould

hop

e th

at th

e w

ays

in w

hich

it d

eals

with

the

chal

leng

es p

osed

by

the

spee

ch s

igna

l are

app

licab

le in

oth

er d

omai

ns.

activ

atio

n m

odel

s th

an w

ith m

odel

s in

any

oth

er computational frame-

wor

k, s

uch

as e

xper

t sys

tem

s or

pro

duct

ion

syst

ems.

.0

-

TH

E T

RA

CE

MO

DE

L

The

Im

porl

twce

of

the

Rig

ht A

rchi

tect

ure

All

four

of

the

cons

ider

atio

ns li

sted

abo

ve p

laye

d an

impo

rtan

t rol

e in

the

form

ulat

ion

of th

e T

RA

CE

mod

el. T

he m

odel

is a

n in

stan

ce o

f an

inte

ract

ive

activ

atio

n m

odel

, but

it is

. by

no m

eans

the

only

inst

ance

of

such

a m

odel

that

we

have

con

side

red

or th

at c

ould

be

cons

ider

ed, O

ther

form

ulat

ions

,we

cons

ider

ed s

impl

y di

d no

t app

ear

to o

ffer

a s

atis

fact

ory

fram

ewor

k fo

r de

alin

g w

ith th

ese

four

asp

ects

of

spee

ch (

see

Elm

an &

McC

lella

nd, ,

1984

, for

dis

cuss

ion)

. Thu

s, th

e T

RA

CE

mod

el h

inge

s as

muc

h on

the

part

icul

ar p

roce

ssin

g ar

chite

ctur

e it

prop

oses

for

spe

ech

perc

eptio

n as

it d

oes

on th

e in

tera

ctiv

e ac

tivat

ion

proc

esse

s th

at o

ccur

with

in th

is a

rchi

tect

ure.

Inte

ract

ive~

activ

atio

n m

echa

nism

s ar

e a

clas

s to

o br

oad

to s

tand

or

fall

on th

e m

erits

of a

sin

gle

mod

el, T

o th

e ex

tent

that

com

puta

tiona

lly a

ndps

ycho

logi

cally

ade

quat

e m

odel

s ca

n be

bui

lt w

ithin

the

fram

ewor

k, th

eat

trac

tiven

ess

of th

e fr

amew

ork

as a

who

le is

, of

cour

se, i

ncre

ased

, but

the

adeq

uacy

of

any

part

icul

ar m

odel

will

gen

eral

ly d

epen

d on

the

par-

ticul

ar a

ssum

ptio

ns th

at m

odel

em

bodi

es. I

t is

no d

iffer

ent w

ith in

tera

ctiv

e-

Ove

rvie

w

The

TR

AC

E m

odel

con

sist

s pr

imar

ily o

f a

very

larg

e nu

mbe

r of

uni

tsorganized into three levels,

thefealllre. phoneme,

and

It'o

rd

leve

ls, E

ach

unit

stan

ds f

or a

hyp

othe

sis

abou

t a p

artic

ular

per

cept

ual o

bjec

t occ

urri

ngat

!a p

artic

ular

poi

nt in

tim

e de

fined

rel

ativ

e to

the

begi

nnin

g of

the

ut-

.te

ranc

e.A

sm

all s

ubse

t of

the

units

in T

RA

CE

II,

the

vers

ion

of th

e m

odel

we

focu

s on

in th

is p

aper

, is

illus

trat

ed in

Fig

s, 2

,3,

and

4, E

ach

of th

e th

ree

figu

res

repl

icat

es th

e sa

me

set o

f un

its, i

llust

ratin

g a

diff

eren

t pro

pert

yof

the

mod

el in

eac

h ca

se. I

n th

e fi

gure

s, e

ach

rect

angl

e co

rres

pond

s to

a se

para

te p

roce

ssin

g un

it, T

he la

belS

on

the

units

and

alo

ng th

e si

dein

dica

te th

e sp

oken

obj

ect (

feat

ure,

pho

nem

e, o

r w

ord)

for

whi

ch e

ach

unit

stan

ds, T

he le

flan

d ri

ght e

dges

of

each

rec

tang

le in

dica

te th

e po

rtio

nof

the

inpu

t the

uni

t spa

ns,

At t

he f

eatu

re le

vel,

ther

e ar

e se

vera

l ban

ks o

f fe

atur

e de

tect

ors,

one

for

each

of

seve

ral d

imen

sion

s of

spe

ech

soun

ds. E

ach

bank

is r

eplic

ated

for'

each

of s

ever

dl s

ucce

ssiv

e m

omen

ts in

tim

e, o

r tim

e sl

ices

, At.

the

phon

eme

leve

l, th

ere

are

dete

ctor

s fo

r ea

ch o

f th

e ph

onem

es, T

here

ison

e co

py o

f ea

ch p

hone

me

dete

ctor

cen

tere

d ov

er e

very

thre

e tim

e sl

ices

.E

ach

unit

span

s si

x tim

e sl

ices

, so

units

with

adj

acen

t cen

ters

spa

n ov

er-

lapp

ing

rang

es o

f sl

ices

, At t

he w

ord

leve

l, th

ere

are

dete

ctor

s fo

r ea

chw

ord.

The

re is

one

cop

y of

eac

h w

ord

dete

ctor

cen

tere

d ov

er e

very

thre

efe

atur

e sl

ices

. Her

e ea

ch d

etec

tor

span

s a

stre

tch

of fe

atur

e sl

ices

cor

-re

spon

ding

to th

e en

tire

leng

th o

f ' th

e w

ord.

Aga

in, t

hen,

uni

ts w

ith a

d-ja

cent

cen

ters

spa

n ov

erla

ppin

g ra

nges

of s

lices

,In

put t

o th

e m

odel

, in

the

form

of

a pa

ttern

of

activ

atio

n to

be

appl

ied

to th

e un

its a

t the

fea

ture

leve

l, is

pre

sent

ed s

eque

ntia

lly to

the

feat

urc-

leve

l uni

ts in

suc

cess

ive

sliC

es, a

s it

wou

l(J if

it w

ere

a re

al s

peec

h st

ream

,un

fold

ing

in ti

me.

Moc

k-sp

eech

inpu

ts o

n th

e th

ree

illus

trat

ed d

imen

sion

sfo

r th

e ph

rase

"te

a cu

p" (/tik"p/

)' ar

e sh

own

in F

ig. 2

, A

t any

inst

ant,

inpu

t is

arri

ving

onl

y at

the

units

in o

ne s

lice

at th

e fe

atur

e le

vel.

In te

rms

of th

e di

spla

y in

Fig

, 2, t

hen,

we

can

visu

aliz

e th

e in

put b

eing

app

lied

tosu

cces

sive

slic

es o

f th

e ne

twor

k at

~uc

cess

ive

mom

ents

in ti

me.

How

ever

,it

is im

port

ant t

o re

mem

ber

that

all

the

units

are

con

tinua

lly in

volv

ed in

proc

essi

ng, a

nd p

roce

ssin

g of

the

inpu

t arr

ivin

g at

one

tim

e is

just

beg

in-

ning

as

the

inpu

t is

mov

ed a

long

to th

e ne

xt ti

me

slic

e.. T

he e

ntir

e ne

twor

k of

uni

ts is

cal

led

"the

Tra

ce,"

bec

ause

the

patte

rnof

act

ivat

ion

left

by

a sp

oken

inpu

t is

a tr

ace

of th

e an

alys

is o

f th

e in

put

at e

ach

of th

e th

ree

proc

essi

ng le

vels

. Thi

s tr

ace

is u

nlik

e m

~i\y

trac

es

TR

AC

E M

OD

EL

kAp

i~i~

i~i~

i~i~

i~i

. p

rlnr

~t~t

~t~t

~t'

1111

: , :

: : I

: III

1'rn

n:l:!

t!t!

,!t'

1111

1: , III

IIII I

'r~

r~r~

r~r~

I~.r

~I'

.L:-

a..

i~i~

i~i~

i~i~

i~i'

, - 11-

I:h;

ctl~

A. P

-Fl

o. 2

, A s

ubse

l of

the

units

in T

RA

CE

II.

Eac

h re

ctan

gle

repr

esen

ts a

dif

fere

nt u

nit,

The

labe

ls in

dica

te th

e ite

m fo

r w

hich

the

unit

stan

ds, a

nd th

e ho

rizo

ntal

edg

es o

f th

e re

ctan

gle

indi

cale

the

port

ion

of th

e T

race

spa

nned

by

each

uni

t. T

he in

put f

eatu

re s

peci

fica

tions

for

the

phra

se "

tea

cup.

" pr

eced

ed a

nd f

ollo

wed

by

sile

nce.

are

indi

cate

d fo

r th

e th

ree

iIIu

s-tr

ated

dim

ensi

ons

by th

e bl

acke

ning

of

the

corr

espo

ndin

g fe

atur

e un

its.

thou

gh, i

n th

at it

is d

ynam

ic, s

ince

it c

onsi

sts

of a

ctiv

atio

ns o

f pr

oces

sing

elem

ents

. and

thes

e pr

o ces

sing

ele

men

ts ' c

ontin

ue to

inte

ract

as

time

goes

on. T

he d

istin

ctio

n be

t!w

een

perc

eptio

n an

d (p

rim

ary)

mem

ory

is c

om-

plet

ely

blur

red~

.sin

ce th

e pe

rcep

t is

unfo

ldin

g in

the

sam

e st

ruct

ures

that

serv

e as

wor

king

mem

ory,

and

per

cept

ual p

roce

ssin

g of

old

er p

ortio

ns o

fth

e in

put c

ontin

ues

even

as

new

er p

ortio

ns a

re c

omin

g in

to th

e sy

stem

,T

hese

con

tinui

ng in

tera

ctio

ns p

erm

it th

e m

odel

to in

corp

orat

e rig

ht c

on-

text

eff

ects

, and

allo

w ~

he m

odel

to a

ccou

nt d

irec

tly f

or c

erta

in a

spec

ts

MC

CLE

LLA

ND

AN

D E

LMA

N

kAp

i~i~

i~i~

i~i~

i~i'

.L:-

a..

rlrA

r~'A

rArA

rlr'

I :1

11: I

II. :

I :

I : I

',t'

ttt'l,

!,t'l

t'11111: III! I

:1 :

I'II

r:

flf~

ilr:I

:I:I

'i~

i~i~

T~i

!i!i

!i'

~ ~

I~ :

, .

JI-

FIG. 3. The connections orthe unit for the phoneme

Ik/,

cent

ered

ove

r T

ime

Slic

e :!4

. The

rectangle for this unit is highlighted with a bold outline. The

Ikl

unit

has

mut

ually

exc

iluto

ryco

nnec

tions

to a

ll th

e w

ord-

and

fea

ture

- lev

el u

nits

col

ored

eith

er p

urtly

or

who

lly in

blu

ck;

The

mor

e co

lorin

g on

a u

nits

' rec

tang

le. t

he g

reat

er th

e st

reng

th o

f the

con

nect

ion.

The

Ikl

unit

has

mut

ually

inhi

bito

ry c

onne

ctio

ns to

all

of th

e ph

onem

e-le

vel u

nits

col

ored

pur

tlyor

who

lly in

gre

y. A

gain

. the

rel

ativ

e am

ount

of

inhi

bitio

n is

indi

cate

d by

the

exte

nt o

f th

eco

lori

ng o

f th

e un

it: it

is d

irec

tly p

ropo

rtio

nal t

o th

e ex

tent

of

the

tem

pora

l ove

rlap

of

the

units

. of short-te

rm m

emor

y, s

uch

as th

e fa

ct th

at m

ore

info

rmat

ion

can

bere

tain

ed f

or s

hort

per

iods

of

time

if it

han

gs to

geth

er to

for

m a

coh

eren

tw

hole

, Pr

oces

sing

take

s pl

ace

thro

ugh

the

exci

tato

ry a

nd inhibitory interac-

tions

of t

he u

nits

in th

e T

race

. Uni

ts o

n di

ffere

nt le

vels

that

are

mut

ually

cons

iste

nt h

ave

mut

ually

exc

itato

ry c

onne

ctio

ns. w

hile

uni

ts o

n th

e sa

me

TR

AC

E M

OD

EL

MCCLELLAND AND ELMAN

. kl\p

visu

al m

o.de

l elim

inat

e th

ese

betw

een-

leve

l inh

ibito

.ry

co.n

nect

ions

. sin

ceth

ese

co.n

nect

io.n

s ca

n in

terf

ere

with

suc

c~ss

ful u

se o

.f pa

rti~

1 in

form

atio

n(McClelland, 1985; McClelland

, 198

6), L

ike

thes

e ne

wer

ver

sio.

ns o

.f th

evi

sual

mo.

del,

TR

AC

E li

kew

ise

co.n

tain

s , n

o. b

etw

een-

leve

l inh

ibiti

o.n.

We

will

see

that

this

fea

ture

o.f

TR

AC

E p

lays

a v

ery

impo

.rta

nt r

ole

in it

sab

ility

to. s

imul

ate

a nu

mbe

r o.

f em

piri

cal p

heno

.men

a.SO

Im:e

s of

TR

AC

E' s

lIrL'hitectllre,

The

insp

iratio

.n fo

.r th

e ar

chite

ctur

eo.

f T

RA

CE

go.

es b

ack

to. t

he H

EA

RSA

Y S

peec

h un

ders

tand

ing

syst

em(E

rman

& L

esse

r, 1

980;

Red

dy e

t al..

197

3), H

EA

RSA

Y in

trod

uced

the

no.ti

o.n

o.f a

Bla

ckbo

.ard

, a s

truc

ture

sim

ilar

to. t

he T

race

in th

e T

RA

CE

mo.

del.

The

mai

n di

ffer

ence

is th

at th

e T

race

is a

dyn

amic

pro

cess

ing

stru

ctur

e th

at is

sel

f-up

datin

g, w

hile

the

Bla

ckbo

.ard

in H

EA

RSA

Y w

asa

pass

ive

data

str

uctu

re th

ro.u

gh w

hich

ant

o.no

.mo.

us p

roce

sses

sha

red

info

.rm

atio

.n.

The

arc

hite

ctur

e o.

fTR

AC

E b

ears

a s

tro.

ng r

esem

blan

ce to

. the

"ne

ural

spec

trog

ram

" propo.sed by Cro.wder (1978, 1981) to

. acc

o.un

t fo.

r in

terf

er-

ence

eff

ects

bet

wee

n su

cces

sive

item

s in

sho.rt-term memo.ry.

. Lik

e ~

UI'

Tra

ce, C

row

ders neural spectro.gram pro.vides a dy

nam

ic w

o.rk

ing

mem

o.ry

rep

rese

ntat

io.n

o.f

a sp

oken

inpu

t. T

here

are

two.

impo

.rta

nt d

if-fe

renc

es b

etw

een

the

Tra

ce a

nd C

ro.w

der

s ne

ural

spe

ctro

gram

, ho.

wev

er.

Firs

t o.f

all,

the

neur

al s

pect

ro.g

ram

was

ass

umed

o.n

ly to

. rep

rese

nt th

efr

eque

ncy

spec

trum

o.f

the

spee

ch w

ave

o.ve

r tim

e; th

e T

race

, o.n

the

othe

rha

nd, r

epre

sent

s th

e sp

eech

wav

e in

:term

s o.

fa la

rge

num

ber

o.f d

itfer

ent

feature dimensio.ns, as well as in terms of the ph

o.ne

mes

and

wo.

rds

co.n

-si

sten

t with

the

patte

rn o

.f activatio.n at the feature level, In this re

gard

TR

AC

E m

ight

be

seen

as

an e

xten

sio.

n o.

f the

neu

ral s

pect

rogr

am id

ea,

The

sec

o.nd

dif

fere

nce

is th

at C

row

der

po.s

tula

tes

inhi

bito

.ry

inte

ract

io.n

sbe

twee

n de

tect

o.rs

fo.r

spe

ctra

l co.

mpo

.nen

ts s

pace

d up

to. s

ever

al h

undr

edm

illis

eco.

nds

apar

t. T

hese

inhi

bito

.ry

Inte

ract

io.n

s ex

tend

co.

nsid

erab

ly fa

r-th

er th

an th

o.se

we

have

incl

uded

in th

e fe

atur

e le

vel o

.f th

e T

race

. Thi

sdi

ffer

ence

do.

es n

o.t r

efle

ct a

' dis

agre

emen

t with

Cro

wde

rsa

ssum

ptio

.ns.

Tho

.ugh

we

have

no.

t , fo

.und

it n

eces

sary

, to.

ado

.pt t

his

assu

mpt

io.n

to. a

c-co

unt f

o.r

the

phen

o.m

ena

we fo.cus on in this article, lateral extensio.n o.f

inhi

bitio

.n in

the

time

do.m

ain

mig

ht w

ell a

llo.w

the

TR

AC

E fr

amew

o.rk

to.

inco

.rpo

.rat

e m

any

o.f

the

find

ings

Cro

.wde

r di

scus

ses

in th

e tw

o. a

rtic

les

cite

d.

i~i~

i~i~

;~;~

i~i'

Q.)

Q.)

..c:.

a..

~ 10

ID S

hi

j i '?

.

FI(j

, 4. T

he c

onne

clio

ns o

f Ih

e hi

ghlig

hled

uni

l for

Ihe

hig

h va

lue

on I

he V

ocal

ic f

elllu

redi

men

sion

in T

ime'

Slic

e 9

and

for

Ihe

high

lighl

ed u

nil f

or I

he w

ord

Ik' p

l starling in Slice

24. E

xcila

lory

con

necl

ions

are

rf(

rese

nled

in b

lack

. inh

ibito

ry c

onne

ctio

ns in

gre

y. a

s in

Fig. 3.

leve

l tha

t are

inco

.nsi

sten

t hav

e m

utua

lly in

hibi

to.r

y co.nnectio.ns, All co.n-

nect

io.n

s ar

e bi

dire

ctio

.nal

. Bid

irect

io.n

al e

xcita

to.r

y an

d in

hibi

to.r

y'co

.n-

nect

io.n

s o.

f the

unit fo.r

Ikl

cent

ered

o.v

er F

eatu

re-s

lice

24 (

co.u

ntin

g fr

om. 0

) ar

e sho.wn ,n Fig. 3; co.nnectio.ns far the high

valu

e o.

f the feature

Vo.

calic

in S

lice

9.an

d fo

.r th

ewo.

rd Ik

" pl with the

Ikl

cent

ered

o.v

er S

lice

24 a

re s

ho.w

n i~

Fig

. 4.

The

inte

ract

ive

activ

atio

.n mo.del o.f visual w

ard

reco

.gni

tio.n

(M

c-C

lella

nd &

Rum

elha

rt, 1

981)

incl

uded

inhi

bito

.ry

co.n

nect

io.n

s be

twee

nea

ch u

nit o

.n th

e fe

atur

e le

vel a

nd le

tters

that

did

no.

t co.

ntai

n th

e fe

atur

e,an

d be

twee

n ea

ch le

tter

unit

and

the

wo.

rds

that

did

no.

t co.

ntai

n th

e le

tter.

Thu

s th

e un

its f

o.r

T in

the

firs

t let

ter

po.s

itio.

n in

hibi

ted

the

units

fo.r

all

wo.rds that did no

.t be

gin

with

T. H

o.wever, mo.re recent versio.ns

o.f

the

Con

text

-Sen

sitiv

e T

lIni

ngof

Pho

nem

e U

nits

The

co.

nnec

tio.n

s, b

etw

een

the

feat

ure

and

pho.

nem

e le

vel d

eter

min

ewhat pattern

of activations o.ver the feature units will mo.st slrongly ac-

tivate the detecto.r fo

.r e

ach

phon

eme.

To. co.pe with the fact that the

feat

ures

rep

rese

ntin

g ea

ch p

ho.n

eme

vary

acc

o.rd

ing

to. t

he p

ho.n

emes

sur

-ro

undi

ng th

em, t

he m

odel

adj

usts

the

conn

ectio

ns f

rom

uni

ts a

l the

fea

-tu

re le

vel t

o. u

nits

at t

he n

hone

me

leve

l as

a fu

nctio

n nf

Iu'tiv:llinn" al 'hI"

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

TRACE land TRACE

In d

evel

opin

g T

RA

CE

, and

i(l t

ryin

g to

test

its

com

puta

tiona

l and

psy

-ch

olog

ical

ade

quac

y, w

e fo

und

that

we

wer

e so

met

imes

led

in r

athe

rdi

ffer

ent d

irec

tions

, We

wan

ted

to s

how

that

TR

AC

E c

ould

pro

cess

rea

lsp

eech

, but

to b

uild

a m

odel

that

did

so

it w

as n

eces

sary

to w

orry

abo

utex

actly

wha

t fea

ture

s m

ust b

e ex

trac

ted

from

the

spee

ch s

igna

l, ab

out

diff

eren

ces

in d

urat

ion

of d

iffe

rent

fea

ture

s of

dif

fere

nt p

hone

mes

, and

abou

t how

to c

ope

with

the

way

s in

whi

ch f

eatu

res

and

feat

ure

dura

tions

vary as a function of context. Obviously, these are important pr

oble

ms,

wor

thy

of c

onsi

dera

ble

atte

ntio

n. H

owev

er, c

once

rn w

ith th

ese

issu

este

nded

to o

bscu

re a

ttent

ion

to th

e fu

ndam

enta

l pro

pert

ies

of th

e m

odel

and

the

mod

el's

abi

lity

to a

ccou

nt f

or b

asic

asp

ects

of

the

psyc

h(jlo

gica

l

data

obt

aine

d in

man

y ex

perim

ents

.T

o co

pe w

ith th

ese

conf

lictin

g go

als,

we

have

dev

elop

ed tw

o di

ffer

ent

vers

ions

of

the

mod

el, c

alle

d T

RA

CE

1 a

nd T

RA

CE

II,

Bot

h m

odel

s

spri

ng f

rom

the

sam

e ba

sic

assu

mpt

ions

, but

foc

us o

n di

ffer

ent a

spec

tsof

spe

ech

perc

eptio

n. T

RA

CE

1 w

as d

esig

ned

to a

ddre

ss s

ome

of th

ech

alle

nges

pos

ed b

y th

e ta

sk o

f rec

ogni

zing

pho

nem

es f

rom

rea

l spe

ech,

Thi

s ve

rsio

n of

the

mod

el is

des

crib

ed in

det

ail i

n E

lman

and

McC

lella

nd(i

n pr

ess)

. With

this

ver

sion

of

the

mod

el, w

e w

ere

able

to s

how

that

the

TR

AC

E f

ram

ewor

k co

uld

inde

ed b

e us

ed to

pro

cess

rea

l spe

ech-

albe

itfr

om a

sin

gle

spea

ker

utte

ring

isol

ated

mon

osyl

labl

es a

t thi

s po

int.

We

wer

e al

so a

ble

to d

emon

stra

te th

e ef

ficac

y of

the

idea

of a

djus

ting

feat

ure

to p

hone

me

conn

ectio

ns o

n th

e ba

sis

of a

ctiv

atio

ns p

rodu

ced

by s

ur-

roun

ding

con

text

. With

con

nect

ion

stre

ngth

adj

ustm

ent i

n pl

ace

' the

mod

el w

as a

ble

to id

entif

y th

e st

op c

onso

nant

in 9

0% o

f a

set b

f is

olat

edm

onos

ylla

bles

cor

rect

ly, u

p fr

om 7

9% w

ith a

n in

vari

ant s

et o

f co

nnec

-tio

ns. T

his

leve

l of

perf

orm

ance

is c

ompa

rabl

e to

wha

t has

bee

n ac

hiev

edby other machine-ba

sed

phon

eme

iden

tific

atio

n sc

hem

es (

e,g.

, Kop

ec,

1984

) an

d ill

ustr

ates

the

prom

ise

of th

e co

nnec

tion

stre

ngth

adj

ustm

ent

sche

me

for

copi

ng w

ith v

aria

bilit

y du

e to

loca

l pho

netic

con

text

. Ide

asfo

r ex

tend

iqg

the

conn

ectio

n st

reng

th a

djus

tmen

t sch

eme

to d

eal w

ith th

ew

ays

in w

hich

cue

s to

pho

nem

e id

entif

icat

ion

vary

with

glo

bal v

aria

bles

(rat

e, s

peak

er c

hara

cter

istic

s, e

Jc,)

are

con

side

red

in th

e ge

nera

l dis

cus-

sion

.T

RA

CE

II,

the

vers

ion

desc

ribe

d in

the

pres

ent p

aper

, was

des

igne

dto

acc

ount

prim

arily

for

lexi

cal i

nflu

ence

s on

pho

nem

e pe

rcep

tion

and

for

wha

t is

know

n ab

out o

n-lin

e re

cogn

ition

of

wor

ds, t

houg

h w

e us

e it

to il

lust

rate

how

cer

tain

oth

er a

spec

ts o

f ph

onem

e pe

rcep

tion

fall

out o

fth

e T

RA

CE

fra

mew

ork,

Thi

s ve

rsio

n of

the

mod

el is

act

ually

a s

impl

ifie

dve

rsio

n of

TR

AC

E 1

. Mos

t im

port

antly

, we

elim

inat

ed th

e co

nnec

tion-

stre

ngth

adj

ustm

ent f

acili

ty, a

nd w

e re

plac

ed th

e re

al s

peec

h in

puts

toT

RA

CE

I w

ith m

ock

spee

ch, T

his

moc

k sp

eech

inpu

t con

sist

ed o

f ov

er-

lapp

ing

but c

onte

xtua

lly in

vari

ant s

peci

fica

tions

of

the

feat

ures

of

suc-

cess

ive

phon

emes

, Obv

ious

ly, t

hen,

TR

AC

E I

I si

dest

eps

man

y fu

nda-

mental issues about speech, But it makes "it

muc

h ea

sier

to s

ee h

ow th

em

echa

nism

can

acc

ount

for

a nu

mbe

r of

asp

ects

of p

hone

me

and

wor

dre

cogn

ition

, A n

umbe

r of

furt

her

sim

plify

ing

assu

mpt

ions

wer

e m

ade

tofa

cilit

ate

exam

inat

ion

of b

asic

pro

pert

ies

of th

e in

tera

ctiv

e ac

tivat

ion

pro-

cess

es ta

king

pla

ce w

ithin

the

mod

el,

The

fol

l9w

ing

sect

ions

des

crib

e T

RA

CE

II

in m

ore

deta

il, F

irst

we

cons

ider

the

spec

ific

atio

ns o

f th

e m

ock-

spee

ch in

()ut

to th

e m

odel

, and

then

we

cons

ider

the

units

and

con

nect

ions

that

mak

e up

the

Tra

ce a

t

each

of t

he th

ree

leve

ls,

Moc

k-Sp

eech

Inp

uts

The

inpu

t to

TR

AC

E I

I w

as a

ser

ies

of s

peci

fica

tions

for

inpu

ts to

uni

tsat

the

feat

ure

leve

l, on

e fo

r ea

ch 2

5-m

s tim

e sl

ice

of th

e m

ock

utte

ranc

e,T

hese

spe

cific

atio

ns w

ere

gene

rate

d by

a s

impl

e co

mpu

ter

prog

ram

from

a se

quen

ce o

f to

-be-

pres

ente

d se

gmen

ts p

rovi

ded

by th

e hu

man

use

r of

the

sim

ulat

ion

prog

ram

. The

allo

wed

seg

men

ts c

onsi

sted

of

the

stop

con

-so

nant

s Ib

l, Ip

l, Id

l, It/

,lgI,

an

d Ik

l, the fricatives

Isl

and

ISI

sh" as in

ship

), the liquids

III

and

Irl,

and the vowels

Ia!

(as

in "

pot"

),

IiI

(as

in

beet

),

lul

(as

in "

boot

"), and

rI

(as

in "

but

).

rI

was

als

o us

ed to

repr

esen

t red

uced

vow

els

such

as

the

seco

nd v

owel

in "

targ

et." There

was

als

o a

"sile

nce"

segment represented by

I-I.

Sp

ecia

l seg

men

ts, s

uch

as a segment halfway between

Ibl

and

Ipl,

wer

e al

so u

sed;

thei

r pr

oper

ties

are

desc

ribed

in d

escr

iptio

ns o

f the

rel

evan

t sim

ulat

ions

,A

set

of

seve

n di

men

sion

s w

as u

sed

in T

RA

CE

lIto represent the

feat

ure-

leve

l inp

uts,

Fiv

e of

the'

dim

ensi

ons

(Con

sona

ntal

, Voc

alic

, Dif-

fuse

ness

, Acu

tene

ss, a

nd V

oici

ng)

wer

e ta

ken

from

cla

ssic

al w

ork

inph

onol

ogy

(Jak

obso

n, F

ant,

& H

alle

, 195

2), t

houg

h w

e tr

eat e

ach

of th

ese

dim

ensi

ons

as c

ontin

ua, i

n th

e sp

irit

ofO

den

and

Mas

saro

(197

8), r

athe

rth

an a

s bi

nary

fea

ture

s, A

six

th d

imen

sion

, Pow

er, w

as in

clud

ed b

ecau

seit

has

been

foun

d us

eful

for

phon

eme

iden

tific

atio

n in

var

ious

mac

hine

syst

ems

(e,g

., R

eddy

, 197

6), a

nd it

was

inco

rpor

ated

her

e to

add

an

ad-

ditio

nal d

imen

sion

to in

crea

se th

e di

ffer

entia

tion

of th

e vo

wel

s an

d co

n-so

nant

s, T

he s

even

th d

imen

sion

, the

am

plild

de o

f th

e bu

rst o

f no

ise

that

occu

rs a

t the

beg

inni

ng o

f w

ord

initi

al s

tops

, was

incl

uded

to p

rovi

de a

nad

ditio

nal b

asis

for

dist

ingu

ishi

ng th

e st

op c

onso

nant

s, w

hich

oth

erw

ise

diff

ered

fro

m e

ach

othe

r on

onl

y on

e or

two

dim

ensi

ons,

Of

cour

se, t

hese

phon

eme

leve

l in

prec

edin

g an

d fo

llow

ing

time

slic

es, F

or e

xam

ple,

whe

nthe phoneme

It I

is preceded or followed by the vowel

Iii,

the feature

pattern corresponding to the

It I

is very different than it is when the

It I

preceded or followed by another vowel, such as

la/.

Acc

ordi

ngly

, whe

n

the unit for

Iii

in a particular sl

ice:

is a

ctiv

e, it

cha

nges

the pattern of

connections for units for

It I

in

pre

cedi

ng a

nd fo

llow

ing

slic

es.

TR

AC

E M

OD

EL

dim

ensi

ons

an;:

inte

ntio

nal s

impl

ific

atio

ns o

f th

e re

al a

cous

tid s

truc

ture

of s

peec

h, in

muc

h th

e sa

me

way

that

the

font

use

d by

McC

lella

nd a

ndR

umel

hart

(19

81)

in th

e in

tera

ctiv

e-ac

tivat

ion

mod

el o

f vi

sual

wor

d re

c-og

nitio

n W

as a

n in

tent

iona

l sim

plifi

catio

n. o

f the

rea

l str

uctu

re o

f pr

int.

Eac

h di

men

sion

was

div

ided

into

eig

ht v

alue

ran

ges.

Eac

h ph

onem

ew

as a

ssig

ned

a va

lue

on e

ach

dim

ensi

on; t

he v

alue

s on

the

Voc

alic

, Oif

-fu

sene

ss, a

nd A

cute

ness

dim

ensi

ons

for

the

phon

emes

in th

e ut

tera

nce

!tik

.p!

are

show

n in

Fig

. 2, T

he f

ull s

et o

f va

lues

are

sho

wn

in T

able

I,N

umbe

rs in

the

cells

of t

he ta

ble

indi

cate

whi

ch v

alue

on

the

indi

cate

ddi

men

sion

was

mos

t str

ongl

y ac

tivat

ed b

y th

e fe

atur

e pa

ttern

for

the

indi

cate

d ph

onem

e, V

alue

s ra

nge

from

I

very low

to 8 =

very high,

The

last

two

dim

ensi

ons

wer

e al

tere

d fo

r th

e ca

tego

rica

l per

cept

ion

and

trad

ing

rela

tions

sim

ulat

ions

,V

alue

s w

ere

assi

gned

to a

ppro

xim

ate

the

valu

es r

eal p

hone

mes

wou

ldha

ve o

n th

ese

dim

ensi

ons

and

to m

ake

phon

emes

that

fall

into

the

. sam

eph

onet

ic c

ateg

ory

have

iden

tical

val

ues

on m

any

of th

e di

men

sion

s, T

hus,

.fo

r ex

ampl

e, a

ll st

op c

onso

nant

s w

ere

assi

gned

the

sam

e va

lues

on

the

Pow

er, V

ocal

ic, a

nd C

onso

nant

al d

imen

sion

s, W

e do

not

cla

im to

hav

eca

ptur

ed th

e de

tails

of p

hone

me

sim

ilarit

y ex

actly

, Ind

eed,

one

can

not

do s

o in

a fi

xed

feat

ure

set b

ecau

se th

e si

mila

ritie

s va

ry a

s a

func

tion

ofco

ntex

t. H

owev

er, t

he f

eatu

re s

ets

do h

ave

the

prop

erty

that

the

feat

ure

patte

rn f

or o

ne p

hone

me

is m

ore

sim

ilar

to th

e fe

atur

e pa

ttern

for

oth

erph

onem

es in

the

sam

e ph

gnet

ic c

ateg

ory

(sto

p, f

rica

tive,

liqu

id, o

r vo

wel

)th

an it

is to

the

patte

rns

for

phon

emes

in o

ther

cat

egor

ies.

Am

ong

the

stop

s, th

ose

phon

emes

sha

ring

pla

ce o

f ar

ticul

atio

n or

voi

cing

are

mor

esi

mila

r th

an th

ose

shar

ing

neith

er a

ttrib

ute.

The

cor

rela

tions

of

the

feat

ure

patte

rns

for

the

15 p

hone

mes

use

d ar

esh

own

in T

able

2. I

t is

thes

e co

rrel

atio

ns o

f th

e pa

ttern

s as

sign

ed to

the

~ -

!II :J

, !II

II:)

I:!

1.1:

1 is '"

:;;

'")

~ 1

!

"" ~

~~

~~

~ ~

~~

~~

I~

....

-D - -D

..., ~

"0 "1

r-; r-; I ~

0 -

;:::~

I~~~

~T

AB

LE I

Phon

eme

Feal

ure

Val

ues

Use

d in

TR

AC

E I

I

Phun

eme

Pow

Voc

alic

Dif

fuse

AC

Ule

CO

Ins.

Voi

ced

Our

s.

11.

Co,

r)

- "0

~ "

" on

II:

) ..

01 ,- :J,.

,r)

~ I~

;:::~

~

I~;::

:~~~

:;;

~8~~

~

00...

.

"! '")

~~ I

~

~ I

~~

~8 I

~~

~

~ 18

I ~~

~ I I ~"'!

"',

....

'")

r--

'") '"

).:.

:;;.

,

,r)

"ii .

,r) :0-

..c !II

..!!

.... !II

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

diff

eren

t pho

nem

es. r

athe

r th

an th

e ac

tual

val

ues

assi

gned

to p

artic

ular

phon

emes

or

even

the

labe

ls a

ttach

ed to

the

diff

eren

t moc

k-sp

eech

di-

men

sion

s. th

at d

eter

min

e th

e be

havi

or o

f the

sim

ulat

ion

mod

el.

sinc

e it

is th

ese

corr

elat

ions

that

det

erm

ine

how

muc

h an

inst

ance

of o

ne p

ho-

nem

e w

ill te

nd to

exc

ite th

e de

tect

or f

or a

noth

er,

The

feat

ure

patte

rns

wer

e co

nstr

u~t

ed in

suc

h a

way

that

it w

as p

ossi

ble

to c

reat

e fe

atur

e pa

ttern

s th

at w

ould

act

ivat

e tw

o di

ffere

nt p

hone

mes

inth

e sa

me

cate

gory

(st

op. l

iqui

d. f

rica

tive.

or vowel) to an equal extent

by a

vera

ging

the

valu

es o

f th

e tw

o ph

onem

es o

n on

e or

mor

e di

men

sion

s,In

this

way

, it w

as a

sim

ple

mat

ter

to m

ake

up a

mbi

guou

s in

puts

. hal

fway

betw

een

two

phon

times

. or

to c

onst

ruct

con

tinua

var

ying

bet

wee

n ' tw

oph

onem

es o

n on

e or

mor

e di

men

sion

s.T

he f

eatu

re s

peci

fica

tion

of e

ach

phon

eme

in th

e in

put s

trea

m e

xten

ded

over

II

time

slic

es o

f th

e in

put.

The

str

engt

h of

the

patte

rn g

rew

to a

peak

at t

he 6

th s

lic~

and

fell

off a

gain

. as

illus

trat

ed in

Fig

, 2, P

eaks

of

succ

essi

ve p

hone

mes

wer

e se

para

ted

by 6

slic

es, T

hus.

spe

cifi

catio

ns o

fsu

cces

sive

pho

nem

es o

verl

appe

d. a

s th

ey d

o in

rea

l spe

ech

(Fow

ler.

198

4;L

iber

man

, 197

0).

Gen

eral

ly. t

here

wer

e no

cue

s to

wor

d boundaries in the speech

stre

am- t

he fe

atU

lie s

peci

ficat

ion

for

the

last

pho

nem

e of

one

wor

dov

erla

pped

with

the

, fir

st p

hone

me

of th

e ne

xt in

just

the

sam

e w

ay f

eatu

resp

ecif

icat

ions

of

adj~

\cen

t pho

nem

es o

verl

ap w

ithin

wor

ds, H

owev

er. e

n-tir

e ut

tera

nces

pre

sent

ed to

the

mod

el fo

r pr

oces

sing

-whe

ther

they

wer

ein

divi

dual

syl

labl

es.,

wor

ds. o

r st

rings

of w

ords

-wer

e pr

eced

ed a

nd fo

l-lo

wed

by

sile

nce,

Sile

nce

was

nol

sim

ply

the

abse

nce

ofan

y in

put;

rath

er.

it w

as a

pat

tern

of

feat

ure

valu

es. j

ust l

ike

the

phon

emes

, Thu

s. a

nin

thva

lue

on e

ach

of th

e is

even

dim

ensi

ons

was

ass

ocia

ted

with

sile

nce,

The

seva

lues

wer

e ac

tual

ly o

utsi

de th

e ra

nge

of v

alue

s w

hich

occ

urre

d in

the

phon

emes

them

selv

es. s

o th

at th

e fe

atur

es o

f si

lenc

e w

ere

com

plet

ely

unco

rrel

ated

with

the

feat

ures

of

any

of th

e ph

onem

es u

sed,

The

Pho

nem

e Le

vel a

nd F

eatu

re- P

hone

me

Con

nect

ions

At t

he p

hone

me

leve

l. th

ere

is a

set

of detectors for each of the 15

phon

emes

list

ed a

bove

, In

addi

tion.

ther

e is

a s

et of detectors for the

pres

ence

of

sile

nce,

The

se s

ilenc

e de

tect

ors

are

trea

ted

like

all o

ther

phon

eme

dete

ctor

s. E

ach

mem

ber

of th

e se

t of

dete

ctor

s fo

r a

part

icul

arph

onem

e is

cen

tere

d ov

er a

diff

eren

t tim

e ~

;ce

at th

e fe

atur

e le

vel,

and

the

cent

ers

are

spac

ed th

ree

time

slic

es a

part

. The

uni

t cen

tere

d ov

er a

part

icul

ar s

lice

rece

ived

exc

itato

ry in

put f

rom

fea

ture

uni

ts in

a r

ange

of

slic

es, e

xten

ding

bot

h fo

rwar

d an

d ba

ckw

ard

from

the

slic

e in

whi

ch th

eph

onem

e un

it is

loca

ted,

It a

lso

send

s ex

cita

tory

fee

dbac

k do

wn

to th

esame feature units in the same range of slices.

The

con

nect

ion

stre

ngth

s be

twee

n th

e fe

atur

e-le

vel u

nits

and

a p

artic

-ul

ar p

hone

me-

leve

l uni

t exa

ctly

mat

ch th

e fe

atur

e pa

ttern

the

phon

eme

is g

iven

in it

s in

put s

peci

fica

tion,

Thu

s. a

s ill

ustr

ated

in F

ig. 3

. the

strengths of the connections between the node for

Ikl

cent

ered

ove

r T

ime

Slic

e 24

and

the

node

s at

the

feat

ure

leve

l are

exa

ctly

pro

port

iona

l to

the

patte

rn o

f in

put t

o th

e fe

atur

e le

vel p

rodu

ced

by a

n in

put s

peci

ficat

ion

containing the featur~s of

Ikl

cent

ered

in th

e sa

me

time

slic

e.T

here

are

inhi

bito

ry c

onne

ctio

ns b

etw

een

units

at t

he p

hone

me

leve

l.U

nits

inhi

bit e

ach

othe

r to

the

exte

nt th

at th

e sp

eech

obj

ects

they

sta

ndfo

r re

pres

ent a

ltern

ativ

e in

terp

reta

tions

of

the

cont

ent o

f th

e sp

eech

stre

am a

t the

sam

e po

int i

n th

e ut

tera

nce.

Not

e th

at. a

lthou

gh th

e fe

atur

esp

ecif

icat

ion

of a

pho

nem

e is

spr

ead

over

a w

indo

w o

f II

slic

es, s

ucce

s-si

ve p

hone

mes

in th

e in

put h

ave

thei

r , c

ente

rs 6

slic

es a

part

. Thu

s ea

chph

onem

e-le

vel u

nit i

s th

ough

t of a

s sp

anni

ng 6

feat

ure-

level slices. as

illus

trat

ed in

Fig

. 3. E

ach

unit

inhi

bits

oth

ers

in p

ropo

rtio

n to

thei

rov

erla

p, T

hus,

a p

hone

me

dete

ctor

inhi

bits

oth

er p

hone

me

dete

ctor

scen

-te

red

over

the

sam

e sl

ice

twic

e as

muc

h as

it in

hibi

ts d

etec

tors

cen

tere

d3

slic

es a

way

, and

inhi

bits

det

ecto

rs c

ente

red

6 or

mor

e sl

ices

aw

ay n

otat all, (

Fc'

lIlIIr

e Le

l'el V

nit.

f and

Co"

"ect

ion.

The

uni

ts a

t the

fea

ture

leve

l are

det

ecto

rs f

or f

eatu

res

of th

e sp

eech

stre

am a

t par

ticul

ar , m

omen

ts in

tim

e. I

n T

RA

CE

II.

ther

e w

as a

uni

t for

each of the nine values on each of the seven dimensions in each time

slic

e of

the

Tra

ce, T

he f

igur

es s

how

thre

e se

ts o

f fe

atur

e un

its in

sev

eral

time

slic

es, U

nits

for

fea

ture

s on

the

sam

e di

men

sion

with

in th

e sa

me

time

slic

e ar

e m

utua

lly in

hibi

tory

, Thu

s, th

e un

it fo

r th

e hi

gh v

alue

of

the

Voc

alic

dim

ensi

on in

Tim

e Sl

ice

9 in

hibi

ts th

e un

its f

or o

ther

val

ues

onth

e sa

me

dilJ

lens

ion

in th

e sa

me

time

slic

e. a

s ill

ustr

ated

in F

ig. 4

. Thi

sfig

ure

also

illu

stra

tes

the

mut

ually

exc

itato

ry c

onne

ctio

ns o

f th

is s

ame

feat

ure

unil

with

uni

ts a

t the

pho

nem

e le

vel.

In th

e ne

xt s

ectio

n w

e re

-de

scri

be th

ese

conn

ectio

ns f

rom

the

poin

t of

view

of

the

phon

em~

leve

l,

Wor

d V

nits

and

Wor

d-P

hone

me

Con

nec'

tions

The

re is

a u

nit f

or e

very

wor

d in

eve

ry ti

me

slic

e, E

ach

of th

ese

units

repr

esen

ts a

dif

fere

nt h

ypot

hesi

s ab

out a

wor

d id

entit

y an

d st

artin

g lo

-cation in the 'Irace. For example, the unit for the word

Ik.p

l in Slice 24

. (hi

ghlig

hted

in F

ig, 4

) re

pres

ents

the

hypo

thes

is th

at th

e in

put c

onta

ins

the

wor

d " c

up"

star

ting

in S

lice

24, M

ore

exac

tly, i

t rep

rese

nts

the

hy-

poth

esis

that

the

inpu

t con

tain

s th

e w

ord

" cup

" w

ith it

s fi

rst p

hone

me

centered in Time Slice 24.

Wor

d un

its r

ecei

ve e

xcita

tion

from

the

units

for

the

phon

emes

they

cont

ain

in a

ser

ies

of o

verl

appi

ng w

indo

ws.

Thu

s, th

e un

it fo

r " c

up" in

Time Slice 24 will receive excitation from

Ikl

in s

lices

nei

ghbo

ring

Slic

e

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

24, from

rI

in slices neighboring Slice 30, and from

Ipl

in slices neigh-

bori

ng S

lice

36. A

s w

ith th

e fe

atur

e-ph

onem

e co

nnec

tions

, the

se c

on-

nect

ions

are

str

onge

st a

t the

cen

ter

of th

e w

indo

w a

nd fa

ll of

f lin

earl

y on

either side,

The

inhi

bito

ry c

onne

ctio

ns a

t the

wor

d le

vel a

re s

imila

r to

thos

e at

the

phon

eme

leve

l, A

gain

, the

str

engt

h of

the

inhi

bitio

n be

twee

n tw

o w

ord

units

dep

ends

on

the

num

ber

of ti

me

slic

es in

whi

ch th

ey o

verl

ap. T

hus,

units

rep

rese

ntin

g al

tern

ativ

e in

terp

reta

tions

of

the

sam

e st

retc

h of

pho

-ne

me

units

are

str

ongl

y co

mpe

titiv

e, b

ut u

nits

repr

esen

ting

inte

rpre

ta-

tions

of

nono

verl

appi

ng s

eque

nces

of

phon

emes

~o

not c

ompe

te a

t all.

TR

AC

E I

I ha

s de

tect

ors

for

the 211 words found in a computerized

phon

etic

wor

d lis

t tha

t met

all

of th

e fo

llow

ing

cons

trai

nts:

(a)

the

wor

dco

nsis

ted

only

of t

he p

hone

mes

list

ed a

bove

; (b)

it w

as n

ot a

n in

flect

ion

of s

ome

othe

r w

ord

that

cou

ld b

e m

ade

by a

ddin

g "-

ed," "

os, " or

ing

; (c)

the

wor

d to

geth

er w

ith it

s "-

ed,"

" -s," and "

ing" inflections

occu

rred

wiih

a f

requ

ency

of

20 o

r m

ore

per

mill

ion

in th

e K

ucer

a an

dFr

anci

s (1

967)

wor

d co

unt.

It is

not

cla

imed

that

the

mod

el's

lexi

con

is a

nex

haus

tive

list o

f w

ords

mee

ting

this

cri

teri

on, s

ince

the

com

pute

rize

dph

onet

ic le

xico

n w

as n

ot c

ompl

ete,

but

it is

rea

sona

bly

clos

e to

this

, To

mak

e sp

ecif

ic p

oint

s ab

out t

he b

ehav

ior

of th

e m

odel

, det

ecto

rs f

or th

efo

llow

ing

thre

e w

ords

not

in th

e m

ain

list w

ere

adde

d: "

blus

h,

" "

rega

l,an

d "

slee

t."

The

mod

el a

lso

had

dete

ctor

s at

the

wor

d le

vel f

or s

ilenc

e(I

-I),

w

hich

was

trea

ted

like

it on

e-ph

onem

e w

ord,

inde

fini

tely

, tho

ugh

for

prac

tical

pur

pose

s it

is a

lway

s te

rmin

ated

. aft

er

som

e pr

edet

erm

ined

num

ber

of ti

me

cycl

es h

as ~

Iaps

ed,

...

Pres

enta

tion

tlnd

Proc

e!jti

'ing

of tm

Ulle

rtln

c'

Bef

ore

proc

essi

ng o

f an

utte

ranc

e be

gins

, the

act

ivat

ions

of

all o

f th

eun

its a

re s

et a

t the

ir r

estin

g va

lues

. At t

he s

tart

of processing, the input

to th

e in

itial

slic

e of

feat

ure

units

is a

pplie

d, A

ctiv

atio

ns a

re th

en u

pdat

ed,

endi

ng th

e in

itial

tim

e cy

cle,

On

the

next

tim

e cy

cle,

the

inpu

t to

the

next

slic

e of

fea

ture

uni

ts is

app

lied

, and

exc

itato

ry a

nd in

hibi

tory

inpu

ts to

each

uni

t res

ultin

g fr

om th

e pa

ttern

of

activ

atio

n le

ft a

t the

end

of

the

prev

ious

tim

e sl

ice

are

com

pute

d,It

is im

port

ant t

o re

mem

ber

that

the

inpu

t is

appl

ied

, one

slic

e at

atim

e, p

roce

edin

g fr

om le

ft to

rig

ht a

s th

ough

it w

ere

an ongoing stream

of s

peec

h "w

ritin

g on

" the successive time sl

ices

of t

he T

race

, The

in-

tera

ctiv

e-ac

tivat

ion

proc

ess

is o

ccur

ring

thrc

ugho

ut th

e Trace on each

time

slic

e, e

ven

thou

gh th

e ex

tern

al b

otto

m-u

p in

put i

s on

ly c

omin

g in

toth

e fe

atur

e un

its o

ne s

lice

at a

tim

e. P

roce

ssin

g in

tera

ctio

ns c

an c

ontin

ueev

en a

fter

the

left

to r

ight

sw

eep

thro

ugh

the

inpu

t rea

ches

the

end

of th

eT

race

. Onc

e th

is h

appe

ns, t

here

are

sim

ply

no n

ew in

put s

peci

fica

tions

appl

ied

to th

e T

race

; the

con

tinui

ng in

tera

ctio

ns a

re b

ased

on

wha

t has

alre

ady

been

pre

sent

ed. T

his

inte

ract

ion

proc

ess

is a

ssum

ed to

con

tinue

Det

ails

of P

roce

ssin

g D

ynam

kti,

The

inte

ract

ive

activ

atio

n pr

oces

s in

the

Tra

ce m

odel

follo

ws

thed

y-na

mic

ass

umpt

ions

laid

out

in M

cCle

lland

and

Rum

elha

rt (

1981

), E

ach

unit

has

a re

stin

g ac

tivat

ion

valu

e ar

bitr

arily

set

at 0

, a m

axim

um a

ctiv

atio

nvalue arbitrarily set at 1,0,

and

a m

inim

um a

ctiv

atio

n se

t at -

.3.

On

ever

y tim

e cy

cle

of p

roce

ssin

g, a

ll th

e w

eigh

ted

exci

tato

ry a

nd in

hibi

tory

sign

als

impi

ngin

g up

on a

uni

t are

add

ed to

geth

er, T

he s

igna

l fro

m o

neun

it to

ano

ther

is ju

st th

e ex

tent

to w

hich

its

activ

atio

n ex

ceed

s 0;

if it

sac

tivat

ion

is le

ss th

an 0

, the

sig

nal '

is 0

.1 G

loba

l lev

el-s

peci

fic

exci

tato

ry,

inhi

bito

ry, a

nd d

ecay

par

amet

ers

scal

e th

e re

lativ

e m

agni

tude

s of

dilf

eren

ttypes of influences on the activation of each unit. Values for these pa-

ram

eter

s ar

e gi

ven

belo

w,

Aft

er th

e ne

t inp

ut to

eac

h un

it ha

s be

en d

eter

min

ed b

ased

on

the

prio

rac

tivat

ions

of

the

units

, the

act

ivat

ions

of

the

units

arc

all

upda

ted

for

the

next

pro

cess

ing

cycl

e, T

he n

ew v

alue

of

the

activ

atio

n of

the

unit

isa

func

tion

of it

s ne

t inp

ut f

rom

oth

er u

nits

and

its

prev

ious

act

ivat

ion

valu

e, T

he e

xact

fun

ctio

n us

ed (

see

McC

lella

nd &

Rum

elha

rt, 1

981)

kee

ps

unit

activ

atio

ns b

ound

ed b

etw

een

thei

r m

axim

um a

nd m

inim

um v

alue

s.G

iven

a c

onst

ant i

nput

, the

act

ivat

ion

of a

uni

t will

sta

biliz

e at

a p

oint

betw

een

its m

axim

um a

nd m

inim

um th

at d

epen

ds o

n th

e st

reng

th a

ndsi

gn (

exci

tato

ry o

r in

hibi

tory

) of

the

inpu

t. W

ith a

net

inpu

t of 0, the

activ

atio

n of

the

unit

will

gra

dual

ly r

etur

n to

its

rest

ing

leve

l.E

ach

proc

essi

ng ti

me

cycl

e co

rres

pond

s to

a s

ingl

e tim

e sl

ice

at th

efe

atur

e le

vel.

Thi

s is

act

ually

a p

aram

eter

of

the

mod

el-t

here is no

intr

insi

c re

ason

why

ther

e sh

ould

be

a si

ngle

cyc

le o

f th

e in

tera

ctiv

e-ac

tivat

ion

proc

ess

sync

hron

ized

with

the

arri

val o

f ea

ch s

ucce

ssiv

e sl

ice

of th

e in

put.

A h

ighe

r ra

te o

f cy

clin

g w

ould

spe

ed th

e pe

rcol

atio

n of

effe

cts

of n

ew in

put t

hrou

gh th

e ne

twor

k re

lativ

e to

the

rate

of

pres

en-

tatio

n,

Out

put A

ssum

ptio

ns

Act

ivat

ions

of

units

in th

e T

race

ris

e an

d fa

ll as

the

inpu

t sw

eeps

acr

oss

the

feat

ure

leve

l. A

t any

tim

e, a

dec

isio

n ca

n be

mad

e ba

sed

on th

e pa

ttern

of a

ctiv

atio

n as

it s

tand

s at

that

mom

ent.

The

dec

isio

n m

echa

nism

can

,w

e as

sum

e, b

e di

rect

ed to

con

side

r th

e se

t of u

nits

loca

ted

with

in a

sm

all

win

dow

of

adja

cent

slic

es w

ithin

any

leve

l. T

he u

nits

in th

is s

et th

enI

At t

he w

ord

leve

l, th

e in

hibi

tory

sig

nal f

rom

one

wor

d to

ano

ther

is ju

st. t

he s

quar

e of

the

exte

nt to

whi

ch th

e se

nder

s ac

tivat

ion

exce

eds

zero

. Thi

s te

nds

to s

moo

th I

he e

fli:.

:hof

man

y un

its s

udde

nly

beco

min

g sl

ight

ly a

ctiv

ated

. and

of

cour

se il

als

o in

crea

ses

Ihe

dom

inan

ce o

f on

e ac

tive

wor

d ov

er m

any

wea

kly

activ

ated

one

s,

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

Sj =

kaj,

Eve

n w

ith a

ll th

e si

mpl

ifica

tions

des

crib

ed a

bove

. the

TR

AC

E m

odel

still

has

a n

umbe

r of

free

par

amet

ers.

The

se p

aram

eter

s ar

e lis

ted

in T

hble

3, I

t sho

uld

be n

oted

that

par

amet

ers

are

not i

f'! g

ener

al d

irect

ly c

ompa

-ra

blea

cros

s le

vels

, For

exa

mpl

e. p

hone

me-

to-p

hone

me

and

wor

d-to

-w

ord

inhi

bitio

n ar

e no

t dir

ectly

com

para

ble

to e

ach

othe

r or

to f

eatu

re-

to-p

hone

me

inhi

bitio

n. s

ince

fea

ture

-lev

el u

nits

con

lpet

e on

ly w

ithin

asi

ngle

slic

e. w

hile

pho

nem

e an

d w

ord

units

com

pete

in p

ropo

rtio

n to

thei

rov

erla

p,T

here

was

som

e tr

ial a

od e

rror

in fi

ndin

g 'h

e se

t of p

aram

eter

s us

ed in

the

repo

rted

sim

ulat

ions

. but

. in

gene

ral.

the

qual

itativ

e be

havi

or o

f the

mod

el w

as r

emar

kabl

y ro

bust

und

er p

aram

eter

var

iatio

ns. a

nd n

o sy

s~te

mat

ic s

earc

h of

the

spac

e of

par

amet

ers

was

nec

essa

ry, G

ener

ally

. ma-

nipu

latio

ns o

f pa

ram

eter

s si

mpl

y in

flue

nce

t hem

agni

tude

or

the

timin

gof

one

eff

ect o

r an

othe

r w

ithou

t cha

ngin

g th

e ba

sic

natu

re o

f th

e ef

fect

sob

serv

ed, F

or e

xam

ple.

str

onge

r bo

ttom

-up

exci

tatio

n sp

eeds

thin

gs u

pan

d ca

n in

dire

ctly

influ

ence

the

si~

e of

top-

dow

n ef

fects. since. for ex-

ampl

e. s

tron

ger

wor

d le

vel a

ctiv

atio

ns p

rodu

ce s

tron

ger

feed

back

to th

e. p

hone

me

leve

l. St

rong

er to

p-do

wn

exci

tatio

n. o

f cou

rse.

dire

ctly

influ

-en

ces

the

mag

nitu

de o

f le

xica

l eff

ects

, The

one

par

amet

er th

at a

ppea

red

to in

fluen

ce th

e qu

alita

tive

beha

vior

of t

he m

odel

was

the

stre

ngth

of

with

in- l

evel

inhi

bitio

n, S

tron

ger

with

in-l

evel

inhi

bitio

n m

ake

the

mod

elco

mm

it its

elf

mor

e st

rong

ly to

slig

ht e

arly

dif

fere

nces

in a

ctiv

atio

n am

ong

com

petin

g al

tern

ativ

es. T

here

was

. the

refo

re. s

ome

tuni

ng o

f thi

s pa

ram

-et

er to

avo

id e

arly

ove

rcom

mitm

ent t

hat w

ould

pre

vent

rig

ht c

onte

xt fr

omex

ertin

g an

infl

uenc

e un

der

som

e ci

rcum

stan

ces,

Fin

ally

. a lo

w r

ate

offe

atur

e-le

vel d

ecay

was

use

d to

allo

w f

eatu

re-l

evel activations to persist

, aft

er th

e in

put m

oved

on

to la

ter

slic

es,

The

par

amet

er v

alue

s w

ere

held

con

stan

t at t

he v

alue

s sh

own

in th

e

cons

titut

e th

e se

t of

resp

onse

alte

rnat

ives

. des

igna

ted

by th

e id

entit

y of

the

item

for

whi

ch th

e un

it st

ands

(no

te th

at w

ith s

ever

al a

djac

ent s

lices

incl

uded

in th

e se

t. se

vera

l uni

ts in

the

alte

rnat

ive

set m

ay c

orr~

spon

d to

the

sam

e ov

ert r

espo

nse)

, Wor

d id

entif

icat

ion

resp

onse

s ar

e as

sum

~d

tobe based on

. rea

dout

fro

m th

e w

ord

leve

l. an

d ph

onem

e id

entif

icat

ion

resp

onse

s ar

e as

sum

ed to

be

base

d. o

n re

adou

t fro

m th

e ph

onem

e le

vel.

As

far

as p

hone

me

iden

tific

atio

n is

con

cern

ed, t

hen.

it h

Ol:n

~gen

eous

mec

hani

sm is

ass

umed

to b

e us

ed w

ith b

oth

wor

d an

d no

nwor

d st

imul

i.T

he d

ecis

ion

mec

hani

sm c

an b

e as

ked

to m

ake

a re

spon

se e

ither

(a)

at a

criterialtime during processirig

or (

b) w

hen

a un

it in

the

alte

rnat

ive

set

reac

hes

a cr

iteri

al s

tren

gth

rela

tive

to th

e ac

tivat

ion

of o

ther

alte

rnat

ive

units

. Onc

e a

deci

sion

has

bee

n m

ade

to m

ake

a re

spon

se. o

ne o

f the

alte

rnat

ives

is c

hose

n fr

om th

e m

embe

rs o

f th

e se

t, T

he p

roba

bilit

y of

choo

sing

a p

artic

ular

alte

rnat

ive

i is

then

given by the Luce (1959)

choi

ce r

ule:

peR

i~ S

whe

n in

dexe

s th

e m

embe

rs o

f th

e al

tern

ativ

e se

t. an

d

The

exp

onen

tial t

rans

form

atio

n en

sure

s th

at a

ll ac

tivat

ions

are

pos

itive

and

give

s gr

eat w

eigh

t to

stro

nger

act

ivat

ions

. and

the

Luc

e ru

le e

nsur

esth

at th

e su

m o

f al

l of

the

resp

onse

pro

babi

litie

s ad

ds u

p to

1, 0

. Sub

stan

-tia

lly th

e sa

me assumptions were used by McClelland and Rumelhart

(198

1),

Mil1

imiz

il1R

the

Num

ber

of P

aram

eter

sA

t the

exp

ense

oC

cons

ider

able

rea

lism

. we

have

trie

d to

kee

p T

RA

CE

II s

impl

e by

usi

ng h

omog

eneo

us p

aram

eter

s w

here

ver

poss

ible

. Thu

s, a

sal

read

y no

ted.

the

feat

ure

spec

ific

atio

ns o

f al

l pho

nem

es w

ere

spre

ad o

utov

er th

e sa

me

num

ber

of ti

me

slic

es. e

ffect

ivel

y gi

ving

all

phon

emes

the

sam

e du

ratio

n, T

he s

tren

gth

of th

e to

tal e

xcita

tion

com

ing

into

a p

artic

-ul

ar p

hone

me

unit

~rom

the

feat

ure

units

was

nor

mal

ized

to, t

he s

ame

value for all phonelT1es. thus m

akin

g ea

ch p

hone

me

equa

lly e

xcita

ble

byits

ow

n ca

noni

cal p

atte

rn, O

ther

sim

plif

ying

ass

umpt

ions

sho

uld

be n

oted

as w

ell.

For

exa

mpl

e. th

ere

wer

e no

diff

eren

ces

in c

onne

ctio

ns o

r re

stin

gle

vels

for

wor

ds o

f d~

ffere

nt fr

eque

ncy,

It w

ould

hav

e be

en a

sim

ple

mat

ter

to in

corp

orat

e fr

eque

ncy

as M

cCle

lland

and

Rum

elha

rt (

1981

) di

d. a

nd a

com

plet

e m

ltdel

wou

ld. o

f co

urse

. inc

lude

som

e ac

coun

t for

the

ubiq

uito

usef

fect

s of

wor

d fr

eq~e

ncy.

We

left

it o

ut h

ere

to f

acili

tate

an

exam

inat

ion

of th

e m

any

othe

r f~

ctor

s th

at a

ppea

r to

influ

ence

the

proc

ess

of w

ord

reco

gniti

on in

spe

ech

perc

eptio

n,

TA

BL

E 3

Para

met

ers

of T

RA

CE

II

Para

met

erV

alue

Feat

ure-

phon

eme

exci

tatio

nP

hone

me-

wor

d ex

cita

tion

Wor

d-ph

onem

e ex

cita

tion

Phon

eme-

feature excitation

Feat

ure-

leve

l inh

ibiti

onPh

onem

e-le

vel i

nhib

ition

"W

ord-

leve

l inh

ibiti

on"

Feat

ure-

leve

l dec

ayPh

onem

e-le

vel d

ecay

Wor

d-le

vel d

ecay

" P

er th

ree

time-

slic

es o

f ove

rlap.

TR

AC

E M

OD

EL

tabl

e th

roug

hdut

the

sim

ulat

ions

, exc

ept i

n th

e si

mul

atio

ns o

f cat

egor

ical

perc

eptio

n an

d tr

adi' n

g re

latio

ns, S

ince

we

wer

e no

t exp

licitl

y co

ncer

ned

with

the

effe

ds o

f fe

edba

ck to

the

feat

ure

leve

l in

any

of th

e ot

her

sim

-ul

atio

ns, w

e st

h th

e fe

edba

ck fr

om th

e ph

onem

e le

vel t

o th

e fe

atur

e le

vel

to z

ero

to s

peed

up

the

sim

ulat

ions

in a

ll ot

her cases. In the categorical

perc

eptio

n an

d tr

adin

g re

latio

ns s

imul

atio

ns th

is p

aram

eter

was

set

at ,

OS,

Phon

eme-

to- f

eatu

re f

eedb

ack

tend

ed to

slo

w th

e ef

fect

ive

rate

of

deca

yat

the

feat

ure

leve

l and

to in

crea

se th

e ef

fect

ive

dist

inct

iven

ess

of d

iffe

rent

feat

ure

patte

rris

, Rat

e of

dec

ay o

f fea

ture

- lev

el a

ctiv

atio

ns a

nd s

tren

gth

of p

hone

me-

to'-

phon

eme

com

petit

ion

wet

e se

t to

, 03

and

.05

to c

ompe

n-sa

te fo

r th

ese

effe

cts,

No

lexi

con

was

use

d in

the

cate

goric

al p

erce

ptio

nan

d tr

adin

g re

liitio

ns s

imul

atio

ns, w

hich

is e

quiv

alen

t to

setti

ng th

e ph

o-ne

me

to w

ord

~xdt

atio

n pa

ram

eter

to z

ero,

't!

C 0

.

:: g~

+

-4;

QJ

.c:

Il.

MC

CLE

LLA

ND

AN

D E

LMA

N

045+

II'!

.

1.1 Ii

! !

~ ~I

1IliI

~.:

r '

fl!f

tlllf

l!I

:.~t!

1

I -

B I

a- b

g.. b~ b

I' F

IG. S

. Pho

nem

e- a

nd w

ordc

levet activiltions at several points in Ihe un'tllding of iI ~cgl1lCl1t

ambiguous between

Ibl

and

Ipl

followed by

III, 0

and

Ig!.

See

texl

Itlr

ilfu

ll cx

plal

1aliu

l1,

TH

E D

YN

AM

ICS

OF

PHO

NE

ME

PE

RC

EPT

ION

In th

e in

trod

uctio

n, w

e m

otiv

ated

the

appr

oach

take

n in

the

TR

AC

Em

odel

in g

ener

al te

rms.

In

this

sec

tion,

we

see

. that

the

sim

ple

conc

epts

that

lead

to T

RA

CE

pro

vide

a c

oher

ent a

nd s

ynth

etic

acc

ount

of

a la

rge

num

ber

of d

iffe

rent

kin

ds o

f fin

ding

s on

the

perc

eptio

n of

pho

nem

es,

Prev

ious

mod

e:ls

hav

e be

en a

ble

to p

rovi

de f

airl

y ac

cura

te a

ccou

nts

of a

num

ber

of th

ese

phen

omen

a, F

or e

xam

ple,

Mas

saro

and

Ode

ns

feat

ure

inte

grat

ion

mod

el (

Mas

saro

, 198

1; M

assa

ro &

Ode

n, 1

980a

, 198

0b; O

den

& M

assa

ro, 1

978)

acc

ount

s in

det

ail f

or a

larg

e bo

dy o

f da

ta o

n th

ein

flue

nces

of

mul

tiple

cue

s to

pho

nem

e id

entit

y, a

nd th

e Pi

soni

/Fuj

isak

i-Kawashima m

bdel

of

cate

gori

cal p

erce

ptio

n (F

ujis

aki &

Kaw

ashi

ma,

1968; Pisoni, 1973, 1975) accounts for a large bo

dy o

f dat

a on

the

con-

ditio

ns u

nder

whi

ch s

ubje

cts

can

disc

rim

inat

e so

unds

with

in th

e sa

me

phon

etic

cat

egor

y. M

arsl

er, W

ilson

s C

OH

OR

T m

odel

can

acc

ount

for

the

time

cour

se o

f lex

ical

influ

ence

s on

pho

nem

e id

entif

icat

ion.

Wha

t we

hope

to s

how

her

e is

that

TR

AC

E b

ring

s th

ese

phen

omen

a, a

nd s

ever

alot

hers

not

con

side

red

by e

ither

mod

el, t

oget

her

into

a c

oher

ent p

ictu

reof

the

proc

ess

of p

hone

me

perc

eptio

n as

it u

nfol

ds in

tim

e,T

he p

rese

nt s

ectio

n co

nsis

ts o

f th

ree

mai

n pa

rts.

The

fir

st f

ocus

es o

nle

xica

l effe

Cts

On

phon

eme

iden

tific

atio

n an

d th

e co

nditi

ons

unde

r w

hich

thes

e ef

fect

s ar

e ob

tain

ed. H

ere,

we

see

how

TR

AC

E c

an a

ccou

nt fo

rth

e ba

sic

lexi

cal e

ffect

, and

we

mak

e it

clea

r w

hy le

xica

l effe

cts

are

only

obta

ined

und

er s

ome

cond

ition

s, T

he s

econ

d pa

rt o

f th

is s

ectio

n fo

cuse

son

the

ques

tion

of th

e ro

le o

f pho

nota

ctic

rul

es- t

hat i

s, r

ules

spe

cify

ing

whi

ch p

hone

mes

can

occ

ur to

geth

er in

Eng

lish-

in p

hone

me

iden

tific

a-tio

n, H

ere,

we

see

how

TR

AC

E m

imic

s , th

e ap

pare

ntly

rul

e-go

vern

edbe

havi

or o

f hu

man

sub

ject

f. in

term

s of

a "

cons

pira

cy" of the le

xica

lite

ms

that

inst

antia

te th

e ru

le. T

he. t

hird

par

t foc

uses

on

two

aspe

cts

ofph

onem

e id

entif

icat

ion

ofte

n co

nsid

ered

qui

te s

epar

atel

y fr

om le

xica

l ef-

fect

s-na

mel

y, th

e co

ntra

stin

g ph

enom

ena

of c

ue tr

adeo

fTs

in p

hone

me

perc

eptio

n an

d ca

tego

rica

l per

cept

ion,

Her

e w

e se

e th

at T

RA

CE

pro

vide

san

acc

ount

of

both

eff

ects

as

wel

l as

deta

ils o

f th

eir

time

cour

se, A

ll th

ree

part

s of

this

sec

tion

illus

trat

e 'h

ow th

e si

mpl

e m

echa

nism

s of

mut

ual e

x-ci

tatio

n an

d in

hibi

tion

amon

g th

e pr

oces

sing

uni

ts o

f th

e T

race

pro

vide

ana

tura

l way

of

acco

untin

g fo

r th

e re

leva

nt p

heno

men

a, T

he s

ectio

n en

dsw

ith a

bri

ef c

onsi

dera

tion

of th

e w

ays

in w

hich

TR

AC

E m

ight

be

ex-

tend

ed to

cop

e w

ith s

ever

al o

ther

asp

ects

of p

hone

me

iden

tific

atio

n an

dpe

rcep

tion,

Lexical EffeL'

YO

ll ca

n te

ll a

phon

eme

by Ih

e co

mpa

ny Ih

m il

keep

j'2

In th

is s

ectio

n,we describe a simple simulation of the basic lexical effect

on

phon

eme

iden

tific

atio

n re

port

ed b

y G

anon

g (1

980)

, We

star

t with

this

phe

nom

enon

beca

use

it. a

nd th

e re

late

d ph

onem

ic r

esto

ratio

n ef

fect

, wer

e am

ong

the

prim

ary

reas

ons

why

we

felt

that

the

inte

ract

ive-

activ

atio

n ap

proa

chw

ould

be

appr

opri

ate

for

spee

ch p

erce

ptio

n as

wel

l as

visu

al w

ord

rec-

ogni

tion

and

read

ing,

For

the

firs

t sim

ulat

ion,

the

inpu

t to

the

mod

el c

onsi

sted

of a

feat

ure

specification which activated

Ibl

and

Ipl

equa

lly, f

ollo

wed

by

(am

I par

tially

overlapping with) the feature specifications for

III

then

n,

th

en

Ig!.

Fi

gure

5 sh

ows

phon

eme

and

wor

d-level activations at several points in the

unfo

ldin

g of

this

inpu

t spe

cifi

catio

n. E

ach

pane

l of

the

figu

re r

epre

sent

s

2 T

his

titte

is a

dapJ

ed f

rom

the

tille

of

a ta

lk b

y D

-dvi

d E

, Rum

elha

rl on

rel

illcd

phe

nol1

lcni

lin

telle

r pe

rcep

tion.

The

se f

indi

ngs

are

desc

ribe

d in

Rom

elha

rt a

nd M

cCle

lland

(198

2/, W

eIh

ank

Dav

e fo

r hi

s pe

rmis

sion

to a

dapt

the

title

TR

AC

E M

OD

EL

a di

ffere

nt p

oint

in ti

me

durin

g th

e pr

esen

tatio

n an

d co

ncom

itant

pro

-ce

ssin

g of

the

inpu

t. T

he u

pper

por

tion

of e

ach

pane

l is

used

to d

ispl

ayac

tivat

ions

at t

he w

ord

leve

l; th

e lo

wer

pan

el is

use

d fo

r ac

tivat

ions

at

the

phon

eme

leve

l. E

ach

unit

is r

epre

sent

ed b

y a

rect

angl

e, la

bele

d w

ithth

e id

entit

y of

the

item

the

unit

stan

ds f

or, T

he h

oriz

onta

l ext

ensi

on o

fth

e re

ctan

gle

indi

cate

s th

e po

rtio

n of

the

inpu

t spa

nned

by

the

unit.

The

vert

ical

pos

ition

of

the

rect

angl

e in

dic

ates

the

degr

ee o

f ac

tivat

ion

of th

eun

it. I

n th

is a

nd s

ubse

quen

t fig

ures

, act

ivat

ions

of

the

phon

eme

units

loca

ted

betw

een

the

peak

s of

the

inpu

t spe

cifi

catio

ns o

f th

e ph

onem

es(at Slices 3, 9, 15. etc,)

have

bee

n de

lete

d fr

om th

e di

spla

y fo

r cl

arity

(the activations of these units genera1ly get suppressed by the model,

sinc

e th

e un

its o

n th

e pe

aks

tend

to d

omin

ate

them

), T

he in

put i

tsel

f is

indi

cate

d be

low

eac

h pa

nel,

with

the

succ

essi

ve p

hone

mes

pos

ition

ed a

tth

e te

mpo

ral p

ositi

ons

of th

e ce

nter

s of

thei

r in

put s

peci

fica

tions

, The

rt

along the

axis represents the point in the presentation of the input

stre

am a

t whi

ch th

e sn

apsh

ot w

as t!

lken

,T

he fi

gure

illu

stra

tes

the

gradual' buildup of activation of the tw

o in

-te

rpre

tatio

ns o

f th

e fi

rst p

hone

me,

fol

low

ed b

y gr

adua

l bui

ldup

s in

act

i-va

tion

for

subs

eque

nt p

hone

mes

, As

thes

e pr

oces

ses

unfo

ld, t

hey

begi

nto

pro

duce

wor

d-le

vel a

ctiv

atio

ns, I

t is

diff

icul

t to

reso

lve

any

wor

d-le

v~1

activ

atio

ns in

the

firs

t few

fra

mes

,. h

owev

er, s

ince

in these frames, the

info

rmat

ion

at th

e p~

onem

e le

vel s

impl

y ha

s no

t evo

lved

to th

e po

int

whe

re it

pro

vide

s en

ough

con

stra

int t

o se

lect

any

one

part

icul

ar w

ord.

In this case, it is only after the

Igl

has

com

e in

that

the

mod

el h

as in

for-

mat

ion

telli

ng it

whe

~he

r th

e in

put i

s cl

oser

to "

plug

," " pl

us," "

blus

h,or "bl

ood"

(T

RA

CE

's le

xico

n co

ntai

ns n

o ot

her

wor

ds beginning with

Iprt

or fbr/), After that point, as ill

ustr

ated

in th

e fo

urth

pan

el, "

plug

win

s th

e co

mpe

titio

n at

the

wor

d le

vel a

nd, t

hrou

gh f

eedb

ack

supp

ort t

oIp

/, ca

uses

Ip

l to dominate

Ibl

at the ph

onem

e le

vel.

The

mod

el, t

hen,

prov

ides

an

expl

icit

acco

unt f

or th

e w

ay in

whi

ch le

xica

l inf

orm

atio

n ca

nin

fluen

ce p

hone

me

iden

tific

atio

n,T

wo

thin

gs a

bout

the

lexi

cal e

ffec

t obs

erve

d in

this

cas

e ar

e w

orth

y of

note

. Firs

t. th

e ef

fect

is r

athe

r sm

all,

Sec

ond,

it d

oes

not e

mer

ge u

ntil

wel

l aft

er th

e am

bigu

ous

segm

ent i

tsel

f ha

s co

me

and

gone

, The

re is

aslight advantage of

Ipl

over

Ib

l in

Fra

mes

2 a

nd 3

of

the

figu

re. I

n th

ese

case

s, h

owev

er, t

he a

dvan

tage

is n

ot d

ue to

the

spec

ific

info

rmat

ion

that

this

item

is th

e w

ord

"plu

gth

e m

odel

can

hav

e no

way

of k

now

ing

this at these points in processing, The slight advantage for

Ipl

at these

earl

y po

ints

is d

ue to

the

fact

that

ther

e ar

e m

ore

wor

ds b

egin

ning

with

Ipll

than Ibltin the model's

lexi

con,

and

in p

artic

ular

, the

re a

re m

ore

beginning with

Iprl

th

an

Ibrt

. So, when the input is

nrd/

, w

ith th

e?standing for the ambiguous

Ib/-

/pl

segm

ent,

the

mod

el m

ust a

ctua

lly o

ver-

com

e th

is s

light

Ip/

-war

d bi

as, E

vent

ually

, it d

oes

so,

. Fig

ure

6 sh

ows

the

tem

pora

l cou

rse

of b

uild

up o

f th

e st

reng

th o

f th

e

MCCLELLAND AND ELMAN

:-.. 1.00

::: :0 0.

!II

6: 0.

1/1 C 0

.

1/1 ~ 0.

00

12 18 24 30 38 42 48 54 80 88 72

Processing Cycles

FIG. 6. The time course or the buitdup in the strength or the

Ipl

resp

onse

bas

ed o

n ac

ti-va

tions

or

phon

eme

units

in S

lice

12. i

n proces1iing an ambiguous

Ibl-

lpl

segm

ent i

n '-I

'g/,

and the same segment in

I'SI.

T

he a

mbi

guou

s se

gmen

t is

indi

cate

d by

the

"?,' .

AI~o

show

n is

the

build

up o

r re

spon

se s

tren

gth

ror

proc

essi

ng a

n un

ambi

guou

~ Ip

l se

gmen

t in

Ipl'g

/. T

he v

ertic

al li

ne to

pped

with

"?" indicates the point in time co

rres

pond

ing

to th

ece

nter

or

the

initi

al s

egm

ent i

n th

e in

put s

trea

m. S

ucce

ssiv

e ve

rtic

al li

nes

indi

cate

cen

ters

or s

ucce

ssiv

e ph

onem

es.

Ipl

resp

onse

bas

ed o

n ac

tivat

ions

of

the

phon

eme

units

. in Slice 12 for

two cases in which the initial segment is ambiguous between

Ipl

and

Ib/.

In one case, the ambiguous segment is followed by

Irgl

(a

s in

"pl

ugin

the

othe

r, it

is fo

llowed by

IrSI

(a

s in

"bl

ush"

), G

iven

the

mod

el's

rest

rict

ed le

xico

n, w

hich

doe

s no

t con

tain

the

~ord

"pl

ush,

" the lexical

effect should lead to eventual dominance of the

Ipl

resp

onse

in th

e fi

rst

case, but a suppression of the

Ipl

resp

onse

in th

e se

cond

cas

e, T

he d

if-fe

renc

es b

etw

een

the

cont

exts

do

not b

egin

to s

how

up

until

aft

er th

ece

nter

of

the

fina

l pho

nem

e, w

hich

occ

urs

at S

lice

30. T

he r

easo

n fo

r th

isis

sim

ply

that

the

info

rmat

ion

is. n

ot a

vaila

ble

until

that

poi

nt, b

ecau

seth

e ph

onem

e th

at s

igna

ls w

hat t

he w

ord

will

be

com

es a

t the

ver

y en

d of

the

wor

d. T

he e

ffect

take

s an

othe

r fe

w ti

me

slic

es to

beg

in to

influ

ence

the activation of the

' ini

tial p

hone

me,

bec

ause

it p

erco

lat~

s to

the

firs

tph

onem

e by

way

of

the

feed

back

fro

m th

e w

ord

or w

ords

that

con

-ta

in it

, .Elimination of the lexical effect by time pressure,

Fox

(198

2) h

as r

e-po

rted

that

the

lexi

cal e

ffect

on

wor

d in

itial

seg

men

ts is

elim

inat

ed if

subj

ects

are

giv

en a

dea

dlin

e to

res

pond

with

in 5

00 m

s of

the

ambi

guou

sse

gmen

t. T

houg

h th

ey c

an c

orre

ctly

iden

tify

unam

bigu

ous

segm

ents

inre

spon

ses

mad

e be

fore

the

dead

line,

thes

e ea

rly r

espo

nses

sho

w n

o se

n-

sitiv

ity to

the

lexi

cal s

tatu

s of

the

alte

rnat

ives

, Sim

ilar findings are also

repo

rted

by

Fox

(198

4).

Our

mod

el is

com

plet

ely

cons

iste

nt w

ith F

oxs

resu

lts, I

ndee

d, w

e ha

ve

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

alre

ady

seen

that

the

activ

atio

ns in

the 1i"ace only begin to reflect the

lexi

cal e

ffec

t abo

ut o

ne p

hone

me

or s

o af

ter

the

phon

eme

that

est

ablis

hes

the

lexi

cal i

dent

ity o

f th

e ite

m, G

iven

that

this

seg

men

t doe

s no

t occ

ur,

in F

oxs experiments, until the second or third segment after the ambig-

uous

seg

men

t, th

ere

is n

o w

ay th

at a

lexi

cal e

ffect

cou

ld b

e ob

serv

ed in

earl

y re

spon

ses.

But

wha

t abq

ut th

e fa

ct th

at e

arly

res

pons

es to

una

mbi

guou

s se

gmen

tsca

n be

acc

urat

e? T

RA

CE

acc

ount

s fo

r th

is to

o. I

n Fi

gure

7 w

e sh

ow th

est

ate

of th

e T

race

at v

ario

us d

iffe

rent

poi

nts

afte

r th

e un

ambi

guou

s Ib

l

Ibrgl, Here, the

Ibl

dominates the

Ipl

from

the

earl

iest

poi

nt. T

he a

nal-

ogou

s re

sult

is !

obtained, when the stimulus is

Ipl

in Iprgl, and the actio

vatio

n fo

r th

e ih

itial

pho

nem

e is

qui

te in

depe

nden

t of

whe

ther

or

not t

heite

m is

a w

ord.

The

res

pons

e st

reng

th f

or th

e ca

se w

hen

Iprg

l is

pres

enttd

in F

ig, 6

sho

ws

that

the

prob

abili

ty o

f cho

osin

g Ip

l is

nea

r un

ity w

ithin

12 processing cycles, or 300 ms of the in

itia,

seg

men

t, w

ell b

efor

e th

ede

adlin

e w

ould

be

reac

hed-

and

wel

l bef

ore

wor

d id

entit

y sp

ecif

ying

info

rmat

ion

is I

/.vai

labl

e,Lexictll effec'ts Itlte in tI word.

In th

e m

odel

, lex

ical

effe

cts

on w

ord-

initi

al s

egm

ents

! dev

elop

rat

her

late

, at l

east

in th

e ca

se w

here

ther

e is

no

cont

ext p

rece

dIng

the

wor

d, O

f cou

rse,

the

exac

t tim

ing

of th

e de

velo

p-m

ent o

f any

lexi

cal e

ffect

wou

ld b

e de

pend

ent u

pon

the

set o

f wor

dsac

tivat

ed b

y th

b st

imul

us; i

f on

e w

ord

pred

omin

ated

ear

ly o

n, a

lexi

cal

effe

ct c

ould

dev

elop

rat

her.

ear

lier,

In

gene

ral,

thou

gh, w

ord-

initi

al a

m-

bigu

ities

will

req

uire

tim

e to

res

olve

on

the

basi

s of

lexi

cal i

nfor

mat

ion,

How

ever

, whe

n th

e am

bigu

ous

segm

ent c

omes

late

in th

e w

ord

, and

the

info

rmat

ion

that

pre

cede

s th

e am

bigu

ous

segm

ent h

as a

lrea

dy e

stab

lishe

dw

hich

of t

he tw

o al

tern

ativ

es fo

r th

e am

bigu

ous

segm

ent i

s co

rrec

tT

RA

CE

sho

ws

a le

xica

l effe

ct th

at d

evel

ops

as th

e di

rect

per

cept

ual

info

rmat

ion

rele

vant

to th

e id

entit

y of

the

targ

et s

egm

ent i

s be

ing

pro-

cess

ed. T

his

phen

omen

on is

illu

Str

ated

in F

ig, 8

, whi

ch s

how

s th

e st

ate

of th

e 1i

"ace

at s

ever

al p

oint

s in

tim

e re

lativ

e to

an

ambi

guou

s fin

al s

eg-

ment tha~ could be a

It I

or a

Idl,

at th

e en

d of

the

cont

ext I

targ

I, W

ithin

the

dura

tion

of a

sin

gle

phon

eme

afte

r th

e ce

nter

of

the

ambi

guou

s se

g-m

ent,

It!

already has an advantage over

Idl,

We

ther

efor

e pr

edic

t tha

tFo

xs

resu

lts w

ould

com

e ou

t diff

eren

tly, w

ere

he to

use

wor

d-fi

nal,

asop

pose

d to

wor

d-in

itial

, am

bigu

ous

segm

ents

, In

such

a c

ase

we

wou

ldex

pect

the

lexi

cal e

ffec

t to

show

up

wel

l with

in th

e 50

0-m

s de

adlin

e,D

epen

denc

'e o

f the

lexi

CtlI

effe

ct o

n ph

onol

ogic

' (11

tlmbi

gllit

y,

One

fur-

ther

asp

ect o

fthe

lexi

cal e

ffect

that

was

not

ed b

y G

anon

g (1

980)

des

erve

sco

mm

ent,

Thi

s is

the

fact

that

the

lexi

cal e

ffect

on

the

iden

tity

of a

. pho

nem

e on

ly o

ccur

s w

ith s

egm

ents

whi

ch f

all i

n th

e bo

unda

ry r

egio

nb~

twee

ntw

o ph

onem

es. F

or s

egm

ents

whi

ch a

re u

nam

bigu

ous

exam

ples

of o

ne c

ateg

ory

or th

e ot

her,

the

effe

ct is

not

obt

aine

d, T

RA

CE

is e

ntir

ely

cons

iste

nt w

ith th

is a

spec

t of t

he d

ata,

The

influ

ence

of t

he le

xico

n is

sim

ply

anot

her

sour

ce o

f ev

iden

ce, l

ike

that

com

ing

from

the

feat

ure

- b

- b

Har

ll-lf

Eli . FLIl

8 ff

:Wff

:WiI

:W!i

lW

- t

- t

a r

1a I'

a 1"1

I k

klSI

-

I 1

I' k

- f

- B .

-tar

-tar

g--t

ara-

- t a

r a

- t -

-bl-a-

-bl

- I- -

bl- I- -

bl-

FIG

, 7. T

he s

tate

of

the

Tra

ce a

t var

ious

sta

ges

of p

roce

ssin

g th

e st

ream

Ibr

gl.

FIG

. 8. T

he s

tale

of

the

Tra

ce a

l sev

eral

sta

ges

of p

roce

ssin

g Ih

e st

ream

con

sisl

ing

ofIt

arg

' followed by Ii segment ambiguous bel ween

III

and

Id/.

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

leve

l, in

fluc

ncin

g th

e ac

tivat

ion

of o

ne p

hone

me

unit

or a

noth

er. W

hen

the

botto

m-u

p in

put i

s de

cisi

ve, i

t can

pre

empt

any

lexi

cal b

ias

effe

cts.

We

have

ver

ifie

d th

is in

sim

ulat

ions

pre

sent

ing

unam

bigu

ous

toke

ns o

fIp

l or

fb

i, followed either by Irgl or

IrS/

. In

thes

e si

mul

atio

ns, t

he u

nit

for

the

pres

ente

d in

itial

seg

men

t rea

ches

a v

ery

high

leve

l of

activ

atio

n,in

depe

nden

t of

the

follo

win

g co

ntex

t. W

hen

the

segm

ent c

omes

at t

heen

d of

the

wor

d, th

e co

ntex

t exe

rts

stro

nger

eff

ects

, thu

s ac

coun

ting

for

the

fact

that

spe

ech

dist

ortio

ns a

re e

asie

r to

det

ect w

hen

they

com

e ea

rlyin

a w

ord

than

whe

n th

ey c

ome

late

(M

arsl

en-W

ilson

& W

elsh

, 197

8),

How

ever

, eve

n th

ere,

it is

pos

sibl

e to

ove

rrid

e le

xica

lly b

ased

act

ivat

ions

with

cle

ar b

otto

m-u

p si

gnal

s, a

lthou

gh th

ere

may

be

som

e sl

owin

g of

the

activ

atio

n pr

oces

s w

hich

wou

ld p

roba

bly

show

up

in r

eact

ion

times

.H

sho

uld

be n

oted

that

TR

AC

E's

acc

ount

of l

exic

al e

ffect

s is

qui

tesi

mila

r to

the

acco

unt o

ffer

ed b

y th

e fe

atur

e in

tegr

atio

n th

eory

of

Mas

saro

and

Ode

n (1

980a

). I

ndee

d, M

assa

ro a

nd O

den

s m

odel

pro

vide

s qu

anti-

tativ

e fi

ts to

Gan

ong

s fi

ndin

gs. W

e w

ill m

ake

som

e m

entio

n of

the

slig

htdi

ffer

ence

s in

qua

ntita

tive

assu

mpt

ions

bet

wee

n th

e m

odel

s be

low

. For

. now

, we

note

a m

o~e

cruc

ial d

iffe

renc

e: T

RA

CE

inco

rpor

ates

spe

cifi

cas

sum

ptio

ns a

bout

the

time

cour

se o

f pr

oces

sing

whi

ch a

llow

s it

to a

c-co

unt f

or th

e co

nditi

ons

unde

r w

hich

lexi

cal e

ffect

s w

ill b

e obtained, as

wel

l as

for

the

infl

uenc

e (o

r a

lack

ther

eoO

of

lexi

cal e

ffec

ts o

n re

actio

ntimes, to which we now turn,

Ah.

H'IIn' (~(lexicaleffed

ill some reaction-time studies,

Foss

and

Bla

nk(1

980)

pre

sent

ed s

ome

resu

lts w

hich

see

med

to p

ose

a ch

alle

nge

to in

-te

ract

ive

mod

els

of p

hone

me

iden

tific

atio

n in

spe

ech

perc

eptio

n, T

hey

gave

sub

ject

s th

e ta

~k o

f lis

teni

ng to

spo

ken

sent

ence

s fo

r oc

curr

ence

sof

a p

artic

ular

pho

nem

e in

wor

d-in

itial

pos

ition

, Rea

ctio

n tim

e to

pre

ssa

resp

onse

key

fro

m th

e on

set o

f th

e ta

rget

pho

nem

e w

as th

e de

pend

ent

varia

ble.

In o

ne e

xam

ple,

the

targ

et w

as Ig

I and the sentence was,

At t

heen

d (~

"'a.~t year, the Rovemment,

, , .

The

sub

ject

's ta

sk w

as s

impl

y to

pres

s th

e re

spon

se k

ey u

pon

hear

ing

the

IgI a

t the

beg

inni

ng o

f the

wor

dR

Ol'e

rllm

ellt.

. The pr

inci

ple

find

ing

of F

oss

and

Bla

nk's

stu

dy w

as th

at it

mad

e no

diffe

renc

e w

heth

er th

e ta

rget

cam

e at

the

begi

nnin

g of

a w

ord

or a

non

-word. Later studies by Foss and Gernsbacher (1983) in

dica

te th

at o

ther

expe

rimen

ts w

hich

hav

e fo

und

lexi

cal o

r ev

en s

eman

tic a

nd s

ynta

ctic

ntex

t effe

cts

on m

onito

ring

late

ncie

s ar

e fla

wed

, and

that

mon

itorin

gtim

es fo

r w

ord-

initi

al p

hone

mes

are

pri

mar

ily in

flue

nced

by

acou

stic

fact

ors

affe

ctin

g ph

onem

e de

tect

abili

ty, r

athe

r th

an le

xica

l, se

man

tic, o

rsyntactic fact

ors,

The

con

clus

ion

that

pho

nem

e m

onito

ring

is u

naffe

cted

by

the

lexi

cal

status of the target-be

arin

g ph

onem

e st

ring

see

ms

at v

aria

nce

with

the

spir

it of

the

TR

AC

E m

odel

, sin

ce in

TR

AC

E, t

he le

xica

l lev

el is

alw

ays

invo

lved

in th

e pe

rcep

tual

pro

cess

, How

ever

. we

have

alr

eady

see

n th

atth

ere

are

cond

ition

s un

der

whi

ch th

e le

xica

l lev

el d

oes

not g

et m

uch

ofa

c~an

ce to

exe

rt a

n ef

fect

, In

the

prev

ious

sec

tion

we

saw

that

ther

e is

no le

xica

l eff

ect o

n id

entif

icat

ion

of a

mbi

guou

s w

ord-

initi

al ta

rget

s w

hen

the

subj

ect ~

s un

der

time

pres

sure

to r

espo

nd q

uick

ly; s

impl

y be

caus

e th

esu

bjec

t mus

t res

pond

bef

ore

info

rmat

ion

is e

ven

avai

labl

e th

at w

ould

allo

w th

e m

odel

-or

any

othe

r m

echa

nism

-to

prod

uce

a le

xica

l effe

ct.

In th

e Fo

ss a

nd B

lank

situ

atio

n, th

ere

is e

ven

less

rea

son

to e

xpec

t ale

xica

l effe

ct, s

ince

the

targ

et is

not

an

am

bigu

ous

segm

ent.

We

alre

ady

saw

that

act

ivat

ion

curv

es r

ise

rapi

dly

for

unam

bigu

ous

segm

ents

; in

the

present case, they can reach near-pe

ak le

vels

wel

l bef

ore

the

acou

stic

info

rmat

ion

that

indi

cate

s w

heth

er th

e ta

rget

is in

a w

ord

or n

onw

ord

has

reac

hed

the

s~bj

ect's

ear.

T

he' r

esul

ts o

f a s

imul

atio

n ru

n ill

ustr

atin

g th

ese

poin

ts a

re s

how

n in

Fig.

9. F

or th

is e

xam

ple,

we

imag

ine

that

the

targ

et is

Itl,

Not

e ho

w d

urin

gth

e in

itial

syl

labl

e of

bot

h st

ream

s, li

ttle

activ

atio

n at

the

wor

d le

vel h

asbe

en e

stab

lishe

d, E

ven

tow

ard

the

end

of th

e st

ream

, whe

re th

e in

for-

. mation is

just

com

ing

in w

hich

det

erm

ines

thai

"tr

ugus

" is

not

a w

ord,

ther

e is

littl

e di

ffer

ence

, bec

ause

in b

oth

case

s, th

ere

are

seve

ral a

ctiv

ew

ord-

leve

l can

dida

tes,

all

supp

ortin

g th

e w

ord-

initi

al I

t/. I

t is

only

aft

erth

e en

d of

the

stre

am th

at a

rea

l cha

nce

for

a di

ffere

nce

has

occu

rred

, Wel

lbe

fore

this

tim

e ar

rive

s, th

e su

bjec

t will

hav

e m

ade

a re

spon

se, s

ince

the

strength of the

It!

resp

onse

rea

ches

a le

vel s

uffi

cien

t to

guar

ante

e a

high

accu

racy

by

abou

t Cyc

le 3

0, w

ell b

efor

e th

e en

d of

the

wor

d, a

s ill

ustr

ated

:in

Fig

, 10,

E

ven

thou

gh a

ctiv

atio

ns a

re q

uite

rap

id f

or u

nam

bigu

ous

segm

ents

,th

ese

can

still

be

infl

uenc

ed b

y le

xica

l eff

ects

, pro

vide

d th

at th

e le

xica

l.in

form

atio

n is

ava

ilabl

e in

tim

e, I

n Fi

g, I

I, w

e ill

ustr

ate

this

poi

nt f

or th

eph

onem

e It

I i'n

the

stre

ams

Isik

rtl

(the

wor

d "s

ecre

t")

and

Igld

A

guld

ut,"

a n

onw

ord)

, The

fig

ure

show

s th

e st

reng

th o

f th

e It

I r

espo

nse

as a

fun

ctio

n of

pro

cess

ing

cycl

es, r

elat

ive

to a

ll ot

her

resp

onse

s ba

sed

on a

ctiv

atio

ns o

f ph

onem

e un

its a

t Cyc

le 4

2, th

e pe

ak o

f th

e in

put s

pec-

ific

atio

n fo

r th

e It

/. C

lear

ly, r

espo

nse

stre

n~' h

gro

ws

fast

er fo

r th

e It!

inIs

ikr

tl th

an f

or th

e It

! in

Ig

ldAt!

; pic

king

an

arbi

trar

y th

resh

old

of .

9 fo

rresponse initiation, we find that the

It!

in Is

ikr

tl re

ache

s cr

iteri

on a

bout

3 cy

cles

or

75 m

s so

oner

than

the

It I i

n Ig

ld"t

/.Studies showing lexical effects in reaction times.

Mar

slen

-Wils

on(1

980)

has

rep

orte

d an

exp

erim

ent t

hat d

emon

stra

tes

the

exis

tenc

e of

lexi

cal e

ffec

ts in

pho

nem

e m

onito

ring

for

pho

nem

es c

omin

g at

late

r po

i~ts

in w

ords

. For

pho

nem

es c

omin

g at

the

begi

nnin

g of

a w

ord

or a

t the

end

of th

e fi

rst s

ylla

ble,

he

foun

d no

fac

ilita

tion

for

phon

emes

in w

ords

rel

-

TR

AC

E M

OD

EL

IN.l*

,,,~

U

-1,1

II I

;.., 1.

:=:

:.0 0.

111

!:

40-

Q.. ~ 0.

MC

CLE

LLA

ND

AN

D E

LMA

N

00

12 1

6 24

30

36 4

2 48

54

Processing Cycles

FIG, 10. Time course

of growlh in Ihe probabililY

of

Ihe

III

resp

onse

bas

ed o

n ilc

livill

illns

of

phoneme unils in Slice 12, during processing

of

Ilar

gll ilnd I

I(g

s/.

The

v.:r

lical

lin.

:sin

dica

le th

e pe

aks

on Ih

e fe

alur

e pa

uern

s co

rres

pond

ing

10 !h

e su

cces

siv.

: pho

n.:m

.:s o

f Ih

epr

eseR

led

wor

d.-L

arl-

L-

-Lar

. I-L

--L

arl-

L-

ms

adva

ntag

e co

mpa

red

to c

orre

spon

ding

pos

ition

s in

non

words. This

com

pare

s qu

ite c

lose

ly w

ith th

e va

lue

of a

bout

75

ms

we

obta

ined

for

the

Isik

rt/-

ld't

l exa

mpl

e. A

t the

end

s of

eve

n lo

nger

wor

ds, t

he w

ord

ad-

vant

age

incr

ease

d in

siz

e to

185 ms. Marslen-

Wils

ons

resu

lt Ih

us c

on-

firm

s th

at th

ere

are '

inde

ed le

xica

l effe

cts

in p

hone

me

mon

ilori

ng-e

ven

for unambiguous inputs-

but u

nder

scor

es th

e ta

ct th

at th

ere

is n

o w

ord

adva

ntag

e fo

r ph

onem

es w

hose

pro

cess

ing

can

be c

ompl

eted

long

bef

ore

lexi

cal i

nflu

ence

s w

ould

ha\

:,e a

cha

nce

to s

how

up,

_d__

000 _

LJ..J

L1

12 16 24

30

36 4

2 48

54 60 66 72

Processing Cycles

FIG. t t. ProbabililY

of

the

It I

response as a funclion

of

proc

essi

ng c

ycle

s. b

ased

on

acli-

vatio

n of

pho

nem

e un

its a

t Cyc

l.:A

2. f

or th

e st

ream

Isi

k..

.1 (

"se

cre.

, and

Id'

guld

ut" )

. Ver

tical

line

s in

dica

te th

e pe

aks

of th

e in

put p

atte

rns

corr

espo

ndin

g 10

Ihe

succ

essi

ve p

hone

mes

in e

ither

slr

eam

.

IIIm

m

B I

100

.!:

.... ~

0.II

I1.

0

.... en

0.

III g 0.

III

III

020

-Lr-

s- -Lr-a-

s- -

Lr- a

-e-

FIG. 9. Stale of Ihe ltace al three di

ffer

ent p

ainl

s du

ring

the

proc

essi

ng o

f th

e w

ord

targ

el(/

targ

t/!

and

the

nonw

ord

"tru

gus "

(/tr

sf),

ativ

e to

pho

nem

es in

non

wor

ds (

in f

act t

here

was

a n

on w

ord

adva

ntag

efo

r th

ese

earl

y ta

rget

con

ditio

ns).

For

targ

ets

occu

rrin

g at

the

end

of th

ese

cond

syl

labl

e of

a tw

o-sy

llabl

e w

ord

(lik

e " s

ecre

tth

ough

the

stim

uli

in th

is p

artic

ular

exp

erim

ent w

ere

Dut

ch)

Mar

slen

- Wilson found an 85-

- -- ----

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

The

TR

AC

E m

odel

and

Mar

slen

-Wils

ons

CO

HO

RT

mod

el (

Mar

slen

-W

ilson

& T

yler

, 198

0; M

arsl

en-W

ilson

& W

elsh

, 1978) offer fairly similar

inte

rpre

tatio

ns o

f le

xica

l eff

ects

in p

hone

me

mon

itori

ng, B

oth

mod

els

acco

unt f

or th

e gr

owth

in th

e ef

fect

as

a fu

nctio

n of

pos

ition

in th

e w

ord,

As

in C

OH

OR

T, l

exie

alef

fect

s in

TR

AC

E d

epen

d on

the

poin

t at w

hich

the

patte

rn o

f act

ivat

ion

at th

e w

ord

leve

l beg

ins

to s

peci

fy th

e id

entit

ies

of the ph

onem

es, I

nC

OH

OR

T, t

here

is a

dis

cret

e m

omen

t whe

n th

isoc

curs

-whe

n th

e co

hort

of

item

s co

nsis

tent

with

the

inpu

t is

redu

ced

to a single item. In T~R

AC

E, t

hing

s ar

e no

t qui

te s

o di

scre

te, H

owev

er,

it w

ill s

till g

ener

ally

be

the

case

in T

RA

CE

that

the

size

of t

he le

xica

lef

fect

will

var

y w

ith th

e lo

catio

n of

the

"uni

que

poin

t,"

the

poin

t at w

hich

the

botto

m-u

p in

put r

emai

ns c

onsi

sten

t with

onl

y a

sing

le w

ord,

How

-ever, since Marslen-

Wils

ons

expe

rimen

ts w

ere

perf

orm

ed w

ith D

utch

wor

ds, w

e ha

ve n

ot b

een

able

to s

imul

ate

his

expe

rim

enta

l dem

onst

ratio

nof

this

eff

ect i

n de

tail.

TR

AC

E a

nd C

OH

OR

T m

ake

sim

ilar

pred

ictio

ns in

som

e si

tuat

ions

,bu

t not

in a

ll. I

n th

e ne

xt s

ectio

n, w

e co

nsid

er a

phe

nom

enon

whi

chT

RA

CE

acc

ount

s fo

r ,v

ia th

e sa

me

mec

hani

sms

it us

es to

acc

ount

for

the

lexi

cal e

ffec

ts w

e ha

ve b

een

cons

ider

ing.

Her

e, th

e gr

aded

fee

dbac

k fr

omth

e w

ord

leve

l to

the,

pho

nem

e le

vel a

llow

s T

RA

CE

to a

ccou

nt f

or a

nef

fect

that

wou

ld n

ot b

e pr

edic

ted

by C

OH

OR

T, u

nles

s ad

ditio

nal a

s-su

mpt

ions

wer

e m

ade,

A

re P

lrOllO

toct

ic R

ille

Ejfe

ct.f the Res"lt of a Co1lspiracy?

Rec

ently

, Mas

saro

;;tn

d C

ohen

(19

83)

have

rep

orte

d ev

iden

ce th

ey ta

keas

sup

port

for

the

use

of p

hono

tact

ic r

ules

in p

hone

me

iden

tific

atio

n. I

non

e ex

peri

men

t, M

assa

ro a

nd C

ohen

s st

imul

i con

sist

ed o

f pho

nolo

gica

lsegments ambiguous between

Irl

and

III

in d

iffe

rent

con

text

s. I

n on

e co

n-text (fLi/)

Irl

is permissible in English, but

III

is n

ot. I

n an

othe

r co

ntex

t(/5-i/) /11

is permissible in English but

Irl

is not. In a third context

(/L

i/)both are permissible, and in a fourth

(/v_

i/)

neith

er is

per

mis

sibl

e. M

assa

roan

d C

ohen

foun

d a

bias

to p

erce

ive

ambiguous segments as

Irl

whe

n Ir

lwas permissible or as

III

whe

n 11

/ w

as p

erm

issi

ble.

No

bias

app

eare

d in

eith

er o

f the

oth

er tw

o co

nditi

ons.

With

mos

t of

thes

e st

imul

i, ph

onot

actic

acc

epta

bilit

y is

con

foun

ded

with the actual lexica1 status of the item; thus

/nil

and

ffri

l fl

ee" and

free

) are both words, as is

Itri

l bul not

Illil

, In the

Is_i

l co

ntex

t, ho

w-

ever. neither Islil or

Isri

l ar

e w

ords

, yet

Mas

saro

and

Coh

en f

ound

a b

ias

to hear the ambiguous segment as

III,

in accordance with phonotactic

rule

s.It

turn

s ou

t tha

t TR

AC

E p

rodu

ces

the

sam

e ef

fect

, eve

n th

ough

it la

cks

phon

otac

tlc r

ules

, The

rea

son

is th

at th

e am

bigu

ous

stim

ulus

pro

duce

s

part

ial a

ctiv

atio

ns o

f a n

umbe

r of

wor

ds (

'~sl

eep" and "sleet" in the

mod

el' s

lexi

con;

it w

ould

als

o ac

tivat

e "s

leev

e,

" " sl

eek,

and

othe

rs in

a m

odel

with

a f

ulle

r le

xico

n). N

one

of th

ese

wor

d un

its g

ets

as a

ctiv

eas

it w

ould

if th

e en

tire

wor

d ha

d be

en p

rese

nted

, How

ever

, all

of th

em(i

n th

e si

mul

atio

n, th

ere

are

ony

two,

but

the

prin

cipl

e st

ill a

pplie

s) a

repa

rtia

lly a

ctiv

ated

, and

all

cons

pire

toge

ther

and

con

trib

ute

to th

e ac

ti-vation of

III.

This feedback support for the

III

allo

ws

it to

dom

inat

e th

eIr

l, just as it would if

Islil

w

ere

an a

c~ua

l wor

d, a

s sh

own

in F

ig, 1

2,

The

hyp

othe

sis

that

pho

nota

ctic

rul

e ef

fect

s ar

e re

ally

bas

ed o

n w

ord

activ

atio

ns le

ads

to a

pre

dict

ion:

that

we

shou

ld b

e ab

le to

rev

erse

thes

eef

fect

s if

we

pres

ent i

tem

s th

at a

re s

uppo

rted

str

ongl

y by

one

or

mor

ele

xica

l ite

ms

even

if th

ey v

iola

te p

hono

tact

ic r

ules

, A r

ecen

t exp

erim

ent

by E

lman

(19

83)

conf

irm

s th

is p

redi

ctio

n, I

n th

is e

xper

imen

t, am

bigu

ous

phonemes (for example, halfway between

Ibl

and

Id/)

w

ere

pres

ente

d in

thre

e di

ffere

nt ty

pes

of c

onte

xts,

In a

ll th

ree

type

s, o

ne o

f the

two

(in th

iscase, the

Id/)

was phonotactically acceptable, while the other (the

Ib/)

was

not

. How

ever

, the

con

text

s di

ffere

d in

thei

l' re

latio

n to

wor

ds. I

n on

eca

se, t

he le

gal i

tem

act

ually

occ

urre

d in

a w

ord

("bw

indl

edw

indl

eIn

a s

econ

d ca

se, n

eith

er it

em m

ade

a w

ord,

but

the

illeg

al it

em w

as v

ery

cI()

se to

a w

ord

("bw

acel

et"

dwac

elet

"). I

n a

thir

d ca

se, n

eith

er it

em

EiI

TllJ

IIT

rntil

ltil

l

9tIJ

JE

!l. 1

;..1

- 5

S J

1- -51- -81- -5

FIG

. 12.

Sta

te (

If th

e 1i

'ace

at s

ever

al p

oint

s in

pro

cess

ing

a se

gmen

t am

bigu

ous

betw

een

111

and

Irl,

in the context

Is_i

/. T

he u

nits

for

"sl

eep "

IIs

lip/)

and

"sl

eet"

(/s

lit/)

are

box

edto

geth

er s

ince

they

take

on

iden

tical

act

ivat

ion

valu

es.

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

was

par

ticul

arly

clo

se to

a w

ord

("bw

ime

dwim

eR

esul

ts

of

the

expe

rimen

t are

sho

wn

in Th

ble 4. The existence

of

a w

ord

iden

tical

toon

e of

the two alternatives or differing from one

of

the

alte

rnat

ives

by

asingle phonetic feature

of

one

phon

eme

stro

ngly

influ

ence

d th

e su

bjec

t'ch

oice

s be

twee

n th

e tw

o al

tern

ativ

es, I

ndee

d, in

the

case

whe

re th

e ph

o-notactically irregular alternative ("bw

acel

et)

was

one

fea

ture

aw

ay f

rom

a pa

rtic

ular

lexi

cal i

tem

(" b

race

let"

), s

ubje

cts

tend

ed to

hea

r th

e am

big-

uous

item

in a

ccor

d w

ith th

e si

mila

r le

xica

l ite

m (

that

is, a

s a

Ibl)

even

thou

gh it

was

pho

nota

ctic

ally

inco

rrec

t.. To determine whether the model w

ould

als

o pr

oduc

e su

ch a

reve

rsal

of

the phonotactic rule effects with the appropriate kinds

of

stim

uli,

ran a simulation using a simulated inputambiguous between

Ipl

and

It I i

nthe context I-Iuli/,

Ipl

is p

hono

tact

ical

ly a

ccep

tabl

e in

this

con

text

, but

It I i

n th

is c

onte

xt m

akes

an

item

that

is v

ery

clos

e to

the

wor

d " t

ruly

,The results

of

this

run

, at t

wo

diff

eren

t poi

nts

duri

ng p

roce

ssin

g, a

resh

own

in F

ig. 1

3, E

arly

on

in p

roce

ssin

g, th

ere

is a

slig

ht b

ias

in fa

vor

of

the

Ipl

over the

Itl,

because at first a large number

of

Ipll

wor

ds a

reslightly more activated than any words beginning with

Itl,

Lat

er, t

houg

h,th

e It

I get

s th

e up

per

hand

as

the

wor

d " t

ruly

" co

mes

to d

omin

ate

at th

eword level. Thus, by the end

of

the

wor

d or

sho

rtly

ther

eaft

er, t

he c

lose

stw

ord

has

begu

n to

pla

ya d

omin

atin

g ro

le, c

ausi

ng th

e m

odel

to p

refe

rthe phonotactically inappropriate interpretation

of

the

ambi

guou

s in

itial

segm

ent.

Of

cour

se, a

t the

sam

e tim

e th

e w

ord

" tru

ly" tends to support

Irl

rath

erth

an

III for the second segment.. Thus, even. though th

is s

egm

ent i

s no

tambiguous, and the III would suppress the

Irl

inte

rpre

tatio

n in

a m

ore

neutral context, the

Irl

stay

s qu

ite a

ctiv

e,

Tra

ding

Rel

atio

ns a

nd C

ateg

oriL

'al P

erc'

eptio

n

In th

e si

mul

atio

ns c

onsi

dere

d th

us fa

r, p

hone

me

iden

tific

atio

~ is

intlu

-enced by two different kinds

of

fact

ors,

fea

tura

l and

lexi

cal.

Whe

n on

eso

rt

of

info

rmat

ion

is la

ckin

~, th

e ot

her

can

com

pens

ate

for

it. T

he im

age

tha, emerges from these kinds

of

findings is

of

a sy

stem

that

exh

ibits

grea

t fle

xibi

lity

by b

eing

abl

e to

bas

e id

entif

icat

ion'

dec

isio

ns o

n di

ffere

ntso

urce

s of

information, It is.

of course, well established il1

at w

ithin

the

feat

ura

l dom

ain

each

pho

nem

e is

generally signaled by a number

of

dif-

ferent cues, and that human subjects can trade these cues

off

agai

nst e

ach

othe

r, T

he T

RA

CE

mod

el e

xhib

its th

i-s

sam

e fl

exib

ility

, as

we

deta

ilsh

ortly

.But there is something

of

a pa

rado

x, W

hile

the

p(:r

cept

ual m

echa

nism

sex

hibi

t gre

at f

lexi

bilit

y in

the

cues

that

they

rel

y on

for

pho

nem

e id

enti-

fica

tion,

they

als

o ap

pear

to b

e qu

ite "

cate

gori

cal"

in n

atur

e. T

hat i

sth

ey p

rodu

ce m

uch

shar

per

boun

dari

es b

etw

een

phon

etic

cat

egor

ies

than

we

mig

ht e

xpec

t bas

ed o

n th

eir

sens

itivi

ty to

mul

tiple

cues; and they

appe

ar to

trea

t aco

ustic

ally

dis

tinct

feat

ure patterns as perceptually

equi

vale

nt, a

s lo

ng a

s th

ey a

re id

entif

ied

as in

stan

ces

of

the

sam

e ph

o-ne

me.

In th

is s

ectio

n, w

e ill

ustr

ate

that

in T

RA

CE

, jus

t as

in h

uman

spe

ech

. per

cept

ion,

fle

xibi

lity

in f

eatu

re in

terp

reta

tion-

spec

ifica

lly, t

he a

bilit

yto trade one feature

of

a ph

onem

e of

f aga

inst

ano

ther

-coe

xist

s w

ith a

stro

ng te

nden

cy to

war

d ca

tego

rica

l per

cept

ion.

For

thes

e si

mul

atio

ns, t

he m

odel

was

str

ippe

d do

wn

to th

e es

sent

ial

min

imum

nec

essa

ry, s

o th

at th

e ba

sic

mec

hani

sms

prod

ucin

g cu

e tr

adc-

n:::u

u:n

JIT

!iI:

TI

!a:it

Ln

u::r

::ill

fillJ

8iam

u I

I U

I i

-f I

I I

P r

a r

iP r

,,

TA

BL

E 4

Perc

enla

ge C

hoic

e of

Pho

nola

clic

ally

Irr

egul

ar C

onso

nant

Stim

ulus

type

Leg

al w

ord/

illeg

al n

on w

ord

Leg

al n

on w

ord/

illeg

al n

onw

ord

Leg

al n

onw

ord/

illeg

al n

earw

ord

Exa

mpl

e

dwin

dle/

bwin

dle

dwim

e/bw

ime

dwac

elel

/bw

acel

el

Perc

enta

ge o

f id

enlif

iclil

ions

as "

illeg

al"

phon

eme

F(2,34) = 26.414, p

c:: .

001.

luli- _

lull- _

luli- _

luli-

FIG. 13. Slate of the Trace al several points in processing an ambiguous

Ipl-

/11

segm

enl

followed by Ilulil

TR

AC

E M

OD

EL

. MC

CLE

LLA

ND

AN

D E

LMA

N

100

150 300

seve

ral c

ateg

o~ic

al p

erce

ptio

n st

udie

s of

VO

T c

ontin

ua (u

sing

Ig

/-/k

/.

Id/-

/tl.

or

Ib/-

/pl

stim

uli)

hav

e co

vari

ed b

oth

VO

T a

nd F

IOF.

if o

nly

beca

use

FIO

F te

nds

to c

ovar

y w

ith V

OT

Whl

.ll r

ealis

tic s

timul

i are

use

d(e

.g..

Piso

ni &

Laz

arus

. 1974: Samuel. 1977), Though the simulations us

e

Ig/-

/kl

cont

inuu

m. w

e co

nsid

er s

ever

al c

ateg

oric

al p

erce

ptio

n ex

peri

-ments using

Id/-

/tl

and

Ibl-

lpl

cont

inua

. sin

ce th

e sa

me

dim

ensi

ons

can

diff

eren

tiate

the

two

mem

bers

of

both

of

thes

e ot

her

pair

s, W

e al

so c

on-

side

r da

ta o

btai

ned

in e

xper

imen

ts o

n ot

her

cont

inua

. usi

ng o

ther

cue

s,W

e co

uld

easi

ly h

ave

repe

ated

the

sim

ulat

ions

with

oth

er s

ets

of c

ontin

ua; .

how

ever

. the

gen

eral

qua

litat

ive

form

of

the

resu

lts w

ould

be

the

sam

e,W

hat w

ould

var

y fr

om c

ase

to c

ase

wou

ld b

e th

e m

agni

tude

of

the

effe

ctof

a s

tep

alon

g a

give

n di

men

sion

,T

he p

atte

rn o

f ex

cita

tory

inpu

t to

the

VO

T a

nd F

IOF

dete

ctor

s pr

o-duced by the canonical mock speech

Igl

and

Ikl

used

in th

e si

mul

atio

nsar

e ill

ustr

ated

in F

ig. 1

5,

Trad;"g relat;OIu,

TR

AC

E q

uite

nat

ural

ly te

nds

to p

rodu

ce tr

adin

gre

latio

ns b

etw

een

feat

ures

. sin

ce it

rel

ies

on th

e w

eigh

ted

sum

of

the

exci

tato

ry in

puts

to d

eter

min

e ho

w s

tron

gly

the

inpu

t will

act

ivat

e a

par-

ticul

ar p

hone

me

unit.

All

else

bei

ng e

qual

. the

pho

nem

e un

it re

ceiv

ing

the

larg

est s

um b

otto

m-u

p ex

cita

tion

will

be

mor

e st

rong

ly a

ctiv

ated

than

any

othe

r, a

nd w

ill th

eref

ore

be th

e m

ost l

ikel

y re

spon

se w

hen

a ch

oice

mus

t be

mad

e be

twee

n on

e ph

onem

e an

d an

othe

r, S

ince

the

net b

otto

m-

up input is just the sum of all of the inputs, no one input is necessarily

deci

sive

in th

is r

egar

d,G

ener

ally

, exp

erim

ents

dem

onst

ratin

g tr

adin

g re

latio

ns b

etw

een

two

or .

mor

e cu

es m

anip

ulat

e ea

ch o

f the

cue

s ov

er a

num

ber

of v

alue

s ra

ngin

gbe

twee

n a

valu

e m

ore

typi

cal o

f on

e of

two

phon

emes

and

a v

alue

mor

ety

pica

l of t

he o

ther

, Sum

mer

fiel

d an

d H

agga

rd d

id th

is f

or V

OT

and

FIO

F, a

nd f

ound

the

typi

cal r

esul

t. na

mel

y th

at th

e va

lue

of o

ne c

ue th

atgives rise to 50% choices of

Ikl

was

affe

cted

by'

the

valu

e of

the

othe

rcu

e: th

e hi

gher

the

valu

e of

FIO

F, th

e sh

orte

r th

e va

lue

of V

QT

nee

ded.

for

50%

cho

ices

of

Ik/.

Unf

ortu

nate

ly; t

hey

did

not p

rese

nt f

ull c

urve

sre

latin

g ph

onem

e id

entif

icat

ion

to th

e va

lues

use

d on

eac

h of

the

two

dim

ensi

ons,

In

lieu

of th

is, w

e pr

esen

t cur

ves

in F

ig, 1

6 fr

om a

cla

ssic

trad

ing

rela

tions

exp

erim

ent,

by D

enes

(195

5), S

imila

r pa

ttern

s of

res

ults

have

bee

n re

port

ed in

oth

er s

tudi

es, u

sing

oth

er c

ues

(e,g" Massaro.

1981

, Fig

s. 4

and

5),

thou

gh th

e tr

ansi

tions

are

oft

en s

omew

hat s

teep

er(s

ee b

elow

for

a d

iscu

ssio

n of

the

is~u

e of

ste

epne

ss).

We

have

cho

sen

to p

rese

nt th

e sh

allo

wer

cur

ves

repo

rted

by

Den

es b

ecau

se in

them

we

see

clea

rly.

that

ther

e ar

e ca

ses

in w

hich

a c

ue th

at f

avor

s on

e of

the

two

phon

emes

to a

mod

erat

e de

gree

will

giv

e ri

se to

the

perc

eptio

n of

the

othe

r ph

onem

e w

hen

pair

ed u

p w

ith a

str

ong

cue

that

fav

ors

the

othe

r

offs

and

cat

egod

cal p

erce

ptio

n co

uld

be b

roug

ht to

the

fore

. The

wor

dle

vel w

as e

limin

ated

alto

geth

er. a

nd a

t the

rho

nem

elev

el th

ere

wer

e on

lythree phonemes.

tal. Ig/.

and

Ik/,

plus silence

(I-I

).

From

thes

e fo

ur it

ems.

inputs and percepts of the form

ga-

and

ka-

coul

d be

con

stru

cted

.. T

he fo

llow

ing

addi

tiona

l con

stra

ints

wer

e im

pose

d on

the

feat

ure

spec

i-

fications of each of the phonemes: (I) the

Ial

and

I-I

had no overlap with

eith

er

Igl

or

Ik/,

so that neither

Ial

nor

I-I

wou

ld b

ias

the

activ

atio

ns o

fth

e Ig

l an

d Ik

l ph

onem

e un

its w

here

they

ove

rlap

ped

with

the

cons

onan

t:(2

) Ig

l an

d Ik

l w

ere

iden

tical

on

five

of

the

seve

n di

men

sion

s. a

nd d

iffe

red

only

on

the

rem

aini

ng tw

o di

men

sion

s,

The two dimensjons which differentiated

Igl

and

Ikl

wer

e vo

ice

onse

ttim

e (V

OT

) an

d th

e ()

nset

fre

quen

cy o

f th

e fi

tst f

orm

ant (

FIO

F), T

hese

dim

ensi

ons

repl

aced

the

voic

ing

and

burs

t am

plitu

de d

imen

sion

s us

ed in

all o

f th

e ot

her

sim

ulat

ions

, Fig

ure

14 il

lust

rate

s ho

w F

IOF

tend

s to

incr

ease

as

voic

e on

set t

ime

is d

elay

ed.

Sum

mer

fiel

d an

d H

agga

rd (

1977

) ha

ve s

how

n th

at s

ubje

cts

are

sens

itive

both

to V

aT a

nd to

FIO

F an

d th

at it

is p

ossi

ble

to tr

ade

one

of th

ese

cues off against the other. Thus. the boundary between

Igal

an

d Ik

al

shif

tsto

long

er V

OT

swhe

n FI

sta

rts

off

low

er r

athe

r th

an h

ighe

r,C

ateg

oric

al p

erce

ptio

n an

d tr

adin

g re

latio

ns a

mon

g cu

es h

ave

been

stud

ied

on a

var

iety

of d

iffer

ent c

ontin

ua b

y a

varie

ty o

f diff

eren

t inv

es-

tigat

ors,

We

have

chi

osen

to f

ocus

on

the

VO

T a

nd F

IOF

feat

ures

. as

exemplified by the

Igal

-/kal

co

ntin

uum

. bec

ause

ther

e is

dat

a on

trad

e-of

fs b

etw

een

thes

e cu

es (

Sum

mer

fiel

d &

Hag

gard

, 197

7). a

nd b

ecau

se

2000

1500

i'510

00Ii

I. 0:lL 500

TIM

E

FlU

, 14,

Sch

emat

ic d

iag~

am of a syllable that will be heard as

Igal

or

Ik

al,

depe

ndin

g on

the

poin

t in

the

sylla

ble

at w

hich

voi

cing

beg

ins,

Prio

r to

the

onse

t of v

oici

ng. F

2 '(l

OP

curv

el is

ene

rgiz

ed b

y ap

erio

dic

nois

e so

urce

s. a

nd F

I is

"cu

t bac

k" (

the

nois

e so

urce

has

liUle

or

no e

nerg

y in

this

ran

gel.

Bec

ause

of t

he fa

ct th

at F

t ris

es o

ver

time

afte

r sy

llabl

eon

set (

as th

e vo

cattr

uct m

oves

from

a s

hape

con

sist

ent w

ith th

e co

nson

ant i

nto

a. s

hape

cons

iste

nt w

ith...

he v

owel

l. its

freq

uenc

y at

the

onse

t of v

oici

ng is

hig

her

for

late

r va

lues

of V

OT

. Par

amet

ers

used

in c

onst

ruct

ing

this

sch

emat

ic s

ylla

ble

are

deri

ved

from

Kew

ley-

!'ort

's (

1982

1 an

alys

is o

f the

par

amet

ers

of fo

rman

ts. i

n na

tura

l spe

ech.

and

are

sim

ilar

toth

ose

used

in m

any

perc

eptu

al e

xper

imen

ts,

....

..5 0.

:5 0,

I.. U)

0.

....

..5 075

:5 0.

till

s..

en 025

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

Ioo

~80

I!i 4

9

, ~20

r 0

III

12345 Ikl

I .

Voi

ce O

nset

Tim

e10

0 20

0FR

ICA

TIO

N D

UR

AT

ION

(M

SEC

)

FIG

. .16

. Res

ulls

of a

n ex

perim

enl d

emon

slra

ling

Ihe

Irad

e-of

f bel

wee

n IW

O c

ues

10 Ih

eidentity of

Isl

and

Iii.

Dala from Denes, 1955

, fill

ed b

y th

e m

odel

of

Mas

saro

and

Coh

en,

1977. e. so ms; 0, 100 ms; 8, ISO ms; A

, 200

ms,

Rep

rinl

ed w

ilh p

erm

issi

on f

rom

Mas

saro

and

Coh

en (

1977

).

1.00

1&1

1234

5 Ik

l

trad

e-of

f cur

ves

as h

ave

been

gen

eral

ly r

epor

ted,

we

gene

rate

d a

set o

f25

inte

rmed

iate

pho

netic

seg

men

ts m

ade

up b

y pa

irin

g ea

ch o

f fi

ve d

if-

fere

nt in

term

edia

te p

atte

rns

on th

e V

OT

dim

ensi

on w

ith e

ach

of li

vedi

ffere

nt in

term

edia

te p

atte

rns

on th

e FI

OF

dim

ensi

on. T

he d

ilfcr

ent

feat

ure

patte

rns

used

on

each

dim

ensi

on a

re s

how

n in

Fig

. 15,

alo

ng w

iththe canonical feature patterns for

IgJ

and

Ikl

on e

ach

of th

e Iw

o di

men

-si

ons,

On

the

rem

aini

ng fi

ve d

imen

sion

s, th

e in

term

edia

te s

egm

ents

all

had the common canonical feature values for

Ig/

and

Ik/.

The

mod

el w

as te

sted

with

eac

h of

the

25 s

timul

i. pr

eced

ed b

y si

lenc

e(I

- I) and followed by

la-I.

In th

is a

nd

all s

ubse

quen

t sim

ulat

ions

we

repo

rtin

this

pap

er. t

he p

eak

of th

e in

itial

sile

nce

phon

eme

occu

rred

at T

ime

Slic

e 6

in th

e in

put.

and

the

peak

s of

suc

cess

ive

phon

eme

segm

ents

oc-

curred at six sl

ice

inte

rval

s. T

hus.

for

thes

e st

imul

i. th

e pe

ak o

n th

ein

term

edia

te p

hone

tic s

egm

ent o

ccur

red

at S

lice

12. t

he p

eak

of th

e fo

l-lo

win

g vo

wel

occ

urre

d at

Slic

e 18

. and

~he

pea

k of

the

fina

l sile

nce

oc-

curr

ed a

t Slic

e 24

. For

eac

h in

put '

pres

ente

d. th

e in

tera

ctiv

e ac

tivat

ion

proc

ess

was

allo

wed

to c

ontin

ue th

roug

h a

tota

l of 6

0 tim

e sl

ices

. wel

lpa

st th

e en

d of

the

inpu

t. T

he s

tate

of t

he T

race

at v

ario

us p

oint

s in

proc

essi

ng. f

or th

e m

ost/g

/~Ii

ke o

f th

e 25

stim

uli,

is s

how

n in

Fig

. 17.

At

the

end

of th

e 60

th ti

me

slic

e. w

e re

cord

ed th

e ac

tivat

ion

of th

e un

its f

orIg

/ an

d Ik

l in

Tim

e Sl

ice

12 a

nd th

e . probability of choosing

Igl

base

d on

thes

e ac

tivat

ions

, (It

mak

es n

o di

ffer

ence

to th

e qu

alita

tive

appe

aran

ceof

the

resu

lts if

a d

iffer

ent d

ecis

ion

time

is u

sed;

ear

lier

deci

sion

tim

esar

e as

soci

ated

with

sm

alle

r di

ffer

ence

s in

rel

ativ

e ac

tivat

ion

betw

een

the

IgI

and

Ikl

phon

eme

units

. and

late

r on

es w

ith la

rger

dif

tere

nces

. but

the

gene

ral p

atte

rn is

the

sam

e,

Ft Onset Frequency

FIG

. 15.

Can

onic

al fe

atur

e-level inpul for Ig! and I

kI,

on I

helw

o di

men

sion

s Ih

al d

islin

guis

h .

them

. and

Ihe

palle

rns

used

for

the

live

inle

rmed

iale

val

ues

used

in th

e Ir

adin

g re

lalio

nssi

mul

atio

n, A

long

Ihe

absc

issa

of e

ach

dim

ensi

on Ih

e ni

ne u

nils

for

the

nine

dil1

eren

l val

uerdnges of the dimension are armyed. The curves labeled Ig! and

Ikl

jndi

cale

Ihe

rela

live

slre

nglh

of

the

exci

tato

ry in

pullo

eac

h i,)

f Ihe

se u

nils

, pro

duce

d by

Ihe

indi

cale

d ph

onem

e.T

he c

anon

ical

cur

ves

also

indi

cale

Ihe

slr

engl

hs o

f th

e fe

atur

e-la

- pho

nem

e co

nnec

lions

for

Ig!.

an

d Ik

l on

Ihe

se d

imen

sion

s. T

hai i

s. I

he c

anon

ical

inpu

t pal

lern

for

eac

h ph

onem

eex

aclly

mal

ches

Ihe

slr

engl

hs o

f Ih

e co

rres

pond

ing

feat

ure-

phon

eme

conn

eclio

ns. N

um-

bere

d cu

rves

on

each

dim

ensi

on s

how

Ihe

feat

ure

palle

rns

used

in Ih

e Ir

adin

.: re

lalio

nssi

mul

alio

n.

phon

eme,

An

addi

tiona

l fin

ding

is th

e bo

win

g of

the

curv

es; t

hey

tend

tobe

app

roxi

mat

ely

linea

r th

roug

h th

e m

iddl

e of

thei

r ra

nge,

but

to le

vel

off a

t bot

h en

ds. w

here

' the

val

ues

on b

oth

dim

ensi

ons

agre

e in

poi

ntin

gto

one

alte

rnat

ive

or th

e ot

her,

To

see

if T

RA

CE

wou

ld s

imul

ate

the

basi

c tr

ade-

off

effe

ct o

btai

ned

bySu

mm

erfi

eld

and

Hag

gard

. and

to s

ee if

it w

ould

prd

duce

the

sam

e sh

ape

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

~ 1,

00"-

060

-..c

Ik/-

like

valu

es o

n bo

th d

imen

sion

s, In

term

s of

Sum

mer

field

and Hag-

gard

's m

easu

re. t

he v

alue

of

VaT

nee

ded

to a

chie

ve 5

0% p

roba

bilit

y of

repo

rtin

g Ik

/. w

e ca

n se

e th

at th

e V

aT n

eede

d in

crea

ses

as th

e FI

OF

decr

ease

s, ju

st a

s th

ese

inve

stig

ator

s fo

und.

C

ue tr

ade-

offs

in p

hone

me

iden

tific

atio

n ar

e ac

coun

ted

for

in d

etai

l by

the

feat

ure

inte

grat

ion

mod

el o

fOde

n an

d M

assa

ro (

1978

; Mas

saro

. 198

1;

Mas

sarQ

and

Ode

n. I

980a

. 198

0b);

Whi

le w

e ha

ve s

how

n ho

w T

RA

CE

can

acco

unt f

or th

e ba

sic

trad

e-of

f ef

fect

and

the

gene

ral f

orm

of

the

trad

e-of

f cur

ves.

we

have

not

yet

atte

mpt

ed th

e ki

nds

of d

etai

led

fits

that

Mas

saro

, Ode

n, a

nd c

olla

bora

tors

hav

e re

port

ed in

a n

umbe

r of

stu

dies

,H

owev

er. t

he m

odel

s ar

e qu

ite s

imila

r. s

o it

seem

s ra

ther

unl

ikel

y th

atcu

e tr

ade-

off

data

wou

ld b

e ab

le to

diS

crim

inat

e be

twee

n th

em, A

nd b

oth

mak

e sp

ecia

l ass

umpt

ions

abo

ut la

ck o

f in

vari

ance

of

cues

to p

hone

me

iden

tity

acro

ss c

onte

xts,

O

ne a

ppar

ent d

issi

mila

rity

bet

wee

n th

e m

odel

s de

serv

es c

omm

ent.

Whe

reas

cue

str

engt

hs a

re c

ombi

ned

mul

tiplic

ativ

ely

in th

e de

term

inat

ion

of r

espo

nse

stre

ngth

s in

the

feat

ure

inte

grat

ion

mod

el. t

hey

are

com

bine

dad

ditiv

eiy

in th

e bo

ttom

-up

inpu

ts to

the

units

in T

RA

CE

, How

ever

, in

TR

AC

E, t

wo

furt

her

com

puta

tiona

l ste

ps ta

ke p

lace

bef

ore

thes

e in

puts

result in resp

onse

str

engt

hs. F

irst

, the

inte

ract

ive-

activ

atio

n process en-

hanc

es d

iffe

renc

es b

etw

een

com

petin

g un

its, S

econ

d, th

e re

sulti

ng u

nit

activ

atio

ns a

re s

ubje

cted

to a

n ex

pone

ntia

l tra

nsfo

rmat

ion.

Jus

t thi

s. second step by its

elf

wou

ld tr

ansf

orm

infl

uenc

es th

at h

ave

addi

tive

effe

cts

on u

nit a

ctiv

atio

ns in

to in

flue

nces

that

. hav

e m

ultip

licat

ive

effe

cts

on r

e-sp

onse

str

engt

h. T

hus,

the

mod

els

wou

ld b

e m

athe

mat

ical

ly e

quiv

alen

tif

the

inte

ract

ive

activ

atio

n pr

oces

s w

ere

sim

ply

repl

aced

by

a lin

ear,

addi

tive

com

bina

tion

of in

puts

to th

e un

its. I

n qu

antit

ativ

e fo

rmul

atio

nsof

the

inte

ract

ive

activ

atio

n pr

oces

s cl

osel

y re

late

d to

the

ones

we

use

(Gro

ssbe

rg, 1

978)

, wha

t the

inte

ract

ive

activ

atio

n pr

oces

s do

es is

sim

ply

resc

ale

the

unit

activ

atio

ns, p

rese

rvin

g th

e ra

tios

of th

eir

botto

m-u

pac

tivat

ion

but k

eepi

ng th

em b

ound

ed. T

houg

h ou

r ve

rsio

n of

thes

e eq

ua-

tions

doe

s no

t do

this

exa

ctly

, the

way

s in

whi

ch it

dev

iate

s fr

om th

isw

ould

be

diff

icul

t to

use

as th

e ba

sis

for

an e

mpi

rica

l dis

tinct

ion

betw

een

the

TR

AC

E a

ppro

ach

and

the

feat

ure

inte

grat

ion

mod

el"

Thu

s, u

p to

apo

int,

we

can

see

TR

AC

E a

s (a

ppro

xim

atel

y) im

plem

entin

g th

e co

mpu

-ta

tions

spe

cifi

ed in

ade

n an

d M

assa

ros

mod

el. T

he m

odel

s di

ffer,

thou

gh, i

n th

at T

RA

CE

is d

ynam

ic a

nd in

that

it in

corp

orat

es f

eedb

ack

to th

e ph

onem

e le

vel.

Thi

s al

low

s T

RA

CE

to a

ccou

nt f

or c

ateg

oric

alpe

rcep

tion

in a

diff

eren

t way

.Categorical perception.

In s

pite

ofth

e fa

ct th

at T

RA

CE

is q

uite

flex

ible

in th

e w

ay it

com

bine

s in

form

atio

n fr

om d

iffe

rent

fea

ture

s to

det

erm

ine

the identity of a ph

onem

e, th

e m

odel

is q

uite

categorical in its overt

resp

onse

s, T

his

is il

lust

rate

d in

two

way

s: f

irst

. the

mod

el s

how

s a

muc

hsh

arpe

r tr

ansi

tion

in it

s ch

oice

s of

res

pons

es a

s w

e m

ove

from

Ig/ to

Ikl

07+

- g

II..

g 04

~ 03

5;!.

0 I

Xn"

-X

..- -

Xa-

+2

-X..- +.

1'10

. 17,

The

sta

te o

f the

'/i'ac

e at

var

ious

poi

nts

durin

g an

d af

ter

the

pres

enta

tion

of a

sylla

hle

cuns

istil

fg (

,f th

e m

ost I

gI-l

ike

ot th

e 2S

inte

rmed

iate

seg

men

ts u

sed

in th

e tr

adin

grelations experiment. represented by

I'!(/

. preceded by silence and followed by

lal,

then

anot

her

sile

nce.

Res

pons

e pr

obab

ilitie

s w

ere

com

pute

d us

ing

the

form

ulas

giv

en e

arlie

rfo

r co

nver

ting

activ

atio

ns to

res

pons

e st

reng

ths

and

stre

ngth

s in

to p

rob-

abili

ties,

The

res

ultin

g re

spon

se p

roba

bilit

ies,

for

eac

h of

the

25 c

ondi

-tio

ns o

f th

e ex

peri

men

t, ar

e sh

own

' in

Fig

, 18

. The

pat

tern

of

resu

lts is

quite

sim

ilar

to th

at o

btai

ned

in D

enes

(1955) experiment on the

1st-

cont

inuu

m. T

he c

ontr

ibut

ion

of e

ach

cue

is a

ppro

xim

atel

y lin

ear

and

addi

tive

in th

e m

iddl

e of

the

rang

e; b

ut th

e cu

rves

fla

tten

out a

t the

extr

emes

, as

in th

e D

enes

(19

55)

expe

rim

ent.

Mor

e im

port

antly

, the

mod

-el

's b

ehav

ior

exhi

bits

the

abili

ty to

trad

e on

e cu

e of

f ag

ains

t ano

ther

. For

exam

ple,

ther

e ar

e th

ree

diffe

rent

com

bina

tions

of f

eatu

re v

alue

s w

hkh

lead

to a

pro

babi

lity

betw

een

.82

and

,85 of choosing

Ik/:

(I)

the

neut

ral

valu

e of

the

VO

T d

imen

sion

cou

pled

with

the

mos

t Ik/

-lik

e va

lue

on th

e1'

101'

dim

ensi

on: (

2) th

e ne

utra

l val

ue o

n th

e F

IOF

dim

ensi

on c

oupl

edw

ith th

e m

ost I

k/-l

ike

valu

e of

the

VaT

dim

ensi

on; a

nd (

3) th

e so

mew

hat

...;' '- 060-

Yoke Olisel.Tirne

FI(L III, Simulated prob;lbility of choosing

Ik/ll

t T

ime

Slic

e 1i

0, fo

r ea

ch o

f the

25

stim

uli

used

in 'h

e tr

adin

g re

latio

ns s

imul

atio

n ex

peri

men

t. N

umbe

rs n

ext t

o ea

ch c

urve

ref

er to

the

inte

rmed

iate

p;ll

Iern

on,

the

FIO

F c

ontin

uum

use

d in

the

five

stim

uli c

ontr

ibut

ing

toea

ch c

urve

, Uig

her

num

bers

cor

resp

ond

to h

ighe

r va

lues

of F

IOF

.

:..,

::= 0

40-

020

a.. 0,

0 I

3, 4

6

7 8

\I 10 II 12

Stim

ulus

Num

ber

FIG

. 20.

Eff

ects

of

com

petit

ion

on p

hone

me

activ

iltio

ns. T

he f

irst

pan

el s

how

s re

lativ

eamounts of bollom-up excitatory input to

Igl

and

IkJ

produced by each of the II st

imul

ius

ed in

the

cate

goric

al p

erce

ptio

n si

mul

atio

n, T

he s

econ

d pa

nel s

how

s th

e ac

tivat

ions

ul"

units for Ig/ and

Ikl

at T

ime

Cyc

le 6

0, S

timul

i 3 a

nd 9

cor

resp

und

10 I

he c

anon

ical

/gl a

ndIk

/, re

spec

tivel

y.

of th

e un

its f

or /g

/ and

/k/ a

t the

end

of

60 c

ycle

s of

pro

cess

ing.

The

slig

htdi

ffer

ence

s in

net

inpu

t hav

e be

en g

reat

ly a

mpl

ified

. and

the

activ

atio

ncu

rves

exh

ibit

a m

uch

stee

per

tran

sitio

n th

an th

e re

lativ

e bo

ttom

-up

ex-

cita

tion

curv

es.

The

re a

re tw

o re

ason

s w

hy th

e ac

tivat

ion

curv

es ,a

re s

o m

uch

shar

per

than

the

initi

al b

otto

m-u

p ex

cita

tion

func

tions

. The

pri

mar

y re

ason

iscompetitive inhibition.

The

eff

ect o

f th

e co

mpe

titiv

e in

hibi

tion

at th

e ph

o-ne

me

leve

l is

to g

reat

ly m

agni

fy th

e sl

ight

diff

eren

ce in

the

exci

tato

ryin

puts

to th

e tw

o ph

onem

es. I

t is

easy

to s

ee w

hy th

is h

appe

ns. O

nce

one

phon

eme

is s

light

ly m

ore

stro

ngly

act

ivat

ed th

an th

e ot

her.

it e

xert

sa

stro

nger

inhi

bito

ry in

fluen

ce o

n th

e ot

her

than

the

othe

r ca

n ex

ert o

nit.

The

net

res

ult i

s th

at "

the

rich

get r

iche

r," This general property of

com

petit

ive

inhi

bitio

n m

echa

nism

s w

as d

iscu

ssed

by

McC

lella

nd a

nd R

u-m

elha

rt (

1981

), fo

llow

ing

earli

er o

bser

vatio

ns b

y G

ross

berg

(se

e G

ross

-berg, 1978, f

or a

dis

cuss

ion)

and

Lev

in (

1976

); it

is a

lso

wel

l kno

wn

ason

e po

ssib

le b

asis

' of e

dge

enha

ncem

ent e

ffec

ts in

low

leve

ls o

f vi

sual

TR

AC

E M

OD

EL

alon

g th

e V

aT a

nd F

IOF

dim

ensi

ons

than

we

wou

ld e

xpec

t fro

m th

esl

ight

cha

nges

in th

e re

lativ

e ex

cita

tion

of th

e /g

/ and

/kI

units

. Sec

ond,

.th

e m

odel

tend

s to

obl

itera

te d

iffer

ence

s be

twee

n di

ffere

ntin

puts

whi

chit

iden

tifie

s as

the

sam

e ph

onem

e, w

hile

sha

rpen

ing

diff

eren

ces

betw

een

inpu

ts a

ssig

ned

to d

iffe

rent

cat

egor

ies,

We

will

con

side

r ea

ch o

f th

ese

two

poin

ts in

turn

, aft

er w

e de

scrib

ethe

stim

uli u

sed

in the simulations.

Ele

ven

diff

eren

t con

sona

nt f

eatu

re p

atte

rns

wer

e us

ed, e

mbe

dded

inth

e sa

me

sim

ulat

ed /-

/ context as in the trading relations simulation,

The

stim

uli v

arie

d fr

om v

ery

low

val

ues

of b

oth

VaT

and

FIOF, more

extr

eme

than

the

cano

nica

l /g/

, thr

ough

ver

y hi

gh v

alue

s on

bot

h di

men

-sions, more extreme than the canonical

/kl.

All

the

stim

uli w

ere

spac

edeq

ual d

ista

nces

apa

rt o

n th

e V

aT a

nd F

IOF

dim

ensi

ons,

The

loca

tions

of th

e pe

ak a

ctiv

atio

n va

lues

on

each

of

thes

e tw

o co

ntin

ua a

re s

how

nin

Fig

, 19,

F

igur

e 20

indi

cate

s th

e re

lativ

e in

itial

bot

tom

-up

activ

atio

n of

the

/g/

, and

/k/ p

hone

me

units

for

eac

h of

the

II stimuli used in the simulation.

The

firs

t thi

ng to

not

e is

that

the

rela

tive

botto

m-u

p ex

cita

tion

of th

e tw

oph

onem

e un

its d

iffe

r on

ly s

light

ly, F

or e

xam

ple,

the

cano

nica

l fea

tl,Jr

epa

ttern

for

/g/ s

ends

75%

as

muc

h ex

cita

tion

(0 /g

/ as

it se

nds

to /k

/, T

hefe

atur

e pa

ttern

two

step

s to

war

d/g/

from

/k/ (

Stim

ulus

5),

sen

ds 8

8% a

sm

uch

activ

atio

n to

/g/ a

s to

/k/.

The

fig

ure

also

indi

cate

s, in

the

seco

nd p

anel

, the

res

ultin

g ac

tivat

ions

r:: 0 1.

::;.... 0

0.c.

J

iii 0.

::;

026

r::

!:! 1.

....

::; 0. 0:

10

5 0.

.r:: Il.

/s/

/k/

1 2 3 4 5 6 7 8 91011

Voi

ce O

nsel

Tim

e

/s/

/k/

1 2

3 4

5 6

7 8

9 10

11

0 2

Ft Onsel Frequency

FtG

. t9.

Loc

atio

ns o

f pe

ak a

ctiv

atio

ns a

long

Ihe

VaT

and

FtO

F di

men

sion

s. lo

r ea

ch o

fth

e II

stim

uli u

sed

in th

e ca

tego

rica

l per

cept

ion

sim

ulat

ion.

MC

CLE

LLA

ND

AN

D E

LMA

N

/8/

/k/

...

1'2

Stim

ulus

Num

ber

/s/

/k/

TR

AC

E M

OD

EL

:46

MC

CLE

LLA

ND

AN

D E

LMA

N

/81

Ikl

Thi

s ob

viou

sly

brin

gs o

ut th

e fa

ct th

at th

e ap

pare

nt s

teep

ness

of

the

iden

tific

atio

n fu

nctio

n de

pend

s on

the

grai

n of

the

sam

plin

g of

diff

eren

tpo

ints

alo

ng th

e co

ntin

uum

bet

wee

n tw

o st

imul

i, as

wel

l as

a ho

st

othe

r fa

ctor

s (L

ane,

196

5), W

heth

er a

n em

piri

cal o

r si

mul

ated

iden

tifi-

catio

n fu

nctio

n lo

oks

stee

p or

not

dep

ends

on

the

sele

ctio

n of

stim

uli b

yth

e ex

peri

men

ter

or m

odel

er, H

owev

er, i

t is

wor

th n

otin

g th

at th

e st

eep-

ness

of

the

iden

tific

atio

n fu

nctio

n is

inde

pend

ent o

f th

e pr

esen

ce o

ftr

adin

g re

latio

ns, a

t lea

st in

the

sim

ulat

ion

mod

el, T

hat i

s, if

we

had

used

mor

e w

idel

y se

para

ted

step

s al

ong

the

VO

T a

nd F

IOF

dim

ensi

on, w

e

wou

ld h

ave

obta

ined

muc

h st

eepe

r id

entif

icat

ion funct1Qns. The additivity

of e

xcita

tory

inpu

ts w

ould

stil

l app

ly, a

nd th

us it

wou

ld s

till b

e po

ssib

leto trade cues off against e~ch other,

In T

RA

CE

, the

cat

egor

ical

out

put o

f th

e m

odel

com

es a

bout

onl

y af

ter

an interactive competition process that greatly sharpens the differences

in the activation of the detectors for the relevant units, This interactive

proc

ess

take

s tim

e. I

n th

e si

mul

atio

n re

sults

rep

orte

d he

re, w

e as

sum

edth

at s

ubje

cts

wai

ted

a fi

xed

time

befo

re r

espo

ndin

g. B

ut, i

f w

e as

sum

e, t

hat s

ubje

cts

are

able

to r

espo

nd a

s so

on a

s th

e re

spon

se st

reng

th r

atio

reac

hes

som

e cr

iteri

alle

vel,

we

wou

ld f

ind

that

sub

ject

s w

ould

be

able

to r

espo

nd m

ore

quic

kly

to s

timul

i nea

r th

e pr

otot

ype

of e

ach

cate

gory

than

they

can

to s

timul

i nea

r th

e bo

unda

ry, T

his

is e

xact

ly w

hat w

as

foun

d by

Pis

o~i a

nd T

ash

(197

4).

The

sha

rpen

ing

the

mod

el im

pose

s on

the

iden

tific

atio

n fu

nctio

n,

conj

unct

ion

with

the

faC

t tha

t it c

an tr

ade

one

feat

ure

off

agai

nst a

noth

er,

show

s ho

w th

e m

odel

, lik

e hu

man

per

ceiv

ers

of s

peec

h, c

an b

e bo

th

flex

ible

and

dec

isiv

e at

the

sam

e tim

e, T

hese

asp

ects

of T

RA

CE

are

shar

ed w

ith th

e fe

atur

e in

tegr

atio

n m

odel

(M

assa

ro, 1

981)

,. How

ever

, the

TR

AC

E m

odel

's d

ecis

iven

ess

exte

nds

eve.

1 fu

rthe

r th

an w

e ha

veob

-

serv

ed th

us f

ar: f

eedb

ack

from

the

phon

eme

to th

e fe

atur

e le

vel t

ends

to.

caus

e th

e m

odel

to o

blite

rate

the

diffe

renc

es b

etw

een

inpu

t fea

ture

pat

-te

rns

that

res

ult i

n th

e id

entif

icat

ion

of th

e sa

me

phon

eme,

thus

allo

win

gth

e m

odel

to p

rovi

de a

n ac

coun

t not

onl

y fo

r sh

arp

iden

tific

atio

n fu

nc-

tions

, but

als

o fo

r th

e fa

ct th

at d

iscr

imin

abili

ty o

f spee

ch s

ound

s is

far

poor

er w

ithin

cat

egor

ies

than

it is

bet

wee

n ca

tego

ries

.S

tric

tly s

peak

ing,

at l

east

as

defin

ed b

y Liberman, Cooper, Shank-

wei

ler,

and

Stu

dder

t-K

enne

dy (

1967

), tr

ue c

ateg

oric

al p

erce

ptio

n is

onl

yex

hibi

ted

whe

n th

e ab

ility

to d

iscr

imin

ate

diff

eren

t sou

nds

is n

o be

tter

than

. cou

ld b

e ex

pect

ed '

base

d on

the

assu

mpt

ion

that

the

only

bas

is a

liste

ner

has

for

disc

rim

inat

ion

is th

e ca

tego

rica

l ass

ignm

ent o

f th

e st

im-

ulus

to a

par

ticul

ar p

hone

tic c

ateg

ory,

How

ever

, it i

s co

nced

ed th

attr

ue"

cate

gori

cal p

erce

ptio

n in

this

sem

o: is

nev

er in

fac

t obs

erve

d(S

tudd

ert-

Ken

nedy

, Lib

erm

an, H

arri

s, &

Coo

per,

197

0), W

hile

it is

true

that

the

disc

rimin

atio

n o

f so

unds

is m

uch

bette

r fo

r so

unds

whi

ch p

er-

info

rmat

ion

proc

essi

ng, A

sec

ond

caus

e of

the

shar

peni

ng o

f th

e ac

tiva-

tion

curv

es is

the

phon

eme-

to-f

eatu

re fe

edba

ck, w

hich

we

cons

ider

in

deta

il in

a m

omen

t. T

he id

entif

icat

ion

func

tions

that

res

ult f

rom

app

lyin

g th

e L

uce

choi

ceru

le to

the

activ

atio

n va

lues

sho

wn

in th

e se

cond

pan

el o

f Fi

g, 2

0 ar

e

show

n in

Fig

. 21 along with the

lBX

di

scri

min

atio

n fu

nctio

n, w

hich

is

disc

usse

d be

low

. The

iden

tific

atio

n fu

nctio

ns a

re e

ven

shar

per

than

the

activ

atio

n cu

rves

; the

re is

onl

y a

4% c

hanc

e th

at th

e m

odel

will

choo

se

/k/ i

nste

ad o

f /g

/ for

Stim

ulus

5, f

or w

hich

/k/ r

ecei

ves

88%

as

muc

h

botto

m-u

p su

ppor

t as

/g/,

The

in~r

ease

d sh

arpn

ess

is d

ue to

th~

prop

ertie

s

of th

e re

spon

se s

tren

gth

assu

mpt

ions

. The

se a

ssum

ptio

ns e

ssen

tially

im-

plem

ent t

he n

otio

n th

at th

e se

nsiti

vity

of

the

deci

sion

mec

hani

sm, i

n

terms of

d'

for

choo

sing

the

mos

t str

ongl

y. a

ctiv

ated

of

two

units

, is

a

linea

r fu

nctio

n of

the

diff

eren

ce in

act

ivat

ion

of th

e tw

o un

its, W

hen

the

activations are far enough apart,

d'

)Viii

be

suffi

cien

t to

ensu

re n

ear-

lOO

%

corr

ect p

elfo

rman

ce, e

ven

thou

gh b

oth

units

hav

e gr

eate

r th

an 0

act

iva-

tion,

Of

cour

se, t

he .

amou

nt o

f se

para

tion

in th

e ac

tivat

ions

that

is n

ec-

essa

ry f

or a

ny g

iven

leve

l of

perf

orm

ance

is a

mat

ter

of p

aram

eter

s; th

ere

leva

nt p

aram

eter

her

e is

the

scal

e fa

ctor

use

d in

the

expo

nent

ial t

rans

-fo

rmat

ion

of a

ctiv

atio

ns. T

he v

alue

use

d fo

r th

is p

aram

eter

in th

e pr

esen

tsi

mul

atio

ns (

10)

was

the

sam

e as

that

use

d in

all

othe

r ca

ses

whe

re w

etr

ansl

ate

activ

atio

n in

to r

espo

nse

prob

abili

ty, i

nclu

ding

the

trad

ing:

rela

-tio

ns s

imul

atio

n.

Som

e re

ader

s m

ay b

e pu

zzle

d as

to w

hy T

RA

CE

II

exhi

bits

a s

harp

iden

tific

atio

n fu

nctio

n in

the

cate

gori

cal p

erce

ptio

n ex

peri

men

t, bu

tsh

ows

a m

uch

mor

e gr

adua

l tra

nsiti

on b

etw

een

/g/ a

nd /k

/ in

the

trad

ing

rela

tions

sim

ulat

ion,

The

rea

son

is s

impl

y th

at f

iner

ste

ps a

long

the

VO

Tan

d FI

OF

cont

inua

wer

e us

ed in

the

trad

ing

rela

tions

sim

ulat

ion,

All

of

the stimuli for the tl1ading relations si

mul

atio

n lie

bet

wee

n St

imul

i 6 a

nd4

in th

e ca

tego

rica

l per

cept

ion

sim

ulat

ion.

~ 1. 10

0

~ o~-

~ 0.

'-.. 0.

.. 6: 0. 00

0

020

10 II

Stim

ulus

F"L 21. Simulated identilicalion functions and forced-choice accuracy in the

AB

X

task

.

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

ceiv

ers

assi

gn to

dif

fere

nt c

ateg

orie

s th

an f

or s

ound

s th

ey a

ssig

n to

the

sam

e ca

tego

ry, t

here

is a

lso

at le

ast a

tend

ency

for

disc

rimin

atio

n to

be

som

ewha

t bet

ter

than

pre

dict

ed b

y th

e id

entif

icat

ion

func

tion,

eve

n be

-tw

een

stim

uli w

hich

are

alw

ays

assi

gned

to th

e. s

ame

cate

gory

. TR

AC

EII

pro

duce

s th

is k

ind

of a

ppro

xim

ate

cate

gori

cal p

erce

ptio

n.T

he w

ay it

wor

ks is

this

, Whe

n a

feat

ure

patte

rn c

omes

in, i

t sen

dsm

ore

exci

tatio

n to

som

e ph

onem

e un

its th

an o

ther

s; a

s th

ey b

ecom

eac

tive,

they

beg

in to

com

pete

, and

one

gra

dual

ly c

omes

to d

omin

ate

the

othe

rs, T

his

muc

h w

e ha

ve. a

lread

y ob

serv

ed, B

ut a

s th

is c

ompe

titio

npr

oces

s is

goi

ng o

n, th

ere

is a

lso

feed

bpck

from

the

phon

eme

leve

l to

the

feat

ure

leve

l. T

hus,

as

a pa

rtic

ular

pho

nem

e be

com

es a

ctiv

e, it

tend

s to

impo

se it

s ca

noni

cal p

atte

rn o

f act

ivat

ion

on th

e fe

atur

e le

vel,

The

effe

ctof

the

feed

back

bec

omes

par

ticul

arly

str

ong

as ti

me

goes

on,

sin

ce th

efe

atur

e in

put o

nly

exci

tes

the

feat

ure

units

ver

y br

iefly

; the

orig

inal

pat

-te

rn o

f ac

tivat

ion

prod

uced

by

the

phon

eme

units

is, t

here

fore

, gra

dual

lyre

plac

ed b

y th

e ca

noni

cal p

atte

rn im

pose

d by

the

feed

back

from

the

pho-

" ne

me

leve

l, T

he r

esul

t is

tha~

the

patte

rn o

f ac

tivat

ion

rem

aini

ng a

t the

feat

ure

leve

l aft

er 6

0 cy

cles

of

proc

essi

ng h

as b

ecom

e as

sim

ilate

d to

the

prot

otyp

e, I

n th

is w

ay, f

eatu

re p

atte

rns

for

diff

eren

t inp

uts

assi

gned

toth

e sa

me

cate

gory

are

ren

dere

d ne

arly

indi

stin

guis

habl

e,A

n im

pres

sion

of

the

mag

nitu

de o

f th

is e

ffec

t is

illus

trat

ed in

Fig

, 22,

whi

ch s

how

s ho

w d

iffe

rent

the

feat

ure

patte

rns

of a

djac

ent s

timul

i are

at

the

end

of 6

0 cy

cles

of

proc

essi

ng. T

he m

easu

re o

f di

ffere

nce

is s

impl

yI -

"b'

whe

re

"b

stan

ds f

or th

e co

rrel

atio

n of

the

patte

rns

prod

uced

by

stim

uli

and

b,

Onl

y th

e tw

o di

men

sion

s w

hich

act

ually

dif

fer

betw

een

the canonical

IgI

and

Ikl

are

cons

ider

ed in

the

diffe

renc

e m

easu

re, F

ur-

ther

mor

e, th

e co

rrel

atio

n co

nsid

ers

only

the

feat

ure

patte

rn o

n th

e fe

atur

e

units

in T

ime

Slic

e 12

, rig

ht a

t the

cen

ter

of th

e in

put s

peci

fica

tion.

If

all

dim

ensi

ons

are

cons

ider

ed, t

he v

alue

s of

the

diff

eren

ce m

easu

re a

re r

e-du

ced

over

all,

but t

he p

atte

rn is

the

sam

e, In

clus

ion

of ft

!'dtu

re p

atte

rns

from

sur

roun

ding

slic

es li

kew

ise

mak

es li

ttle

diffe

renc

e.T

o re

late

the

diffe

renc

e be

twee

n tw

o st

imul

i ~o

prob

abili

ty c

orre

ctchoice performance in the

AB

X

task

gen

eral

ly u

sed

in c

ateg

oric

al p

er-

cept

ion

expe

rimen

ts, w

e on

ce a

gain

use

the

Luce

(19

59) choice model.

The

pro

babi

lity

of id

entif

ying

stim

ulus

with alternative

in is given

by

Ix=

,,)

II.(

w

here

Sax is the "st

reng

th"

of th

e si

mila

rity

between (/ and

x.

Thi

s is

given simply by the exponential of the correlation of

and

"x = e

k,r"

x

g 0.

is 0.

and similarly for

Sbx'

(T

he e

xpon

entia

l tra

nsfo

rmat

ion

is r

equi

red

to tr

ans-

late

cor

rela

tions

, ran

ging

fro

m +

Ito

- I,

into

pos

itive

val

ues,

so

that

Luc

es

ratio

rul

e ca

n be

use

d. T

he s

ame

tran

sfor

mat

ion

is u

sed

for

tran

s-la

ting

activ

atio

ns in

to r

espo

nse

stre

ngth

s in

iden

tific

atio

n ta

sks.

) Here

is th

e pa

ram

eter

that

sca

les

the

rela

tion

betw

een

corr

elat

ions

and

stre

ngth

s, T

hese

ass

umpt

ions

are

con

sist

ent w

ith th

e ch

oice

ass

umpt

ions

mad

e fo

r id

entif

icat

ion

resp

onse

s, T

he r

esul

ting

resp

onse

pro

babi

litie

s,for one choice of the parameter

,.

(5)

are

show

n in

Fig

; 21

(the

exp

onen

-

tiation parameter

,.

is different than the parameter

used

in g

ener

atin

g

iden

tific

atio

n pr

obab

ilitie

s fr

om a

ctiv

atio

ns b

ecau

se c

orre

latio

ns a

nd a

c-tivations are not on equivalent scales),

Bas

ical

ly, t

he f

igur

e sh

ows

that

the

effe

ct o

f fe

edba

ck is

to m

ake

the

feat

ure

patte

rns

for

inpu

ts w

ell w

ithin

eac

h ca

tego

ry m

ore

sim

ilar

than

thos

e fo

r in

puts

nea

r th

e bo

unda

ry b

et~e

en categories. Differences be-

twee

n st

imul

i nea

r th

e pr

otot

ype

of th

e' s

ame

phon

eme

are

alm

ost o

bli-

tera

ted.

Whe

n tw

o st

imul

i str

addl

e th

e bo

unda

ry, t

he fe

atur

e-level pat-

tern

s ar

e m

uch

mor

e di

stin

ct. A

s a

resu

lt, th

e pr

obab

ility

of c

orre

clly

disc

rim

inat

ing

stim

uli w

ithin

a p

hone

me

cate

gory

is m

uch

low

er I

han

Ihe

prob

abili

ty o

f di

scri

min

atin

g st

imul

i in

diff

eren

t cat

egor

ies.

The

pro

cess

of

"can

onic

aliz

atio

n" of the representation of a speech

soun

d vi

a th

e fe

edba

ck m

echa

nism

take

s tim

e. O

urin

g Ih

is li

me,

Iw

oth

ings

are

hap

peni

ng: o

ne is

that

the

activ

atio

ns in

itial

ly p

rodu

ced

by th

esp

eech

inpu

t are

dec

ayin

g; a

noth

er is

that

the

feed

back

, whi

ch d

rive

s th

ere

pres

enta

tion

tow

ard

the

prot

otyp

e, is

bui

ldin

g up

. In

the

sim

ulat

ions

,

we

allo

wed

a c

onsi

dera

ble

amou

nt o

f tim

e fo

r th

ese

proc

esse

s be

fore

r:::

030

I 2

7 8

8 10. II 12

Stim

ulus

Num

ber

FIG

. 22.

Diff

eren

ces

betw

een

palle

rns

of a

ctiv

atio

n at

the

feat

ure

leve

l at C

ycle

60.

I()r

pairs of stimuli one step apart along the

Ir/-

iki

cont

inuu

m u

sed

for

prod

ucin

g th

e id

entif

i-ca

tion

func

tions

sho

wn

prev

ious

ly in

Fig

. 21.

The

dif

fere

nce

mea

sure

is th

e co

rrel

atio

n of

the

two

patte

rns,

sub

trac

ted

from

1.0

; thu

s, if

the

two

patte

rns

corr

elat

ed p

erfe

ctly

, the

irdifference would be O.

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

L~ '

com

putin

g si

mila

ritie

s of

dif

fere

nt a

ctiv

atio

n pa

ttern

s to

eac

h ot

her,

Ob-

viou

sly.

if w

e ha

d le

ft le

ss ti

me.

ther

e w

ould

not

hav

e be

en a

s m

uch

ofan

opp

ortu

nity

for

thes

e fo

rces

to o

pera

te. T

hus,

TR

AC

E is

in a

gree

men

twith the finding that there tends to be an increase in within-category

disc

rimin

atio

n w

hen

n ta

sk is

use

d w

hich

allo

ws

subj

ects

to b

ase

thei

r

resp

onse

s on

judg

m~n

ts o

f th

e si

mila

rity

of

stim

uli s

pace

d cl

osel

y to

-ge

ther

in ti

me

(Pis

onl&

Laz

arus

, 197

4).

It s

houl

d be

not

ed th

at it

wou

ld b

e po

ssib

le to

acc

ount

for

cat

egor

ical

perc

eptio

n in

TR

AC

E w

ithou

t inv

okin

g fe

edba

ck f

rom

the

phon

eme

leve

lto

the

feat

ure

leve

l, A

ll w

e w

ould

nee

d to

~o

is a

ssum

e th

at th

e fe

atur

ein

form

atio

n th

at g

ives

ris

e to

pho

nem

e id

entif

icat

ion

is in

acce

ssib

le, a

s. p

ropo

sed

by th

e m

otor

theo

ry o

f sp

eech

per

cept

ion

(Lib

erm

an e

t ai"

1967

). o

r is

rap

idly

lost

as

prop

osed

by

the

"dua

l-co

de"

mod

el (

Fujis

aki

& K

awas

him

a, 1

968;

Mas

saro

. 1975, 1981; Pisoni, 1973, 1975,)

The

dua

l-

code

mod

el, w

hich

has

had

con

side

rabl

e su

cces

s ac

coun

ting

for

cate

gor-

ical

per

cept

ion

data

, ass

umes

that

pho

nem

e id

entif

icat

ion

can

be b

ased

eith

er o

n pr

ecat

egor

ical

info

rmat

ion

or o

n th

e re

sults

of t

he p

hone

me

iden

tific

atio

n pr

oces

s, S

ince

it is

ass

umed

that

fea

ture

info

rmat

ion

deca

ysra

pidl

y (e

spec

ially

for

cons

onan

t fea

ture

s-se

e be

low

), r

espo

nses

mus

t

ofte

n be

bas

ed s

olel

y on

the

outp

ut o

f th

e ph

onem

e id

entif

icat

ion

proc

ess,

whi

ch is

ass

umed

to "

rovi

de a

dis

cret

e co

de o

fthe

seq

uenc

e of

pho

nem

es.

Thi

s in

terp

reta

tion

acco

unts

for

muc

h of

the

data

on

cate

gori

cal p

erce

p-tio

n qu

ite w

ell.

Inde

ed, i

t is

fairl

y di

fficu

lt to

find

way

s of

dis

tingu

ishi

ngbe

twee

n a

feed

back

f!1o

del a

nd o

ne th

at a

ttrib

utes

cat

egor

ical

per

Cep

tion

to a

loss

of

info

rmat

ion

from

the

feat

ure

leve

l cou

pled

with

a r

elia

nce

ona

mor

e ab

stra

ct c

ode,

Bot

h fe

edba

ck m

odel

s an

d du

al c

ode

mod

els

can

acco

mm

odat

e th

e fa

ct th

at v

owel

s sh

ow le

ss o

f a

tend

ency

tow

ard

cat-

egor

ical

per

cept

ion

than

con

sona

nts

(Fry

, Abr

amso

n, E

imas

, & L

ib-

erm

an, 1

962;

Pis

oni,

1973

). It

is s

impl

y ne

cess

ary

to a

ssum

e th

at v

owel

feat

ures

are

mor

e pe

rsis

tent

than

con

sona

nt f

eatu

res

(Cro

wde

r, 1

978,

1981

; Fuj

isak

i & K

awas

him

a, 1

968;

Pis

oni,

1973

, 197

5), H

owev

er, t

hetw

o cl

asse

s of

inte

rprt

etat

ions

do

diff

er in

one

way

, The

fee

dbac

k ac

coun

tse

ems

to d

iffe

r m

ost c

lear

ly f

rom

a li

mite

d fe

atur

e ac

cess

acc

Qun

t in

itspr

edic

tions

of p

erfo

rman

ce in

dis

crim

inat

ing

two

stim

uli,

both

aw

ay fr

omth

e ce

nter

of

a ca

tego

ry, b

ut s

till w

ithin

it H

ere,

TR

AC

E te

nds

to s

how

grea

ter

disc

rim

inat

ion

than

it s

how

s be

twee

n st

imul

i squ

arel

y in

the

mid

dle

of a

cat

egor

y,

Sta

ndar

d in

terp

reta

tions

of c

ateg

oric

al p

erce

ptio

n ca

n ac

coun

t for

in-

crea

ses

in ~

lo;c

rimin

abili

ty n

ear

the

boun

dary

bet

wee

n tw

o ca

tego

ries

(whe

re id

entif

icat

ion

.may

in fa

ct b

e so

mew

hat v

aria

ble)

, sim

ply

in te

rms

of th

e fa

ct th

at m

argi

nal s

timul

i are

mor

e lik

ely

to g

ive

rise

to d

iffer

ent

cate

gory

labe

ls, B

ut T

RA

CE

can

acc

ount

for

incr

ease

s in

dis

crim

inab

ility

at e

xtre

me

valu

es o

f fea

ture

con

tinua

whi

ch w

ould

not

giv

e ris

e to

dif-

fere

nt c

ateg

ory

labe

ls. I

n T

RA

CE

, the

rea

son

for

this

incr

ease

in d

iscr

im-

inab

ility

is th

at th

e ac

tivat

ion

of th

e ap

prop

riate

item

at t

he p

hone

me

leve

l is

,wea

ker,

and

ther

efor

e th

e fe

edba

ck s

igna

l is

wea

ker,

than

it is

whe

n th

e in

put o

ccur

s ne

ar th

e ce

nter

of

the category. For example,

Stim

ulus

I in

our

sim

ulat

ions

fal

ls b

elow

the

cano

nica

l/g/ s

timul

us, a

ndth

eref

ore

activ

ates

the

Ig/ p

hone

me

dete

ctor

less

str

ongl

y th

an s

timul

icloser to the canonical

Ig/,

A similar thing happens with the

Ik/.

Thi

s

resu

lts in

less

"ca

noni

caliz

atio

n"

of th

e ex

trem

e st

imul

i, an

d pr

oduc

es a

-sha

ped

disc

rim

inat

ion

func

tion,

as

show

n in

Fig

. 22,

The

re is

som

e ev

iden

ce b

eari

ng o

n th

is a

spec

t of

TR

AC

E's

acc

ount

of

cate

gori

cal p

erce

ptio

n, S

amue

l (1977) has reported

AB

X

disc

rim

inat

ion

data

that

sho

w n

otic

eabl

e m

inim

a in

the

disc

: im

inat

ion

func

tion

near

the

canonical stim~1i within each category on a

Id/-

/tl

cont

inuu

m, I

ndee

d,

Sam

uel's

acc

ount

of

this

eff

ect,

thou

gh n

ot c

ouch

ed in

term

s of

inte

rac-

tive

activ

atio

n pr

oces

ses,

has

a g

reat

dea

l of

sim

ilari

ty to

wha

t we

see

inT

RA

CE

; he

sugg

ests

that

nea

r-ca

noni

cal i

tem

s ar

e m

ore

stro

ngly

ass

im-

ilate

d to

the

cano

nica

l pat

tern

, Unf

ortu

nate

ly th

e ef

fect

we

seek

is fa

irly

subt

le, a

nd s

o it

will

be

diff

icul

t to

sepa

rate

fro

m n

oise

. In

Sam

uel'

expe

rim

ent.,

the

effe

ct is

fai

rly

clea

r-cu

t at b

oth

extr

emes

of t

he V

OT

cont

inuu

m in

thre

e ob

serv

ers

at th

e en

d of

ext

ensi

ve tr

aini

ng, a

s sh

own

in F

ig, 2

3, a

nd e

ven

unpr

actic

ed s

ubje

cts

tend

to s

how

the

effe

ct to

war

dthe high end of the VOT continuum, well past the prototype for

It/.

In s

umm

ary,

TR

AC

E a

ppea

rs to

pro

vide

a f

airl

y ac

cura

te a

ccou

nt o

fth

e ph

enom

ena

of c

ue tr

ade-

offs

and

cat

egor

ical

per

cept

ion

of s

peec

hso

unds

, It a

ccou

nts

for

cate

goric

al p

erce

ptio

n w

ithou

t rel

ying

on

the

no-

tion

that

the

phen

omen

on d

epen

ds o

n re

adou

t fro

m a

n ab

stra

ct le

vel o

fpr

oces

sing

; it a

ssum

es in

stea

d th

at th

e fe

atur

e le

vel,

like

othe

r le

vels

of

the

syst

em, i

s su

bjec

t to

feed

back

from

hig

her

leve

ls w

hich

act

ually

chan

ges

the

repr

esen

tatio

n as

it is

bei

ng r

etai

ned

in m

emor

y, p

ushi

ng

tow

ard

a ca

noni

cal r

epre

sent

atio

n of

the

phon

eme

mos

t str

ongl

y ac

tivat

edby

the

inpu

t.

Oth

er P

heno

men

a at

the

Pho

nem

e Le

vel

The

lite

ratu

re o

n ph

onem

e pe

rcep

tion

incl

udes

sev

eral

furt

her

findi

ngs

we

have

not

yet

bee

n ab

le to

con

side

r in

det

ail.

The

nex

t few

. par

agra

phs

cons

ider

one

of

thes

e fi

ndin

gs a

nd h

ow it

mig

ht b

e ac

com

mod

ated

in th

eTRACE model.

Effects of global and local context on phoneme identification.

In o

ur

sim

ulat

ions

of

trad

ing

rela

tions

, we

have

sho

wn

that

the

crite

rial

val

uene

eded

on

one

dim

ensi

on o

f st

imul

us v

aria

tion

can

be a

ffec

ted

by o

t~er

dim

ensi

ons.

Thu

s, w

hen

the

onse

t of

FI is

rel

ativ

ely

high

, sho

rter

voi

cing

late

ncie

s ar

e ne

eded

to p

erce

ive

a so

und

as u

nvoi

ced,

Oth

er f

acto

rs a

lso

innu

ence

the

phon

eme

perc

eive

d as

a r

esul

t of

a pa

rtic

ular

fea

tura

l inp

ut.

TR

AC

E M

OD

EL

TRAINED SUBJECTS

100

LZ

:un

.

. '

.0 "

/ -

20 '

AG

S

.....

I&J

..J ..J I&J

III

..J ... 100

c( 0

I&J

......

MD

S

100

....

80 ..

.40

\.20

MCB01

0205

0405

0101

010

'"'

MC

CLE

LLA

ND

AN

D E

LMA

N

CONTROL GROUP

spea

ker

para

met

ers,

Our

mai

n po

int h

ere

is th

at c

onne

ctio

n m

odul

atio

nis

qui

te a

diff

eren

t mec

hani

sm th

an th

e si

mpl

e a

dditi

ve ,

com

bina

tion

ofex

cita

tory

influ

ence

s th

at u

nder

lies

the

way

TR

AC

E a

ccoO

'nts for trade-

offs

am

ong

the

cues

to a

sin

gle

phon

eme

or f

or th

e ef

fect

s of

top-

dow

nin

flue

nces

on

the

phon

eme

boun

dary

,

Sum

mar

y of

Pho

nem

e Id

entif

icat

ion

Sim

ulat

iolls

We

have

con

side

red

a nu

mbe

r of

phe

nom

ena

conc

erni

ng th

e id

entit

i-ca

tion

and

perc

eptio

n of

pho

nem

es, T

hese

incl

ude

lexi

cal i

nflu

ence

s on

phpn

eme

iden

tific

atio

n, a

nd th

e la

ck th

ereo

f, b

oth

in r

eact

ion

time

and

in r

espo

nse

choi

ce m

easu

res;

"ph

onot

actic

rul

e" effects on ph

onem

eid

entif

icat

ion

and

the

role

of s

peci

fic

lexi

cal i

tem

s in

infl

uenc

ing

thes

eef

fect

s; th

e in

tegr

atio

n of

mul

tiple

cue

s to

pho

nem

e id

entit

y an

d th

e ca

t-eg

oric

al n

atur

e of

the

perc

ept t

hat r

esul

ts fr

om th

is in

tegr

atio

n. T

RA

CE

inte

grat

es a

ll of

thes

e ph

enom

ena

into

a s

ingl

e ac

coun

t tha

t inc

orpo

rate

sas

pect

s of

the

acco

unts

off

ered

for

par

ticul

ar a

spec

ts o

f th

ese

resu

lts b

yot

her

mod

els,

In th

e ne

xt s

ectio

n, w

e sh

ow h

ow T

RA

CE

can

also en-

com

pass

a n

umbe

r of

phe

nom

ena

conc

erni

ng th

e re

cogn

ition

of s

poke

nw

ords

,

. ,""

."

\.

CG

I

/ "

, ,..' "

. .. "

CG

2

CG

3

0 10 20 50 40 50 IiO

10

.0

TH

E T

IME

CO

UR

SE

OF

WO

RD

RE

CO

GN

ITIO

N

The

stu

dy o

f sp

oken

wor

d re

cogn

ition

has

a lo

ng h

isto

ry, a

nd m

any

mod

els

have

bee

n pr

opos

ed, M

orto

ns

now

-cla

ssic

logo

gen

mod

el(M

orto

n, 1

969)

was

the

first

to p

rovi

de a

n ex

plic

it ac

coun

t of t

he in

te-

grat

ion

of c

onte

xtua

l and

sen

sory

info

rmat

ion

in w

ord

reco

gniti

on. O

ther

mod

els

of th

is p

erio

d (e

,g.,

Bro

adbe

nt, 1

967) concentrated primarily on

effe

cts

of w

ord

freq

uenc

y, U

ntil

the

mid

197

0s, h

owev

er, t

here

was

littl

eex

plic

it co

nsid

erat

ion

of th

e tim

e co

urse

of s

poke

n w

ord

reco

gniti

on.

Sev

eral

stu

dies

by

Mar

slen

-Wils

on a

nd h

is c

olla

bora

tors

(M

arsl

en-

Wilson, 1973; Marslen-W

ilson

& T

yler

, 1975) and by Cole and hiscollab-

orat

ors

(Col

e, 1

973;

Col

e &

Jak

imik

, 1978, 1980) pioneered the in

vest

i-ga

tion

of th

is p

robl

em,

Mar

slen

-Wils

ons

CO

HO

RT

mod

el (

Mar

slen

~W

ilson

& T

yler

, 198

0;

M!i

rsle

n-W

ilson

& W

elsh

, 197

8) o

f spe

ech

perc

eptio

n w

as b

ased

on

this

earl

y w

ork

on th

e tim

e co

urse

of

spok

en w

ord

reco

gniti

on. T

he C

OH

OR

Tm

odel

was

one

of

the

sour

ces

of in

spir

atio

n fo

r T

RA

CE

, for

two

mai

nre

ason

s" F

irst

, it p

rovi

ded

an e

xplic

it ac

coun

t of

the

way

top-

dow

n an

dbo

ttom

-up

info

rmat

ion

coul

d be

com

bine

d to

pro

duce

a w

ord

reco

gniti

onm

echa

nism

that

act

ually

wor

ked

in r

eal t

ime.

Sec

ond,

it a

ccou

nted

for

the

findi

ngs

of a

num

ber

of im

port

ant e

xper

imen

ts d

emon

stra

ting

the

" on

-

line"

character of the speech recognition process. H

owev

er, s

ever

al d

e-fi

cien

cies

of

the

CO

HO

RT

mod

el h

ave

been

poi

nted

out

, as

we

shal

l see

,B

ecau

se T

RA

CE

was

mot

ivat

ed in

larg

e pa

rt b

y a

desi

re to

kee

p w

hat

is g

ood

abou

t CO

HO

RT

and

impr

ove

upon

its

wea

knes

ses,

we

begi

n th

is

VO

ICE

ON

SET

TIM

E (

mile

)FIG, 23. Identification (solid curves) and

AB

X

disc

rim

inat

ion

data

(da

shed

cur

ves)

fro

mIh

ree

prac

ticed

and

thre

e na

ive

subj

ects

. Sim

plifi

ed a

nd r

eprin

ted,

with

per

mis

sion

, fro

mSa

mue

l(

1977

).

The

iden

tity

of p

hone

mes

sur

roun

ding

a ta

rget

pho

nem

e, th

e ra

te o

fsp

eech

of

a, s

ylla

ble

in w

hich

a p

artic

ular

feat

ure

valu

e oc

curs

, as

wel

l as

char

acte

rist

ics

of th

e sp

eake

r an

d th

e la

ngua

ge b

eing

spo

ken

all i

nflu

ence

the

inte

rpre

tatio

ns o

f fe

atur

es. S

ee R

epp

and

Lib

erm

an (1984) for a dis-

cuss

ion

of a

ll of

thes

e so

rts

of in

flue

nces

on

the boundaries between

phon

emes

, It

has

bee

n su

gges

ted

by M

iller

, Gre

en, a

nd S

cher

mer

(198

4) a

nd b

yR

epp

and

Libe

rman

(19

84)

that

thes

e di

ffere

nt e

ffect

s m

ay h

ave

diffe

rent

sour

ces,

In

part

icul

ar, M

iller

et a

l. (1

984)

sug

gest

that

lexi

cal e

ffec

ts a

nd, s

eman

tic a

nd s

ynta

ctic

influ

ence

s on

the

one

hand

may

be

due

to a

dif-

fere

nt m

echa

nis~

than

infl

uenc

es s

uch

as s

peec

h ra

te a

nd c

oart

icul

ator

yin

flue

nces

due

to lo

cal p

hone

tic c

onte

xt.

The

ass

umpt

ions

we

have

inco

rpor

ated

into

TR

AC

E m

ake

a si

mila

rdi

stin

ctio

n, I

n T

RA

CE

I, w

e ha

ve a

ccou

nted

for

eff

ects

of

phon

etic

con

-te

xt b

y al

low

ing

activ

atio

ns o

f un

its to

infl

uenc

e th

e fe

atur

e-to

- pho

nem

eco

nnec

tions

in a

djac

ent t

ime

slic

es (

see

Elm

an &

McC

lella

nd, i

n pr

ess,

for

deta

ils).

In

the

disc

ussi

on,

we

' con

side

r w

ays

of e

xten

ding

the

con-

nect

ion

mod

ulat

ion

idea

to a

ccom

mod

ate

effe

cts

of v

aria

tions

in r

ate

and

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

sect

ion

by c

onsi

derin

g th

e C

OH

OR

T m

odel

in s

ome

deta

il. F

irst w

e re

-vi

ew th

e ba

sic

assu

mpt

ions

of

the

mod

el, t

hen

cons

ider

its

stre

ngth

s an

dw

eakn

esse

s. T

here

app

ear

to b

e fo

ur b

asic

ass

umpt

ions

of t

he C

OH

OR

Tm

odel

.

J. T

he m

odel

use

s th

e fir

st s

ound

(in

Mar

slen

-Wils

on &

Tyl

er, 1

980,

the

initi

al c

onso

nant

clu

ster

-plu

s-vo

wel

) of

the

wor

d to

det

erm

ine

whi

chw

ords

will

be

in a

n in

itial

coh

ort o

r ca

ndid

ate

set,

2. O

nce

the

cand

idat

e se

t is

esta

blis

hed,

the

mod

el e

limin

ates

wor

ds

from

the

coho

rt im

med

iate

ly, a

s"ea

ch s

ucce

ssiv

e ph

onem

e ar

rive

s, if

the

new

pho

nem

e fa

ils to

mat

ch th

e ne

xt p

hone

me

in th

e w

ord,

Wor

ds c

anal

so b

e el

imin

ated

on

the

basi

s of

sem

antic

con

stra

ints

, alth

ough

the

initi

alco

hoI'I

is a

ssum

ed to

'be determined by acoustic input alone.

3. W

ord

recognition occurs immediately, as

. soo

n as

the cohort has

been

red

uced

to a

sin

gle

mem

ber;

in a

n au

dito

ry le

xica

l dec

isio

n ta

sk,

the

deci

sion

that

an

item

is a

non

wor

d ca

n be

mad

e as

soo

n as

ther

e ar

eno

rem

aini

ng m

embe

rs in

the

coho

rt,

4. W

ord

reco

gniti

on c

an in

fluen

ce th

e id

entif

icat

ion

of ph

onem

es in

a

wor

d on

ly a

fter

the

wor

d ha

s be

en r

ecog

nize

d,

The

re is

a c

onsi

de~a

ble

body

of

data

that

sup

port

s va

riou

s pr

edic

tions

of th

e C

OH

OR

T m

odel

, It h

as b

een

obse

rved

in a

var

iety

of

para

digm

s

thai

lexi

cal i

nflu

ence

s on

pho

nem

e id

entif

icat

ion

resp

onse

s ar

e m

uch

grea

ler

lale

r in

wor

ds th

an a

t the

ir b

egin

ning

s (B

agle

y, 1

900;

Col

e an

d

Jakimik, 1978, 1980; Marslen-Wilson, 1980; Marslen-Wilson and Welsh,

1978

). W

e co

nsid

ered

som

e of

this

evi

denc

e in

earlier section~.. A

noth

er

impo

rtan

t fin

ding

suJ

i)po

rtin

g C

OH

OR

T is

the

fact

that

the

reat

tion

time

to d

ecid

e th

at a

n ite

m is

a n

on w

ord

is c

onst

ant,

whe

n m

easu

red

from

the

occu

rren

ce o

f the

firs

t pho

nem

e th

at r

ules

out

the

last

rem

aini

ng w

ord

inth

e co

hort

(M

arsl

en-W

ilson

, 198

0),

Perh

aps

the

mos

t dir

ect s

uppo

rt f

or th

e ba

sic

wor

d re

cogn

ition

as-

sum

ptio

ns o

f C

OH

OR

T c

omes

fro

m th

e ga

ting

para

digm

, int

rodu

ced

firs

tby

Gro

sjea

n (1

980)

, In

this

par

adig

m, s

ubje

cts

are

requ

ired

to g

uess

the

iden

t it y

of a

wor

d af

ter

hear

ing

succ

essi

ve p

rese

ntat

ions

of

the

wor

d, T

hefir

st p

rese

ntat

ion

is c

ut o

fT so

that the subject hears only the first

(N

= 3

0 to

50

in d

iffe

rent

stu

dies

). L

ater

pre

sent

atio

ns a

re s

ucce

ssiv

ely

leng

then

ed in

N-m

s in

crem

ents

unt

il ev

entu

ally

the

who

le w

ord

is p

re-

sent

ed. T

he d

urat

ion

at w

hich

hal

fthe

sub

ject

s co

rrec

tly id

entif

y th

e w

ord

is c

alle

d th

e "i

sola

tiQn

poin

t. "

Con

side

rabl

y m

ore

inpu

t is

requ

ired

befo

resubjects are. reason~bly sure of the identity of the w

ord;

that

poi

nt is

tenn

ed th

e "a

ccep

tanc

e po

int." Grosjean

s in

itial

stu

dy c

onfi

rmed

man

y

basi

c pr

edic

tions

of

CO

HO

RT

, tho

ugh

it al

so r

aise

d a

few

dif

ficu

lties

for

it (s

ee b

elow

). I

n a

mor

e re

cent

stu

dy u

sing

the

sam

e m

etho

d, T

yler

and

Wes

sels

(19

83)

carr

ied

out a

ver

y cl

ose

anal

ysis

of

the

rela

tion

betw

een

the

empi

rica

lly d

eter

min

ed is

olat

ion

poin

t and

the

poin

t at w

hich

the

inpu

t

the

subj

ect h

as r

ecei

ved

is c

onsi

sten

t with

one

and

onl

y on

e re

mai

ning

item

, the

poi

nt a

t whi

ch r

ecog

nitio

n w

ould

be

exep

ecte

d to

occ

ur in

the

CO

HO

RT

mod

el. T

hey

repo

rt th

at th

e is

olat

ion

poin

t fal

ls v

ery

clos

e to

this

theo

retic

ally

der

ived

rec

ogni

tion

poin

t, st

rong

ly s

uppo

rtin

g th

e ba

sic

immediacy assumptions of the COHORT model,

It s

houl

d be

not

ed th

at th

e ga

ting

task

is n

ot a

tim

ed ta

sk, a

nd s

o it

does

not

. pro

vide

a d

irec

t measure of what the su

bjec

t kno

ws

as th

e

spee

ch in

put i

s un

fold

ing,

How

ever

, it i

s no

w in

fair

ly w

ide

use,

and

Cotton and Grosjean (1984) have established that the basic patterns of

resu

lts o

btai

ned

in G

rosj

ean

s (1

980)

pio

neer

ing

gatin

g ex

peri

men

t do

not

depe

nd o

n th

e pr

esen

tatio

n of

suc

cess

ivel

y lo

nger

and

long

erpr

esen

ta-

tions

of

the

sam

e st

imul

us.

A dilemma for COHORT,

Tho

ugh

the

CO

HO

RT

mod

el a

ccou

nts

for

ala

rge

body

of d

ata,

ther

e ar

e se

vera

l diff

icul

t:"s

with

it. W

e co

nsid

er f

irst

the

one

that

see

ms

the

mos

t ser

ious

: as

stat

ed, C

OH

OR

T r

equi

res

ac-

cura

te, u

ndis

tort

ed in

form

atio

n ab

out t

he id

entit

y of

the

phon

emes

in a

wor

d up

to th

e is

olat

ion

poin

t. W

ords

can

not e

nter

into

cons

ider

atio

n

unle

ss th

e in

itial

con

sona

nt c

lust

er p

lus

vow

el is

hea

rd. a

nd th

ey a

r~discarded from it as soon as a ph

onem

e co

mes

alo

ng th

at th

ey f

ail t

om

atch

. No

expl

icit

proc

edur

e is

des

crib

ed f

or r

ecov

erin

g w

ords

into

the

coho

rt o

nce

they

hav

e be

en e

xclu

ded

from

it, o

r w

hen

the beginning of

the

wor

d is

not

acc

urat

ely

perc

eive

d du

e to

noi

se o

r el

isio

n,T

hese

asp

ects

of

CO

HO

RT

mak

e it

very

diff

icul

t for

the

mod

el to

explain recognition of words with distorted be

ginn

ings

. suc

h as

dwib

ble"

(Norris, 1982), or w

ords

who

se b

egin

ning

s ha

ve b

een

repl

aced

by n

oise

(Sa

Jass

o &

Pis

oni,

1985

). F

rom

a c

ompu

tatio

nal p

oint

of

view

,th

is m

akes

the

mod

el a

n ex

trem

ely

britt

le o

ne; i

n pa

rtic

ular

it f

ails

to d

eal

with

the

prob

lem

of

nois

e an

d un

ders

peci

fica

tion

whi

ch is

so

cruc

ialf

orre

cogn

ition

of r

eal s

peec

h (T

hom

pson

. 1984

),

The

rec

ogni

zabi

lity

of d

isto

rted

item

s lik

e "dw

ibbl

e" might be taken

as s

ugge

stin

g th

at w

hat w

e ne

ed to

do

is lib

eral

ize

the

crite

rion

for

en-

teri

ng a

nd r

etai

ning

wor

ds in

the

coho

rt. T

hus,

the

coho

rt c

ould

be

de-

fined

as

the

set o

f wor

ds c

onsi

sten

t with

wha

t has

bee

n he

ard

or m

ild(e

,g" one or two fe

atur

es)

devi

atio

ns f

rom

wha

t has

bee

n he

ard.

Thi

swould allow mild distortions like replacing

Irl

with

Iw

l not to disqualify

a w

ord

from

the

coho

rt. I

t wou

ld a

lso

allo

w th

e m

odel

to c

ope

with

cas

esw

here

the

begi

nnin

g of

the

wor

d is

und

ersp

ecifi

ed; i

n- th

ese

case

s. th

e

initi

al c

ohor

t wou

ld s

impl

y be

larg

er th

an in

the

case

whe

re th

e in

put

dear

ly s

peci

fied

the

initi

al p

hone

mes

.H

owev

er. t

here

is s

till a

pro

blem

. Som

etim

es w

e ne

ed to

be

able

toru

le o

ut it

ems

whi

ch m

ism

atch

the

inpu

t on

one

or tw

o di

men

sion

s an

d

som

etim

es w

e do

not

. Con

side

r th

e ite

ms

"plea

sant" and "

blac

elet

." In

the

firs

t cas

e. w

e ne

ed to

exclude "

pres

ent" from the cohort, so the

TR

AC

E M

OD

EL

MC CLELLAND AND ELMAN

slig

ht d

iffe

renc

e be

twee

n II

I an

d Ir

l mus

t be

suff

icie

nt to

rul

e it

out;

in th

ese

cond

cas

e, w

e do

not

wan

t to

lose

the

wor

d " b

race

let,

" si

nce

it pr

o-vides the best fit overall to the input. Thus, in this case, the difference

betw

een

III a

nd Ir

l mus

t not

be

allo

wed

to r

ule

a w

ord

cand

idat

e ou

t.T

hus

the

dile

mm

a: o

n th

e on

e ha

nd, w

e w

ant a

mec

hani

sm th

at w

ill b

eab

le to

sel

ect t

he c

orre

ct w

ord

as s

oon

as a

n un

dist

orte

d in

put s

peci

fies

it un

ique

ly, t

o ac

coun

t for

the

Tyl

er a

nd W

esse

ls r

esul

ts. O

n th

e ot

her

hand

, we

do n

ot w

ant t

he m

odel

to c

ompl

etel

y el

imin

ate

poss

ibili

ties

whi

ch m

ight

late

r tu

rn o

ut to

. be

corr

ect,

We

shal

l sho

rtly

see

that

TR

AC

Epr

ovid

es...

way

out

of

this

dile

mm

a.

Another problem for COHORT.

Gro

sjea

n (1

985)

has

rec

ently

poi

nted

out a

noth

er p

robl

em f

or C

OH

OR

T, n

amel

y, th

e po

ssib

ility

that

the

sub-

ject

may

be

unce

rtai

n ab

out t

he location of the beginning of each suc-

cess

ive

wor

d, A

taci

t ass

umpt

ion

of th

e m

odel

is th

at th

e su

bjec

t goe

sin

to th

e be

ginn

ing

of e

ach

wor

d kn

owin

g th

at it

is' t

he b

egin

ning

. In

the

rela

ted

mod

el' o

f Col

e an

d Ja

kim

ik (

1980) this as

sum

ptio

n is

mad

e ex

plic

it.U

nfor

tuna

tely

, it i

s no

t alw

ays

poss

ible

to k

now

in a

dvan

ce w

here

one

wor

d st

arts

and

the

next

wor

d en

ds. A

s w

e di

scus

sed

in th

e in

trod

uctio

n,ac

oust

ic c

ues

to ju

nctu

re a

re n

ot a

lway

s re

liabl

e,' a

nd in

the

abse

nce

ofac

oust

ic c

ues,

eve

n an

opt

imal

ly e

ffic

ient

mec

hani

sm ~

anno

t alw

ays

, know th

at it

has

hea

rd th

e en

d of

one

wor

d un

til it

hea

rs e

noug

h of

the

next

to r

ule

out t

he p

ossi

ble

cont

inua

tions

of t

he fi

rst w

ord.

Wha

t is

need

ed, t

hen.

is a

mod

el th

at c

an a

ccou

nt fo

r C

OH

OR

T'

succ

esse

s, a

nd o

verc

ome

thes

e tw

o im

port

ant d

efic

ienc

ies,

The

nex

t tw

ose

ctio

ns s

how

that

TR

AC

E d

oes

quite

wel

l on

both

cou

nts.

The

fir

st o

fth

ese

sect

ions

exa

min

es T

RA

CE

' s b

ehav

ior

in p

roce

ssin

g w

ords

who

sebe

ginn

ings

and

end

ings

are

cle

arly

del

inia

ted

for

it by

the

pres

ence

of

sile

nce,

The

sec

ond

cons

ider

s th

e pr

oces

sing

of

mul

tiwor

d in

puts

, whi

chth

e m

odel

mus

t par

se fo

r its

elf.

One

Wor

d tit

(t T

ime

In th

is s

ectio

n w

e se

e ho

w T

RA

CE

res

olve

s th

e di

lem

ma

faci

ng C

O-

HO

RT

, in

that

it is

imm

edia

tely

sen

sitiv

e to

new

info

rmat

ion

but i

s st

illab

le to

cop

e w

ith u

nder

spec

ifie

d or

dis

tort

ed w

ord

begi

nnin

gs, W

e al

soco

nsid

er h

ow th

e m

odel

acc

ount

s fo

r th

e pr

efer

ence

for

sho

rt-w

ord

re-

spon

ses

earl

y in

pro

cess

ing

a lo

ng w

ord,

The

sec

tion

conc

lude

s w

ith a

disc

ussi

on o

f w

ays

the

mod

el c

ould

be

exte

nded

to a

ccou

nt fo

r w

ord

freq

uenc

y an

d co

ntex

tual

influ

ence

s,C

ompe

titio

n ~'

S bottom-lip inhibition.

TR

AC

E d

eals

with

CO

HO

Rrs

dile

mm

a by

usi

ng c

ompe

titio

n. r

athe

r th

an p

hone

me-

to-w

ord

inhi

bitio

n.T

he e

ssen

ce o

f th

e id

ea is

sim

ply

this

, Pho

nem

e un

its h

ave

exci

tato

ryco

nnec

tions

to a

ll th

e w

ord

units

they

are

con

sist

ent w

ith. T

hus,

whe

n-ev

er a

pho

nem

e be

com

es a

ctiv

e in

a p

artic

ular

slic

e of

the

Tra

ce, i

t sen

ds.

exci

tatio

n to

all

the

wor

d un

its c

onsi

sten

t with

that

pho

nem

e in

that

slic

e.T

he w

ord

units

then

com

pete

with

eac

h ot

her;

item

s th

at c

onta

in e

ach

succ

essi

ve p

hone

me

dom

inat

e al

l oth

ers,

but

if n

o w

ord

"mat

ches

per

-fe

ctly

, a w

ord

that

pro

vide

s a

clos

e tit

to th

e phoneme sequence can

even

taul

ly w

in o

ut o

ver

wor

ds th

at p

rovi

de le

ss a

dequ

ate

mat

ches

. The

exac

t met

ric

of "

clos

enes

s of

fit

" de

pend

s. o

f co

urse

. on

a la

rge

num

ber

of d

etai

ls, I

n th

e ab

senc

e of

suc

h a

met

ric,

a s

impl

e co

unt o

f th

e nu

mbe

rof

aco

ustic

feat

ures

diff

erin

g be

twee

n a

lexi

cal i

tem

.an

d a

pres

ente

d st

im-

ulus

can

pro

vide

a u

sefu

l fir

st a

ppro

xim

atio

n. b

ut o

ther

fac

tors

suc

h as

stre

ss, l

ocat

ion

of d

iffer

ence

s w

ithin

the

wor

d, a

nd d

iscr

imin

abili

ty o

f the

diffe

ring

feat

ure~

. will

of c

ours

e co

me

into play.

Con

side

r, f

rom

this

poi

nt o

f vi

ew, o

ur tw

o ite

ms

" ple

asan

t" a

nd "

blac

e-le

t" a

gain

, In

the

firs

t ins

tanc

e. "

plea

sant

" w

ill r

ecei

ve m

ore

botto

m-u

pex

cita

tion

than

"pr

esen

t," and so w

ill w

in o

ut in

the

com

petit

ion.

We

have

alre

ady

seen

, in

our

anal

ysis

of c

ateg

oric

al p

erce

ptio

n at

the

pho-

nem

elev

el, h

ow e

ven

slig

ht d

iffer

ence

s in

initi

al b

otto

m-u

p ex

cita

tion

can

be m

agni

fied

by

the

join

t eff

ects

of

com

petit

ion

and

feed

back

. But

the

real

bea

uty

of th

e co

mpe

titio

n m

echa

nism

is th

at th

is a

ctio

n is

con

tinge

nton

the

activ

atio

n of

oth

er w

ord

cand

idat

es, T

hus,

in th

e ca

se o

f " b

lace

-le

t", s

ince

ther

e is

no

wor

d "b

lace

let

" "

brac

el~t

" w

ill n

ot b

e Sl

Ip-

pres

sed,

Ini

tially

, it i

s tr

ue, w

ords

like

"bl

ame "

and "

blat

ant"

will tend

t~ d

omin

ate

"bra

cele

t," but since the input matches "

brac

elet

" be

tter

than

any

oth

er w

ord,

"br

acel

et" wjll eventually co

me

to d

omin

ate

the

other possibilities,

Thi

s be

havi

or o

f th

e m

odel

is .

illus

trat

ed u

sing

~xa

mpl

es f

rom

its

re-

stri

cted

lexi

con

in F

ig. 2

4. I

n on

e ca

se. t

he in

put i

s " l

egal

," a

nd th

e w

ord

rega

l" is

com

plet

ely

dom

inat

ed b

y "l

egal

." In the other case. the input

is "

lugg

ed, "

and

the

wor

d "r

ugge

d" e

vent

ually

dom

inat

es, b

ecau

se th

ere

is n

o w

ord

" lug

ged"

(pr

onou

nced

to r

hym

e w

ith "

rugg

ed"

the

wor

dlu

g"

is n

ot in

the

mod

el' s

lexi

con)

, Her

e "r

ugge

d~' m

ust c

ompe

te w

ithot

her

part

ial m

atch

es o

f " l

ugge

d,"

of c

ours

e, a

nd it

is le

ss e

ffect

ive

inth

is r

egar

d th

an it

wou

ld b

e if

the

inpu

t ,ex

actly

mat

ched

it, b

ut it

doe

sw

in o

ut in

the

end.

It

sho

uld

be n

oted

that

the

deta

ils o

f w

hat w

ord

will

be

mos

t str

ongl

yac

tivat

ed in

suc

h ca

ses

depe

nd o

n a

num

ber

of f

acto

rs, i

nclu

ding

, in

part

icul

ar, t

he d

istin

ctiv

enes

s of

mis

mat

chin

g ph

onem

es. A

lso,

it is

pos

-si

ble

to f

ind

case

s in

whi

ch a

wor

d th

at c

orre

ctly

spa

ns a

par

t of

a lo

nger

strin

g do

min

ates

a lo

nger

wor

d th

at s

pans

the

who

le s

trin

g bu

t mis

ses

out o

n a

phon

eme

in o

ne p

lace

or

anot

her.

An

item

like

"vi

gore

tte" may

or m

ay n

ot b

e a

case

in p

oint

. In

such

cas

es, t

houg

h, th

e m

ost i

mpo

rtan

tth

ing

mig

ht n

ot tu

rn o

ut to

be

win

ning

and

losi

ng, b

ut r

athe

r th

e fa

ct th

atbo

th te

nd to

sta

y in

the

gam

e, S

uch

neol

ogis

ms

can

sugg

est a

poe

tic

...

TR

AC

E M

OD

EL

MC

CLE

LI,-

AN

D A

ND

ELM

AN

~Jj

fIT

ClJ

tEH

'.=-f

1

tIT

iI

q;-

EliT

Ia:

:w

- Ji

g ~

I- I

i g

I' a

. . I i g - 1-

- I

I g

- I

-llg~l- +2

phon

emes

, In

this

sec

tion,

we

exam

ine

how

wel

l TR

AC

E e

mul

ates

the

CO

HO

RT

mod

el, i

n ca

ses

whe

re th

e in

put i

s an

und

isto

rted

rep

rese

nta-

tion

of s

ome

part

icul

ar w

ord.

In

part

icul

ar, w

e w

ante

d to

see

how

clo

se.

TR

AC

E w

ould

com

e to

beh

avin

g in

acc

ord

with

CO

HO

RT

's a

ssum

ptio

nth

at in

corr

ect w

ords

are

dro

pped

fro

m th

e co

hort

of

activ

e ca

ndid

ates

as

soon

as

the

inpu

t div

erge

s fr

om th

em,

To

exam

ine

this

pro

cess

, we

cons

ider

ed th

e pr

oces

sing

of

the

wor

d "p

rodu

ct"

(/pr

ad"c

t/). F

igur

e 25

sho

ws

the

stat

e of

the

Tha

ce a

tva

riou

s po

ints

in p

roce

ssin

g th

is' w

ord,

and

Fig

. 26

show

s th

e re

spon

sest

reng

ths

of s

ever

al u

nits

rel

ativ

e to

the

stre

ngth

of

the

wor

d "p

rodu

ct"

itsel

f, a

s a

func

tion

of ti

me

rela

tive

to th

e ar

riva

l of

the

succ

essi

ve p

ho-

nem

es in

the

inpu

t. In

this

fig

ure,

the

resp

onse

str

engt

h of

"pr

oduc

t" is

sim

ply

set t

o 1,

0 at

eac

h tim

esl

ice

and

the

resp

onse

str

engt

hs o

f uni

tsfo

r ot

her

wor

ds a

re p

lotte

d in

term

s of

the

ratio

of

thei

r st

reng

th. d

ivid

edby

the

stre

ngth

of

"pro

duct

." T

he c

urve

s sh

own

are

for

the

wor

ds !'

trot

,po

ssib

le," priest,

" "

prog

ress

," and "

prod

uce

; the

se w

ords

diff

erfr

om th

e w

ord

"pro

duct

" (a

ccor

ding

to th

e si

mul

atio

n pr

ogra

ms

stre

ss-

less

enc

odin

g of

them

!) ir

, the

1st

, 2nd

, 3d,

4th

, and

5th

pho

nem

es, r

e-sp

ectiv

ely,

Fig

ure

26 s

how

s th

at th

ese

item

s be

gin

to d

rop

out o

f "c

on-

tent

ion

" ju

st a

fter

eac

h su

cces

sive

pho

nem

e co

mes

in, O

f co

urse

, the

reis

not

hing

har

d an

d fa

st o

r ab

solu

te a

bout

dro

ppin

g a

cand

idat

e in

TR

AC

E. W

hat w

e se

e in

stea

d is

that

mis

mat

chin

g ca

ndid

ates

sim

ply

begi

n to

fad

e as

the

inpu

t div

erge

s fr

om th

em in

fav

or o

f so

me

othe

rca

ndid

ate.

Thi

s is

just

the

kind

of

beha

vior

the

CO

HO

RT

mod

el w

ould

fi' -

j! "

...!!

;

G (E!J

If-;

;-'

(E!J

S - r I

lit I

.,;:!

d" If

tE.i.

.!t

~ d

- I -

g ~

d -

- I

'to

I..

ra

k II

i..u"

l8l8

tIl8

111

tr ~

~I u 91

- p

r ad

- k

r a

ull

I II u

DfI

g-d-

-g-

d- -

,;-d- +2

FIG, 24, SIBle of Ihe lrace al

lwo

poin

ls during processing of "'e

ga'"

and

"'u

gged

.

conj

unct

ion

of m

eani

ngs,

if u

sed

just

rig

ht: "

He

wal

ked

bris

kly

dow

n th

est

reet

, puf

fing

his

vigo

rette

.T

ime

CO

llr.fe of w(ird recognition in

TR

AC

E.

So

far

we

have

sho

wn

how

TR

AC

E o

verc

omes

a d

ific

ulty

with

the

CO

HO

RT

mod

el in

cas

esw

here

the

begi

nnin

g of

a w

ord

has

been

dis

tort

ed. I

n ea

rlie

r se

ctio

ns o

nph

onem

e pr

oces

sing

,so

me

of th

e si

mul

atio

ns il

lust

rate

that

the

mod

el is

capa

ble

of r

ecog

nizi

ng w

ords

with

und

ersp

ecif

ied

(i, e

" am

bigu

ous)

initi

al

prad

~kl

- -p

rad-

kl-

-pra

d~kl

- -p

rad-

kl-

FIG, 25. State of th

elhl

ce a

t var

ious

poi

nts

in p

roce

ssin

g th

e w

ord

"pro

duct

" (/prad'kt

/'.

12 1

8 24

30

38 4

2 48

!i4

80 8

8 Pr

oces

sing

Cyc

les

FIG

. 26.

Res

pons

e st

reng

ths

of tt

~ u

nits

for

seve

ral w

ords

rel

ativ

e to

the

resp

onse

str

engt

hof

the

unit

for

" pro

duct

" (/

prad

- kt/)

. as

a fu

nctio

n of

tim

e re

lativ

e to

the

peak

of

the

firs

tph

onem

e th

at fa

ils to

mat

ch th

e w

ord,

The

suc

cess

ive

curv

es c

omin

g of

f of t

he h

oriz

onta

llin

e re

pres

entin

g th

e no

rmal

ized

res

pons

e st

reng

th o

f " p

rodu

ct"

are

for

the

wor

ds "

Irot

." ,

poss

ible

," "

prie

sl," "

prog

ress

, " and "

prod

uce." respectively. In our lexicon they are

, rendered as

Itni

l/,

Ipas

I/, I

pris

t/, I

prag

rs/

, and

Ipra

dus/

, res

pect

ivel

y.

.... ~

2.~

1.

.... VJ

1.80

~ 1.

S 1

. 100

Q)

,D::: 0.

Q)

0.~

0.'ii

' 0.

D::: 0.

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

We

wer

e at

fir

st s

omew

hat d

istu

rbed

by

this

asp

ect o

f th

e m

odel

'sbe

havi

or, b

ut it

turn

s ou

t to

corr

espo

nd q

uite

clo

sely

with

res

ults

obt

aine

din

exp

erim

ents

by

Gro

sjea

n (1

980)

and

Cot

ton

and

Gro

sjea

n (l9

H4)

usi

ngth

e ga

ting

para

digm

, Bot

h pa

pers

fou

nd th

at s

ubje

cts

hear

ing

the

begi

n-ni

ngs

of w

ords

like

"ca

ptai

n" tended to report shorter words consistent

with

wha

t the

y ha

d he

ard

(e.g.

, "

cap

). H

owev

er, w

e sh

ould

obs

erve

that

in th

e ga

ting

para

digm

, whe

n th

e w

ord

" cap

tain

" is truncated just

after the

Ipl,

it w

ill s

ound

qui

te a

bit

like

" cap

" followed by silence, In

TR

AC

E, t

his

sile

nce

wou

ld a

ctiv

ate

sile

nce

units

at t

he p

hone

me

and

wor

d le

vels

, and

the

wor

d-le

vel s

ilenc

e un

its w

ould

com

pete

with

uni

tsfo

r w

ords

that

ext

end

into

the

sile

nce.

It w

ill r

einf

orce

the

pref

eren

ce o

fth

e m

odel

for

sho

rt-w

ord

inte

rpre

tatio

ns, b

ecau

se th

e de

tect

ion

of th

esi

lenc

e w

ill in

hibi

t the

det

ecto

r fo

r th

e lo

nger

wor

d, T

hus,

ther

e ar

e ac

-tu

ally

two

reas

ons

why

TR

AC

E m

ight

fav

or s

hort

-wor

d in

terp

reta

tions

over

long

-wor

d in

terp

reta

tions

in a

gat

ing

expe

rim

ent.

Whe

ther

hum

ansu

bjec

ts s

how

a r

esid

ual p

refe

renc

e fo

r sh

orte

r in

terp

reta

tions

ove

r lo

nger

ones

in th

e ab

senc

e of

a fo

llow

ing

sile

nce

durin

g th

e co

urse

of p

roce

ssin

gis

not

yet

cle

ar f

rom

ava

ilabl

e da

ta,

We

shou

ld p

oint

out

that

the

expe

rim

enta

l lite

ratu

re in

dica

tes

that

the

adva

ntag

e of

sho

rter

wor

ds o

ver

long

er o

nes

hold

s on

ly u

nder

the

spec

ial

circ

umst

ance

s of

gat

ed p

rese

ntat

ion

and

then

onl

y w

ith e

arly

gat

es, w

hen

shor

ter

wor

ds a

re r

elat

ivel

y m

ore

com

plet

e th

an lo

nger

one

s w

ould

be.

It h

as b

een

wel

l kno

wn

for

a lo

ng ti

me

that

long

er w

ords

are

gen

eral

lym

ore

read

ily r

ecog

nize

d th

an s

hort

er o

nes

whe

n th

e w

hole

wor

d is

pre

-se

nted

for

iden

tific

atio

n ag

ains

t a b

ackg

roun

d of

noi

se (

Lic

klid

er &

Mill

er, 1

951)

, Pre

sum

ably

, the

rea

son

for

this

is s

impl

y th

at lo

nger

wor

dsge

nera

lly p

rovi

de a

larg

er n

umbe

r of

cue

s th

an s

hort

er w

ords

do

and

henc

e ar

e si

mpl

y le

ss c

onfu

sabl

e.Frequency a"d context effects,

The

re ,ar

e, o

f co

urse

, oth

er fa

ctor

sw

hich

infl

uenc

e w

hen

wor

d re

cogn

ition

will

occ

ur b

eyon

d th

ose

we

have

cons

ider

ed th

us f

ar, T

wo

very

impo

rtan

t one

s ar

e w

ord

freq

uenc

y an

dco

ntex

tual

pre

dict

abili

ty, T

he li

tera

ture

on

thes

e t)

oVo

fact

ors

goes

bac

kto the turn of the century (Bagley, 1900).\ M

orto

ns

(196

9) lo

goge

n m

odel

effe

ctiv

ely

deal

s w

ith s

ever

al im

port

ant a

spec

ts o

f th

is h

uge

liter

atur

ethough not with the time course of these effects,

We

have

not

yet

incl

uded

eith

er w

ord

freq

uenc

y or

hig

her

leve

l con

-te

xtua

l inf

luen

ces

in T

RA

CE

, tho

ugh

of c

ours

e w

e be

lieve

they

are

im-

port

ant.W

ord

freq

uenc

y ef

fect

s co

uld

be a

ccom

mod

ated

, as

they

wer

ein

the

inte

ract

ive-

activ

atio

n m

odel

of w

ord

reco

gniti

on, i

n te

rms

of v

arat

ion

in th

e re

stin

g ac

tivat

ion

leve

l of

wor

d un

its, o

r in

term

s of

var

iatio

nin

the

stre

ngth

of

phon

eme-

to-w

ord

conn

ectio

ns. C

onte

xtua

l inf

luen

ces

can

be th

ough

t of

as s

uppl

ying

act

ivat

ion

to w

ord

units

fro

m e

ven

high

erle

vels

of

proc

essi

ng th

an th

e w

ord

leve

l. In

this

way

, bas

ic a

spec

ts o

f

prod

uce

in th

is c

ase,

thou

gh o

f cou

rse

the

drop

-off

wou

ld b

e as

sum

ed to

be a

n ab

rupt

, dis

cret

e ev

ent,

The

re is

one

asp

ect o

f TR

AC

E' s

beh

avio

r w

hich

dif

fers

fro

m th

aI o

fC

OH

OR

T: a

mon

g th

ose

wor

ds th

at a

re c

onsi

st~n

t with

the

inpu

t up

to a

part

icul

ar p

oint

in ti

me.

TR

AC

E s

how

s a

bias

in f

avor

of

shor

ter

wor

dsov

er lo

nger

wor

ds, T

hus,

"pr

iest

" ha

s a

slight advantage before the

Ial

com

es in

, and

"pr

oduc

e" is well ahead of "pr

oduc

t" u

ntil

the

tlcom

esin

(in

pho

nem

es, "

prod

uce.

" is

one

sho

rter

than

"pr

oduc

t"T

his

adva

ntag

e fo

r sh

orte

r w

ords

is d

ue to

the

com

petit

ion

mec

hani

sm,

Rec

all t

hat w

ord

units

com

pete

with

eac

h ot

her

in p

ropo

rtio

n to

the

over

lap

of th

e se

ts o

f tim

e sl

ices

spa

nned

by

each

of

the

wor

ds, O

verl

apis

, of

cour

se, s

ymm

etri

cal,

so lo

ng a

nd s

hort

wor

ds in

hibi

t eac

h ot

her

toan

equ

al e

xten

t. B

ut lo

nger

wor

ds s

uffe

r m

ore

inhi

bitio

n fr

om o

ther

long

wor

ds th

an s

hort

wor

ds d

o. F

or e

xam

ple,

"pr

ogre

ss" and "

prob

able

inhi

bit "

prod

uct "

mor

e th

an th

ey in

hibi

t "pr

iest

" an

d " p

rodu

ce. "

Thu

sun

its f

or lo

nger

wor

ds a

re g

ener

ally

sub

ject

ed to

ext

ra in

hibi

tion,

par

tic-

ular

ly e

arly

on

whe

n m

any

cand

idat

es a

re a

ctiv

e, a

nd s

o th

ey te

nd to

suff

er in

com

pari

son

to s

hort

wor

ds a

s a

resu

lt.3

The

dat

a re

port

ed b

y T

yler

and

Wes

sels

act

ually

app

ears

to in

dica

te a

n e,ven more

imm

edia

te d

rop-

off

than

is s

een

in th

is s

imul

atio

n. H

owev

er, i

l sho

uld

be r

emem

bere

d t h

atth

e cu

rves

sho

wn

in F

ig. 2

6 ar

e on

- lin

e re

spon

se s

tren

gth

curv

es, a

nd th

us r

enec

t the lags

inherent in the percolation of input from the feature to the word level. The gating task, on

the other hand, does not require subjects 10 respond on,lin

e. "

If th

e i n

put i

s' s

impl

y tu

rned

off

at th

e pe

ak o

f ea

ch p

hone

me

s in

put s

peci

fica

tion,

and

then

allo

wed

to r

un f

ree

for

afe

w c

ycle

s, th

e dr

opou

t poi

nt s

hift

s ev

en e

arlie

r.

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

thes

e tw

o ki

nds

of in

nuen

ces

can

be c

aptu

red.

We

leav

e it

to fu

ture

rese

arch

. how

ever

. to

dete

rmin

e to

wha

t ext

ent t

hese

ela

bora

tions

of

TR

AC

E w

ould

pro

vide

a d

etai

led

acco

unt o

f the

dat

a on

the

role

s of

thes

e fa

ctor

s, F

or n

ow. w

e tu

rn to

the

prob

lem

of d

eter

min

ing

whe

re o

new

ord

ends

and

the

next

one

beg

ins,

we

can

say

eith

er it

em in

a w

ay th

at m

akes

it s

ound

like

a s

ingl

e w

ord

or li

ke tw

o w

ords

, the

re is

an

inte

rmed

iate

way

of

sayi

ng th

em s

o th

atth

e fi

rst s

eem

s to

be

two

wor

ds a

nd th

e se

cond

see

ms

like

only

one

.T

o se

e w

hat T

RA

CE

II

wou

ld d

o w

ith s

ingl

e- a

nd m

ultip

le-w

ord

inpu

ts,

we

ran

sim

ulat

ion

expe

rim

ents

with

eac

h in

divi

dual

wor

d in

the

mai

n 2

I 1-

wor

d le

xico

n pr

eced

ed a

nd fo

llow

ed b

y si

lenc

e, a

nd th

en w

ith 2

I I p

airs

of w

ords

, with

a s

ilenc

e at

the

begi

nnin

g an

d at

the

end

of th

e en

tire

stre

am. T

he p

airs

wer

e m

ade

by s

impl

y pe

rmut

ing

the

lexi

con

twic

e an

dth

en a

butti

ng th

e tw

o pe

rmut

atio

ns s

o th

at e

ach'

wor

d oc

curr

ed o

nce

asth

e fi

rst w

ord

and

once

as

the

seco

nd w

ord

in th

e en

tire

set o

f 21

1 pa

irs,

We

stre

ss, o

f co

urse

, tha

t rea

l spe

ech

wou

ld te

nd to

con

tain

cue

s th

atw

ould

mar

k w

ord

boun

dari

es in

man

y ca

ses;

the

expe

rim

ent i

s si

mpl

yde

sign

ed. t

o sh

ow w

hat T

RA

CE

wou

ld d

o in

cas

es w

here

thes

e cu

es a

rela

ckin

g,W

ith th

e in

divi

dual

wor

ds, T

RA

CE

mad

e no

mis

take

s-th

at is

, by

afe

w s

lices

aft

er th

e en

d of

the

wor

d, th

e w

ord

that

spa

nned

the

entir

ein

put w

as m

ore

stro

ngly

act

ivat

ed th

an a

ny o

ther

wor

d, A

n ex

ampl

e of

this is shown using the item

Ipar

til

in Fig. 27. The stream

Ipar

til

mig

ht b

eei

ther

one

wor

d ("

part

y)

or tw

o ("

par tea" or "par tee

the

mod

elknows of only one word pronounced

Iti/)

. A

t ear

ly p

oint

s in

'pr

oces

sing

the

wor

d, "

par" dominates over "

part

y" and other longer words, for

reas

ons

disc

usse

d in

the

prev

ious

sec

tion,

By

the

time

the

mod

el h

as h

ada

chan

ce to

pro

cess

the

end

of th

e w

ord,

however, "

part

y" comes to

dominate. .

Why

doe

s a

sing

le lo

nger

wor

d ev

entu

ally

win

out

ove

r tw

o sh

orte

r

Lex

ical

Bas

;. ~ (

~r W

OI:

d Se

gmen

tatio

n

How

do

we

know

whe

n on

e w

ord

ends

and

the

next

wor

d be

gins

? T

his

is b

y no

mea

ns a

n ea

sy ta

sk. a

s w

e no

ted

in th

e in

trod

uctio

n, T

o re

cap

our

earl

ier

argu

men

t. th

ere

are

som

e cu

es in

the

spee

ch s

trea

m. b

ut a

sse

vera

l inv

estig

ator

s ha

ve p

oint

ed o

ut (

Col

e &

Jak

imik

. 198

0; G

rosj

ean

& Gee. 19

84: T

hom

pson

. 198

4), t

hey

are

not a

lway

s su

ffic

ient

. par

ticu-

larl

y in

flu

ent s

peec

h, I

t wou

ld th

us a

ppea

r th

at th

ere

is a

n im

port

ant r

ole

for

lexi

cal k

now

ledg

e to

pla

y in

det

erm

inin

g w

here

one

wor

d en

ds a

ndth

e ne

xt w

ord

begi

ns; a

s w

ell a

s in

iden

tifyi

ng th

e ob

ject

s th

at r

esul

t fro

mthe process of segmentation. Indeed. as R

eddy

(19

76)

has

sugg

este

d,se

gmen

tatio

n an

d id

entif

icat

ion

may

be

join

t res

ults

of

the

mec

hani

sms

of word recognition.

Col

e an

d Ja

kim

ik (

1980

) di

scus

s th

ese

poin

ts a

nd p

rese

nt e

vide

nce

that

sem

antic

and

syn

tact

ic c

onte

xt c

an g

uide

seg

men

tatio

n in

cas

es w

here

the

lexi

con

is c

onsi

s~en

t with

two

read

ings

("c

ar g

o" vs "

carg

o).

Our

pres

ent m

odel

lack

s ~y

ntac

tic a

nd s

eman

tic le

vels

. so

it ca

nnot

mak

e us

eof

thes

e hi

gher

leve

r co

nstr

aint

s; b

ut it

can

mak

e us

e of

its

know

ledg

eabout words, not only to identify individual w

ords

in is

olat

ion,

but

topi

ck o

ut a

seq

uenc

e of

wor

ds in

con

tinuo

us s

trea

ms

of p

hone

mes

. Wor

did

entif

icat

ion

and

se~m

enta

tione

mer

ge to

geth

er f

rom

the

i"te

riJc

tive~

ac-

tivat

ion

proc

ess,

as

part

and

par

cel o

f the

pro

cess

of w

ord

activ

atio

n,T

his

sect

ion

cons

ider

s se

vera

l asp

ects

of

the

way

in w

hich

wor

d se

g-

men

tatio

n em

erge

s f~

om th

e in

tera

ctiv

e-ac

tivat

ion

proc

ess,

as

obse

rved

in s

imul

atio

ns w

ith T

RA

CE

II,

Bef

ore

'we

cons

ider

thes

e, it

is w

orth

reca

lling

the

deta

ils e

lf so

me

of th

e as

sum

ptio

ns m

ade

abou

t the

bot

tom

-up

act

ivat

ion

of w

ord'

uni

ts a

nd a

bout

com

petit

ive

inhi

bitio

n be

twee

n w

ord

units

. Fir

st, t

he e

xten

t to

whi

ch a

par

ticul

ar p

hone

me

exci

tes

a pa

rtic

ular

wor

d un

it is

inde

pen

dent

of

the

leng

th o

f th

e w

ord,

Sec

ond,

the

exte

ntto

whi

ch a

par

ticul

ar w

ord

unit

inhi

bits

ano

ther

wor

d un

it is

pro

port

iona

lto

the

tem

pora

l ove

rlap

of th

e tw

o w

ord

units

. Thi

s m

eans

that

wor

dsw

hich

do

not o

verl

ap in

tim

e w

ill n

ot in

hibi

t eac

h ot

her,

but

will

gan

g up

on o

ther

wor

ds th

at p

artia

lly o

verla

p ea

ch o

f th

em. T

hese

two

assu

mp-

tions

for

m m

ost o

f th

~ ba

sis

of th

e ef

fect

s w

e ob

serv

e in

the

sim

ulat

ions

,

..,.

11/e bollndary

~ ill th

e ea

r of

the

"beh

eOl'

eI",

Firs

t, w

e co

nsid

er th

eba

sic

fact

that

the

num

ber

of w

ords

we

hear

in a

seq

uenc

e of

pho

nem

esca

n de

pend

on

our

know

ledg

e of

the

num

ber

of w

ords

the

sequ

ence

mak

es. C

onsi

der

the

two

utte

ranc

es, "

she

can

t" a

nd "

seca

nt".

Tho

ugh

ili:I

TI:

nili

:IT

I:n

m.u

II r

af

t II

tP~

ITJJ

iIJI

DiI

JID

II r

tII

ri -

u I

P

u I

pllrti- -pB

rti-

-pB

rl'

- -

pBrl

i-F

lo. 2

7. T

he s

tate

of t

he 'l

htce

at v

ario

us p

oint

s du

ring

proc

essi

ng o

f Ip

arti/

,

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

m:I

Trn

ffi:W

ilJJ

imB

m::!

LD

a r l

m::u

:rn

i!!I

IDilJ

Ju:

:nliJ

l

l -

l . -

b r

l i- P

r i

- P

- a

and

"tea

do n

ot o

verla

p. T

hus,

"ar

t " receives in

hibi

tion

from

hot

hba

r " and "

tea," while "

bar " and "

tea "

each receive in

hibi

tion

only

from "

art." Thus two words th

at d

o no

t ove

rlap

with

eac

h ot

her

can

gang

up

on a

third

eac

h ov

erla

ps w

ith p

artly

, and

dri

ve it

oul

.T

hese

rem

arka

bly

sim

ple

mec

hani

sms

of a

ctiv

atio

n an

d co

mpe

titio

n do

a ve

ry g

ood

job

of w

ord

segm

enta

tion,

with

out t

he a

id o

f an

y sy

llabi

fi-

catio

n, s

tres

s, p

hone

tic w

ord

boun

dary

cue

s, o

r se

man

tic a

nd s

ynta

ctic

constraints. In 189 of the 211 w

ord

pairs

test

ed in

the

sim

ulat

ion

expe

r-im

ent,

the

mod

el c

ame

up w

ith th

e co

rrec

t par

se, i

n th

e se

nse

that

no

othe

r w

ord

was

mor

e ac

tive

than

eith

er o

f th

e tw

o w

ords

that

had

bee

npr

esen

ted,

Som

e of

the

failu

res

of th

e m

odel

occ

urre

d in

cas

es w

here

the

inpu

t was

act

ually

con

sist

ent w

ith tw

o pa

rses

, eith

er a

long

er s

pann

ing

wor

d ra

ther

than

a s

ingl

e w

ord

(as

in "

part

y)

or a

dif

fere

nt p

arse

into

two

wor

ds, a

s in

"part rust"

for

"par trusl." In such cases T

RA

CE

tend

sto

pre

fer

pars

es in

whi

ch th

e lo

nger

wor

d co

mes

firs

t. T

here

wer

e, h

ow-

ever

, som

e ca

ses

in w

hich

the

mod

el d

id n

ot c

ome

up w

ith a

val

id p

arse

,th

at is

, a p

atte

rn th

at r

epre

sent

s co

mpl

ete

cove

rage

of

the

inpu

t hy

a se

tof

non

over

lapp

ing

wor

ds. F

or e

xam

ple,

con

side

r th

e in

put I

park

i/.Though this makes the

two

wor

ds "

par " and "

key," the word "

park

"has a stronger activation than either "

par" or "

key." as illustrated in

Fig. 28,

Thi

s as

pect

of

TR

AC

E I

I's

beha

vior

indi

cate

s th

at th

e pr

esen

t vcr

sion

of th

e m

odel

is f

ar f

rom

the

fina

l wor

d on

wor

d se

gmen

tatio

n. A

com

plet

em

odel

wou

ld a

lso

expl

oit s

ylla

bifi

catio

n, s

tres

s, a

nd o

ther

cue

s to

wor

did

entit

y to

hel

p el

imin

ate

som

e of

the

poss

ible

inte

rpre

tatio

ns o

f T

RA

CE

II's

sim

ple

phon

eme

stre

ams,

The

' act

ivat

ion

and

com

petit

ion

mec

ha-

nism

s in

TR

AC

E I

I ar

e su

ffici

ent t

o do

qui

te a

bit

of th

e w

ord

segm

en-

tatio

n w

ork,

but

we

do n

ot e

xpec

t the

m to

do

this

per

fect

ly in

all

case

sw

ithou

t the

aid

'of other cues.

Som

e re

ader

s m

ay b

e tr

oubl

ed b

y a

mec

hani

srr

that

doe

s no

t ins

ist

upon

a p

arse

in w

hich

eac

h ph

onem

e is

cov

ered

by

one

and

only

one

wor

d, A

ctua

lly, t

houg

h, th

is c

hara

cter

istic

of

the

mod

el is

oft

en a

vir

tuc,

sinc

e in

man

y ca

ses

the

last

pho

nem

e of

h w

ord

mus

t do

doub

le d

uty

asth

e fi

rst p

hone

me

of th

e ne

xt, a

s in

"ho

und

dog"

or "

brush shop," Whilc

spea

kers

tend

to s

igna

l the

dou

blin

g in

car

eful

spe

ech,

the

cues

to s

ingl

evs

dou

ble

cons

onan

ts a

re n

ot a

lway

s su

ffici

ent f

or d

isam

bigu

atio

n, a

s is

clea

r w

hen

stri

ngs

with

mul

tiple

inte

rpre

tatio

ns a

re u

sed

as s

timul

i. Fo

rex

ampl

e, a

n ut

tera

nce

inte

nded

as

'no

not

ion

" w

ill s

omet

imes

be

hear

das

"kn

own

notio

n"

(Nak

atan

i & D

ukes

, 197

7). T

he m

odel

is n

ot in

clin

edto

sup

pres

s ac

tivat

ions

of

part

ially

ove

rlap

ping

wor

ds, e

ven

whe

n a

non-

over

lapp

ing

pars

e is

ava

ilabl

e. T

his

beha

vior

of

TR

AC

E is

illu

stra

ted

with

IbA

stap

l ("b

us top" or "

bus

stop

) in

Fig

. 29.

In

this

cas

e, h

ighe

r le

vels

coul

d pr

ovid

e an

add

ition

al s

ourc

e of

info

rmat

ion

that

wou

ld h

elp

the

mod

el c

hoos

e be

twee

n ov

erla

ppin

g an

d no

nove

rlapp

ing

inte

rpre

tatio

ns.

ones

in T

RA

CE

? T

here

are

two

mai

n re

ason

s, F

irst o

f all,

a lo

nger

wor

dev

entu

ally

rec

eive

s m

ore

botto

m-u

p su

ppor

t tha

n ei

ther

sho

rter

wor

d,si

mpl

y be

caus

e th

ere

are

mor

e ph

onem

es a

ctiv

atin

g th

e lo

nger

wor

d th

anth

e sh

orte

r w

ord.

The

sec

ond

reas

on h

as to

do

with

the

sequ

entia

l nat

ure

of th

e in

put,

In th

e ca

se o

f Ipa

rtil,

by

the

time

the

Itil i

s co

min

g in

, the

word "

part

y"

is w

ell e

noug

h es

tabl

ishe

d th

at it

kee

ps I

til f

rom

get

ting

asst

rong

ly a

ctiv

ated

as

it w

ould

oth

erw

ise,

as

illus

trat

ed in

Fig

. 27.

Thi

sbe

havi

or o

f the

mod

el le

ads

to th

e pr

edic

tion

that

sho

rt w

ords

em

bedd

edin

the

ends

of

long

er w

ords

sho

uld

not g

et a

s st

rong

ly a

ctiv

ated

as

shor

ter

wor

ds c

omin

g ea

rlie

r in

the

long

er w

ord.

Thi

s pr

edic

tion

coul

d be

test

edus

ing

the

gatin

g pa

radi

gm, o

r a

cros

s-m

odal

pri

min

g pa

radi

gm s

uch

asth

e on

e us

ed b

y Sw

inne

y (1

982)

.H

owev

er, i

t. sh

ould

be

note

d th

at th

is a

spec

t of t

he b

ehav

ior

of th

em

odel

can

be

over

ridde

n if

ther

e is

bot

tom

-up

info

rmat

ion

favo

rine

the

two-

wor

d in

terp

reta

tion,

Cur

rent

ly, t

his

can

only

hap

p~n

in T

RA

CE

thro

ugh

the

inse

rtio

n of

a b

rief

sile

nce

betw

een

the

"par

" and the "te

a.A

s sh

own

in F

ig, 2

8, th

is r

esul

ts in

"pa

r" a

nd "

tea"

dom

inat

ing

all o

ther

word candidates,

Wha

t hap

pens

whe

n th

ere

is n

o lo

ng w

ord

that

spa

ns th

e en

tire

stre

am,

as in

Iba

rtil?

In

this

cas

e, th

e m

odel

set

tles

on th

e tw

o-w

ord

inte

rpre

tatio

nba

r te

a,"

as s

how

n in

Fig

, 28.

Not

e th

at o

ther

wor

ds, s

uch

as "

art,

that

spa

n ap

ortio

n of

the

inpu

t, ar

e le

ss successful than either "

bar " or

tea.

" T

he r

easo

n is

that

the

inte

rpre

tatio

ns "

bar" and "

art" overlap

with

eac

h ot

her,

and

"ar

t" a

nd "

tea"

ove

rlap

with

eac

h ot

her,

but

"ba

r

part

i- '+

3 -p

ar-t

1-+

3 -b

arf

j- +

3 -p

ark i- +3

FIG

. 28,

Sla

le o

f th

e 'lt

ace

afte

r pr

oces

sina

the

stre

ams

/par

liJ,

/par

-tiJ

,/b

arliJ

, uni

t Ipa

rki/.

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

~!'

fl~

P -

- b

esta

blis

h w

here

a w

ord

will

end

eve

n be

fore

i. a

ctua

lly d

oes

end,

par

tic-

ular

ly in

the

case

of l

onge

r w

ords

or

whe

n ac

tivat

ions

at t

he w

ord

leve

lar

e ai

ded

by s

ynta

ctic

and

sem

antic

con

stra

ints

, How

ever

, it i

s m

uch

hard

er to

est

ablis

h th

e en

d of

a n

onw

ord,

sin

ce th

e fa

ct th

at it

is a

non

-w

()rd

mea

ns th

at w

e ca

nnot

exp

loit

any

know

ledg

e of

whe

re it

sho

uld

end

to d

oso

,T

his

fact

may

acc

ount

for

the

find

ing

of Foss and Blank (1

980)

that

subj

ects

are

muc

h sl

ower

to r

espo

nd to

targ

et p

hone

mes

at t

he b

egin

ning

of a word preceded by a non w

ord

than

at t

he b

egin

ning

of a

wor

dpreceded by a word. For example, responses to detect word initial

Idl

wer

e fa

ster

in s

timul

i lik

e th

e fo

llow

ing:

At t

he e

nd o

f las

t yea

r, th

e go

vern

men

t dec

ided

. . .

b-sl

ap-

-br-

Sap.

FIG. 29. State of the Trace at the end of the streams Ibustapl ("bus stop"

or "bus top

and

Ibru

Sapl

("b

rush

sho

p

than

they

wer

e w

hen

the

wor

d pr

eced

ing

the

targ

et (

in th

is c

ase

gove

rn-

men

t) w

as r

epla

ced

by a

non

wor

d su

ch a

s "g

atabont." It should be noted

that

the

targ

ets

wer

e sp

ecifi

ed a

s w

ord-

initi

al s

egm

ents

, The

refo

re, t

hesu

bjec

ts h

ad n

ot o

nly

to id

entif

y th

e ta

rget

pho

nem

e, th

ey h

ad to

det

er-

min

e th

at it

fel

l at t

he b

egin

ning

of

a w

ord,

as,

wel

l, T

he f

aef

that

rea

ctio

ntim

es w

ere

fast

er w

hen

the

targ

et w

as p

rece

ded

by a

wor

d su

gges

ts th

atsu

bjec

ts w

ere

able

to u

se th

eir

know

ledg

e of

whe

re th

e w

ord

"gov

ern-

men

t" e

nds

to h

elp

them

det

erm

ine

whe

re th

e ne

xt w

ord

begi

ns,

An

exam

ple

of h

ow T

RA

CE

allo

ws

one

wor

d to

hel

p es

tabl

ish

whe

reits

suc

cess

or b

egin

s is

illu

stra

ted

in F

ig, 3

0; I

n th

e ex

ampl

e, th

e. m

odel

rece

ives

the

stre

am "

possible target" or "

pagu

sle

targ

et." and we

imag

ine

that

the

targ

et is

wor

d-in

itial

/t/. I

n th

e fi

rst c

ase.

the

wor

d "p

os-

, sib

leis

cle

arly

est

ablis

hed

and

com

petit

ors

unde

rnea

tIJ

it ha

ve b

een

completely crushed by the time the initial

It I

in

"ta

rget

" be

com

es a

ctiv

eat

the

phon

eme

leve

l (se

cond

pan

el in

the

uppe

r pa

rt o

f th

e fi

gure

). s

othere is no ambiguity about the fact that this

It I

is

at t

he b

egin

ning

of t

hene

xt w

ord,

(T

he d

ecis

ion

mec

hani

sm w

ould

. of

cour

se. b

e re

quir

ed to

note

that

the

mod

el h

ad established the location of the end of the

prec

edin

g w

ord,

We

have

not

yet

inco

rpor

ated

exp

licit

assu

mpt

ions

abo

utho

w th

is w

ould

be

done

.) In

the

seco

nd c

ase.

wor

ds b

egin

ning

and

end

ing

at a

num

ber

of. d

iffer

ent p

lace

s. in

clud

ing

som

e th

at o

verl

ap w

ith th

elocation of the

Itl,

are

part

ly a

ctiv

ated

, Thu

s. th

e su

bjec

t wou

ld h

ave

tow

ait u

ntil

he is

wel

l int

o th

e w

ord

"tar

get"

bef

ore

it be

com

es c

lear

that

the first

It I

in

targ

et is

in fa

ct a

wor

d-in

itial

It

/.

In r

ealit

y, th

e si

tuat

ion

is p

roba

bly

not a

s bl

eak

for

the

perc

eive

r as

itap

pear

s in

this

exa

mpl

e, b

ecau

se in

man

y ca

ses

ther

e w

ill b

e cu

es in

the

man

ner

of p

ronu

ncia

tion

and

the

sylla

bifi

catio

n of

the

inpu

t tha

t will

hel

pto

indi

cate

the

loca

tion

of th

e w

ord

boun

dary

. How

ever

. giv

en '

the

im-

prec

isio

n an

d fr

eque

nt a

bsen

ce o

f su

ch c

ues.

it is

not

sur

pris

ing

that

the

The

sim

ulat

ions

we

have

rep

orte

d sh

ow th

at th

e w

ord

activ

atio

n/co

m-

petit

ion

mec

hani

sm c

an g

o a

long

way

tow

ard

prov

idin

g a

com

plet

e in

-terpretation of the input stream as a seq,ue

nce

of w

ords

, As

a w

ord

isbe

ginn

ing

to c

ome

in. t

he m

odel

tend

s to

pre

fer

shor

ter

wor

ds c

onsi

sten

tw

ith th

e in

put s

trea

m o

ver

long

er o

nes.

As

the input unfolds through

time.

how

ever

. the

mod

el te

nds

to p

refe

r to

inte

rpre

t streams of pho-

nem

es a

s si

ngle

long

er w

ords

rat

her

than

as

a se

quen

ce o

f sh

ort w

ords

;an

d it

tend

s to

fin

d pa

rses

that

acc

ount

for

eac

h ph

onem

e on

ce. B

ut it

does

not

insi

st u

pon

this

. and

will

occ

asio

nally

pro

duce

an

inte

rpre

tatio

nth

at le

aves

par

t of

the

stre

am o

f ph

onem

es u

nacc

ount

ed f

or o

r w

hich

acco

unts

for

part

of t

he s

trea

m o

f pho

nem

es tw

ice,

Ofte

n en

ough

, it w

illal

so le

ave

an a

ltern

ativ

e to

its

"pre

ferr

ed p

aise

" in a strong position. so

that both the preferred parse and the al

tern

ativ

e w

ould

be

avai

labl

e to

high

er le

vels

and

sub

ject

to p

ossi

ble

rein

forc

emen

t by

them

.T

hus

far

in th

is s

ectio

n, w

e ha

ve c

onsi

dere

d th

e ge

nera

l pro

pert

ies

ofth

e w

ay in

whi

ch T

RA

CE

use

s le

xica

l inf

orm

atio

n to

seg

men

t a s

peec

hst

ream

into

wor

ds. b

ut w

e ha

ve n

ot c

onsi

dere

d m

uch

in th

e w

ay o

f em

-pi

rica

l dat

a th

at th

ese

aspe

cts

of th

e m

odel

she

d lig

ht o

n, H

owev

er. t

here

are

two

find

ings

in th

e lit

erat

ure

whi

ch c

an b

e in

terp

rete

d in

acc

orda

nce

with

TR

AC

E' s

han

dlin

g of

mul

tiwor

d sp

eech

str

eam

s,W

here

doe

s 1I 1I00lword elld?

A n

umbe

r of

inve

stig

ator

s (e

,g,.

Col

e &

Jaki

mik

. 198

0) h

ave

sugg

este

d th

at w

hen

one

wor

d is

iden

tifie

d. it

s id

en-

tity

can

be u

sed

to d

eter

min

e w

here

it e

nds

and

ther

efor

e w

here

the

next

wor

d be

gins

. In

TR

AC

E. t

he in

tera

ctiv

e ac

tivat

ion

proc

ess

can

ofte

n

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

a s -

as-

a s -

ElD

as-b

lif

a . '

tl!.!

!J!.

.:tgi

iII2

ili 8

H,j,

.. -

II

- p

- b

u I

r -'I

:0 ~

r 8

or "

tarn

ishe

d" o

r on

e of

sev

eral

oth

er p

ossi

bilit

ies,

It i

s on

ly a

fter

mor

ctim

e ha

s pa

ssed

. and

we

have

per

ceiv

ed e

ither

a s

ilenc

e or

eno

ugh

of th

ene

xt w

ord

to r

ule

out a

ny o

f th

e co

ntin

uatio

ns o

f It

arl,

that

we

can

deci

dew

e ha

ve h

eard

the

wor

d "t

ar, "

Thi

s si

tuat

ion.

as

it ar

ises

in T

RA

CE

with

the

sim

ple

utte

ranc

e It

arba

ksl (

" tar

box

) is illustrated in Fig. 31.

Though "

tar"

is s

omew

hat m

ore

activ

e th

an th

e lo

nger

wor

d " t

arge

twhen the

Irl

is c

omin

g in

. it i

s on

ly w

hen

the

wor

d "b

ox" emerges as

the

inte

rpre

tatio

n of

the

phon

emes

fol

low

ing

" tar

" th

at th

e ri

val "

targ

et"

fina

lly f

ades

as

a se

riou

s co

nten

der,

With

long

er w

ords

the

situ

atio

n is

dif

fere

nt. A

s w

e ha

ve a

lrea

dy s

een

in a

noth

er e

xam

ple.

by

the

time

the

end

of a

long

er w

ord

is r

each

ed it

is

pas'

b-Il

arl-

~-pa

s-b-

Ilar

l-l-

pas-

b-Il

arl-

l-II

TD

...-r

!i;-

~IC

OI

ar:w

!i:I

!:D

!!J!

Dj

s a

iE!!

llllI

a rb

. ra

k

Pili

Pil

II I

u I !

!~

III

I

- p' .

Elii

.'!E

bEn

lli!!

i!::i

EE

TIl

W!i

.!-

s t:-

. -

fii.i

4P:~

=:.

'-II

- . . 1111

i2ili

9L__

_.C

iLl1

- s

- P

a

. -

r d

ja

S a

-lar

baka

--I

arb,

ka-

-Iar

b,",

--I

,rba

k,-

pal-s

-llar

,-I-

-P"

I-s-

Ilarg

-t-

-pal

-s-

llsrl

-l-

FIG

. 30,

Sta

te o

f th

e T

race

at s

ever

al p

oint

s du

ring

Ihe

pro

cess

ing

of "

poss

ible

targ

et"

and

pagu

sle

targ

et.

rjb-

;' .,

S)

fCIT

iI

u::L

fi

11m

iIT

IDI,

~ili

liE

!!I

a k

a r

s -

a k

u I

u I

PII

I.ia

d -

. lex

ical

sta

tus

of o

ne p

art o

f a

spee

ch s

trea

m p

lays

an

impo

rtan

t rol

e in

dete

rmin

ing

whe

re th

e be

ginn

ing

of th

e ne

xt w

ord

mus

t be.

The

lollg

tlllJ

~'horl of lI'ort! ideillifi('tllioll,

One

pro

blem

atic

fea

ture

of

spee

ch is

the

fact

that

it is

not

alw

ays

poss

ible

to id

entifya word un-

ambi

guou

sly

until

one

has

hea

rd th

e w

ord

afte

r it.

Con

side

r. f

or e

xam

ple.

the

wor

d "t

ar,"

If w

e ar

e lis

teni

ng to

an

utte

ranc

e an

d ha

ve g

otte

n ju

stto the

Irl

in "

The

man

saw

the

tar

box." though "

tar" will tend to be

the

pref

erre

d hy

poth

esis

at t

his

poin

t. w

e do

not

hav

e en

ough

info

rmat

ion

to s

ay u

nequ

ivoc

ally

that

the

wor

d " t

ar"

will

not

turn

out

to b

e " t

arge

t

,-Ia

rbak

,-I-

Iarb

,",-

I-I,

rb,k

.-I-

Iarb

aks-

FtG

. 31.

Sia

le o

f Ihe

Tra

ce a

l sev

eral

poi

nts

in p

roce

ssin

g "t

ar b

ox" and "

guita

r bo

x,

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

muc

h m

ore

likel

y th

at o

nly

one

wor

d ca

ndid

ate

will

rem

ain,

Inde

ed, w

ithlo

nger

wor

ds it

is o

ften

pos

sibl

e to

hav

e en

ough

info

rmat

ion

to id

entif

yth

e w

ord

unam

bigu

ousl

y w

ell b

efor

e th

e en

d of

the

wor

d. A

n ill

ustr

atio

nof

this

situ

atio

n is

pro

vide

d by

a simulation using the utterance "

guita

rbo

x" Ig

tarb

aks/

, By

the

time

the

Irl h

as r

egis

tere

d, "

guita

r " is clearly

dom

inan

t at t

he w

ord

leve

l. an

d ca

n be

unai11biguously identified without

furt

her

ado.

Rec

ently

, an

expe

rim

ent b

y G

rosj

ean

(198

5) h

as d

emon

stra

ted

thes

esa

me

effe

cts

empi

rica

lly, G

rosj

ean

pres

ente

d su

bjec

ts w

ith lo

ng o

r sh

ort

wor

ds f

ollo

wed

by

ase

cond

w()

rd a

nd m

easu

red

how

muc

h of

the

wor

dan

d its

suc

cess

or th

e su

bjec

t nee

ded

to h

ear

to id

entif

y th

e ta

rget

. With

long

er w

ords

, sub

ject

s co

uld

usua

lly g

uess

the

wor

d co

rrec

tly w

ell b

efor

eth

e en

d of

the

wor

d, ;

and

by th

e en

d of

the

wor

d th

ey w

ere

quite

sur

e of

the

wor

d's

iden

tity,

With

mon

osyl

labi

c w

ords

, on

the

othe

r ha

nd, m

any

of th

e w

ords

cou

ld n

ot b

e id

entif

ied

corr

~ctly

unt

il w

ell i

nto

the

next

wor

d, O

n th

e av

erag

e, s

ubje

cts

wer

e no

t sur

e of

the

wor

d's

iden

tity

until

abou

t the

end

of t

he n

ext w

ord,

or

the

begi

nnin

g of

the

one

afte

r, A

sGrosjean (1985) points out, a m

~or

reas

on f

or th

is is

sim

ply

that

the

spok

en in

put o

ften

does

not

uni

quel

y sp

ecify

the

iden

tity

of a

sho

rt w

ord.

In s

uch

case

s, th

e pe

rcep

tual

sys

tem

is o

ften

forc

ed to

pro

cess

the

shor

tw

ord,

and

its

succ

esso

r, a

t the

sam

e tim

e.RecoRllizilll: the words

ill

a short selltellce,

One

last

exa

mpl

e of

TR

AC

E I

I's p

erfo

rman

ce in

seg

men

ting

wor

ds is

illu

stra

ted

in F

ig, 3

2,T

he fi

gure

sho

ws

the

stat

e of

the

lrace

at s

ever

al p

oint

s du

ring

the

pro-

cessing of the stream ISiS"

t"ba

ks/.

By

the

end,

the

wor

ds o

f th

e ph

rase

She

shu

t a b

ox, "

whi

ch f

ils th

e in

put p

erfe

ctly

with

no

over

lap,

dom

i-na

te a

ll ot

hers

. .T

his

exam

ple

illus

trat

es h

ow f

ar it

is s

omet

imes

pos

sibl

e to

go

inpa

rsin

g a

stre

am o

f pho

nem

es in

to w

ords

, with

out e

ven

cons

ider

ing

syn-

tacl

ic a

nd s

eman

tic '(

onst

rain

ts, o

r st

ress

, syl

labi

ficat

ion,

and

junc

ture

cues

to w

ord

iden

tific

atio

n. T

he e

xam

ple

also

illu

stra

tes

the

diff

icul

ty th

em

odel

has

in p

erce

ivin

g sh

ort,

unst

ress

ed w

ords

like

". T

his

is, o

fco

urse

, jus

t an

extr

eme

vers

ion

of th

e di

ffic

ulty

the

mod

el h

as in

pro

-ce

ssin

g m

ol1o

sylla

bic

wor

ds li

ke "

tar,

" an

d is

con

sist

ent w

ith G

rosj

ean

data

on

the

diff

icul

ty s

ubje

cts

have

with

iden

tifyi

ng s

hort

wor

ds. I

n fa

ct,

Gro

sjea

n an

d G

ee (

1984

) re

port

pilo

t dat

a in

dica

ting

that

thes

e di

ffic

ultie

sar

e ev

en m

ore

seve

re w

ith f

unct

ion

wor

ds li

ke "

" and "

of. " It should

be n

oted

that

TR

AC

E m

akes

no

spec

ial d

istin

ctio

n be

twee

n co

nten

t and

func

tion

wor

ds, p

er s

e, a

nd n

eith

er d

o G

rosj

ean

and

Gee

, How

ever

, fun

c-tio

n w

ords

are

usu

ally

uns

tres

sed

and

cons

ider

ably

sho

rter

than

con

tent

wor

ds. T

hus,

it is

not

nec

essa

ry to

poi

nt to

any

spe

cial

mec

hani

sms

for

clos

ed v

ersu

s op

en c

lass

mor

phem

es to

acc

ount

for

Gro

sjea

n an

d G

eere

sults

.

m:n

IDJ

IH&

fnJi

JE

EJJ

5 I

s -

p u

s u

II i

S \I

-SIS

-l-b

aks-

SiS-

t-ba

ks-

SiS-

l-ba

ks-

tE:D

1~~

J3l~

Iru s

-

~ , 1t

-lt:: ~~

- 1- b

b.,;

s I S

s

I Silk

S I

pug S

SIS"

'I-ba

ks-

SIS-

l-ba

ks-

SiS-

l-bl

lks-

FIG

. 32.

The

sta

te o

f the

Tra

ce a

t sev

erat

poi

nts

durin

g th

e pr

oces

sing

of t

he s

trea

mIS

is

Tba

ksl (

" She

shu

t 8 b

ox

,.

Sum

mar

y of

Wor

d Id

emiji

catio

n Si

mul

atio

ns

Whi

le p

hone

me

iden

tific

atio

n ha

s be

en s

tudi

ed fo

r m

any

year

s, d

ata

from on-lin

e st

udie

s of

wor

d re

cogn

ition

is ju

st b

egin

ning

to a

ccum

ulat

e;T

here

is a

n ol

der

liter

atur

e on

acc

urac

y of

wor

d id

entif

icat

ion

in n

oise

.bu

t it h

as o

nly

been

qui

te r

ecen

tly th

at u

sefu

l tec

hniq

ues

have

bee

n de

-ve

lope

d fo

r st

udyi

ng w

ord

reco

gniti

on in

rea

l tim

e.W

hat e

vide

nce

ther

e is

. tho

ugh

indi

cate

s th

e co

mpl

exity

of

the

wor

d

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

iden

tific

atio

n pr

oces

s, W

hile

the

wor

d id

entif

icat

ion

mec

hani

sm is

sen

-si

tive

to e

ach

new

inco

min

g ph

onem

e as

it a

rriv

es, i

t is nevertheless

robu

st e

noug

h to

rec

over

fro

m u

nder

spec

ific

atio

n or

dis

tort

ion

of w

ord

begi

nnin

gs. A

nd it

app

ears

h..

be c

apab

le o

f so

me

sim

ulta

neou

s pr

oces

sing

of s

ucce

ssiv

e w

ords

in th

e in

put s

trea

m, T

RA

CE

app

ears

to c

aptu

re th

ese

aspe

cts

of th

e tim

e co

urse

of

wor

d re

cogn

ition

. In

thes

e re

spec

ts, i

t im

-pr

oves

upo

n th

e C

OH

OR

T m

odel

, the

onl

y pr

evio

usly

ext

ant m

odel

that

prov

ides

an

expl

icit

acco

unt o

f th

e on

- lin

e pr

oces

s of

wor

d re

cogn

ition

,A

nd th

e m

echa

nism

s it

uses

. to

acco

mpl

ish

this

are

the

sam

e on

es th

at it

used

for

the

sim

ulat

ions

of

the

proc

ess

of p

hone

me

iden

tific

atio

n de

-scribed in the preceding section,

lene

e,th

e m

odel

exh

ibits

imm

edia

te s

ensi

tivity

to in

form

atio

n fa

vorin

gon

e w

ord

inte

rpre

tatio

n ov

er a

noth

er. I

t sho

ws

an in

itial

pre

fere

nce

for

shor

ter

wor

ds r

elat

ive

to lo

nger

wor

ds, b

ut e

vent

ually

a s

eque

nce

ofph

onem

es th

at m

atch

es a

long

wor

d pe

rfec

tly w

ill b

e id

entif

ied

as th

atw

ord,

ove

rtur

ning

the

initi

al p

refe

renc

e fo

r th

e sh

ort-

wor

d in

terp

reta

tion.

The

se a

spec

ts o

f the

mod

el, a

re c

onsi

sten

t with

hum

an d

ata

from

gat

ing

expe

rim

ents

.7,

Tho

ugh

the

mod

el is

hea

vily

influ

ence

d by

wor

d be

ginn

ings

, it c

anre

cove

r fr

om u

nder

spec

ifica

tion

or d

isto

rtio

n of

a w

ord'

s be

ginn

ing.

S, T

he m

odel

can

use

its

know

ledg

e of

the

lexi

con

to p

arse

seq

uenc

esof

pho

nem

es in

to w

ords

, and

to e

stab

lish

whe

re o

ne w

ord

ends

and

the

next

one

beg

ins

whe

n cu

es to

wor

d bo

unda

ries

are

lack

ing.

9, L

ike

hum

an s

ubje

cts,

the

mod

el s

omet

imes

can

not i

dent

ify

a w

ord

until

it h

as h

eard

par

t of

the

next

wor

d, A

lso

like

hum

an s

ubje

cts.

it c

anbe

tter

dete

rmin

e w

here

a w

ord

will

beg

in w

hen

it is

pre

cede

d by

a w

ord

rath

er th

an a

non

wor

d,10

. The

mod

el d

oes

not d

eman

d a

pars

e of

a p

hone

me

sequ

ence

that

incl

udes

eac

h ph

onem

e in

one

and

onl

y on

e w

ord,

Thi

s al

low

s it

to c

ope

grac

eful

ly w

ith e

lisio

n. o

f ph

onem

~s a

t wor

d bo

unda

ries

. It w

ill o

ften

perm

it se

vera

l alte

rnat

ive

pars

es to

rem

ain

avai

labl

e lo

r hi

gher

leve

l in-

flue

nces

to c

hoos

e am

ong,

In a

dditi

on to

thes

e ch

arac

teri

stic

s ob

serv

ed in

the

pres

ent p

aper

, our

sim

ulat

ions

with

TR

AC

E I

sho

w s

ever

al f

urth

er c

orre

spon

denc

es b

e-tw

een

the

mod

el a

nd h

uman

spe

ech.

per

cept

ion,

Mos

t im

port

ant o

f th

ese

is th

e fa

ct th

at th

e m

odel

is a

ble

to u

se a

ctiv

atio

ns o

f pho

nem

e un

its in

one

part

of

the

Tra

ce to

adj

ust t

he c

onne

ctio

n st

reng

ths

dete

rmin

ing

whi

chfe

atur

es w

ill a

ctiv

ate

whi

ch p

hone

mes

in a

djac

ent p

arts

of

the

Tra

ce. I

nthis WaY, the m

odel

can

adj

ust a

s hu

man

sub

ject

s do

to c

oart

icuh

.itor

yin

flue

nces

on

the

acou

stic

pro

pert

ies

of p

hone

mes

(Fo

wle

r. 1

984;

Man

n&

Rep

p, 1

980)

. T

here

is, o

f cou

rse.

mor

e da

ta o

n so

me

of th

ese

poin

ts th

an o

ther

s. II

will

be

very

inte

rest

ing

to s

ee h

ow w

ell r

RA

CE

will

hol

d up

aga

inst

the

data

as

furt

her

empi

rica

l stu

dies

are

car

ried

oul

.

EN

ER

AL

DIS

CU

SSIO

N

Sum

ma,

.y o

f T

RA

CE

' ~' S

ucce

sses

In th

is a

rtic

le, w

e ha

ve s

een

that

TR

AC

E c

an a

ccou

nt f

or a

num

ber

ofdi

ffer

ent a

spec

ts o

f hu

man

spe

ech

perc

eptio

n. W

e be

gin

by li

stin

g th

em

ajor

cor

resp

onde

nces

bet

wee

n T

RA

CE

and

wha

t we

know

abo

ut th

ehu

man

spe

ech

unde

rsta

ndin

g pr

oces

s.

I, T

RA

CE

, lik

e hu

man

s, u

ses

info

rmat

ion

from

ove

rlap

ping

por

tions

of th

e sp

eech

wav

e to

iden

tify

succ

essi

ve p

hone

mes

,2,

The

mod

el s

how

s a

tend

ency

tow

ard

cate

goric

al p

erce

ptio

n of

pho

-ne

mes

, as

do h

uman

sub

ject

s. T

he m

odel

' s te

nden

cy to

war

d ca

tego

rical

perc

eptio

n is

aff

ecte

d by

man

y of

the

sam

e pa

ram

eter

s w

hich

aff

ect t

hede

gree

of

cate

gori

cal p

erce

ptio

n sh

own

by h

uman

sub

ject

s; in

par

ticul

ar.

the

exte

nt to

whi

ch p

erce

ptio

n w

ill b

e ca

tego

rical

incr

ease

s w

ith ti

me

betw

een

stim

uli t

hat m

ust b

e co

mpa

red,

3,

The

mod

el c

ombi

nes

feat

ure

info

rmat

ion

from

a n

umbe

r of

dift

eren

tdi

men

sion

s, a

nd e

xhib

its c

ue tr

ade-

offs

in p

hone

me

iden

tific

atio

n. T

hese

char

acte

rist

ics

of h

uman

spe

ech

perc

eptio

n ha

ve b

een

dem

onst

rate

d in

ave

ry h

irge

num

ber

of s

tudi

es,

4, T

he m

odel

aug

men

ts in

form

atio

n fr

om th

e sp

eech

str

eam

with

fced

-ba

ck f

rom

the

lexi

cal l

evel

in r

each

ing

deci

sion

s ab

out t

he id

entit

y of

phon

emes

, The

se le

xica

l int

luen

ces

on p

hone

me

iden

tific

atio

n oc

cur

inco

nditi

ons

sim

ilar

to th

ose

in w

hich

lexi

cal e

ffect

s ha

ve b

een

repo

rted

,bu

t do

not o

ccur

in c

ondi

tions

in w

hich

thes

e ef

fect

s ha

ve n

ot b

een

ob-

~~. .

5, L

ike

hum

an s

ubje

cts

the

mod

el e

xhib

its a

ppar

ent p

hono

tact

ic r

ule

effe

cts

on p

hone

me

iden

tific

atio

n. th

ough

it h

as n

o ex

plic

it re

pres

enta

tion

of th

e ph

onot

actic

rul

es, T

he te

nden

cy to

pre

fer

phon

otac

tical

ly r

egul

arin

terp

reta

tions

of

ambi

guou

s ph

onem

es c

an b

e ov

erri

dden

by

part

icul

arle

xica

l ite

ms,

just

as

it ca

n in

the

hum

an p

erce

iver

,6. In processing un

ambi

guou

s ph

onem

e se

quen

ces

prec

eded

by

si-

Som

e of

Ihe

Rea

solU

' fo,

. Ihe

Suc

ces~

'es

of T

RA

CE

To

wha

t doe

s th

e T

RA

CE

mod

el o

we

its s

ucce

s~ in

sim

ulat

ing

hum

ansp

eech

per

cept

ion'

! So

me

of T

RA

CE

's

succ

esse

s si

mpl

y de

pend

on

itsab

ility

to m

ake

use

of th

e in

form

atio

n as

it c

omes

il. F

or e

xam

ple.

it f

ails

to s

how

con

text

eff

ects

onl

y w

hen

a re

spon

se m

ust b

e m

ade.

or

can

bem

ade

with

hig

h ac

cura

cy. b

efor

e co

ntex

tual

info

rmat

ion

is a

vaila

ble.

The

re a

re s

ever

al o

ther

rea

sons

for

TR

AC

E's

suc

cess

, One

, we

thin

k.is

the

use

of c

ontin

uous

act

ivat

ion

and

com

petit

ion

proc

esse

s in

pla

ce o

f

/'"

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

disc

rete

dec

isiv

e pr

oces

ses

such

as

segm

enta

tion

and

labe

ling,

Act

ivat

ion

and

com

petit

ion

are

mat

ters

of

degr

ee a

nd p

rote

ct T

RA

CE

fr~m

cat

a-st

roph

ic c

omm

itmen

t in

mar

gina

l cas

es. a

nd th

ey p

rovi

de a

nat

uriif

mea

nsfo

r co

mbi

ning

man

y ~i

ffer

ent s

ourc

es: o

f in

form

atio

n, O

f co

urse

. thi

s fe

a-tu

re o

f th

e m

odel

is s

hare

d w

ith s

ever

al o

ther

mod

els

(e,g

.. M

orto

n. 1

969;

Ode

n &

Mas

saro

. 197

8). t

houg

h on

ly N

usba

um a

nd S

iow

iacz

ek (1

982)

have

pre

viou

sly

inco

rpor

ated

thes

e ki

nds

of a

ssum

ptio

ns in

a m

odel

of.

the

time

cour

se o

f wor

d re

cogn

ition

.Pa

rt o

f th

e su

cces

s of

TR

AC

E is

spe

cifi

cally

due

to th

e us

e of

com

-pe

titiv

e in

hibi

tory

inte

ract

ions

inst

ead

of b

otto

m-u

p (o

r to

p-do

wn)

inhi

-bi

tion.

Com

petit

ion

allo

ws

the

mod

el to

sel

ect t

he b

est i

nter

pret

atio

nav

aila

ble.

sel

l lin

g fo

r an

impe

rfec

t one

whe

n no

bel

ler

one

is a

vaila

ble.

but o

verr

idin

g po

or o

nes

whe

n a

' goo

d on

e is

at h

and,

The

se a

nd o

ther

virt

ues

of c

ompe

titiv

e in

hibi

tion

have

bee

n no

ted

befo

re (

e,g.

. Fel

dman

& Ballard. 1982: G

ro~s

berg

. 197

3; L

evin

. 197

6: R

atlif

f. 1

965;

von

Bek

esy.

1967) in other co

ntex

ts. T

heir

use

fuln

ess

here

atte

sts

to th

e ge

nera

l util

ityof

the

com

petit

ive

inhi

bitio

n m

echa

nism

.T

he e

limin

atio

n of

bet

wee

n-le

vel i

nhib

ition

fro

m th

e in

tera

ctiv

e ac

ti-va

tion

mec

hani

sm p

uts

us in

a v

ery

nice

pos

ition

with

res

pect

to o

nege

nera

l cri

tique

of

inte

ract

ive-

activ

atio

n m

odel

s. I

t is

ofte

n sa

id th

at a

c-tiv

atio

n m

odel

s ar

e ~

oo u

ncon

stra

ined

and

too

flexi

ble

to b

e an

ythi

ngm

ore

than

a la

ngua

ge f

or c

onve

nien

tly d

escr

ibin

g in

form

atio

n pr

oces

sing

,W

e ar

e no

w in

a p

ositi

on to

sug

gest

that

a r

estr

icte

d ve

rsio

n of

the

fram

e-w

ork

is n

ot o

nly

suffi

cien

t but

sup

erio

r. In

tera

ctiv

e-ac

tivat

ion

mod

els

coul

d ex

ploi

t bot

h ex

cita

tory

and

inhi

bito

ry c

onne

ctio

ns b

oth

betw

een

and

with

in le

vels

, bu~

in th

e or

igin

al in

tera

ctiv

e-ac

tivat

ion

mod

el o

f le

tter

perc

eptio

n. o

nly

inhi

bito

ry in

tera

ctio

ns w

ere

allo

wed

with

in a

leve

l. In

mor

e re

cent

ver

sion

s of

the

visu

al m

odel

(M

cCle

lland

. 1985, 1986),

and

in T

RA

CE

, we

have

gon

e ev

en fu

rthe

r, a

llow

ing

only

exc

itato

ryco

nnec

tions

bet

wee

n le

vels

and

onl

y in

hibi

tory

con

nect

ions

with

in le

vels

.F

rom

our

exp

erie

nce,

it a

ppea

rs th

at m

odel

s w

hich

adh

ere

to th

ese

con-

stra

ints

wor

k as

wel

l as

or b

ette

r th

an m

embe

rs o

f th

e m

ore

gene

ral c

lass

that

do

not.

We

hast

e n to

add

that

we

have

no

proo

f tha

t thi

s is

true

, We

have

, how

ever

. no

reas

on to

feel

that

we

coul

d im

prov

e th

e pe

rfor

man

ceof

our

mod

el b

y al

low

ing

eith

er b

etw

een-

leve

l inh

ibito

ry in

tera

ctio

ns o

rw

ithin

- leve

l exc

itatio

n,

Oth

er a

spec

ts o

f th

e su

cces

ses

of T

RA

CE

dep

end

on it

s us

e of

feed

back

from

hig

her

to lo

wer

rev

els,

Fee

dbac

k pl

ays

a ce

ntra

l rol

e in

the

acco

unts

of c

ateg

oric

al p

erce

ptio

n. le

xica

l eff

ects

on

phon

eme

iden

tific

atio

n, a

ndph

onot

actie

rule"

effe

cts,

W

e do

not

cla

im th

at a

ny o

f th

ese

phen

omen

a, ta

ken

indi

vidu

ally

, re-

quir

e th

e as

sum

ptio

n; o

f a fe

edba

ck m

echa

nism

, For

exa

mpl

e, c

onsi

der

the

phen

omen

on o

f ta

tego

rica

l per

cept

ion.

We

use

feed

back

fro

m th

e

phon

eme

to th

e fe

atur

e le

vel t

o dr

ive

feat

ure

patte

rns

clos

er to

the

pro-

totype of the ph

onem

e th

ey m

ost s

tron

gly

activ

ate,

Thi

!! m

echa

nism

.co

uple

d w

ith th

e co

mpe

titio

n m

echa

nism

at t

he p

hone

me

leve

l, ac

coun

tsfo

r be

tter

disc

rim

inat

ion

betw

een

than

with

in c

ateg

orie

s, H

owev

er, w

eco

uld

acco

unt f

or c

ateg

oric

al p

erce

ptio

n by

sug

gest

ing

that

sub

ject

s do

not h

ave

acce

ss to

the

acou

stic

leve

l at a

ll, b

ut o

nly

to th

e re

sults

of

the

phon

eme

iden

tific

atio

n pr

oces

s. S

imila

rly,

lexi

cal e

ffec

ts o

n ph

onem

eid

entif

icat

ion

can

be a

ccou

nted

for

by

assu

min

g th

at s

ubje

cts

(som

etim

es)

read

out

fro

m th

e w

ord

leve

l and

infe

r th

e id

entit

y of

pho

nem

es f

rom

the

lexi

cal c

ode

(Mar

slen

-Wilson, 1980: Marslen-

Wils

on &

Wel

sh, 1

978;

Mor

ton.

1979), In the case of "ph

onot

actic

rul

e" effects, other interpre-

tatio

ns a

re o

f cou

rse

avai

labl

e as

wel

l, O

ne c

ould

. for

exa

mpl

e, s

impl

ysu

ppos

e th

at s

ubje

cts

use

know

ledg

e of

the

phon

otac

tic c

onst

rain

ts. p

er-

haps

cap

ture

d in

uni

ts s

tand

ing

for

lega

l pho

nem

e pa

irs.

and

that

it is

the

outp

ut o

f suc

h un

its th

at a

ccou

nts

for

the

influ

ence

of p

hono

tact

ic r

eg-

ularity on phoneme identification.

We

know

of

no s

ingl

e co

nvin

cing

em

piri

cal r

easo

n to

pre

fer

feed

back

acco

unts

to o

ther

pos

sibi

litie

s, H

owev

er, w

e ha

ve tw

o th

eore

tical

rea

sons

for

pref

erri

ng to

ret

ain

top-

dow

n as

wel

l as

botto

m-u

p in

tera

ctio

ns in

our

activ

atio

n m

odel

s, O

ne r

easo

n ha

s to

do

with

the simplicity of the re-

sulti

ng d

ecis

ion

mec

hani

sms,

Fee

dbac

k al

low

s hi

gher

leve

l con

side

ratio

nsto

infl

uenc

e th

e ou

tcom

e of

pro

cess

ing

at lo

wer

leve

ls in

just

the

sam

ew

ay th

at lo

wer

leve

l con

side

ratio

ns in

flue

nce

the

outc

ome

of p

roce

ssin

gat

hig

her

leve

ls, T

he in

fluen

ces

of le

xica

l and

oth

er c

onst

rain

ts o

n ph

o-ne

me

iden

tific

atio

n ne

ed n

ot b

e pu

shed

out

of

the

theo

ry o

f sp

eech

per

-ce

ptio

n its

elf

into

dec

isio

n pr

oces

ses,

but

are

inte

grat

ed d

irec

tly in

to th

epe

rcep

tual

pro

cess

in a

uni

fied

way

, Giv

en to

p-do

wn

as w

ell a

s bo

ttom

-up

pro

cess

ing,

the

deci

sion

mec

hani

sms

requ

ired

for

gen

erat

ing

' ove

rtre

spon

ses

that

ref

lectlexical and other contextual influences are gr

eatly

sim

plif

ied;

no

spec

ial p

rovi

sion

nee

ds to

be

m.,d

e fo

r co

mbi

ning

lexi

cal

and

phon

etic

out

puts

in th

e de

cisi

on m

echa

nism

,A

sec

ond

reas

on f

or r

etai

ning

feed

back

com

es u

p w

hen

we

cons

ider

the

prob

lem

of

lear

ning

. Alth

ough

we

have

not

dis

cuss

ed h

ow le

arni

ngm

ight

occ

ur in

TR

AC

E, w

e ha

ve a

ssum

ed th

at th

e m

echa

nism

s of

spe

ech

perc

eptio

n ar

e ac

quire

d th

roug

h m

odifi

catio

n of

con

nect

ion

stre

ngth

s.V

ery

roug

hly,

in m

any

lear

ning

sch

emes

, con

nect

ions

bet

wee

n un

its a

rest

reng

then

ed w

hen

two

units

tend

to b

e ac

tivat

ed s

imul

tane

ousl

y, a

t the

expe

nse

of c

onne

ctio

ns b

etw

een

units

that

tend

not

to b

e ac

tivat

ed a

t the

sam

e tim

e (c

f, G

ross

berg

, 197

8; R

osen

blat

t. 19

62: R

umel

hart

& Z

ipse

r,19

85).

In s

uch

sche

mes

. how

ever

. the

re is

a s

erio

us p

robl

em if

act

ivat

ion

is e

ntire

ly b

otto

m-u

p: fo

r in

that

cas

e. o

nce

a pa

rtic

ular

uni

t has

bee

ntu

ned"

to r

espo

nd to

a p

artic

ular

pat

tern

. it i

s di

ffic

ult t

o re

tune

it: i

tfi

res

whe

n its

"ex

pect

ed"

patte

rn is

pre

sent

ed. a

nd w

hen

it fi

res.

its

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

tend

ency

to r

espo

nd to

that

pat

tern

onl

y in

crea

ses.

Fee

dbac

k pr

ovid

es a

way

to b

reak

this

vic

ious

cyc

le, I

f hi

gher

leve

ls in

sist

that

a p

artic

ular

phon

eme

is p

rese

nt. t

hen

the

unit

for

that

pho

nem

e ca

n be

com

e ac

tivat

edev

en if

the

botto

l11-

up in

put w

ould

nor

mal

ly a

ctiv

ate

som

e ot

her

phon

eme

inst

ead;

then

the

lear

ning

mec

hani

sm c

an "

retu

ne" the detector for the

phon

eme

so th

at it

will

nee

d to

dep

end

less

on

the

top-

dow

n in

put t

hene

xt ti

me

arou

nd,

In general. the use offeedback appears to place more

of

the

inte

llige

nce

requ

ired

for

per

cept

ion

and

perc

eptu

al le

arni

ng in

to th

e ac

tual

per

cept

ual

mec

hani

sm it

self

. and

to m

ake

the

mec

hani

sms

whi

ch e

xhib

it th

is in

tel-

ligen

ce e

xplic

it. A

s fo

rmul

ated

her

e. th

ese

mec

hani

sms

are

incr

edib

lysi

mpl

e; y

et th

ey a

ppea

r to

buy

qui

te a

lot w

hich

ofte

n ge

ts p

ushe

d in

toun

spec

ifie

d "d

ecis

ion" and "postperceptual guessing"

proc

esse

s (e

.Forster. 1976),

Fina

lly. t

h~ .

succ

ess

of

TR

AC

E a

lso

depe

nds

upon

its

arch

itect

ure,

rath

er th

an th

e fu

ndam

enta

l com

puta

tiona

l prin

cipl

es' o

f ac

tivat

ion

and

competition. or the decision to include feedback, B

y ar

chite

ctur

e, w

emean the organization

of

the Trace structure into layers consisting

of

units

corr

espo

ndin

g to

item

s oc

curr

ing

at p

artic

ular

tim

es w

ithin

the

utte

ranc

e,A

s w

e no

ted

in th

e in

trod

ucL

ion.

this

arc

hite

ctur

e is

one

we

deci

ded

upon

only after several other kinds

of

arch

itect

ure

had

faile

d,T

here

are

thre

e pr

inci

ple

posi

tive

cons

eque

nces

of

th

e T

RA

CE

arc

hi-

tect

ure.

Fir

st, i

t kee

ps s

trai

ght w

hat o

ccur

red

whe

n in

the

spee

ch s

trea

m,

Com

petit

ion

occu

rs o

nly

betw

een

units

com

petin

g to

rep

rese

nt th

e sa

me

portion of the input stream, Multiple copies of the same phoneme and

wor

d un

its c

an b

e ac

tive

at th

e sa

me

time

with

out p

rodu

cing

con

fusi

on,

Furt

herm

ore.

the

arch

itect

ure

perm

its th

e sa

me

com

petit

ion

mec

hani

smthat chooses among alternative word interpretations

of

a si

ngle

-wor

d ut

-te

ranc

e to

seg

men

t lon

ger

utte

ranc

es in

to w

ords

, No

sepa

rate

con

trol

structure. resetting the mechanism at the beginning

of

each

new

wor

d, is

requ

ired

, S

econ

d, th

e ar

chite

ctur

e pe

rmits

bot

h fo

rwar

d an

d ba

ckw

ard

inte

rac-

tions

. Bac

kwar

d in

tera

ctio

ns a

re a

bsol

utel

y es

sent

ial i

f th

e m

odel

is to

account for the fact that the identity

of

a ph

onem

e (o

r a

wor

d; W

arre

n &

Sher

man

, 1974) can be influenced by w

hat c

omes

afte

r it

as w

ell a

s w

hat

comes beforeiL Some kind

of

reco

rd

of

the

past

is n

eces

sary

to c

aptu

rethese kinds

of

influences. as well as to provide a clear picture

of

the

sour

ces

of

the more conventional effects

of preceding context, and the

Trace construct lays this out in a way that is both comprehensible' an

def

fici

enL

Thi

rd, t

he T

race

str

uctu

re p

rovi

des

an e

xplic

it m

echa

nism

whi

ch in

-st

antia

tes

the

idea

that

ther

e m

ay b

e no

dis

tinct

ion

betw

een

the

mec

ha-

nism

s w

hich

car

ry o

ut p

erce

ptua

l pro

cess

ing

and

thos

e w

hich

pro

vide

a

wor

king

mem

ory

for

the

resu

lts o

f th

e pe

rcep

tual

pro

cess

. At o

ne a

ndth

e sa

me

time.

the

Tra

ce is

a p

erce

ptua

l pro

cess

ing

syst

em a

nd a

mem

ory

syst

em, A

s a

resu

lt. th

e m

odel

aut

omat

ical

ly a

ccou

nts

fori

he f

act t

hat

cohe

rent

mem

ory

trac

es p

ersi

st lo

nger

than

inco

here

nt o

nes.

The

co-

here

nt o

nes

reso

nate

thro

ugh

inte

ract

ive

(tha

t is,

bot

tom

-up

and

top-

dow

n) a

ctiv

atio

n. w

hile

inco

here

nt o

nes

fail

to e

stab

lish

a re

sona

nce

and

ther

efor

e di

e aw

ay m

ore

rapi

dly,

Seve

ral

of

thes

e as

pect

s of

TR

AC

E o

verl

ap w

ith a

ssum

ptio

ns m

ade

inot

her

mod

els,

as

men

tione

d in

pre

viou

s se

ctio

ns; c

ontin

uity

bet

wee

nw

orki

ng m

emor

y an

d th

e pe

rcep

tual

pro

cess

ing

stru

ctur

es h

as b

een

sug-

gest

ed b

y a

num

ber

of o

ther

aut

hors

(e.

g,. C

onra

d,19

62),

and

the

notio

nth

at w

orki

ng m

emor

y is

a d

ynam

ic p

roce

ssin

g st

ruct

ure

rath

er th

an a

pass

ive

data

str

uctu

re h

as p

revi

ousl

y be

en a

dvoc

ated

by

Cro

wde

r (1

978,

1981) and Grossberg (1978), Indeed, G

ross

berg

has

not

ed th

at r

eson

atin

gac

tivat

ion/

com

petit

ion

proc

esse

s ca

n bo

th e

nhan

ce a

per

cept

ual r

epre

-se

ntat

ion

and

incr

ease

the

rete

ntio

n of

a r

epre

sent

atio

n; h

is a

naly

sis

ofin

tera

ctiv

e-ac

tivat

ion

proc

esse

s in

per

cept

ion

and

apem

ory

capt

ures

the

cont

inui

ty o

f pe

rcep

tion

and

mem

ory

as w

ell a

s m

any

othe

r de

sira

ble

prop

ertie

s of

in

tera

ctiv

e-ac

tivat

ion

mec

hani

sms,

Som

e D

efic

ienc

ies

of T

RA

CE

. Alth

ough

TR

AC

E h

as h

ad a

num

ber

of im

port

ant s

ucce

sses

, it a

lso

has

a number of equally important deficiencies. A number

of these deficien-

cies

rel

ate

to s

impl

ifyin

g as

sum

ptio

ns o

f th

e si

mul

atio

n m

odel

. It i

s im

-portant to be clear that such deficiencies are not in

trin

sic

to th

e ba

sic

stru

ctur

e of

the

mod

el b

ut to

the

sim

plifi

catio

ns w

e ha

ve im

pose

d up

onit

to in

crea

se o

ur a

bilit

y to

und

erst

and

its b

asic

pro

pert

ies.

Cer

tain

de-

ficiencies-such as the assumption th

at a

ll ph

onem

es a

re th

e sa

me

leng

th, t

hat a

ll fe

atur

es a

re e

qual

ly s

alie

nt a

nd u

sefu

l, a

nd o

verl

ap a

n eq

ual

amount from one phoneme to another-are no

t pre

sent

in T

RA

CE

I.O

bvio

usly

a f

ully

rea

listic

mod

el w

ould

take

acc

ount

of

such

din

eren

ces.

Oth

er fa

ctor

s th

at s

houl

d be

inco

rpor

ated

in a

mor

e co

mpl

ete

mod

el in

-clude some provision for effects

of

wor

ll fr

eque

ncy,

and

som

e m

echa

-ni

sms

for

expl

oitin

g av

aila

ble

cues

to w

ord

boun

dari

es,

Another deficiency

of

the

mod

el is

that

the

deci

sion

mec

hani

sms

have

not b

een

fully

eno

ugh

elab

orat

ed. F

or e

xam

ple,

as

it st

ands

the

mod

eldo

es n

ot p

rovi

de a

mec

hani

sm f

or ,d

ecid

ing

whe

n a

nonw

ord

has

been

pres

ente

d. N

or h

ave

we

spec

ified

how

dec

isio

n pr

oces

ses

wou

ld a

ctua

llyus

e th

e in

form

atio

n av

aila

ble

at th

e w

ord

leve

l to

loca

te w

ord-

initi

al p

ho-

nem

es, A

rel

ated

pro

blem

is th

e la

ck o

f an

exp

licit

prov

isio

n for vari-

abili

ty in

the

activ

atio

n an

d/or

rea

dout

pro

cess

es. I

ncor

pora

ting

vari

-ab

ility

dir

ectly

into

a s

imul

atio

n m

odel

wou

ld g

reat

ly in

crea

se th

e co

m-

plex

ity

of the simulation process, but would also increase the model's

TR

AC

E M

OD

EL

abili

ty to

cap

ture

the

deta

iled

prop

ertie

s of

rea

ctio

n tim

e di

strib

utio

nsan

d er

rors

(R

atcl

iff.

197

8).

So far we have considered de

fici

enci

es w

hich

we

wou

ld a

ttrib

ute

tosi

mpl

ifyin

g as

sum

ptio

ns a

dopt

ed to

kee

p T

RA

CE

as

sim

ple

and

tran

s-pa

rent

in it

s be

havi

or a

s po

ssib

le. H

owev

er. t

here

are

som

e pr

oble

ms

that

are

intr

insi

c to

the

basi

c st

ruct

ure

of th

e m

odel

,O

ne f

unda

men

tal d

efic

ienc

y of

TR

AC

E is

that

fac

t tha

t it requires

mas

sive

dup

licat

ion

of u

nits

and

con

nect

ions

. cop

ying

ove

r an

d ov

erag

ain

the

conn

ectio

n pa

ttern

s th

aI' d

eter

min

e w

hich

fea

ture

s ac

tivat

ew

hich

pho

nem

es a

nd w

hich

pho

nem

es a

ctiv

ate

whi

ch w

ords

. As

w~

al-

read

y no

ted.

lear

ning

in a

ctiv

atio

n m

odel

s (e

,g" Ackley, Hinton. &

Sejn

owsk

i. 19

85: G

ross

berg

. 197

6: R

umel

hart

& Z

ipse

r, 1985) usually

invo

lves

the

retu

ning

of

conn

ectio

ns b

etw

een

units

dep

endi

ng o

n th

eir

sim

ulta

neou

s ac

tivat

ion,

Giv

en T

RA

CE

's a

rchi

tect

ure.

suc

h le

arni

ngw

ould

not

gen

eral

ize

from

one

par

t of

the

Tra

ce to

ano

ther

and

so

wou

ldno

t be

acce

ssib

le f

or in

puts

ari

sing

at d

iffe

rent

loca

tions

in th

e T

race

, Ase

cond

pro

blem

is th

at th

e m

odel

. as

is. i

s in

sens

itive

to v

aria

tion

in g

loba

lpa

ram

eter

s, s

uch

as s

peak

ing

rate

, spe

aker

cha

ract

eris

tics

and

acce

nt,

and

ambi

ent a

cous

tic c

hara

cter

istic

s, A

thir

d de

fici

ency

is th

at it

fai

ls to

acco

unt f

or th

e fa

ct th

at o

ne p

rese

ntat

ion

of a

wor

d ha

s an

eff

ect o

n th

epe

rcep

tion

of it

a v

ery

shor

t tim

e la

ter

(Nus

baum

& S

iow

iacz

ek, 1

982)

,

These two pr

esen

tatio

ns. i

n th

e cu

rren

t ver

sion

of

the

mod

el. s

impl

yex

cite

sep

arat

e to

kens

for

the

sam

e w

ord

in d

iffer

ent p

arts

of t

he T

race

,A

ll th

ese

defi

cien

cies

ref

lect

the

fact

, tha

t the

TR

AC

E c

onsi

sts

of a

larg

e se

t of

inde

pend

ent t

oken

s of

eac

h fe

atur

e. p

hone

me,

and

wor

d un

it,W

hat a

ppea

rs to

be

calle

d fo

r in

stea

d is

a m

odel

in w

hich

ther

e is

a s

ingl

est

ored

rep

rese

ntat

ion

of e

ach

phon

eme

and

each

wor

d in

som

e ce

ntra

lrt

;pre

sent

atio

nal s

truc

ture

, If

this

str

uctu

re is

acc

esse

d ev

ery

time

the

wor

d is

pre

sent

ed, t

hen

we

coul

d ac

coun

t for

rep

etiti

on p

rimin

g ef

fect

s,L

ikew

ise.

if th

ere

wer

e a

sing

le c

entr

al s

truc

ture

. lea

rnin

g co

uld

occu

r in

just

one

set

of u

nits

, 'as could dynamic returning offeature-

phon

eme

and

phon

eme-

wor

d co

nnec

tions

to ta

ke a

ccou

nt o

f ch

ange

s in

glo

bal p

aram

~et

ers

or s

peak

er c

hara

cter

istic

s,H

owev

er. i

t rem

ains

nec

essa

ry to

kee

p st

raig

ht th

e re

lativ

e ,t

empo

ral

loca

tion

of d

iffer

ent f

eatu

re. p

hone

me.

and

wor

d ac

tivat

ions

. Thu

s it

will

not do to simply abandon the Trace in favor of a single set of units

cons

istin

g of

just

one

cop

y of

eac

h ph

onem

e an

d on

e co

py o

f ea

ch w

ord,

It s

eem

s th

at w

e ne

ed to

hav

e th

ings

bot

h w

ays:

we

need

a c

entr

alre

pres

enta

tion

that

pla

ys a

rol

e in

pro

cess

ing

ever

y ph

onem

e an

d ev

ery

wor

d an

d th

iit is

sub

ject

to le

arni

ng, r

etun

ing.

and

pri

min

g, W

e al

so n

eed

to k

eep

a dy

nam

ic tr

ace

of th

e un

fold

ing

repr

esen

tatio

n of

the

spee

chst

ream

. so

that

we

can

cont

inue

to a

ccom

mod

ate

both

left

and

right

con

"te

xtua

l eff

ects

.

MC

CLE

LLA

ND

AN

D E

LMA

N

We

are

curr

ently

beg

inni

ng to

dev

elop

a m

odel

that

has

thes

e pr

oper

-tie

s, b

ased

on

a sc

hem

e fo

r us

ing

a ce

ntra

l net

wor

k of

uni

ts to

tune

the

conn

ectio

ns b

etw

een

the

units

in th

e T

race

in th

e co

urse

of

proc

essi

ng.

ther

eby

effe

ctiv

ely

prog

ram

ing

it "o

n th

e fly

," S

imila

r id

eas

have

alr

eady

been

app

lied

to v

isua

l wor

d re

cogn

ition

(M

cCle

lland

, 198

5, 1

986)

. Our

hope

is th

at a

new

ver

sifJ

nof

the

mod

el b

ased

on

thes

e id

eas

will

pre

serv

eth

e po

sitiv

e fe

atur

es o

f T

RA

CE

I a

nd T

RA

CE

II.

whi

le o

verc

omin

g th

eir

principle deficiencies,

Som

e G

ener

al I

ssue

s in

Spe

ech

and

Lan

guag

e Pe

rcep

tion

The

re a

re a

num

ber

of g

en~r

al is

sues

in s

peec

h an

d la

ngua

ge' p

erce

p-

tion,

Fou

r qu

estio

ns in

par

ticul

ar a

ppea

r to

lie

clos

e to

the

hear

t of

our

conc

eptio

n of

wha

t spe

ech

perc

eptio

n is

all

abou

t. Fi

rst.

wha

t are

the

basi

c un

its in

spe

ech

perc

eptio

n? S

econ

d. w

hat i

s th

e pe

rcep

t. an

d w

hich

aspe

cts

of th

e pr

oces

sing

of

spok

en la

ngua

ge s

houl

d be

cal

led

perc

eptu

al?

Thi

rd. w

hat i

s th

e re

pres

enta

tion

of li

ngui

stic

rul

es?

Four

th. i

s th

ere

any-

thin

g un

ique

or

spec

ial a

bout

spe

ech

perc

eptio

n? W

e co

nclu

de th

is a

rtic

leby

con

side

ring

eac

h is

sue

from

the

pers

pect

ive

we

have

dev

elop

edth

roug

h th

e co

urse

of

our

~xpl

orat

ions

of

TR

AC

E.

What is the perceptual "nit?

Thr

ough

out t

his

artic

le. w

e ha

ve c

onsi

d-er

ed th

ree

leve

ls o

f pr

oces

sing

-fea

ture

, pho

nem

e, a

nd w

ord.

At e

ach

leve

l, in

divi

dual

pro

cess

ing

units

sta

nd f

or h

ypot

hese

s ab

out t

he f

eatu

res,

phon

emes

. and

wor

ds th

at m

ight

be

pres

ent a

t dif

fere

nt p

oint

s in

the

inpu

tst

ream

, It i

s w

orth

not

ing

that

mos

t asp

ects

of

the

mod

el's

per

form

ance

, are

inde

pend

ent o

f th

e sp

ecif

ic a

ssum

ptio

ns th

at w

e ha

ve m

ade

abou

t the

units

, or

even

the

leve

ls. T

hus.

if w

e re

plac

ed th

e ph

onem

e le

vel w

ithdemisyllables (Fujimura & Lovins, 1978) or

pho

nem

e tr

iple

s (W

icke

lgre

n.19

69),

ver

y lit

tle o

f th

e be

havi

or o

f th

e m

odel

wou

ld c

hang

e. T

hese

uni

tsca

n ca

ptur

e so

me

of th

e co

artic

ulat

ory

infl

uenc

es o

n ph

onem

e id

~nt

ity.

and

they

wou

ld r

educ

e so

me

of th

e w

ord-

boun

dary

am

bigu

ities

face

d by

the

curr

ent v

ersi

on o

f th

e m

odel

, but

nei

ther

coarticulatory influences

nor

wor

d bo

unda

ry a

mbi

guiti

es w

ould

dis

appe

ar a

ltoge

ther

(se

e E

lman

& M

cCle

lland

. in

pres

s, fo

r fu

rthe

r di

scus

sion

),

In f

act,

inte

ract

ive

activ

atio

n m

odel

s lik

e T

RA

CE

can

be

form

ulat

edin

whi

ch e

ach

perc

eptu

al o

bjec

t is

repr

esen

ted.

not

by

a si

ngle

uni

t. bu

tby

a p

atte

rn o

f act

ivat

ion

over

a c

olle

ctio

n of

uni

ts, F

or e

xam

ple.

the

phon

eme

units

in e

ach

time

slic

e of

TR

AC

E m

ight

be

repl

aced

by

adi

ffer

ent s

et o

f un

its w

hich

did

not

hav

e a

one-

to-o

ne c

orre

spon

denc

e to

phon

emes

. A p

hone

me

wou

ld b

e re

pres

ente

d by

a p

artic

ular

pat

tern

of

activ

atio

n ov

er th

e se

t of

units

(ea

ch r

epre

sent

ing,

per

haps

. to

som

e co

n-ju

nctio

n of

low

er le

vel f

eatu

res)

rat

her

than

by

a si

ngle

uni

t in

the

set.

The

re a

re s

ome

com

puta

tiona

l adv

anta

ges

of d

istr

ibut

ed r

epre

sent

atio

nco

mpa

red

to o

ur "

one

unit

one

conc

ept" assumption (Hinton, Mc-

""'

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

LMA

N

Cle

lland

, & R

umel

hart

, in

pres

s), b

ut it

is v

ery

diffi

cult

to fi

nd p

rinci

pled

way

s of

dis

tingu

ishi

ng b

etw

een

loca

l and

dis

trib

uted

rep

rese

ntat

iona

lsc

hem

es e

mpi

rica

lly, I

ndee

d, in

cer

tain

cas

es th

ere

is a

n ex

act m

appi

ngan

d, in

gen

eral

, it i

s po

ssib

le to

app

roxi

mat

e m

ost a

spec

ts o

f th

e be

havi

orof

a lo

cal s

chem

e w

ith a

dis

trib

uted

one

and

vic

e ve

rsa

(Sm

olen

sky,

1986). In light of this, our us

e of

loca

l as

oppo

sed

to d

istr

ibut

ed r

epre

-se

ntat

ions

is n

ot p

erha

ps a

s si

gnifi

cant

as

it m

ight

app

ear

at fi

rst g

lanc

e.W

hat i

s es

sent

ial i

s th

e in

form

atio

n th

at th

e re

pres

enta

tion

capt

ures

,ra

ther

than

whe

ther

it d

oes

so v

ia d

istr

ibut

ed o

r lo

cal r

epre

sent

atio

n, T

heus

e of

loca

l rep

rese

ntat

ior.

.., w

ith e

ach

unit

(at t

he p

hone

me

and

wor

dle

vels

, any

way

) re

pres

entin

g a

mut

ually

exc

lusi

ve a

ltern

ativ

e m

akes

itm

uch

easi

er to

rel

ate

the

stat

es o

f th

e pr

oces

sing

sys

tem

to o

vert

res

pons

eca

tego

ries

but

is n

ot o

ther

wis

e a

fund

amen

tal f

eatu

re o

f th

e st

ruct

ure

ofth

e m

odel

.What is the percept?

At a

num

ber

of p

oint

s in

this

art

icle

, we

have

allu

ded

to w

ays

in w

hich

our

con

cept

ion

of p

erce

ptio

n di

ffer

s fr

om th

eus

age

of o

ther

aut

hors

, Suc

h co

ncep

ts a

s pe

rcep

tion

are

inhe

rent

ly ti

edto

theo

ry, a

nd o

nly

deri

ve th

eir

mea

ning

with

res

pect

to p

artic

ular

theo

-re

tical

con

stru

cts,

Whe

re d

oes

the

TR

AC

E m

odel

pla

ce u

s, th

en, w

ithre

spec

t to

the

ques

tion,

wha

t is

spee

ch p

erce

ptio

n?F

or o

ne th

ing,

TR

AC

E b

lurs

the

dist

inct

ion

betw

een

perc

eptio

n an

dother aspects of cognitive processing, T

here

is r

eally

no

clea

r w

ay in

TR

AC

E to

say

whe

re p

erce

ptua

l pro

cess

ing

ends

and

con

cept

ual p

ro-

cess

es o

r m

emor

y be

gin,

How

ever

, fol

low

ing

Mar

rs

(198

2) d

efin

ition

of

visu

al p

erce

pt.io

n, w

e co

uld

say

that

spe

ech

perc

eptio

n is

the

proc

ess

offo

rmin

g re

pres

enta

tions

of

the

stim

ulus

-the

spe

aker

s ut

tera

nce-

atse

vera

l lev

els

of d

escr

iptio

n, T

RA

CE

pro

vide

s su

ch a

set

of

repr

esen

ta-

tions

, as

wel

l as

proc

esse

s to

con

stru

ct th

em. O

n th

is v

iew

, the

n, th

eT

race

is th

e pe

rcep

t, an

d in

tera

ctiv

e ac

tivat

ion

is th

e pr

oces

s of

per

cep-

tion, A

spec

ts o

f th

is d

efin

ition

are

app

ealin

g. F

or e

xam

ple,

on

this

vie

w, t

hepe

rcep

t is

a ve

ry r

ich

obje

ct, o

ne th

at r

efer

s bo

th to

abs

trac

t, co

ncep

tual

entit

ies

like

wor

ds a

nd p

erha

ps a

t hig

her

leve

ls e

ven

mea

ning

s, a

s w

ell

as to

mor

e co

ncre

te e

ntiti

es li

ke a

cous

tic s

igna

ls a

nd f

eatu

res,

Per

cept

ion

is n

ot r

estr

icte

d to

one

or

a su

bset

of

leve

ls, a

s it

is in

cer

tain

mod

els

(e.g

., M

arsl

en-W

ilson

, 198

0; M

orto

n, 1

979)

.O

n th

e ot

her

hand

, the

def

initi

on s

eem

s ov

erly

libe

ral,

for

ther

e is

evid

ence

sug

gest

ing

that

per

cept

ual e

xper

ienc

e an

d ac

cess

to th

e re

sults

of perceptual processing for the purposes of overt responding ,m

ay n

otbe

com

plet

ely

unco

nstn

tined

, A n

umbe

r of

exp

erim

ents

, bot

h in

spe

ech

(e.g

., Fo

ss &

Sw

inne

y, 1

973;

McN

eil &

Lin

dig,

1973) and reading (D

rew

-no

wsk

i & H

ealy

, 1977; Healy, 1976) suggest that under certain conditions

low

er le

vels

of p

roce

ssin

g ar

e in

acce

ssib

le, o

r ar

e ' a

t bes

t acc

esse

d on

ly

with

ext

ra ti

me

or e

ffor

t. O

n th

is e

vide

nce,

if p

erce

ptio

n is

to f

orm

rep

-re

sent

atio

ns, a

nd if

the

repr

esen

tatio

ns. a

re a

nyth

il18

like

thos

e po

stul

ated

in T

RA

CE

, the

n pe

rcep

tion

is q

uite

inde

pend

ent o

f th

e ex

peri

ence

of

the

perc

eive

r an

d of

acc

ess

to th

e pe

rcep

t. P

ut a

noth

er w

ay, w

e m

ay c

hoos

eto

def

ine

the

'Irac

e as

the

perc

ept,

but i

t is

not t

he p

erce

ptua

l"ex

peri

cnce

.T

his

does

not

see

m to

be

a ve

ry s

atis

fact

ory

stat

e of

affa

irs.

One

coh

eren

t 're

spon

se to

thes

e ar

gum

ents

wou

ld b

e to

say

that the

'Irac

e is

not

the

expe

rienc

e its

elf,

but t

hat s

ome

part

or

part

s of

it m

aybe the

obje

ct

of perceptual experience, It seems sensible

, for

exa

mpl

e,to

sup

pose

that

the

perc

ept i

tsel

f con

sist

s of

that

par

t of t

he T

race

und

ersc

rutin

y by

the

deci

sion

mec

hani

sms,

On

this

vie

w, i

t wou

ld n

ot b

e in

-co

here

nt to

sup

pose

that

rep

rese

ntat

ions

mig

ht b

e fo

rmed

whi

ch w

ould

nevertheless be inaccessible either to experience or to overt re

spon

sepr

oces

ses.

It w

ould

be

a m

atte

r se

para

te f

rom

the

anal

ysis

of

the

inte

r-ac

tive-

activ

atio

n pr

oces

s its

elf t

o sp

ecify

the

scop

e an

d co

nditi

ons

ofac

cess

to th

e T

race

. In

our

sim

ulat

ions

, we

have

ass

umed

that

the

deci

-si

on m

echa

nism

cou

ld b

e di

rect

ed w

ith e

qual

fac

ility

to a

ll le

vels

. but

this

may

turn

out

to b

e an

ass

umpt

ion

that

doe

s no

t app

ly in

all

case

s.HolY are rules represe~ted?

It is

com

mon

in th

eori

es o

f la

ngua

ge to

assu

me

with

out d

iscu

ssio

n th

at li

ngui

stic

rul

es a

re r

epre

sent

ed ".

..' S

lIch

in the mind of the perceiver, and that perception is guided primarily by

cons

ulta

tion

of s

uch

rule

s, H

owev

er, t

here

are

a nu

mbe

r of

dift

icul

ties

asso

ciat

ed w

ith th

is v

iew

, Fir

st, i

t :do

es n

ot e

xpla

in h

ow e

xcep

tions

are

hand

led;

it w

ould

see

m th

at f

or e

very

exc

eptio

n, th

ere

wou

ld h

ave

to b

ea

spec

ial r

ule

that

take

s pr

eced

ence

ove

r th

e m

ore general formulation.

Sec

ond,

it d

oes

not e

xpla

in a

spec

ts o

f rul

e ac

quis

ition

by

child

ren

leai

'nin

gla

ngua

ge, p

artic

ular

ly th

e fa

ct th

at"

rule

s ap

pear

to b

e ac

quire

d, a

t lea

stto

a la

rge

exte

nt, o

n a

wor

d by

wor

d ba

sis;

acq

uisi

tion

is m

arke

d by

agr

adua

l spr

ead

of th

e ru

le f

rom

one

lexi

cal i

tem

or

set o

f le

xica

l ite

ms

toot

hers

. Thi

rd, i

t doe

s no

t exp

lain

how

rul

es c

ome

,into

exi

sten

ce h

isto

ri-

cally

; as

with

acq

uisi

tion,

it a

ppea

rs th

at r

ules

spr

ead

grad

ually

ove

r th

ele

xico

n, I

t is

diff

icul

t to

reco

ncile

sev

eral

ofth

ese

findi

ngs

with

trad

ition

alru

le-b

ased

acc

ount

s of

lang

uage

kno

wle

dge

and

lang

uage

pro

cess

ing.

Mod

els

like

TR

AC

E a

nd th

e in

tera

ctiv

e-ac

tivat

ion

mod

el o

f w

ord

rec-

ogni

tion

take

a v

ery

diff

eren

t per

spec

tive

on th

e is

sue

of li

ngui

stic

rul

es,

The

y ar

e no

t rep

rese

nted

as

such

, but

rat

her

they

are

bui

lt in

to th

e pe

r-ce

ptua

l sys

tem

via

the

exci

tato

ry a

nd in

hibi

tory

con

nect

ions

nee

ded

for

proc

essi

ng th

e pa

rtic

ular

item

s w

hich

em

body

thes

e ru

les.

Suc

h a

mec

h-an

ism

app

ears

to a

void

the

prob

lem

of

exce

ptio

ns w

ithou

t dif

ticul

ty, a

ndto

hol

d ou

t the

hop

e of

acc

ount

ing

for

the

obse

rvat

ion

that

rul

e ac

quis

ition

and

rule

cha

nge

are

stro

ngly

tied

to p

artic

ular

item

s w

hich

em

body

the

ru~.

W

hat i

s sp

edt,!

abo

llt ..

.'pee

ch?

We dose by ra

isin

g a

qucs

tion

that

oft

en

TR

AC

E M

OD

EL

MC

CLE

LLA

ND

AN

D E

l ".'I

AN

RE

FER

EN

CE

S

Bag

ley,

W. C

. (I~), The apperception or

the

:spo

ken

sent

ence

: A s

tudy

in th

e ps

ycho

logy

of language,

Am

eric

an J

ollr

ncII

of

P,fy

dlol

oR."

, 12

, 80-

130.

Ballard. D. H.. Hinton, G. E,. &: Sejnowski, T. J. (1983). l'arallel visual computation.

Na-

Illre (LmIJOII).

306.

21-2

6.B

arro

w, H

. G..

&: T

enen

baum

. J. M

. (19

78).

In

A. R

. Han

son

&: E

. M. R

isem

an (

Eds

.C

ompl

ller

";,f;

C1/

l .V

Slem

s (p

p. 3

-26)

. New

Yor

k: A

cade

mic

Pre

ss.

von Bekesy, G. (1967).

Senmry ;nlrib;l;ml.

Prin

ceto

n,.N

J: P

rinc

eton

.Uni

v. P

ress

.B

ond,

Z. S

., &

: Gar

nes,

S. (

1980

). M

ispe

rcep

tions

of

l1ue

nt s

peec

h. I

n R

. Col

e (E

d,

),

Per-

cep;

;t1/l and pmJllcl;on of/11lenl

fpe'

e'dr

, Hill

sdal

e, N

J: E

rlbau

m.

Broadbent, D. E, (1967), Word frequency effect and response bias.

vdw

loR

kal

Rel

';ell'

74, 1-

15.

Col

e, R

. A. (

1973

). L

iste

ning

for

mis

pron

unci

atio

ns: A

mea

sure

of

wha

t we

hear

dur

ing

spee

ch.

Pe'ru

pl;o

n &

P.fy

dlC

lpII

Y,fi

l".f,

13,

153

-156

, , .

Col

e, R

, A.,

&: J

akim

ik, J

, (19

78),

Und

erst

andi

ng s

peec

h: H

ow w

ords

are

hea

rd. I

n G

.U

nder

woo

d (E

d.

),

Sll"

Ole

R;e

,f af

;nfim

llC/l;

cJ/I

pmce

,u;II

R.

New

Yor

k: A

cade

mic

Pre

ss.

Col

e, R

. A..

&: J

akim

ik. J

. (19

80).

A m

odel

of s

peec

h pe

rcep

tion.

In R

. Col

e (E

d,

),

Per-

cepl;an and proJllcl;on offllle'nl speech.

Hill

sdal

e, N

J: E

rlba

um.

Col

e, R

. A.,

&: R

udni

cky,

A. (

1983

). W

hat

s ne

w in

spe

ech

perc

eptio

n? T

he r

esea

rch

and

idea

s of

Will

iam

Cha

ndle

r B

agle

y. 1

874-

1946

. fy

dwla

Ric

cII

Re'

,';el

\', 9

0, 9

4-10

1.

Con

rad,

R. (

1962

). A

n as

soci

atio

n be

twee

n m

emor

y er

rors

and

err

ors

due

to a

cous

ticm

aski

ngof

spe~

ch.

Nal

llre'

(Lon

JOII

).I9

6,

1314

-13

15.

Cotton. Soo &: Grosjean, F. (1

984)

. The

gad

ng p

arad

igm

: A c

ompa

riso

n of

suc

cess

ive

and

individual presentation formats,

Pe',,

'ep'

;an

f.\:c

llopl

l.\'f

ics,

35

. 41-48

. C

row

der,

R, G

. (19

78).

Mec

hani

sms

of a

udito

ry b

ackw

ard

mas

king

in th

e st

imul

us s

uffi

xef

fect

. Ps

ycho

loR

ical

R

e"~;

e'I\

'85

. 502

-524

.C

row

der,

R. G

. (l9

8\),

The

rol

e of

aud

itory

mem

ory

in s

peec

h pe

rcep

tion

and

disc

rimi-

nation. In T. Myer:s. J. Laver. &: J.

And

erso

n (E

ds.).

TIle ('O

RII

;I;,'e repre.fe

nlal

;ml o

fsp

udl

(pp. 167-

\19)

, New

Yor

k: N

orth

-Hol

land

,Denes, p, (1955), Effect of duration on the perception of voicing.

Jour

nal a

f Ille

AcO

II.f

I;('Q

1

Soc;ely of Amer;ca,

27, 761~764,

Drewnowski. A.. &: Healy. A, (1977). Detection errors on

IIle

\ln

d C

/IIJ

: E

vide

nce

for

read

~ings units larger than the word.

Me'

",ol

)' C

oRn;

I;m

l, 63

6-64

7.

Elman, J, L. (1983). Unpublished results.

Elm

an, J

. Loo

&: M

cCle

lland

, J. L

.tl9

84).

The

irite

ract

ive

activ

atio

n m

odel

of

spee

ch p

er-

cept

ion.

In

Nor

man

Las

s (E

d.

),

LanR

llaR

e' a

nJfp

eed,

(p

p. 3

37-3

74).

New

Yor

k: A

c-ademic Press.

Elm

an, J

. L..

&: M

cCle

lland

, J. L

. (in

pre

ss).

Exp

loiti

ng th

e la

wfu

l var

iabi

lity

in th

e sp

eech

wav

e. I

n J.

S. P

erke

ll. &

: D. H

. Kla

tt (E

ds.

/nl'C

/r;a

nce

and

I'Or;

abili

lof

,fpe

ech

proc

esse

s.

Hill

sdal

e. N

J: E

rlba

um.

Erm

an. L

. D..

&: L

esse

r, U

, R. (

1980

). T

he H

ears

ay-I

I sp

eech

und

erst

andi

ng s

yste

m: A

, tutorial. In W. A. Lea,

Tre

'nJs

;n s

peec

h re

coR

II;I

;c1/

I (p

p. 3

61...

.381

). E

ngle

woo

d C

liffs

,NJ. Prentice-

Hal

l.Fe

ldm

an, J

. A.,

&: B

alla

rd, D

. H. (

1982

), C

onne

ctio

nist

mod

els

and

thei

r 'p

rope

rtie

s.

CoR

-

n;I;,'e Science', 6

, 205

-254

,F

orst

er. K

. I. .

(1976), Accessing the mental lexicon. In R. J, Wales &: E. W

alke

r (E

ds.

New

app

roac

hes

10 lanRuaRe mechanisms.

Am

ster

dam

: Nor

th-H

olla

nd..

Fos

s, D

. J..

&: B

lank

. M. A

. (19

80).

Identifying the speech codes.

CoR

n;I;

,'e P,fy

dwlo

R.\

12, 1

-31.

Fos

s, D

, J,.

&: G

erns

bach

er. M

. A. (

1983

), C

rack

ing

the

dual

cod

e: T

owar

d a

unita

ry m

odel

of phoneme identification.

Jollr

nal o

f V

erba

l Lea

rn;n

R a

nd V

erba

l Bel

la,';

or,

22. 6

09-

633.

com

es u

p in

dis

cuss

ions

of

the

mec

hani

sms

of s

peec

h pe

rcep

tion.

Is

spee

ch s

peci

al?

If s

o. in

wha

t way

s? I

t has

bee

n ar

gued

that

spe

ech

issp

ecia

l bec

ause

of

the

dist

inct

ive

phen

omen

on o

f ca

tego

rica

l per

cept

ion;

beca

use

of th

e en

code

dnes

s of

info

rmat

ion

abou

t one

pho

nem

e in

thos

epo

rtio

ns o

flhe

spe

ech

stre

am th

at a

re g

ener

ally

thou

ght t

o re

pres

ent o

ther

phon

emes

; bec

ause

the

info

rmat

ion

' in

the

spee

ch s

trea

m th

at in

dica

tes

the

pres

ence

of

a pa

rtic

ular

pho

nem

e ap

pear

s no

t to

be in

vari

ant a

t any

obvi

ous

phys

ical

leve

l; be

caus

e Q

f th

e la

ck o

f se

gmen

t bou

ndar

ies.

and

for

a va

riet

y of

oth

er r

easo

ns.

Ove

r th

e la

st s

ever

al y

ears

, a n

umbe

r of

em

piri

cal a

rgum

ents

hav

e be

enpu

t for

war

d th

at s

ugge

st th

at p

erha

ps s

peec

h m

ay n

ot b

e so

spe

cial

, or

at le

ast,

not u

niqu

e, C

ue tr

ade-

offs

and

con

text

ual i

nfluences are. of

cour

se, p

rese

nt in

man

y ot

her

dom

ains

(M

edin

& B

arsa

lou,

in p

ress

).an

d a

larg

e nu

mbe

r of

stu

dies

hav

e re

port

ed c

ateg

oric

al p

erce

ptio

n in

othe

r m

odal

ities

(se

e R

epp.

198

4. fo

r a

disc

ussi

on),

Com

puta

tiona

l wor

kon

pro

blem

s in

vis

ion

have

mad

e cl

ear

that

info

rmat

ion

that

mus

t be

extr

acte

d fr

om v

isua

l dis

play

s is

-of

ten

com

plex

ly e

ncod

ed w

ith o

ther

info

rmat

ion

(Bar

row

& T

enen

baum

; 197

8; M

arl'.

198

2), a

nd th

e la

ck

clea

r bo

unda

ries

bet;w

een

perc

ept m

il un

its in

vis

ion

is n

otor

ious

(B

alla

rdet a!.. 1983: M

arr.

198

2), T

hus,

the

psyc

holo

gica

l phe

nom

ena

that

cha

r-ac

teriz

e hu

man

spe

ech

perc

eptio

n, a

nd th

e co

mpu

tatio

nal p

robl

ems

that

mus

t be

met

by

any

mec

hani

sm o

f spe

ech

perc

eptio

n, a

re n

ot, i

n ge

nera

l,un

ique

to s

peec

h. T

o' b

e su

re. t

he p

artic

ular

con

stel

latio

n of

pro

blem

s th

atm

ust b

e so

lved

in s

peec

h pe

rcep

tion

is d

iffe

rent

than

the

cons

tella

tion

ofpr

oble

ms

face

d in

any

oth

er p

artic

ular

cas

e. b

ut m

ost o

f the

indi

vidu

alpr

oble

ms

them

selv

es d

o ap

pear

to h

ave

anal

ogs

in o

ther

dom

ains

.W

e th

eref

ore

pref

er to

vie

w s

peec

h as

an

exce

llent

test

bed

for

the

deve

lopm

ent o

f an

und

erst

andi

ng o

f m

echa

nism

s w

hich

mig

ht tu

rn o

utto

hav

e co

nsid

erab

ly b

road

er a

pplic

atio

n, S

peec

h is

spe

cial

to u

s, s

ince

it so

ric

hly

capt

ures

the

mul

tiplic

ity o

f th

e so

urce

s of

con

stra

int w

hich

mus

t be

expl

oite

d in

per

cept

ual p

roce

ssin

g, a

nd b

ecau

se it

so

clea

rly

indi

cate

s th

e po

wer

ful i

nflu

ence

s of

the

mec

hani

sms

of p

erce

ptio

n on

the

cons

truc

ted

perc

eptu

al r

epre

sent

atio

n. W

e se

e th

e T

RA

CE

mod

el a

s an

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ple

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larg

e cl

ass

of m

assi

vely

par

alle

l. in

tera

ctiv

e m

odel

s th

atho

lds

grea

t pro

mis

e to

pro

vide

a d

eepe

r un

ders

tand

ing

of th

e m

echa

nism

sge

nera

lly u

sed

in p

erce

ptio

n,

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