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. ..
C()(/
NIT
IH P
SYC
HO
LOG
Y 18
,86 (1986)
0010
-028
5/86
$7.
50C
o"yr
i~hl
~ 1
9II~
hy
Acad
emic
Pre
... In
c,A
ll ri~
h.. o
r r."r
oduc
lion
in a
ny ro
rm re
""ry
ed.
MC
CLE
LLAN
D A
ND
ELM
AN
Cm"'I
'1?i
.f!-
Mel
ltm U
"i,'er
,f;/Y
the
abili
ty to
trad
e cu
es o
ff ag
ains
t eac
h ot
her i
n ph
onem
e id
entif
icat
ion.
At t
hew
ord
leve
l. th
e m
odel
cap
ture
s Ihe
ma.
ior p
ositi
ve fe
atur
e of
Mar
slen
-Wils
onC
OH
OR
T m
odel
of s
peec
h pe
rcep
tion.
in th
at it
sho
ws
imm
edia
te s
ensi
tivity
toin
form
atio
n fa
vorin
g on
e w
ord
or s
et o
f wor
ds o
ver o
ther
s. A
t the
sam
e tim
e, it
over
com
es a
diff
icul
ty w
ith th
e CO
HO
RT m
odel
: it c
an re
cove
r fro
m u
nder
spec
-, i
fical
ion
or m
ispro
nunc
iatio
n of
a w
ord'
s beg
inni
ng. T
RACE
II a
lso u
ses l
exic
alin
form
atio
n to
segm
ent a
stre
am o
f spe
ech
into
a se
quen
ce o
f wor
ds a
nd to
find
wor
d be
ginn
ings
and
end
ings
, and
it s
imul
ates
a n
umbe
r of r
ecen
t fin
ding
s re
late
dto
thes
e po
ints
. The
TR
ACE
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 the
pro
cess
of speech perception. ~ 1
986
Acad
emic
Pre
.., In
c,
The
TRAC
E M
odel
of S
peec
h Pe
rcep
tion
JAM
ES L
. MC
CLE
LLAN
D
AN
DC
onsi
der t
he p
erce
ptio
n of
the
phon
eme
/g/ i
n th
e se
nten
ce "
She
re-
ceiv
ed a
val
uabl
e gi
ft; "
Ther
e ar
e a
larg
e nu
mbe
r of c
ues
in th
is se
nten
ceto
the
iden
tity
of th
is ph
onem
e, F
irst,
ther
e ar
e th
e ac
ousti
c cu
es to
the
iden
tity
of th
e /g
/ itse
lf, S
econ
d. th
e ot
her p
hone
mes
in th
e sa
me
wor
dpr
ovid
e an
othe
r sou
rce
of c
ues.
for i
f we
know
the'
rest
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 fo
rm a
wor
d w
ith, them, Third. the semantic and syntactic context further constrain the
poss
ible
wor
ds w
hich
mig
ht o
ccur
. and
thus
lint
it sti
ll fu
rther
the
poss
ible
inte
rpre
taJio
n of
the
first
phon
eme
in "
gift,
Ther
e is
ampl
e ev
iden
ce th
at a
ll of
thes
e di
ffere
nt s
ourc
es o
f inf
or-
mat
ion
are
used
in re
cogn
izin
g w
ords
and
the
phon
emes
they
con
tain
,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
Bagl
ey (1
900)
ove
r 80
year
sag
o, C
ole
and
Rudn
icky
poi
nt o
ut th
at re
cent
wor
k (w
hich
we
c~m
sider
in d
etai
l bel
ow) h
as a
dded
cla
rity
and
deta
il to
thes
e ba
sic fi
ndin
gs b
utha
s not
lead
to a
theo
retic
al sy
nthe
sis th
at p
rovi
des a
satis
fact
ory
acco
unt
of th
ese
and
man
y ot
her b
asic
asp
ects
of sp
eech
per
cept
ion,
In th
is pa
per.
we
desc
ribe
a m
Ode
l who
se p
rimar
y pu
rpos
e is
to a
ccou
ntfo
r the
inte
grat
ion
of m
ultip
le so
urce
s of i
nfor
mat
ion.
or c
onst
rain
t, in
spee
ch p
erce
ptio
n, T
he m
odel
is c
onstr
ucte
d w
ithin
a fr
amew
ork
whi
chap
pear
s to
beid
eal f
or th
e ex
ploi
tatio
n of
sim',l
tane
ous.
and
ofte
n m
utua
l,co
nstra
ints
. Thi
s fra
mew
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),
This
appr
oach
gre
w o
ut o
f a n
umbe
r of e
arlie
r ide
as. s
ome
com
ing
first
from
rese
arch
on
spok
en la
ngua
ge re
cogn
ition
(Mar
slen-
Wils
on &
Wel
sh.
1978
; Mor
ton.
196
9; R
eddy
. 1976) and others arising from m
ore
gene
ral
cons
ider
atio
ns o
f int
erac
tive
para
llel p
roce
ssin
g (A
nder
son.
197
7; G
ross
-be
rg. 1
978;
McC
lella
nd. 1
979)
,Ac
cord
ing
to th
e in
tera
ctiv
e-ac
tivat
ion
appr
oach
. inf
orm
atio
n pr
o-ce
ssin
g ta
kes p
lace
thro
ugh
the
exci
tato
ry a
nd in
hibi
tory
inte
ract
ions
amon
g a
larg
e nu
mbe
r of p
roce
ssin
g el
emen
ts ca
lled
units
, Eac
h un
it is
a ve
ry si
mpl
e pr
oces
sing
devi
ce, I
t sta
nds f
or a
hyp
othe
sis a
bout
the
inpu
t bei
ng p
roce
ssed
. The
act
ivat
ion
of a
uni
t is
mon
oton
ical
ly re
late
d
,. q, ~
JEFF
REY
L. E
LMAN
U"i
t'er.fi/y of C(/l((omi(/. Stili Dif!1!O
We
desc
ribe
a m
odel
cal
led
the
TRA
CE m
odel
of s
peec
h pe
rcep
tion.
The
mod
elis
base
d on
the
prin
cipl
es o
f int
erac
tive
activ
atio
n. In
form
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
larg
e nu
mbe
r of
simple processing u
rtits,
eac
h w
orki
ng c
ontin
uous
ly to
upd
ate
its o
wn
activ
atio
non
the
basis
of t
he a
ctiv
atio
ns o
f oth
er u
nits
to w
hich
it is
con
nect
ed. T
he m
odel
is ca
lled
the
TRA
CE m
odel
bec
ause
the
netw
ork
of u
nits
form
s a d
ynam
ic p
ro-
cessing structure called "the Trace." w
hich
serv
es a
t onc
e as
the
perc
eptu
alpr
oces
sing
mec
hani
~m a
nd a
s th
e sy
stem
s w
orki
ng m
emor
y. T
he m
odel
is in
-sta
ntia
ted
in tw
o sim
ulat
ion
prog
ram
s. TR
ACE
I, d
escr
ibed
in d
etai
l else
whe
re,
deals with short seg~ents orreal speech. and suggests a m
echa
nism
for c
opin
gw
ith th
e fa
ct th
at th
e cu
es to
the
iden
tity,
of p
hone
mes
var
y as
a fu
nctio
n of
cont
ext.
TRAC
E II_
the
focu
s of t
his a
rticl
e, si
mul
ates
a la
rge
num
ber o
f em
piric
alfin
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,
TRA
CE II
sim
ulat
es th
ein
nuen
ce o
f lex
ical
jnfo
rmat
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 cer
tain
con
ditio
ns b
ut n
ot o
ther
s.Th
e 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 but
can
still
be
used
to in
nuen
ce p
roce
ssin
g of
nove
l. no
nwor
d ul
lera
nces
. The
mod
el a
lso e
xhib
its c
ateg
oric
al p
erce
ptio
n an
d
The
wor
k re
porte
d he
re w
as s
uppo
rted
in p
art b
y a
cont
rdct
from
the
Offi
ce o
f Nav
alResearch 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 C
aree
r Dev
elop
men
t Aw
ard
to th
efir
st au
thor
from
the
Nat
jona
llnsti
tute
of M
enta
l Hea
lth (5
-KO
I-MHOO3851. We thank
Dr.
Joan
ne M
iller f
or a
ver
y u5
eful
dis
cuss
ion
whi
ch in
spire
d us
to w
rite
this
arti
cle
in it
s pr
esen
tfo
rm. D
avid
Piso
ni w
as e
~tre
mel
y he
lpfu
l in
mak
ing
us d
eal m
ore
fully
with
seve
ral i
mpo
rtant
issu
es, a
nd in
.Ier
ling
us to
a la
rge
num
ber o
f use
ful p
aper
s in
the
liter
atur
e, W
e al
so th
ank
Dav
id R
umel
hart
for u
se~u
l dis
cuss
ions
dur
ing
the
deve
lopm
ent o
f the
bas
ic a
rchi
tect
ure
ofTR
ACE
and
Eile
en C
onw
ay, M
ark
John
son.
Dav
e Pa
re, a
nd p
odul
Sm
ith fo
r the
ir as
sista
nce
in p
rogr
amin
g an
d gr
aphi
cs. S
end
requ
esls
for r
eprin
ts 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
Park
. Pills
burg
h, P
A 15
213.
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
to th
e str
engt
h of
the
hypo
thes
is fo
r whi
ch th
e un
it sta
nds,
Cons
train
tsam
ong
hypo
thes
es a
re re
pres
ente
d by
con
nect
ions
. UnU
s w
hich
are
mu-
tual
ly c
onsi
sten
t are
mut
ually
exc
itato
ry, a
nd u
nits
that
are
mut
ually
in-
cons
iste
nt a
re m
utua
lly in
hibi
tory
. Thu
s, th
e un
it fo
r /g/
has
mut
ually
exci
tato
ry c
onne
ctio
ns w
ith u
nits
for w
ords
con
tain
ing
/g/,
and
has
mu-
tual
ly in
hibi
tory
con
nect
ions
with
uni
ts fo
r oth
er p
hone
mes
, Whe
n th
eac
tivat
ion
of a
uni
t exc
eeds
som
e th
resh
old
activ
atio
n va
lue,
it b
egin
s to
influence the
activ
atio
n of
oth
er u
nits
via
its
outg
oing
con
nect
ions
; the
stren
gth
of th
~se
signa
ls de
pend
s on
the
degr
ee o
f the
send
ers a
ctiv
atio
n,Th
e st
ate
of th
e sy
stem
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
essin
g am
ount
s to
the
evol
utio
n of
that
stat
e, o
ver t
ime,
Thr
ough
out
the course
of
proc
essi
ng, e
ach
unit
is c
ontin
ually
rece
ivin
g in
put f
rom
othe
r uni
ts, c
ontin
ually
upd
atin
g its
act
ivat
ion
on th
e ba
sis o
f the
se in
puts,
and,
if it
is o
ver t
hres
hold
, it i
s con
tinua
lly se
ndin
g ex
cita
tory
and
inhi
b-ito
ry si
gnal
s to
othe
r uni
ts. T
his "
inte
ract
ive-
activ
atio
n " ,p
roce
ss a
llow
sea
ch h
ypot
he~i
s bo
th to
con
stra
in a
nd b
e co
nstra
ined
by
othe
r mut
ually
cons
isten
t or i
ncon
siste
nt h
ypot
hese
s,
Crite
rill l
Ind
Colls
tmill
ts O
il M
odel
Dev
elop
men
tTh
ere
are
gene
rally
two
kind
s of m
odel
s of t
he sp
eech
per
cept
ion
pro-
cess
, One
kin
d of
mod
el, w
hich
gro
ws o
ut o
f speech engineering and
artif
ical
inte
llige
nce,
atte
mpt
s to
prov
ide
a m
achi
ne so
lutio
n to
the
prob
lem
of s
~eec
h re
cogn
ition
, Exa
mpl
es o
f thi
s kin
d of
mod
el a
reH
EAR
SAY
(Erm
an &
Les
ser,
1980
; Red
dy, E
rman
, Fen
nell.
& N
eely
,19
73) H
WIM
(Wol
f & W
oods
, 197
8), H
ARP
Y (L
ower
re, 1
976)
, and
LAFS
/SCR
IBER
(Kla
tt, 1
980)
, A se
cond
kin
d of
mod
el, g
row
ing
out o
fex
perim
enta
l ~sy
chol
ogy,
atte
mpt
s to
acc
ount
for a
spec
ts o
f psy
chol
og-
ical
dat
a on
the
perc
eptio
n of
spee
ch. E
xam
ples
of t
his c
lass
of m
odel
sin
clud
e M
arsl
~n- W
ilson
s C
OH
OR
T M
odel
(Mar
slen
- Wils
on &
Tyl
er,
1980
; Mar
slen
~ Wils
on &
Wel
sh, 1
978;
Nus
baum
& S
iow
iacz
ek, 1
982)
;M
assa
ros
feat
ure
inte
grat
ion
mod
el (M
assa
ro, 1
981;
Mas
saro
& O
den,
I 980
a, 1
980b
; Ode
n &
Mas
saro
, 197
8); C
ole
and
Jaki
mik
' s (1978, 1980)
mod
el o
f aud
itory
wor
d pr
oces
sing,
and
the
mod
el o
f aud
itory
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).
Each
app
roac
h ho
nors
a d
iffer
ent c
riter
ion
for s
ucce
ss. M
achi
nemodels are ju4ged in terms of actual performance in
reco
gniz
ing
real
spee
ch. P
sych
olog
ical
mod
els a
re ju
dged
in te
rms o
f the
ir ab
ility
toac
-co
unt f
or d
etai
ls 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
spee
ch p
erce
ptio
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
tribu
te to
war
d th
e de
velo
pmen
t of a
com
puta
tiona
lly s
uffi-
cien
t fra
mew
ork
for s
peec
h pe
rcep
tion?
Sec
ond ,
cou
ld it
acc
ount
for w
hat
is kn
own
abou
t the
psy
chol
ogy
of sp
eech
per
cept
ion?
In sh
ort,
we
wan
ted
to k
now
, was
the
appr
oach
frui
tful,
both
on
com
puta
tiona
l and
psy
cho-
logi
cal g
roun
ds.
Two
fact
s im
med
iate
ly b
ecam
e ap
pare
nt. F
irst,
spok
en la
ngua
ge in
tro-
duce
s man
y ch
alle
nges
that
mak
e it
far f
rom
cle
ar h
ow w
ell t
he in
tera
c-tiv
e-ac
tivat
ion
appr
oach
will
serv
e w
hen
exte
nded
from
prin
t to
spee
ch.
Seco
nd, t
he a
ppro
ach
itsel
f is
too
broa
d to
pro
vide
a c
oncr
ete
mod
el,
with
out f
urth
er a
ssum
ptio
ns, H
ere
we
revi
ew se
vera
l fac
ts ab
out s
peec
hth
at p
laye
d a
role
in sh
apin
g th
e sp
ecifi
c as
sum
ptio
ns e
mbo
died
inTR
ACE
.
Som
e Im
porta
nt F
acts
abou
t Spe
ech
Our
inte
ntio
n he
re is
not
to p
rovi
de a
n ex
tens
ive
surv
ey o
f the
nat
ure
of sp
eech
and
its p
erce
ptio
n, b
ut ra
ther
to p
oint
to se
vera
l fun
dam
enta
las
pect
s of s
peec
h th
at h
ave
play
ed im
porta
nt ro
les i
n th
e de
velo
pmen
tof
the
mod
el w
e de
scrib
e 'h
ere,
A v
ery
usef
ul d
iscus
sion
of se
vera
l of
thes
e po
ints
is av
aila
ble
in K
latt
(198
0).
Tem
pora
l nat
ure
of th
e speec'h stimulus,
It do
es n
ot, o
f cou
rse,
take
asc
ient
ist to
obs
erve
one
fund
amen
tal d
iffer
ence
bet
wee
n sp
eech
and
prin
t: sp
eech
is a
sign
al w
hich
is e
xten
ded
in ti
me,
whe
reas
prin
t is . a
stim
ulus
whi
ch is
ext
ende
d in
spa
ce, T
he se
quen
tial n
atur
e of
spee
chpo
ses p
robl
ems f
or a
mod
eler
, in
that
to a
ccou
nt fo
r con
text
effe
cts,
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 s
peec
h if
each
succ
essiv
e po
rtion
of t
he sp
eech
inpu
t wer
e pr
o-ce
ssed
inde
pend
ently
of a
ll of
the
othe
rs, b
ut in
fact
, thi
s is c
lear
ly rio
tth
e ca
se. T
he p
rese
nce
of c
onte
xt e
ffect
s in
spee
ch p
erce
ptio
n re
quire
sa
mec
hani
sm th
at k
eeps
som
e re
cord
of t
hat c
onte
xt, i
n a
form
that
allo
ws
it to
influ
ence
th~
inte
rpre
tatio
n of
subs
eque
nt in
put.
A fu
rther
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 c
onte
xt b
ut a
lso su
bseq
uent
con
text
that
influ
ence
s per
cept
ion,
(Thi
s and
rela
ted
poin
ts ha
ve re
cent
ly b
een
mad
e by
Gro
sjean
& G
ee, 1
984;
Sal
asoo
& P
isoni
, 198
5; a
nd T
hom
pson
,19
84).
For e
xam
ple,
Gan
ong
(198
0) re
porte
d th
at th
e id
entif
icat
ion of a
sylla
ble-
initi
al sp
eech
soun
d th
at w
as c
onstr
ucte
d to
be
betw
een
/gI a
nd/k
/ was
;ptlu
ence
d by
whe
ther
the
rest
of t
he s
ylla
ble
was
Iisl
(as
inki
ss) o
r /lft
l (as
in "
gift"
), Su
ch' "
right
con
text
efte
cts "
(Thompson,
1984) indicate that the pe
rcep
tion
of w
hat c
omes
in n
ow b
oth
influ
ence
san
d is
influ
ence
d by
the
perc
eptio
n of
wha
t com
es in
late
r. Th
is fa
cisu
gges
ts th
at th
e re
cord
of w
hat h
as a
lread
y be
en p
rese
nted
can
not n
otbe
a st
atic
repr
esen
tatio
n , b
ut sh
ould
rem
ain
in a
mal
leab
le fo
rm. s
ubje
ctto
alte
ratio
n as
a re
sult
of in
fluen
ces
aris
ing
from
sub
sequ
ent c
on/e
x!.
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
::.-
LLI
LLI
0::
:.....
..
wor
d se
gmen
tatio
n (B
ond
& G
arne
s, 19
80).
and
certa
in se
gmen
tatio
nde
cisio
ns a
re e
asily
influ
ence
d by
con
text
ual f
acto
rs (C
ole
& Ja
kiin
ik.
1980
), Th
us. i
t 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 str
eam
into
sepa
rate
wor
d un
its. a
nd
man
y ca
ses s
uch
a se
gmen
tatio
n w
ould
per
forc
e ex
clud
e fro
m o
ne o
f the
wor
ds a
shar
ed se
gmen
t tha
t is d
oing
dou
ble
duty
in e
ach
of tw
o su
cces
-siv
e w
ords
, .C
Oflt
ext-s
emiti
t'ity
of m
e.f,
A th
ird m
ajor
fact
abo
ut sp
eech
is th
at th
ecu
es fo
r 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 tra
nsiti
on oftht second formant carries a
great deal of information about the identity of the stop consonant
Ibl
Fig,
I. b
ut th
at fo
rman
t wou
ld lo
ok q
uite
diff
eren
t had
the
sylla
ble
been
big"
or "
bog"
instead of "
bag.
" Thu
s the
con
text
.in
whi
ch a
pho
nem
eoc
curs
restr
uctu
res t
he c
ues t
o th
e id
entit
y of
that
pho
nem
e (L
iber
man
,19
70).
The
exte
nt o
f the
restr
uctu
ring
depe
..ds o
n th
e un
it se
lect
ed a
ndon
the
parti
cula
r cue
invo
lved
. But
the
prob
lem
is u
biqu
itous
in sp
eech
,N
ot o
nly
are
the
cues
for e
ach
phon
eme
dram
atic
ally
affe
cted
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 s
uch
as ra
te o
f spe
ech
(Mill
er. 1
981)
. by
mor
phol
ogic
al a
nd p
ro-
sodi
c fa
ctor
s suc
h as
pos
ition
in w
ord
and
in th
e str
ess c
onto
ur o
f the
utte
ranc
e. a
nd b
y ch
arac
teris
tics o
f the
spea
ker s
uch
as si
ze a
nd sh
ape
of th
e vo
cal t
ract
. fun
dam
enta
l fre
quen
cy o
f the
spea
king
voi
ce. a
nddialectical variations (see Klatt, 1980. a
nd R
epp
& L
iber
man
. 1984. for
disc
ussi
ons)
, .A
num
ber o
f diff
eren
t app
roac
hes t
o th
e pr
oble
m h
ave
been
trie
d by
diffe
rent
inve
stiga
tors
. One
app
roac
h is
to tr
y to find relatively invar-
iant
-generally relational-
feat
ures
(e.g
.. St
even
s & B
lum
stein
. 198
1),
Ano
ther
appr
oach
has
bee
n to
rede
fine
the
unit
so th
at it
enco
mpa
sses
the
cont
ext a
nd th
eref
ore
beco
mes
mor
e in
varia
nt (F
ujim
ura
& L
ovin
s.19
82; K
latt.
198
0; W
icke
lgre
n, 1
969)
, Whi
le th
ese
are
both
sen
sibl
e an
dus
eful
app
roac
hes,
the
first
has n
ot y
et su
ccee
ded
in e
stab
lishi
ng a
suf
-fic
ient
ly in
varia
nt se
t of c
ues,
and
the
seco
nd m
ay a
llevi
ate
but d
oes n
otel
imin
ate
the
prob
lem
; eve
n un
its s
uch
as d
emis
ylla
bles
(Fuj
imur
a &
Lovi
ns, .
1982
), co
ntex
t-sen
sitiv
e al
loph
ones
(Wic
kelg
ren,
196
9). o
r eve
nw
hole
wor
ds (K
latt,
198
0) a
re st
ill in
fluen
ced
by c
onte
xt. W
e ha
ve c
hose
nto
focu
s ins
tead
on
a th
ird p
ossib
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 c
on-
nect
ions
, the
reby
effe
ctiv
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 c
ompo
und
all t
hepr
oble
ms
allu
ded
to a
bove
, the
re is
the
addi
tiona
l fac
t tha
t spe
ech
is o
fteil
perc
eive
d un
der l
ess
than
idea
l circ
umst
ance
s. W
hile
a s
low
and
car
eful
spea
ker i
n a
quie
t roo
m m
ay p
rodu
ce s
uffic
ient
cue
s to
allo
w c
orre
ct
Lack
(~r h
Ollllc!a/";es alld te
mpo
/"al O
I'C'r/
ap.
A se
cond
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 se
vere
at t
he p
hone
me
leve
l. A glance at a schematic speech spectrogram (Liberman. 19
70; F
ig. I
)cl
early
illu
strat
es th
is pr
oble
m. T
here
oar
e no
sep
arab
le p
acke
ts o
f inf
or-
mat
ion
in th
e sp
ectro
gram
like
the
sepa
rate
feat
ure
bund
les t
hat m
ake
uple
tlt~r
s in
prin
ted
wor
ds,
Beca
use
of th
e ov
erla
p of
succ
essiv
e ph
onem
es. i
t is d
iffic
ult a
nd. w
ebelieve. counterproductive to try to divide the speech s
tream
up
into
sepa
rate
pho
nem
e un
its in
adv
ance
of i
dent
ifyin
g th
e un
its. A
num
ber o
fot
her r
esea
rche
rs (e
.g., Fowler, 1984: Klatt, 1980) have m
ade
muc
h th
esa
me
poin
t. A
supe
rior a
ppro
ach
seem
s to
be to
allo
w th
e ph
onem
e id
e;n-
tific
atio
n pr
oces
s to
dam
ine
the
spee
ch s
tream
for c
hara
cter
istic
pat
-te
rns.
with
out f
irst s
egm
entin
g th
e str
eam
into
sepa
rate
u!1i
ts,Th
e pr
oble
m o
f ove
rlap
is le
ss se
vere
for w
ords
than
for p
hone
mes
.bu
t it d
oes n
ot g
o aw
ay c
ompl
ete.
ly, I
nra
pid
spee
ch. w
ords
run
into
eac
hot
her.
and
ther
e ar
e no
pau
ses b
etw
e~n
wor
ds in
runn
ing
spee
ch, 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
fstr
esse
d w
ords
in E
nglis
h. a
nd w
ord
initi
al v
owel
s are
gen
eral
ly p
rece
ded,
by g
lotta
l sto
ps. f
or e
xam
ple.
The
se c
ues h
ave
been
stud
ied
by a
num
ber
of in
vesti
gato
rs. p
artic
tllar
ly L
ehist
e (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) .d
emon
stra
ted
that
perc
eive
rs e
xplo
it so
me
of th
ese
cues
but
foun
d th
at c
erta
in u
ttera
nces
do n
ot p
rovi
de su
ffici
ent c
ues t
o w
ord
boun
darie
s to
perm
it re
liabl
e pe
r-ce
ptio
n of
the
inte
nded
utte
ranc
e, S
peec
h er
rors
ofte
n in
volv
e er
rors
of
TIM
EFI
G, I
, A ~
chcm
alic
spcc
lrngr
am ro
r the
~yJlab'e "
bag,
" indicating the overtap or the
inro
rmat
ion
~pec
iryin
g th
e di
ffere
nt p
hone
mes
. Rep
rinte
d w
ith p
erm
issi
on rr
om L
iber
man
1197
01,
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
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 lev
el c
onstr
aint
s, th
ese
cond
ition
s do
not a
lway
s obt
ain,
People can correctly perceive speech under quite impoverished condi-
tions
, if i
t is s
eman
tical
ly c
oher
ent a
nd s
ynta
ctic
ally
wel
l for
med
(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
func
tion,
eve
n w
ith a
hig
hly
degr
aded
stim
ulus
, In
par-
ticul
ar, a
s Tho
mps
on (1
984)
, Nor
ris (1
982)
, and
Gro
sjea
n an
d G
ee (1
984)
have
poi
nted
out,
the
mec
hani
sms o
f 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 w
ord,
As w
e sh
all s
ee, t
his f
act
pose
s a
serio
us p
robl
em fo
r one
of t
he b
est c
urre
nt p
sych
olog
ical
mod
els
of th
e pr
oces
s of s
poke
n w
ord recognition (Marslen-Wilson & Welsh,
1978
),M
any
of th
e ch
arac
teris
tics t
hat w
e ha
ve re
view
ed d
iffer
entia
te sp
eech
from 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:
mist
ake
to th
ink
that
sim
ilar p
robl
ems a
re n
ot e
ncou
nter
edin
oth
er d
omai
ns. C
erta
inly
, the
sequ
entia
l nat
ure
of sp
oken
inpu
t set
s. speech apart from vi
sion,
in w
hich
ther
e ca
n be
som
e de
gree
of s
imul
-ta
neity
of p
erce
ptio
n, H
owev
er, t
he p
robl
ems
of il
l-defined boundaries,
cont
ext s
ellsi
tivity
of c
ues,
and
noise
and
inde
term
inac
y ar
e ce
ntra
lpr
oble
ms i
n vi
sion
just
as m
uch
as th
ey a
re in
spee
ch (c
f. Ba
llard
, Hin
ton,
an
d Se
jnow
ski,
1983
; Bar
row
& T
enen
baum
, 1978; Marr, 19
82),
Thus
,th
ough
the
mod
el w
e pr
esen
t her
e is
focu
ssed
on
spee
ch p
erce
ptio
n, w
ew
ould
hop
e th
at th
e w
ays i
n 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
-
THE
TRAC
E M
OD
EL
The
Impo
rltw
ce o
f the
Rig
ht A
rchi
tect
ure
All
four
of t
he c
onsid
erat
ions
liste
d ab
ove
play
ed a
n im
porta
nt ro
le in
the
form
ulat
ion
of th
e TR
ACE
mod
el. T
he m
odel
is a
n in
stanc
e of
an
inte
ract
ive
activ
atio
n m
odel
, but
it is
. by
no m
eans
the
only
insta
nce
ofsu
ch a
mod
el th
at w
e ha
ve c
onsid
ered
or t
hat c
ould
be
cons
ider
ed, O
ther
form
ulat
ions
,we
cons
ider
ed si
mpl
y di
d no
t app
ear t
o of
fer a
satis
fact
ory
fram
ewor
k fo
r dea
ling
with
thes
e fo
ur a
spec
ts of
spee
ch (s
ee E
lman
&M
cCle
lland
, ,19
84, f
or d
iscus
sion)
. Thu
s, th
e TR
ACE
mod
el h
inge
s as
muc
h on
the
parti
cula
r pro
cess
ing
arch
itect
ure
it pr
opos
es fo
r spe
ech
perc
eptio
n as
it d
oes
on th
e in
tera
ctiv
e ac
tivat
ion
proc
esse
s tha
t occ
urw
ithin
this
arch
itect
ure.
Inte
ract
ive~
activ
atio
n m
echa
nism
s are
a c
lass
too
broa
d to
stan
d 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 can
be
built
with
in th
e fra
mew
ork,
the
attra
ctiv
enes
s of t
he fr
amew
ork
as a
who
le is
, of c
ours
e, in
crea
sed,
but
the
adeq
uacy
of a
ny p
artic
ular
mod
el w
ill g
ener
ally
dep
end
on th
e pa
r-tic
ular
ass
umpt
ions
that
mod
el e
mbo
dies
. It i
s no
diff
eren
t with
inte
ract
ive-
Ove
rvie
wTh
e TR
ACE
mod
el c
onsis
ts pr
imar
ily o
f a v
ery
larg
e nu
mbe
r of u
nits
organized into three levels,
thefealllre. phoneme,
and
It'or
d le
vels,
Eac
hun
it sta
nds f
or a
hyp
othe
sis a
bout
a p
artic
ular
per
cept
ual o
bjec
t occ
urrin
gat
!a p
artic
ular
poi
nt in
tim
e de
fined
rela
tive
to th
e be
ginn
ing
of th
e ut
- .te
ranc
e.A
smal
l sub
set o
f the
uni
ts in
TRA
CE II
, the
ver
sion
of th
e m
odel
we
focu
s on
in th
is pa
per,
is ill
ustra
ted
in F
igs,
2,3,
and
4, E
ach
of th
e th
ree
figur
es re
plic
ates
the
sam
e se
t of u
nits,
illu
strat
ing
a di
ffere
nt p
rope
rtyof
the
mod
el in
eac
h ca
se. I
n th
e fig
ures
, eac
h re
ctan
gle
corre
spon
ds 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 wor
d) fo
r whi
ch e
ach
unit
stand
s, Th
e le
fland
righ
t edg
es o
f eac
h re
ctan
gle
indi
cate
the
porti
onof
the
inpu
t the
uni
t spa
ns,
At t
he fe
atur
e le
vel,
ther
e ar
e se
vera
l ban
ks o
f fea
ture
det
ecto
rs, o
nefo
r eac
h of
seve
ral d
imen
sions
of s
peec
h so
unds
. Eac
h ba
nk is
repl
icat
edfo
r' ea
ch o
f sev
erdl
succ
essiv
e m
omen
ts in
tim
e, o
r tim
e sli
ces,
At.
the
phon
eme
leve
l, th
ere
are
dete
ctor
s for
eac
h of
the
phon
emes
, The
re is
one
copy
of e
ach
phon
eme
dete
ctor
cen
tere
d ov
er e
very
thre
e tim
e sli
ces.
Each
uni
t spa
ns si
x tim
e sli
ces,
so u
nits
with
adj
acen
t cen
ters
span
ove
r-la
ppin
g ra
nges
of s
lices
, At t
he w
ord
leve
l, th
ere
are
dete
ctor
s for
eac
hw
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 s
pans
a s
tretc
h of
feat
ure
slic
es c
or-
resp
ondi
ng to
the
entir
e le
ngth
of '
the
wor
d. A
gain
, the
n, u
nits
with
ad-
jace
nt c
ente
rs s
pan
over
lapp
ing
rang
es o
f slic
es,
Inpu
t to
the
mod
el, i
n th
e fo
rm o
f a p
atte
rn o
f act
ivat
ion
to b
e ap
plie
dto
the
units
at t
he fe
atur
e le
vel,
is pr
esen
ted
sequ
entia
lly to
the
feat
urc-
leve
l uni
ts in
succ
essiv
e sli
Ces,
as 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 on
the
thre
e ill
ustra
ted
dim
ensio
nsfo
r the
phr
ase
"tea
cup
" (/tik"p/
)' ar
e sh
own
in F
ig. 2
, At a
ny in
stant
,in
put i
s arri
ving
onl
y at
the
units
in o
ne sl
ice
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
slice
s of t
he n
etw
ork
at ~
ucce
ssiv
e m
omen
ts in
tim
e. H
owev
er,
it is
impo
rtant
to re
mem
ber t
hat a
ll th
e un
its a
re c
ontin
ually
invo
lved
inpr
oces
sing,
and
pro
cess
ing
of th
e in
put a
rrivi
ng a
t one
tim
e is
just
begi
n-ni
ng a
s th
e in
put i
s m
oved
alo
ng to
the
next
tim
e sl
ice.
. The
ent
ire n
etw
ork
of u
nits
is ca
lled
"the
Tra
ce,"
bec
ause
the
patte
rnof
act
ivat
ion
left
by a
spok
en in
put i
s a tr
ace
of th
e an
alys
is of
the
inpu
tat
eac
h of
the
thre
e pr
oces
sing
leve
ls. T
his
trace
is u
nlik
e m
~i\y
trac
es
TRAC
E M
OD
EL
kAp
i~i~
i~i~
i~i~
i~i
. p
rlnr~
t~t~
t~t~
t'11
11: ,
: : :
I : I
II1'
rnn:
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 su
bsel
of t
he u
nits
in T
RACE
II. E
ach
rect
angl
e re
pres
ents
a di
ffere
nt u
nit,
The
labe
ls in
dica
te th
e ite
m fo
r whi
ch th
e un
it sta
nds,
and
the
horiz
onta
l edg
es o
f the
rect
angl
ein
dica
le th
e po
rtion
of t
he T
race
span
ned
by e
ach
unit.
The
inpu
t fea
ture
spec
ifica
tions
for
the
phra
se "
tea
cup.
" pre
cede
d an
d fo
llow
ed b
y sil
ence
. are
indi
cate
d fo
r the
thre
e iII
us-
trate
ddi
men
sions
by
the
blac
keni
ng o
f the
cor
resp
ondi
ng fe
atur
e un
its.
thou
gh, i
n th
at it
is d
ynam
ic, s
ince
it c
onsis
ts of
act
ivat
ions
of p
roce
ssin
gel
emen
ts. a
nd th
ese
pro c
essi
ng e
lem
ents
' con
tinue
to in
tera
ct a
s tim
e go
eson
. The
dis
tinct
ion
bet!w
een
perc
eptio
n an
d (p
rimar
y) m
emor
y is
com
-pl
etel
y bl
urre
d~.si
nce
the
perc
ept i
s unf
oldi
ng in
the
sam
e str
uctu
res t
hat
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 e
ven
as n
ewer
por
tions
are
com
ing
into
the
syste
m,
Thes
e co
ntin
uing
inte
ract
ions
per
mit
the
mod
el to
inco
rpor
ate
right
con
-te
xt e
ffect
s, an
d al
low
~he
mod
el to
acc
ount
dire
ctly
for c
erta
in a
spec
ts
MC
CLE
LLAN
D A
ND
ELM
AN
kAp
i~i~
i~i~
i~i~
i~i'
.L:- a..
rlrA
r~'A
rArA
rlr'
I :11
1: II
I.: I
: I :
I',t'
ttt'l,
!,t'lt
'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 Tim
e Sl
ice
:!4. T
herectangle for this unit is highlighted with a bold outline. The
Ikl
unit
has m
utua
lly e
xcilu
tory
conn
ectio
ns to
all
the
wor
d- a
nd fe
atur
e-le
vel u
nits
col
ored
eith
er p
urtly
or w
holly
in b
luck
;Th
e m
ore
colo
ring
on a
uni
ts' r
ecta
ngle
. the
gre
ater
the
stre
ngth
of t
he c
onne
ctio
n. T
heIk
l un
it ha
s 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
rela
tive
amou
nt o
f inh
ibiti
on is
indi
cate
d by
the
exte
nt o
f the
colo
ring
of th
e un
it: it
is d
irect
ly p
ropo
rtion
al to
the
exte
nt o
f the
tem
pora
l ove
rlap
of th
eun
its.
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 fo
r sho
rt pe
riods
of t
ime
if it
hang
s tog
ethe
r to
form
a c
oher
ent
who
le,
Proc
essin
g ta
kes p
lace
thro
ugh
the
exci
tato
ry a
nd in
hibitory interac-
tions
of t
he u
nits
in th
e Tr
ace.
Uni
ts o
n di
ffere
nt le
vels
that
are
mut
ually
cons
isten
t hav
e m
utua
lly e
xcita
tory
con
nect
ions
. whi
le u
nits
on th
e sa
me
TRAC
E M
OD
ELMCCLELLAND AND ELMAN
. kl\p
vi
sual
mo.
del e
limin
ate
thes
e be
twee
n-le
vel i
nhib
ito.ry
co.
nnec
tions
. sin
ceth
ese
co.n
nect
io.n
s ca
n in
terfe
re w
ith s
ucc~
ssfu
l use
o.f
parti
~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,
TRA
CE li
kew
ise c
o.nt
ains
, no.
bet
wee
n-le
vel i
nhib
itio.
n. W
ew
ill se
e th
at th
is fe
atur
e o.
f TR
ACE
play
s a
very
impo
.rtan
t rol
e in
its
abili
ty to
. sim
ulat
e a
num
ber o
.f em
piric
al p
heno
.men
a.SO
Im:e
s of T
RACE
' s lIrL'hitectllre,
The
insp
iratio
.n fo
.r th
e ar
chite
ctur
eo.
f TRA
CE g
o.es
bac
k to
. the
HEA
RSA
Y S
peec
h un
ders
tand
ing
syste
m(E
rman
& L
esse
r, 19
80; R
eddy
et a
l.. 1
973)
, HEA
RSA
Y in
trodu
ced
the
no.ti
o.n
o.f a
Bla
ckbo
.ard
, a s
truct
ure
sim
ilar t
o. th
e Tr
ace
in th
e TR
ACE
mo.
del.
The
mai
n di
ffere
nce
is th
at th
e Tr
ace
is a
dyn
amic
pro
cess
ing
stru
ctur
e th
at is
sel
f-upd
atin
g, w
hile
the
Blac
kbo.
ard
in H
EARS
AY
was
a pa
ssiv
e da
ta s
truct
ure
thro
.ugh
whi
ch a
nto.
no.m
o.us
pro
cess
es sh
ared
info
.rmat
io.n
. Th
e ar
chite
ctur
e o.
fTRA
CE b
ears
a st
ro.n
g re
sem
blan
ce to
. the
"ne
ural
spec
trogr
am" propo.sed by Cro.wder (1978, 1981) to
. acc
o.un
t fo.
r int
erfe
r-en
ce e
ffect
s bet
wee
n su
cces
sive
item
s in sho.rt-term memo.ry.
. Lik
e ~U
I'Tr
ace,
Cro
wde
rs neural spectro.gram pro.vides a d
ynam
ic w
o.rk
ing
mem
o.ry
repr
esen
tatio
.n o
.f a
spok
en in
put.
Ther
e ar
e tw
o. im
po.rt
ant d
if-fe
renc
es b
etw
een
the
Trac
e an
d C
ro.w
der s
neu
ral s
pect
rogr
am, h
o.w
ever
.Fi
rst o
.f al
l, th
e ne
ural
spe
ctro
.gra
m w
as a
ssum
ed o
.nly
to. r
epre
sent
the
frequ
ency
spec
trum
o.ft
he sp
eech
wav
e o.
ver t
ime;
the
Trac
e , o
.n th
e ot
her
hand
, rep
rese
nts
the
spee
ch w
ave
in:te
rms
o.fa
larg
e nu
mbe
r o.f
ditfe
rent
feature dimensio.ns, as well as in terms of the p
ho.n
emes
and
wo.
rds
co.n
-si
sten
t with
the
patte
rn o
.f activatio.n at the feature level, In this r
egar
dTR
ACE
mig
ht b
e se
en a
s an
exte
nsio
.n o
.f th
e ne
ural
spe
ctro
gram
idea
,Th
e se
co.n
d di
ffere
nce
is th
at C
row
der p
o.stu
late
s inh
ibito
.ry in
tera
ctio
.ns
betw
een
dete
cto.
rs fo
.r sp
ectra
l co.
mpo
.nen
ts s
pace
d up
to. s
ever
al h
undr
edm
illise
co.n
ds a
part.
The
se in
hibi
to.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 Tr
ace.
Thi
sdi
ffere
nce
do.e
s no.
t ref
lect
a' d
isagr
eem
ent w
ith C
row
der
sass
umpt
io.n
s.Th
o.ug
h w
e ha
ve n
o.t ,
fo.u
nd it
nec
essa
ry , t
o. a
do.p
t thi
s as
sum
ptio
.n to
. ac-
coun
t fo.
r the
phe
no.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
TRAC
E fra
mew
o.rk
to.
inco
.rpo.
rate
man
y o.
f the
find
ings
Cro
.wde
r dis
cuss
es in
the
two.
arti
cles
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 Ihe
hig
hlig
hled
uni
l for
Ihe
high
val
ue o
n Ih
e V
ocal
ic fe
lllur
edi
men
sion
in T
ime'
Slic
e 9
and
for I
he h
ighl
ighl
ed u
nil f
or Ih
e w
ord
Ik' p
l starling in Slice
24. E
xcila
lory
con
necl
ions
are
rf(re
senl
ed in
bla
ck. i
nhib
itory
con
nect
ions
in g
rey.
as
inFig. 3.
leve
l tha
t are
inco
.nsi
sten
t hav
e m
utua
lly in
hibi
to.ry
co.nnectio.ns, All co.n-
nect
io.n
s ar
e bi
dire
ctio
.nal
. Bid
irect
io.n
al e
xcita
to.ry
and
inhi
bito
.ry' c
o.n-
nect
io.n
s o.
f the
unit fo.r
Ikl
cent
ered
o.v
er F
eatu
re-s
lice
24 (c
o.un
ting
from
. 0) a
re sh
o.wn ,n Fig. 3; co.nnectio.ns far the high
valu
e o.
f the feature
Vo.c
alic
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 sh
o.w
n i~
Fig
. 4.
The
inte
ract
ive
activ
atio
.n mo
.del o.f visual w
ard
reco
.gni
tio.n
(Mc-
Clel
land
& R
umel
hart,
198
1) in
clud
ed in
hibi
to.ry
co.
nnec
tio.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 u
nit a
nd th
e w
o.rd
s th
at d
id n
o.t c
o.nt
ain
the
lette
r.Th
us th
e un
its fo
.r T
in th
e fir
st le
tter p
o.sit
io.n
inhi
bite
d th
e un
its fo
.r al
lwo.rds that did no
.t be
gin
with
T. H
o.wever, mo.re recent versio.ns
o.f
the
Cont
ext-S
ensit
ive
TlIn
ingo
f Pho
nem
e U
nits
The
co.n
nect
io.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 ea
ch p
hone
me.
To. co.pe with the fact that the
feat
ures
repr
esen
ting
each
pho
.nem
e va
ry a
cco.
rdin
g to
. the
pho
.nem
es su
r-ro
undi
ng th
em, t
he m
odel
adj
usts
the
conn
ectio
ns fr
om u
nits
al th
e fe
a-tu
re le
vel t
o. u
nits
at th
e nh
onem
e le
vel a
s a fu
nctio
n nf
Iu'tiv:llinn" al 'hI"
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
TRACE land TRACE
In d
evel
opin
g TR
ACE
, and
i(l t
ryin
g to
test
its c
ompu
tatio
nal a
nd p
sy-
chol
ogic
al a
dequ
acy,
we
foun
d th
at w
e w
ere
som
etim
es le
d in
rath
erdi
ffere
nt d
irect
ions
, We
wan
ted
to sh
ow th
at T
RACE
cou
ld p
roce
ss re
alsp
eech
, but
to b
uild
a m
odel
that
did
so it
was
nec
essa
ry to
wor
ry a
bout
exac
tly w
hat f
eatu
res m
ust b
e ex
tract
ed fr
om th
e sp
eech
sign
al, a
bout
diffe
renc
es in
dur
atio
n of
diff
eren
t fea
ture
s of d
iffer
ent p
hone
mes
, and
abou
t how
to c
ope
with
the
way
s in
whi
ch fe
atur
es a
nd fe
atur
e du
ratio
nsvary as a function of context. Obviously, these are important p
robl
ems,
wor
thy
of c
onsid
erab
le a
ttent
ion.
How
ever
, con
cern
with
thes
e iss
ues
tend
ed to
obs
cure
atte
ntio
n to
the
fund
amen
tal p
rope
rties
of t
he m
odel
and
the
mod
el's
abi
lity
to a
ccou
nt fo
r bas
ic a
spec
ts of
the
psyc
h(jlo
gica
lda
ta o
btai
ned
in m
any
expe
rimen
ts.
To c
ope
with
thes
e co
nflic
ting
goal
s, w
e ha
ve d
evel
oped
two
diffe
rent
vers
ions
of t
he m
odel
, cal
led
TRA
CE 1
and
TRA
CE II
, Bot
h m
odel
ssp
ring
from
the
sam
e ba
sic a
ssum
ptio
ns, b
ut fo
cus o
n di
ffere
nt a
spec
tsof
spee
ch p
erce
ptio
n. T
RACE
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 fr
om re
al sp
eech
,Th
is v
ersi
on o
f the
mod
el is
des
crib
ed in
det
ail i
n El
man
and
McC
lella
nd(in
pre
ss).
With
this
vers
ion
of th
e m
odel
, we
wer
e ab
le to
show
that
the
TRA
CE fr
amew
ork
coul
d in
deed
be
used
to p
roce
ss re
al sp
eech
-alb
eit
from
a si
ngle
spea
ker u
tterin
g iso
late
d m
onos
ylla
bles
at t
his p
oint
. 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 o
f act
ivat
ions
pro
duce
d by
sur-
roun
ding
con
text
. With
con
nect
ion
stren
gth
adju
stmen
t in
plac
e' t
hem
odel
was
abl
e to
iden
tify
the
stop
cons
onan
t in
90%
of a
set b
f iso
late
dm
onos
ylla
bles
cor
rect
ly, u
p fro
m 7
9% w
ith a
n in
varia
nt se
t of c
onne
c-tio
ns. T
his l
evel
of p
erfo
rman
ce is
com
para
ble
to w
hat h
as b
een
achi
eved
by other machine-ba
sed
phon
eme
iden
tific
atio
n sc
hem
es (e
,g.,
Kope
c,19
84) a
nd il
lust
rate
s th
e pr
omise
of t
he c
onne
ctio
n str
engt
h ad
justm
ent
sche
me
for c
opin
g w
ith v
aria
bilit
y du
e to
loca
l pho
netic
con
text
. Ide
asfo
r ext
endi
qg th
e co
nnec
tion
stren
gth
adju
stmen
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
(rate
, spe
aker
cha
ract
erist
ics,
eJc,
) are
con
sider
ed in
the
gene
ral d
iscus
-sio
n. TRA
CE II
, the
ver
sion
desc
ribed
in th
e pr
esen
t pap
er, w
as d
esig
ned
to a
ccou
nt p
rimar
ily fo
r lex
ical
influ
ence
s on
phon
eme
perc
eptio
n an
d
for w
hat i
s kno
wn
abou
t on-
line
reco
gniti
on o
f wor
ds, t
houg
h w
e us
e it
to il
lustr
ate
how
cer
tain
oth
er a
spec
ts of
pho
nem
e pe
rcep
tion
fall
out o
fth
e TR
ACE
fram
ewor
k, T
his v
ersio
n of
the
mod
el is
act
ually
a si
mpl
ified
vers
ion
of T
RACE
1. M
ost i
mpo
rtant
ly, w
e el
imin
ated
the
conn
ectio
n-st
reng
th a
djus
tmen
t fac
ility,
and
we
repl
aced
the
real
spe
ech
inpu
ts to
TRA
CE I
with
moc
k sp
eech
, Thi
s moc
k sp
eech
inpu
t con
siste
d of
ove
r-la
ppin
g bu
t con
text
ually
inva
riant
spec
ifica
tions
of t
he fe
atur
es o
f suc
-ce
ssiv
e ph
onem
es, O
bvio
usly
, the
n, T
RACE
II si
deste
ps m
any
fund
a-mental issues about speech, But it makes "it
muc
h ea
sier t
o se
e ho
w th
em
echa
nism
can
acc
ount
for a
num
ber o
f asp
ects
of p
hone
me
and
wor
dre
cogn
ition
, A n
umbe
r of f
urth
er s
impl
ifyin
g as
sum
ptio
ns w
ere
mad
e to
faci
litat
e ex
amin
atio
n of
bas
ic p
rope
rties
of t
he in
tera
ctiv
e ac
tivat
ion
pro-
cess
es ta
king
pla
ce w
ithin
the
mod
el,
The
foll9
win
g se
ctio
ns d
escr
ibe
TRA
CE II
in m
ore
deta
il, F
irst w
eco
nsid
er th
e sp
ecifi
catio
ns o
f the
moc
k-sp
eech
in()u
t to
the
mod
el, a
ndth
en w
e co
nsid
er th
e un
its a
nd c
onne
ctio
ns th
at m
ake
up th
e Tr
ace
atea
ch o
f the
thre
e le
vels
,
Moc
k-Sp
eech
Inpu
tsTh
e in
put t
o TR
ACE
II w
as a
serie
s of s
peci
ficat
ions
for i
nput
s to
units
at th
e fe
atur
e le
vel,
one
for e
ach
25-m
s tim
e sl
ice
of th
e m
ock
utte
ranc
e,Th
ese
spec
ifica
tions
wer
e ge
nera
ted
by a
sim
ple
com
pute
r pro
gram
from
a se
quen
ce o
f to-
be-p
rese
nted
segm
ents
prov
ided
by
the
hum
an u
ser o
fth
e sim
ulat
ion
prog
ram
. The
allo
wed
segm
ents
cons
isted
of t
he st
op c
on-
sona
nts
Ibl,
Ipl,
Idl,
It/,lg
I, an
d Ik
l, the fricatives
Isl
and
ISI
sh" as in
ship
), the liquids
III
and
Irl,
and the vowels
Ia!
(as i
n "p
ot"),
IiI
(as
inbe
et
),
lul
(as i
n "b
oot"
), and
rI (a
s in
"but
).
rI w
as a
lso
used
tore
pres
ent r
educ
ed v
owel
s suc
h as
the
seco
nd v
owel
in "
targ
et." There
was
also
a "
silen
ce" segment represented by
I-I.
Spec
ial s
egm
ents,
such
as a segment halfway between
Ibl
and
Ipl,
wer
e al
so u
sed;
thei
r pro
perti
esar
e de
scrib
ed in
des
crip
tions
of t
he re
leva
nt s
imul
atio
ns,
A se
t of s
even
dim
ensio
ns w
as u
sed
in T
RACE
lIto represent the
feat
ure-
leve
l inp
uts,
Five
of t
he' d
imen
sion
s (C
onso
nant
al, V
ocal
ic, D
if-fu
sene
ss, A
cute
ness
, and
Voi
cing
) 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 tre
at e
ach
of th
ese
dim
ensio
ns a
s con
tinua
, in
the
spiri
t ofO
den
and
Mas
saro
(197
8), r
athe
rth
an a
s bin
ary
feat
ures
, A si
xth
dim
ensio
n, P
ower
, was
incl
uded
bec
ause
it ha
s be
en fo
und
usef
ul fo
r pho
nem
e id
entif
icat
ion
in v
ario
us m
achi
nesy
stem
s (e
,g.,
Redd
y, 1
976)
, and
it w
as in
corp
orat
ed h
ere
to a
dd a
n ad
-di
tiona
l dim
ensio
n to
incr
ease
the
diffe
rent
iatio
n of
the
vow
els a
nd c
on-
sona
nts,
The
seve
nth
dim
ensio
n, th
e am
plild
de o
f the
bur
st of
noi
se th
atoc
curs
at t
he b
egin
ning
of w
ord
initi
al st
ops,
was
incl
uded
to p
rovi
de a
nad
ditio
nal b
asis
for d
istin
guis
hing
the
stop
con
sona
nts,
whi
ch o
ther
wis
edi
ffere
d fro
m e
ach
othe
r on
only
one
or t
wo
dim
ensio
ns, O
f cou
rse,
thes
e
phon
eme
leve
l in
prec
edin
g an
d fo
llow
ing
time
slice
s, Fo
r exa
mpl
e, w
hen
the 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
nthe 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 p
rece
ding
and
follo
win
g sl
ices
.
TRAC
E M
OD
EL
dim
ensio
ns a
n;: i
nten
tiona
l sim
plifi
catio
ns o
f the
real
aco
ustid
stru
ctur
eof
spe
ech,
in m
uch
the
sam
e w
ay th
at th
e fo
nt u
sed
by M
cCle
lland
and
Rum
elha
rt (1
981)
in th
e in
tera
ctiv
e-ac
tivat
ion
mod
el o
f visu
al w
ord
rec-
ogni
tion
Was
an
inte
ntio
nal s
impl
ifica
tion.
of t
he re
al s
truct
ure
of p
rint.
Each
dim
ensio
n w
as d
ivid
ed in
to e
ight
val
ue ra
nges
. Eac
h ph
onem
ew
as a
ssig
ned
a va
lue
on e
ach
dim
ensio
n; th
e va
lues
on
the
Voc
alic
, Oif-
fuse
ness
, and
Acu
tene
ss d
imen
sions
for t
he p
hone
mes
in th
e ut
tera
nce
!tik.
p! a
re sh
own
in F
ig. 2
, The
full
set o
f val
ues a
re sh
own
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 stro
ngly
act
ivat
ed b
y th
e fe
atur
e pa
ttern
for t
hein
dica
ted
phon
eme,
Val
ues r
ange
from
I very low
to 8 =
very high,
The
last
two
dim
ensio
ns w
ere
alte
red
for t
he c
ateg
oric
al p
erce
ptio
n an
dtra
ding
rela
tions
sim
ulat
ions
,Va
lues
wer
e as
sign
ed to
app
roxi
mat
e th
e va
lues
real
pho
nem
es w
ould
have
on
thes
e di
men
sion
s an
d to
mak
e ph
onem
es th
at fa
ll in
to th
e . s
ame
phon
etic
cat
egor
y ha
ve id
entic
al v
alue
s on
man
y of
the
dim
ensio
ns, T
hus,
.fo
r exa
mpl
e, a
ll sto
p co
nson
ants
wer
e as
signe
d th
e sa
me
valu
es o
n th
ePo
wer
, Voc
alic
, and
Con
sona
ntal
dim
ensio
ns, 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 fe
atur
e se
ts do
hav
e th
e pr
oper
ty th
at th
e fe
atur
epa
ttern
for o
ne p
hone
me
is m
ore
simila
r to
the
feat
ure
patte
rn fo
r oth
erph
onem
es in
the
sam
e ph
gnet
ic c
ateg
ory
(sto
p, fr
icat
ive,
liqu
id, o
r vow
el)
than
it is
to th
e pa
ttern
s for
pho
nem
es in
oth
er c
ateg
orie
s. A
mon
g th
esto
ps, t
hose
pho
nem
es sh
arin
g pl
ace
of a
rticu
latio
n or
voi
cing
are
mor
esi
mila
r tha
n th
ose
shar
ing
neith
er a
ttrib
ute.
The
corre
latio
ns o
f the
feat
ure
patte
rns f
or th
e 15
pho
nem
es u
sed
are
show
n in
Tab
le 2
. It i
s the
se c
orre
latio
ns o
f the
pat
tern
s ass
igne
d to
the
~ -
!II :J , !II
II:)
I:!
1.1:
1 is '"
:;; '")
~ 1!
"" ~~
~~~
~ ~
~~~~
I~
....
-D - -D
..., ~
"0 "1
r-; r-; I ~
0 - ;
:::~
I~~~
~TA
BLE
IPh
onem
e Fe
alur
e V
alue
s Use
d in
TRA
CE II
Phun
eme
Pow
Voc
alic
Diff
use
ACU
leCO
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
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
diffe
rent
pho
nem
es. r
athe
r tha
n th
e ac
tual
val
ues a
ssig
ned
to p
artic
ular
phon
emes
or e
ven
the
labe
ls at
tach
ed to
the
diffe
rent
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. s
ince
itis
thes
e co
rrela
tions
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 fo
r ano
ther
,Th
e fe
atur
e pa
ttern
s w
ere
cons
tru~t
ed in
such
a w
ay th
at it
was
pos
sible
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
(sto
p. li
quid
. fric
ativ
e. o
r vowel) to an equal extent
by a
vera
ging
the
valu
es o
f the
two
phon
emes
on
one
or m
ore
dim
ensio
ns,
In th
is w
ay, i
t was
a si
mpl
e m
atte
r to
mak
e up
am
bigu
ous
inpu
ts. h
alfw
aybe
twee
n tw
o ph
ontim
es. o
r to
cons
truct
con
tinua
var
ying
bet
wee
n ' tw
oph
onem
es o
n on
e or
mor
e di
men
sion
s.Th
e fe
atur
e sp
ecifi
catio
n of
eac
h ph
onem
e in
the
inpu
t stre
am e
xten
ded
over
II ti
me
slice
s of t
he in
put.
The
stren
gth
of th
e pa
ttern
gre
w to
ape
ak a
t the
6th
slic
~ an
d fe
ll of
f aga
in. a
s illu
strat
ed in
Fig
, 2, P
eaks
of
succ
essiv
e ph
onem
es w
ere
sepa
rate
d by
6 sl
ices
, Thu
s. sp
ecifi
catio
ns o
fsu
cces
sive
phon
emes
ove
rlapp
ed. a
s the
y do
in re
al sp
eech
(Fow
ler.
1984
;Li
berm
an, 1
970)
.G
ener
ally
. the
re w
ere
no c
ues t
o w
ord boundaries in the speech
strea
m- th
e fe
atU
lie s
peci
ficat
ion
for t
he la
st p
hone
me
of o
ne w
ord
over
lapp
ed w
ith th
e , fi
rst p
hone
me
of th
e ne
xt in
just
the
sam
e w
ay fe
atur
esp
ecifi
catio
ns o
f adj
~\ce
nt p
hone
mes
ove
rlap
with
in w
ords
, How
ever
. en-
tire
utte
ranc
es p
rese
nted
to th
e m
odel
for p
roce
ssin
g-w
heth
er th
ey w
ere
indi
vidu
al s
ylla
bles
., w
ords
. or s
tring
s of
wor
ds-w
ere
prec
eded
and
fol-
low
ed b
y sil
ence
, Sile
nce
was
nol
sim
ply
the
abse
nce
ofan
y in
put;
rath
er.
it w
as a
pat
tern
of f
eatu
re v
alue
s. ju
st lik
e th
e ph
onem
es, T
hus.
a n
inth
valu
e on
eac
h of
the
isev
en d
imen
sion
s w
as a
ssoc
iate
d w
ith s
ilenc
e, T
hese
valu
es w
ere
actu
ally
out
side
the
rang
e of
val
ues
whi
ch o
ccur
red
in th
eph
onem
es th
emse
lves
. so
that
the
feat
ures
of s
ilenc
e w
ere
com
plet
ely
unco
rrela
ted
with
the
feat
ures
of a
ny o
f the
pho
nem
es u
sed,
The
Phon
eme
Leve
l and
Fea
ture
- Pho
nem
e C
onne
ctio
nsA
t the
pho
nem
e le
vel.
ther
e is
a se
t of d
etectors for each of the 15
phon
emes
liste
d ab
ove,
In a
dditi
on. t
here
is a
set o
f detectors for the
pres
ence
of s
ilenc
e, T
hese
sile
nce
dete
ctor
s are
trea
ted
like
all o
ther
phon
eme
dete
ctor
s. Ea
ch m
embe
r of t
he se
t of d
etec
tors
for a
par
ticul
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 a
re sp
aced
thre
e tim
e sli
ces a
part.
The
uni
t cen
tere
d ov
er a
parti
cula
r slic
e re
ceiv
ed e
xcita
tory
inpu
t fro
m fe
atur
e un
its in
a ra
nge
ofsli
ces,
exte
ndin
g bo
th fo
rwar
d an
d ba
ckw
ard
from
the
slice
in w
hich
the
phon
eme
unit
is lo
cate
d, It
also
send
s exc
itato
ry fe
edba
ck d
own
to th
esame feature units in the same range of slices.
The
conn
ectio
n st
reng
ths
betw
een
the
feat
ure-
leve
l uni
ts a
nd a
par
tic-
ular
pho
nem
e-le
vel u
nit e
xact
ly m
atch
the
feat
ure
patte
rn th
e ph
onem
eis
give
n in
its i
nput
spec
ifica
tion,
Thu
s. as
illu
strat
ed in
Fig
. 3. t
hestrengths of the connections between the node for
Ikl
cent
ered
ove
r Tim
eSl
ice
24 a
nd th
e no
des a
t the
feat
ure
leve
l are
exa
ctly
pro
porti
onal
to th
epa
ttern
of i
nput
to 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.Th
ere
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
stan
dfo
r rep
rese
nt a
ltern
ativ
e in
terp
reta
tions
of t
he c
onte
nt o
f the
spee
chstr
eam
at t
he sa
me
poin
t in
the
utte
ranc
e. N
ote
that
. alth
ough
the
feat
ure
spec
ifica
tion
of a
pho
nem
e is
spre
ad o
ver a
win
dow
of I
I slic
es, s
ucce
s-si
ve p
hone
mes
in th
e in
put h
ave
thei
r ,ce
nter
s 6 sl
ices
apa
rt. T
hus e
ach
phon
eme-
leve
l uni
t is
thou
ght o
f as
span
ning
6 fe
atur
e-level slices. as
illust
rate
d in
Fig
. 3. E
ach
unit
inhi
bits
oth
ers
in p
ropo
rtion
to th
eir
over
lap,
Thu
s, a
pho
nem
e de
tect
or in
hibi
ts o
ther
pho
nem
e de
tect
orsc
en-
tere
d ov
er th
e sa
me
slice
twic
e as
muc
h as
it in
hibi
ts de
tect
ors c
ente
red
3 sl
ices
aw
ay, a
nd in
hibi
ts d
etec
tors
cen
tere
d 6
or m
ore
slic
es a
way
not
at all, (
Fc'lIl
IIre
Lel'e
l Vni
t. f a
nd C
o""e
ctio
n.Th
e un
its a
t the
feat
ure
leve
l are
det
ecto
rs fo
r fea
ture
s of t
he sp
eech
strea
m a
t par
ticul
ar , m
omen
ts in
tim
e. In
TRA
CE II
. the
re w
as a
uni
t for
each of the nine values on each of the seven dimensions in each time
slice
of t
he T
race
, The
figu
res s
how
thre
e se
ts of
feat
ure
units
in se
vera
ltim
e sli
ces,
Uni
ts fo
r fea
ture
s on
the
sam
e di
men
sion
with
in th
e sa
me
time
slice
are
mut
ually
inhi
bito
ry, T
hus,
the
unit
for t
he h
igh
valu
e of
the
Voc
alic
dim
ensio
n in
Tim
e Sl
ice
9 in
hibi
ts th
e un
its fo
r oth
er v
alue
s on
the
sam
e di
lJlen
sion
in th
e sa
me
time
slice
. as i
llustr
ated
in F
ig. 4
. Thi
sfig
ure
also
illu
stra
tes
the
mut
ually
exc
itato
ry c
onne
ctio
ns o
f thi
s sam
efe
atur
e un
il w
ith u
nits
at th
e ph
onem
e le
vel.
In th
e ne
xt se
ctio
n w
e re
-de
scrib
e th
ese
conn
ectio
ns fr
om th
e po
int o
f vie
w o
f the
pho
nem
~ le
vel,
Wor
d Vn
its a
nd W
ord-
Phon
eme
Con
nec'
tions
Ther
e is
a un
it fo
r eve
ry w
ord
in e
very
tim
e sli
ce, E
ach
of th
ese
units
repr
esen
ts a
diffe
rent
hyp
othe
sis a
bout
a w
ord
iden
tity
and
starti
ng lo
-cation in the 'Irace. For example, the unit for the word
Ik.pl
in Slice 24
. (hi
ghlig
hted
in F
ig, 4
) rep
rese
nts t
he h
ypot
hesis
that
the
inpu
t con
tain
sth
e w
ord
" cup
" sta
rting
in S
lice
24, M
ore
exac
tly, i
t rep
rese
nts t
he h
y-po
thes
is th
at th
e in
put c
onta
ins t
he w
ord
" cup
" with
its f
irst p
hone
me
centered in Time Slice 24.
Wor
d un
its re
ceiv
e ex
cita
tion
from
the
units
for t
he p
hone
mes
they
cont
ain
in a
serie
s of o
verla
ppin
g w
indo
ws.
Thus
, the
uni
t for
"cu
p" in
Time Slice 24 will receive excitation from
Ikl
in s
lices
nei
ghbo
ring
Slic
e
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
24, from
rI in slices neighboring Slice 30, and from
Ipl
in slices neigh-
borin
g Sl
ice
36. A
s with
the
feat
ure-
phon
eme
conn
ectio
ns, t
hese
con
-ne
ctio
ns a
re s
trong
est a
t the
cen
ter o
f the
win
dow
and
fall
off l
inea
rly o
neither side,
The
inhi
bito
ry c
onne
ctio
ns a
t the
wor
d le
vel a
re si
mila
r to
thos
e at
the
phon
eme
leve
l, A
gain
, the
stre
ngth
of t
he in
hibi
tion
betw
een
two
wor
dun
its d
epen
ds o
n th
e nu
mbe
rof t
ime
slice
s in
whi
ch th
ey o
verla
p. T
hus,
units
repr
esen
ting
alte
rnat
ive
inte
rpre
tatio
ns o
f the
sam
e str
etch
of p
ho-
nem
e un
its a
re st
rong
ly c
ompe
titiv
e, b
ut u
nits
repr
esen
ting
inte
rpre
ta-
tions
of n
onov
erla
ppin
g se
quen
ces o
f pho
nem
es ~
o no
t com
pete
at a
ll.TR
ACE
II h
as d
etec
tors
for t
he 21
1 words found in a computerized
phon
etic
wor
d lis
t tha
t met
all
of th
e fo
llow
ing
cons
train
ts: (
a) th
e w
ord
cons
iste
d on
ly o
f the
pho
nem
es li
sted
abo
ve; (
b) it
was
not
an
infle
ctio
nof
som
e ot
her 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 "-e
d,
" "
-s," and "
ing"
inflections
occu
rred
wiih
a fr
eque
ncy
of 2
0 or
mor
e pe
r mill
ion
in th
e K
ucer
a an
dFr
anci
s (19
67) w
ord
coun
t. It
is no
t cla
imed
that
the
mod
el's
lexi
con
is an
exha
ustiv
e lis
t of w
ords
mee
ting
this
crite
rion,
sinc
e th
e co
mpu
teriz
edph
onet
ic le
xico
n w
as n
ot c
ompl
ete,
but
it is
reas
onab
ly c
lose
to th
is, T
om
ake
spec
ific
poin
ts ab
out t
he b
ehav
ior o
f the
mod
el, d
etec
tors
for t
hefo
llow
ing
thre
e w
ords
not
in th
e m
ain
list w
ere
adde
d: "
blus
h,
" "
rega
l,an
d "
sleet
." T
he m
odel
also
had
det
ecto
rs a
t the
wor
d le
vel f
or si
lenc
e(I-
I),
whi
ch w
as tr
eate
d lik
e it
one-
phon
eme
wor
d,
inde
finite
ly, t
houg
h fo
r pra
ctic
al p
urpo
ses i
t is a
lway
s ter
min
ated
. afte
rso
me
pred
eter
min
ed n
umbe
r of t
ime
cycl
es h
as ~
Iaps
ed,
...
Pres
enta
tion
tlnd
Proc
e!jti
'ing
of tm
Ulle
rtlnc
'Be
fore
pro
cess
ing
of a
n ut
tera
nce
begi
ns, t
he a
ctiv
atio
ns o
f all
of th
eun
its a
re se
t at t
heir
resti
ng v
alue
s. A
t the
star
t of p
rocessing, 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
slice
of f
eatu
re u
nits
is ap
plie
d, a
nd e
xcita
tory
and
inhi
bito
ry in
puts
toea
ch u
nit r
esul
ting
from
the
patte
rn o
f act
ivat
ion
left
at th
e en
d of
the
prev
ious
tim
e sli
ce a
re c
ompu
ted,
It is
impo
rtant
to re
mem
ber t
hat t
he in
put i
s ap
plie
d, o
ne sl
ice
at a
time,
pro
ceed
ing
from
left
to ri
ght a
s tho
ugh
it w
ere
an on
going stream
of sp
eech
"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 sl
ice
at a
tim
e. P
roce
ssin
g in
tera
ctio
ns c
an c
ontin
ueev
en a
fter t
he le
ft to
righ
t sw
eep
thro
ugh
the
inpu
t rea
ches
the
end
of th
eTr
ace.
Onc
e th
is ha
ppen
s, th
ere
are
simpl
y no
new
inpu
t spe
cific
atio
nsap
plie
d to
the
Trac
e; th
e co
ntin
uing
inte
ract
ions
are
bas
ed o
n w
hat h
asal
read
y be
en p
rese
nted
. Thi
s int
erac
tion
proc
ess i
s ass
umed
to c
ontin
ue
Det
ails
of P
roce
ssin
g D
ynam
kti,
The
inte
ract
ive
activ
atio
n pr
oces
s in
the
Trac
e m
odel
follo
ws
thed
y-na
mic
ass
umpt
ions
laid
out
in M
cCle
lland
and
Rum
elha
rt (1
981)
, Eac
hun
it ha
s a re
sting
act
ivat
ion
valu
e ar
bitra
rily
set a
t 0, a
max
imum
act
ivat
ion
value arbitrarily set at 1,0,
and
a m
inim
um a
ctiv
atio
n se
t at -
.3. O
nev
ery
time
cycl
e of
pro
cess
ing,
all
the
wei
ghte
d ex
cita
tory
and
inhi
bito
rysi
gnal
s im
ping
ing
upon
a u
nit a
re a
dded
toge
ther
, The
sig
nal f
rom
one
unit
to a
noth
er is
just
the
exte
nt to
whi
ch it
s ac
tivat
ion
exce
eds 0
; if i
tsac
tivat
ion
is le
ss th
an 0
, the
sig
nal '
is 0.
1 G
loba
l lev
el-s
peci
fic e
xcita
tory
,in
hibi
tory
, and
dec
ay p
aram
eter
s sca
le th
e re
lativ
e m
agni
tude
s of d
ilfer
ent
types of influences on the activation of each unit. Values for these pa-
ram
eter
s ar
e gi
ven
belo
w,
Afte
r the
net
inpu
t to
each
uni
t has
bee
n de
term
ined
bas
ed o
n th
e pr
ior
activ
atio
ns o
f the
uni
ts, th
e ac
tivat
ions
of t
he u
nits
arc
all u
pdat
ed fo
rth
e ne
xt p
roce
ssin
g cy
cle,
The
new
val
ue o
f the
act
ivat
ion
of th
e un
it is
a fu
nctio
n of
its n
et in
put f
rom
oth
er u
nits
and
its p
revi
ous
activ
atio
nva
lue,
The
exa
ct fu
nctio
n us
ed (s
ee M
cCle
lland
& R
umel
hart,
198
1) k
eeps
unit
activ
atio
ns b
ound
ed b
etw
een
thei
r max
imum
and
min
imum
val
ues.
Giv
en a
con
stant
inpu
t, th
e ac
tivat
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 str
engt
h an
dsi
gn (e
xcita
tory
or i
nhib
itory
) of t
he in
put.
With
a n
et in
put o
f 0, the
activ
atio
n of
the
unit
will
gra
dual
ly re
turn
to it
s res
ting
leve
l.Ea
ch p
roce
ssin
g tim
e cy
cle
corre
spon
ds to
a si
ngle
tim
e sli
ce a
t the
feat
ure
leve
l. Th
is is
actu
ally
a p
aram
eter
of t
he m
odel
-there is no
intri
nsic
reas
on w
hy th
ere
shou
ld b
e a
singl
e cy
cle
of th
e in
tera
ctiv
e-ac
tivat
ion
proc
ess s
ynch
roni
zed
with
the
arriv
al o
f eac
h su
cces
sive
slice
of th
e in
put.
A h
ighe
r rat
e of
cyc
ling
wou
ld sp
eed
the
perc
olat
ion
ofef
fect
s of n
ew in
put t
hrou
gh th
e ne
twor
k re
lativ
e to
the
rate
of p
rese
n-ta
tion,
Out
put A
ssum
ptio
nsA
ctiv
atio
ns o
f uni
ts in
the
Trac
e 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
ision
can
be
mad
e ba
sed
on th
e pa
ttern
of a
ctiv
atio
n as
it st
ands
at t
hat m
omen
t. Th
e de
cisio
n m
echa
nism
can
,w
e as
sum
e, b
e di
rect
ed to
con
side
r the
set
of u
nits
loca
ted
with
in a
sm
all
win
dow
of a
djac
ent s
lices
with
in a
ny le
vel.
The
units
in th
is se
t the
nI A
t the
wor
d le
vel,
the
inhi
bito
ry si
gnal
from
one
wor
d to
ano
ther
is ju
st. th
e sq
uare
of
the
exte
nt to
whi
ch th
e se
nder
s act
ivat
ion
exce
eds z
ero.
Thi
s ten
ds to
smoo
th Ih
e ef
li:.:h
of m
any
units
sudd
enly
bec
omin
g sli
ghtly
act
ivat
ed. a
nd o
f cou
rse
il al
so in
crea
ses I
hedo
min
ance
of o
ne a
ctiv
e w
ord
over
man
y w
eakl
y ac
tivat
ed o
nes,
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
Sj =
kaj,
Even
with
all
the
sim
plifi
catio
ns d
escr
ibed
abo
ve. t
he T
RAC
E m
odel
still
has a
num
ber o
ffree
par
amet
ers.
Thes
e pa
ram
eter
s are
liste
d in
Thb
le3,
It sh
ould
be
note
d th
at p
aram
eter
s are
not
if'! 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 dire
ctly
com
para
ble
to e
ach
othe
r or t
o fe
atur
e-to
-pho
nem
e in
hibi
tion.
sinc
e fe
atur
e-le
vel u
nits
conl
pete
onl
y w
ithin
asin
gle
slice
. whi
le p
hone
me
and
wor
d un
its c
ompe
te in
pro
porti
on to
thei
rov
erla
p,Th
ere
was
som
e tri
al a
od e
rror i
n fin
ding
'he
set
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 re
mar
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 par
amet
ers s
impl
y in
fluen
ce t h
emag
nitu
de o
r the
tim
ing
of o
ne e
ffect
or a
noth
er w
ithou
t cha
ngin
g th
e ba
sic n
atur
e of
the
effe
cts
obse
rved
, For
exa
mpl
e. st
rong
er b
otto
m-u
p ex
cita
tion
spee
ds th
ings
up
and
can
indi
rect
ly in
fluen
ce th
e si
~e o
f top
-dow
n ef
fects. since. for ex-
ampl
e. st
rong
er w
ord
leve
l act
ivat
ions
pro
duce
stro
nger
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 t
he m
agni
tude
of l
exic
al e
ffect
s, Th
e on
e pa
ram
eter
that
app
eare
dto
influ
ence
the
qual
itativ
e be
havi
or o
f the
mod
el w
as th
e st
reng
th o
fw
ithin
- leve
l inh
ibiti
on, S
trong
er w
ithin
-leve
l inh
ibiti
on m
ake
the
mod
elco
mm
it its
elf m
ore
stron
gly
to sl
ight
ear
ly d
iffer
ence
s in
activ
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
righ
t con
text
from
exer
ting
an in
fluen
ce u
nder
som
e ci
rcum
stanc
es, F
inal
ly. a
low
rate
of
feat
ure-
leve
l dec
ay w
as u
sed
toal
low
feat
ure-
level activations to persist
, afte
r the
inpu
t mov
ed o
n to
late
r slic
es,
The
para
met
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 r
espo
nse
alte
rnat
ives
. des
igna
ted
by th
e id
entit
y of
the
item
for w
hich
the
unit
stand
s (no
te th
at w
ith se
vera
l adj
acen
t slic
esin
clud
ed in
the
set.
seve
ral u
nits
in th
e al
tern
ativ
e se
t may
cor
r~sp
ond
toth
e sa
me
over
t res
pons
e), W
ord
iden
tific
atio
n re
spon
ses
are
assu
m~d
tobe based on
. rea
dout
from
the
wor
d le
vel.
and
phon
eme
iden
tific
atio
nre
spon
ses a
re a
ssum
ed to
be
base
d. o
n re
adou
t fro
m th
e ph
onem
e le
vel.
As f
ar a
s pho
nem
e id
entif
icat
ion
is co
ncer
ned,
then
. 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 sti
mul
i.Th
e de
cisio
n m
echa
nism
can
be
aske
d to
mak
e a
resp
onse
eith
er (a
) at a
criterialtime during processirig
or (b
) whe
n a
unit
in th
e al
tern
ativ
e se
tre
ache
s a c
riter
ial s
treng
th re
lativ
e to
the
activ
atio
n of
oth
er a
ltern
ativ
eun
its. O
nce
a de
cisio
n ha
s bee
n m
ade
to m
ake
a re
spon
se. o
ne o
f the
alte
rnat
ives
is c
hose
n fro
m th
e m
embe
rs o
f the
set,
The
prob
abili
ty o
fch
oosin
g a
parti
cula
r alte
rnat
ive
i is t
hen given by the Luce (1959)
choi
ce ru
le:
peRi
~ S
whe
n in
dexe
s the
mem
bers
of t
he a
ltern
ativ
e se
t. an
d
The
expo
nent
ial t
rans
form
atio
n en
sure
s th
at a
ll ac
tivat
ions
are
pos
itive
and
give
s gre
at w
eigh
t to
stron
ger a
ctiv
atio
ns. a
nd th
e Lu
ce ru
le e
nsur
esth
at th
e su
m o
f all
of th
e re
spon
se p
roba
bilit
ies a
dds u
p to
1, 0
. Sub
stan-
tially
the
sam
e assumptions were used by McClelland and Rumelhart
(198
1),
Mil1
imiz
il1R
the
Num
ber o
f Par
amet
ers
At t
he e
xpen
se o
Ccon
sider
able
real
ism. w
e ha
ve tr
ied
to k
eep
TRA
CEII
simpl
e by
usin
g ho
mog
eneo
us p
aram
eter
s whe
reve
r pos
sible
. Thu
s, as
alre
ady
note
d. th
e fe
atur
e sp
ecifi
catio
ns o
f all
phon
emes
wer
e sp
read
out
over
the
sam
e nu
mbe
r of t
ime
slic
es. e
ffect
ivel
y gi
ving
all p
hone
mes
the
sam
e du
ratio
n, T
he s
treng
th o
f the
tota
l exc
itatio
n co
min
g in
to a
par
tic-
ular
pho
nem
e un
it ~r
om th
e fe
atur
e un
its w
as n
orm
aliz
ed to
, the
sam
evalue 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
plify
ing
assu
mpt
ions
shou
ld b
e no
ted
as w
ell.
For e
xam
ple.
ther
e w
ere
no d
iffer
ence
s in
con
nect
ions
or r
estin
gle
vels
for w
ords
of d
~ffe
rent
freq
uenc
y, It
wou
ld h
ave
been
a s
impl
e m
atte
rto
inco
rpor
ate
frequ
ency
as
McC
lella
nd a
nd R
umel
hart
(198
1) d
id. a
nd a
com
plet
e m
ltdel
wou
ld. o
f cou
rse.
incl
ude
som
e ac
coun
t for
the
ubiq
uito
usef
fect
s of w
ord
freq~
ency
. We
left
it ou
t her
e to
faci
litat
e an
exa
min
atio
nof
the
man
y ot
her f
~cto
rs th
at a
ppea
r to
influ
ence
the
proc
ess
of w
ord
reco
gniti
on in
spee
ch p
erce
ptio
n,
TABL
E 3
Para
met
ers o
f TRA
CE II
Para
met
erV
alue
Feat
ure-
phon
eme
exci
tatio
nPh
onem
e-w
ord
exci
tatio
nW
ord-
phon
eme
exci
tatio
nPh
onem
e-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
" Per
thre
e tim
e-sl
ices
of o
verla
p.
TRAC
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 tra
di' n
g re
latio
ns, S
ince
we
wer
e no
t exp
licitl
y co
ncer
ned
with
the
effe
ds o
f fee
dbac
k to
the
feat
ure
leve
l in
any
of th
e ot
her s
im-
ulat
ions
, we
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 c
ases. In the categorical
perc
eptio
n an
d tra
ding
rela
tions
sim
ulat
ions
this
par
amet
er w
as s
etat
, OS,
Phon
eme-
to- f
eatu
re fe
edba
ck te
nded
to sl
ow th
e ef
fect
ive
rate
of d
ecay
at th
e fe
atur
e le
vel a
nd to
incr
ease
the
effe
ctiv
e di
stinc
tiven
ess o
f diff
eren
tfe
atur
e pa
tterri
s, R
ate
of d
ecay
of f
eatu
re- le
vel a
ctiv
atio
ns a
nd st
reng
thof
pho
nem
e-to
'-ph
onem
e co
mpe
titio
n w
ete
set t
o , 0
3 an
d .0
5 to
com
pen-
sate
for t
hese
effe
cts,
No
lexi
con
was
use
d in
the
cate
goric
al p
erce
ptio
nan
d tra
ding
relii
tions
sim
ulat
ions
, whi
ch is
equ
ival
ent t
o se
tting
the
pho-
nem
e to
wor
d ~x
dtat
ion
para
met
er to
zer
o,
't! C 0.::
g~+
-4;
QJ
.c:
Il.
MC
CLE
LLAN
D A
ND
ELM
AN
045+
II'! .
1.1 Ii!
! ~
~I
1IliI
~.: r
'fl!
ftlllf
l!I:
.~t!1
I -
B I
a- b
g.. b~ b
I' FI
G. 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
ilful
l cxp
lal1
aliu
l1,
THE
DY
NA
MIC
S O
F PH
ON
EME
PERC
EPTI
ON
In th
e in
trodu
ctio
n, w
e m
otiv
ated
the
appr
oach
take
n in
the
TRA
CEm
odel
in g
ener
al te
rms.
In th
is se
ctio
n, w
e se
e . th
at th
e si
mpl
e co
ncep
tsth
at le
ad to
TRA
CE p
rovi
de a
coh
eren
t and
synt
hetic
acc
ount
of a
larg
enu
mbe
r of d
iffer
ent k
inds
of f
indi
ngs
on th
e pe
rcep
tion
of p
hone
mes
,Pr
evio
us m
ode:
ls ha
ve b
een
able
to p
rovi
de fa
irly
accu
rate
acc
ount
s of a
num
ber o
f the
se p
heno
men
a, F
or e
xam
ple,
Mas
saro
and
Ode
ns
feat
ure
inte
grat
ion
mod
el (M
assa
ro, 1
981;
Mas
saro
& O
den,
198
0a, 1
980b
; Ode
n&
Mas
saro
, 197
8) a
ccou
nts i
n de
tail
for a
larg
e bo
dy o
f dat
a on
the
influ
ence
s of m
ultip
le c
ues t
o ph
onem
e id
entit
y, a
nd th
e Pi
soni
/Fuj
isaki
-Kawashima m
bdel
of c
ateg
oric
al p
erce
ptio
n (F
ujisa
ki &
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 su
bjec
ts ca
n di
scrim
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 sh
ow h
ere
is th
at T
RACE
brin
gs th
ese
phen
omen
a, a
nd se
vera
lot
hers
not
con
side
red
by e
ither
mod
el, t
oget
her i
nto
a co
here
nt p
ictu
reof
the
proc
ess
of p
hone
me
perc
eptio
n as
it u
nfol
ds in
tim
e,Th
e pr
esen
t sec
tion
cons
ists o
f thr
ee m
ain
parts
. The
firs
t foc
uses
on
lexi
cal e
ffeC
ts O
n ph
onem
e id
entif
icat
ion
and
the
cond
ition
s un
der w
hich
thes
e ef
fect
s are
obt
aine
d. H
ere,
we
see
how
TRA
CE c
an a
ccou
nt fo
rth
e ba
sic
lexi
cal e
ffect
, and
we
mak
e it
clea
r why
lexi
cal e
ffect
s ar
e on
lyob
tain
ed u
nder
som
e co
nditi
ons,
The
seco
nd p
art o
f thi
s sec
tion
focu
ses
on th
e qu
estio
n of
the
role
of p
hono
tact
ic ru
les-
that
is, 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
TRA
CE m
imic
s , th
e ap
pare
ntly
rule
- gov
erne
dbe
havi
or o
f hum
an su
bjec
tf. in
term
s of a
"co
nspi
racy
" of the le
xica
lite
ms t
hat i
nsta
ntia
te th
e ru
le. T
he. th
ird p
art f
ocus
es o
n tw
o as
pect
s of
phon
eme
iden
tific
atio
n of
ten
cons
ider
ed q
uite
sepa
rate
ly fr
om le
xica
l ef-
fect
s-na
mel
y, th
e co
ntra
sting
phe
nom
ena
of c
ue tr
adeo
fTs
in p
hone
me
perc
eptio
n an
d ca
tego
rical
per
cept
ion,
Her
e w
e se
e th
at T
RACE
pro
vide
san
acc
ount
of b
oth
effe
cts a
s wel
l as d
etai
ls of
thei
r tim
e co
urse
, All
thre
epa
rts o
f thi
s se
ctio
n illu
stra
te 'h
ow th
e si
mpl
e m
echa
nism
s of m
utua
l ex-
cita
tion
and
inhi
bitio
n am
ong
the
proc
essin
g un
its o
f the
Tra
ce p
rovi
de a
natu
ral w
ay o
f acc
ount
ing
for t
he re
leva
nt p
heno
men
a, T
he se
ctio
n en
dsw
ith a
brie
f con
sider
atio
n of
the
way
s in
whi
ch T
RACE
mig
ht b
e ex
-te
nded
to c
ope
with
sev
eral
oth
er a
spec
ts o
f pho
nem
e id
entif
icat
ion
and
perc
eptio
n,
Lexical EffeL'
YOll
can
tell
a ph
onem
e by
Ihe
com
pany
Ihm
il ke
epj'
2 In
this
sect
ion,
we describe a simple simulation of the basic lexical effect
on
phon
eme
iden
tific
atio
n re
porte
d by
Gan
ong
(198
0), W
e st
art w
ith th
is p
heno
men
onbe
caus
e it.
and
the
rela
ted
phon
emic
rest
orat
ion
effe
ct, w
ere
amon
g th
epr
imar
y re
ason
s why
we
felt
that
the
inte
ract
ive-
activ
atio
n ap
proa
chw
ould
be
appr
opria
te fo
r spe
ech
perc
eptio
n as
wel
l as v
isual
wor
d re
c-og
nitio
n an
d re
adin
g,Fo
r 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
IIIth
en
n,
then
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
cific
atio
n. E
ach
pane
l of t
he fi
gure
repr
esen
ts2
This
titte
is a
dapJ
ed fr
om th
e til
le o
f a ta
lk b
y D
-dvi
d E,
Rum
elha
rl on
relill
cd p
heno
l1lc
nil
in te
ller p
erce
ptio
n. T
hese
find
ings
are
des
crib
ed in
Rom
elha
rt an
d M
cCle
lland
(198
2/, W
eIh
ank
Dav
e fo
r his
per
mis
sion
to a
dapt
the
title
TRAC
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. Th
e up
per p
ortio
n of
eac
h pa
nel i
s use
d to
disp
lay
activ
atio
ns a
t the
wor
d le
vel;
the
low
er p
anel
is u
sed
for a
ctiv
atio
ns a
tth
e ph
onem
e le
vel.
Each
uni
t is
repr
esen
ted
by a
rect
angl
e, la
bele
d w
ithth
e id
entit
y of
the
item
the
unit
stand
s for
, The
hor
izon
tal e
xten
sion
ofth
e re
ctan
gle
indi
cate
s the
por
tion
of th
e in
put s
pann
ed b
y th
e un
it. T
heve
rtica
l pos
ition
of t
he re
ctan
gle
indi
cate
s the
deg
ree
of a
ctiv
atio
n of
the
unit.
In th
is an
d su
bseq
uent
figu
res,
activ
atio
ns o
f the
pho
nem
e un
itslo
cate
d be
twee
n th
e pe
aks o
f the
inpu
t spe
cific
atio
ns o
f the
pho
nem
es(at Slices 3, 9, 15. etc,) h
ave
been
del
eted
from
the
disp
lay
for c
larit
y(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
), Th
e in
put i
tsel
f is
indi
cate
d be
low
eac
h pa
nel,
with
the
succ
essiv
e ph
onem
es p
ositi
oned
at
the
tem
pora
l pos
ition
s of t
he c
ente
rs o
f the
ir in
put s
peci
ficat
ions
, 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
,Th
e fig
ure
illust
rate
s th
e gradual' buildup of activation of the tw
o in
-te
rpre
tatio
ns o
f the
firs
t pho
nem
e, fo
llow
ed b
y gr
adua
l bui
ldup
s in
acti-
vatio
n fo
r sub
sequ
ent p
hone
mes
, As t
hese
pro
cess
es u
nfol
d, th
ey b
egin
to p
rodu
ce w
ord-
leve
l act
ivat
ions
, It i
s diff
icul
t to
reso
lve
any
wor
d-le
v~1
activ
atio
ns in
the
first
few
fram
es,.
how
ever
, sin
ce 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 eno
ugh
cons
train
t to
sele
ct a
nyon
e pa
rticu
lar 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
tellin
g it
whe
~her
the
inpu
t is
clos
er to
"pl
ug," "
plus
," "
blus
h,or "bl
ood"
(TR
ACE'
s le
xico
n co
ntai
ns n
o ot
her w
ords
beginning with
Iprt
or fbr/), After that point, as ill
ustra
ted
in th
e fo
urth
pan
el, "
plug
win
s the
com
petit
ion
at th
e w
ord
leve
l and
, thr
ough
feed
back
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,Tw
o th
ings
abo
ut th
e le
xica
l effe
ct o
bser
ved
in th
is ca
se a
re w
orth
y of
note
. Firs
t. th
e ef
fect
is ra
ther
sm
all,
Seco
nd, i
t doe
s no
t em
erge
unt
ilw
ell a
fter t
he a
mbi
guou
s seg
men
t itse
lf ha
s com
e an
d go
ne, T
here
is a
slight advantage of
Ipl
over
Ib
l in
Fra
mes
2 a
nd 3
of t
he fi
gure
. In
thes
eca
ses,
how
ever
, the
adv
anta
ge is
not
due
to th
e sp
ecifi
c in
form
atio
n th
atth
is ite
m is
the
wor
d "p
lug
the
mod
el c
an h
ave
no w
ay o
f kno
win
gthis at these points in processing, The slight advantage for
Ipl
at these
early
poi
nts i
s due
to th
e fa
ct th
at th
ere
are
mor
e w
ords
beg
inni
ng w
ithIp
ll than Ibltin the model's
lexi
con,
and
in p
artic
ular
, the
re a
re m
ore
beginning with
Iprl
than
Ib
rt.
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 sli
ght I
p/-w
ard
bias
, Eve
ntua
lly, i
t doe
s so,
. Fig
ure
6 sh
ows t
he te
mpo
ral c
ours
e of
bui
ldup
of t
he st
reng
th o
f the
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 p
hone
me
units
in S
lice
12. i
n proces1iing an ambiguous
Ibl-l
pl
segm
ent i
n '-I
'g/,
and the same segment in
I'SI.
The
ambi
guou
s seg
men
t is i
ndic
ated
by
the
"?,' .
AI~o
show
n is
the
build
up o
r res
pons
e str
engt
h ro
r pro
cess
ing
an un
ambi
guou
~ Ip
l se
gmen
t in
Ipl'g
/. Th
e ve
rtica
l lin
e to
pped
with
"?" indicates the point in time c
orre
spon
ding
to th
ece
nter
or t
he in
itial
segm
ent i
n th
e in
put s
tream
. Suc
cess
ive
verti
cal l
ines
indi
cate
cen
ters
or s
ucce
ssiv
e ph
onem
es.
Ipl
resp
onse
bas
ed o
n ac
tivat
ions
of t
he p
hone
me
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
(as i
n "p
lug
in th
e ot
her,
it is
followed by
IrSI
(as i
n "b
lush
"), G
iven
the
mod
el's
restr
icte
d le
xico
n, w
hich
doe
s not
con
tain
the
~ord
"pl
ush,
" the lexical
effect should lead to eventual dominance of the
Ipl
resp
onse
in th
e fir
stcase, 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 n
ot b
egin
to sh
ow u
p un
til a
fter t
hece
nter
of t
he fi
nal p
hone
me,
whi
ch o
ccur
s at S
lice
30. T
he re
ason
for t
his
is s
impl
y th
at th
e in
form
atio
n is
. not
ava
ilabl
e un
til th
at p
oint
, bec
ause
the
phon
eme
that
sign
als 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 few
tim
e sl
ices
to b
egin
to in
fluen
cethe activation of the
' initi
al p
hone
me,
bec
ause
it p
erco
lat~
s to
the
first
phon
eme
by w
ay o
f the
feed
back
from
the
wor
d or
wor
ds th
at c
on-
tain
it, .
Elimination of the lexical effect by time pressure,
Fox
(198
2) h
as re
-po
rted
that
the
lexi
cal e
ffect
on
wor
d in
itial
segm
ents
is el
imin
ated
ifsu
bjec
ts a
re g
iven
a d
eadl
ine
to re
spon
d w
ithin
500
ms
of th
e am
bigu
ous
segm
ent.
Thou
gh 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 re
spon
ses
show
no
sen-
sit
ivity
to th
e le
xica
l sta
tus o
f the
alte
rnat
ives
, Sim
ilar f
indings are also
repo
rted
by F
ox (1
984)
.O
ur m
odel
is c
ompl
etel
y co
nsist
ent w
ith F
oxs
resu
lts, I
ndee
d, w
e ha
ve
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
alre
ady
seen
that
the
activ
atio
ns in
the 1i"ace only begin to reflect the
lexi
cal e
ffect
abo
ut o
ne p
hone
me
or so
afte
r the
pho
nem
e th
at e
stabl
ishes
the
lexi
cal i
dent
ity o
f the
item
, Giv
en th
at th
is se
gmen
t doe
s not
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
early
resp
onse
s.Bu
t wha
t abq
ut th
e fa
ct th
at e
arly
resp
onse
s to
unam
bigu
ous s
egm
ents
can
be a
ccur
ate?
TRA
CE a
ccou
nts f
or th
is to
o. In
Fig
ure
7 w
e sh
ow th
esta
te o
f the
Tra
ce a
t var
ious
diff
eren
t poi
nts a
fter t
he un
ambi
guou
s Ib
l
Ibrgl, Here, the
Ibl
dominates the
Ipl
from
the
earli
est p
oint
. The
ana
l-og
ous
resu
lt is
!obtained, when the stimulus is
Ipl
in Iprgl, and the actio
vatio
n fo
r the
ihiti
al p
hone
me
is qu
ite in
depe
nden
t of w
heth
er o
r not
the
item
is a
wor
d. T
he re
spon
se st
reng
th fo
r the
cas
e w
hen
Iprg
l is p
rese
nttd
in F
ig, 6
sho
ws
that
the
prob
abilit
y of
choo
sing
Ipl
is n
ear u
nity
with
in12 processing cycles, or 300 ms of the i
nitia
, 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
ecify
ing
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 se
gmen
ts! d
evel
op ra
ther
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 sti
mul
us; i
f one
wor
d pr
edom
inat
ed e
arly
on,
a le
xica
lef
fect
cou
ld d
evel
op ra
ther
. ear
lier,
In g
ener
al, t
houg
h, w
ord-
initi
al a
m-
bigu
ities
will
requ
ire ti
me
to re
solv
e on
the
basis
of l
exic
al in
form
atio
n,
How
ever
, whe
n th
e am
bigu
ous s
egm
ent c
omes
late
in th
e w
ord ,
and
the
info
rmat
ion
that
pre
cede
s the
am
bigu
ous s
egm
ent h
as a
lread
y es
tabl
ished
whi
ch o
f the
two
alte
rnat
ives
for t
he a
mbi
guou
s seg
men
t is c
orre
ctTR
ACE
show
s a
lexi
cal e
ffect
that
dev
elop
s as
the
dire
ct p
erce
ptua
lin
form
atio
n re
leva
nt to
the
iden
tity
of th
e ta
rget
seg
men
t is
bein
g pr
o-ce
ssed
. Thi
s ph
enom
enon
is il
luSt
rate
d in
Fig
, 8, w
hich
show
s the
stat
eof
the
1i"a
ceat
sev
eral
poi
nts
in ti
me
rela
tive
to a
n am
bigu
ous
final
seg-
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
sing
le p
hone
me
afte
r the
cen
ter o
f the
am
bigu
ous s
eg-
men
t, 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-fin
al, a
sop
pose
d to
wor
d-in
itial
, am
bigu
ous s
egm
ents,
In su
ch a
cas
e w
e w
ould
expe
ct th
e le
xica
l effe
ct 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,
This
is th
e fa
ct th
at th
e le
xica
l effe
ct o
n th
e id
entit
y of
a. p
hone
me
only
occ
urs w
ith se
gmen
ts w
hich
fall
in th
e bo
unda
ry re
gion
b~tw
eent
wo
phon
emes
. For
segm
ents
whi
ch a
re u
nam
bigu
ous e
xam
ples
of o
ne c
ateg
ory
or th
e ot
her,
the
effe
ct is
not
obt
aine
d, T
RACE
is e
ntire
lyco
nsis
tent
with
this
asp
ect o
f the
dat
a, T
he in
fluen
ce o
f the
lexi
con
issim
ply
anot
her s
ourc
e of
evi
denc
e, li
ke th
at c
omin
g fro
m th
e fe
atur
e
- b
- b
Har
ll-lf
Eli . FLIl
8 ff:
Wff:
WiI:
W!il
W
- t- t
a r 1
a I'
a 1"1
I k
klSI
-
I 1
I' k
- f- B .
-tar
-targ
--ta
ra-
- t a
r a -
t -
-bl-a-
-bl-I- -
bl- I- -
bl-
FIG
, 7. T
he st
ate
of th
e Tr
ace
at v
ario
us st
ages
of p
roce
ssin
g th
e str
eam
Ibrg
l.
FIG
. 8. T
he st
ale
of th
e Tr
ace
al se
vera
l sta
ges o
f pro
cess
ing
Ihe
strea
m c
onsis
ling
ofIta
rg' followed by Ii segment ambiguous bel ween
III
and
Id/.
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
leve
l, in
flucn
cing
the
activ
atio
n of
one
pho
nem
e un
it or
ano
ther
. Whe
nth
e bo
ttom
-up
inpu
t is d
ecisi
ve, i
t can
pre
empt
any
lexi
cal b
ias e
ffect
s.W
e ha
ve v
erifi
ed th
is in
sim
ulat
ions
pre
sent
ing
unam
bigu
ous t
oken
s of
Ipl
or
fbi,
followed either by Irgl or
IrS/.
In th
ese
sim
ulat
ions
, the
uni
tfo
r the
pre
sent
ed in
itial
segm
ent r
each
es a
ver
y hi
gh le
vel o
f act
ivat
ion,
inde
pend
ent o
f 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 st
rong
er e
ffect
s, th
us a
ccou
ntin
g fo
rth
e fa
ct th
at s
peec
h di
stor
tions
are
eas
ier t
o de
tect
whe
n th
ey c
ome
early
in a
wor
d th
an w
hen
they
com
e la
te (M
arsl
en-W
ilson
& W
elsh
, 197
8),
How
ever
, eve
n th
ere,
it is
pos
sible
to o
verri
de le
xica
lly b
ased
act
ivat
ions
with
cle
ar b
otto
m-u
p sig
nals,
alth
ough
ther
e m
ay b
e so
me
slow
ing
of th
eac
tivat
ion
proc
ess w
hich
wou
ld p
roba
bly
show
up
in re
actio
n tim
es.
H s
houl
d be
not
ed th
at T
RAC
E's
acco
unt o
f lex
ical
effe
cts
is q
uite
simila
r to
the
acco
unt o
ffere
d by
the
feat
ure
inte
grat
ion
theo
ry o
f Mas
saro
and
Ode
n (1
980a
). In
deed
, Mas
saro
and
Ode
ns
mod
el p
rovi
des
quan
ti-ta
tive
fits t
o G
anon
gs f
indi
ngs.
We
will
mak
e so
me
men
tion
of th
e sli
ght
diffe
renc
es in
qua
ntita
tive
assu
mpt
ions
bet
wee
n th
e m
odel
s bel
ow. F
or. n
ow, w
e no
te a
mo~
e cr
ucia
l diff
eren
ce: T
RACE
inco
rpor
ates
spec
ific
assu
mpt
ions
abo
ut th
e tim
e co
urse
of p
roce
ssin
g w
hich
allo
ws i
t to
ac-
coun
t for
the
cond
ition
s un
der w
hich
lexi
cal e
ffect
s w
ill be
obtained, as
wel
l as f
or th
e in
fluen
ce (o
r a la
ck th
ereo
O o
f lex
ical
effe
cts 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 o
f pho
nem
e id
entif
icat
ion
in sp
eech
per
cept
ion,
The
yga
ve su
bjec
ts th
e ta
~k o
f list
enin
g to
spok
en se
nten
ces f
or o
ccur
renc
esof
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
from
the
onse
t of t
he 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
subj
ect's
task
was
sim
ply
topr
ess
the
resp
onse
key
upo
n he
arin
g th
e Ig
I at t
he b
egin
ning
of t
he w
ord
ROl'e
rllm
ellt.
. The pr
inci
ple
findi
ng o
f Fos
s and
Bla
nk's
stud
y 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 eve
n se
man
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 wor
d-in
itial
pho
nem
es a
re p
rimar
ily in
fluen
ced
by a
cous
ticfa
ctor
s affe
ctin
g ph
onem
e de
tect
abili
ty, r
athe
r tha
n le
xica
l, se
man
tic, o
rsyntactic fact
ors,
The
conc
lusi
on th
at p
hone
me
mon
itorin
g is
una
ffect
ed b
y th
e le
xica
lstatus of the target-be
arin
g ph
onem
e str
ing
seem
s at v
aria
nce
with
the
spiri
t of t
he T
RACE
mod
el, s
ince
in T
RACE
, the
lexi
cal l
evel
is a
lway
sin
volv
ed in
the
perc
eptu
al p
roce
ss, H
owev
er. w
e ha
ve a
lread
y se
en th
atth
ere
are
cond
ition
s un
der w
hich
the
lexi
cal l
evel
doe
s no
t get
muc
h of
a c~
ance
to e
xert
an e
ffect
, In
the
prev
ious
sec
tion
we
saw
that
ther
e is
no le
xica
l effe
ct o
n id
entif
icat
ion
of a
mbi
guou
s wor
d-in
itial
targ
ets w
hen
the
subj
ect ~
s und
er ti
me
pres
sure
to re
spon
d qu
ickl
y; si
mpl
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 a
ny o
ther
mec
hani
sm-to
pro
duce
a le
xica
l effe
ct.
In th
e Fo
ss a
nd B
lank
situ
atio
n, th
ere
is ev
en le
ss re
ason
to e
xpec
t ale
xica
l effe
ct, s
ince
the
targ
et is
not
an
ambi
guou
s se
gmen
t. W
e al
read
ysa
w th
at a
ctiv
atio
n cu
rves
rise
rapi
dly
for u
nam
bigu
ous s
egm
ents;
in th
epresent case, they can reach near-pe
ak le
vels
wel
l bef
ore
the
acou
stic
info
rmat
ion
that
indi
cate
s whe
ther
the
targ
et is
in a
wor
d or
non
wor
d ha
sre
ache
d th
e s~
bjec
t's e
ar.
The'
resu
lts o
f a s
imul
atio
n ru
n illu
stra
ting
thes
e po
ints
are
sho
wn
inFi
g. 9
. For
this
exam
ple,
we
imag
ine
that
the
targ
et is
Itl,
Not
e ho
w d
urin
gth
e in
itial
sylla
ble
of b
oth
strea
ms,
little
act
ivat
ion
at th
e w
ord
leve
l has
been
esta
blish
ed, E
ven
tow
ard
the
end
of th
e str
eam
, whe
re th
e in
for-
. mation is
just
com
ing
in w
hich
det
erm
ines
thai
"tru
gus"
is n
ot a
wor
d,th
ere
is lit
tle d
iffer
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 It
/. It
is on
ly a
fter
the
end
of th
e st
ream
that
a re
al c
hanc
e fo
r a d
iffer
ence
has
occ
urre
d, W
ell
befo
re th
is tim
e ar
rives
, the
subj
ect w
ill h
ave
mad
e a
resp
onse
, sin
ce th
estrength of the
It!
resp
onse
reac
hes a
leve
l suf
ficie
nt to
gua
rant
ee a
hig
hac
cura
cy b
y ab
out C
ycle
30,
wel
l bef
ore
the
end
of th
e w
ord,
as
illust
rate
d:in
Fig
, 10,
Ev
en th
ough
act
ivat
ions
are
qui
te ra
pid
for u
nam
bigu
ous s
egm
ents,
thes
e ca
n sti
ll be
influ
ence
d by
lexi
cal e
ffect
s, pr
ovid
ed th
at th
e le
xica
l.in
form
atio
n is
avai
labl
e in
tim
e, In
Fig
, II,
we
illus
trate
this
poin
t for
the
phon
eme
It I i
'n th
e st
ream
s Is
ikrt
l (th
e w
ord
"sec
ret"
) and
Igld
A
guld
ut,"
a n
onw
ord)
, The
figu
re sh
ows t
he st
reng
th o
f the
It I
resp
onse
as a
func
tion
of p
roce
ssin
g cy
cles
, rel
ativ
e to
all
othe
r res
pons
es b
ased
on a
ctiv
atio
ns o
f pho
nem
e un
its a
t Cyc
le 4
2, th
e pe
ak o
f the
inpu
t spe
c-ifi
catio
n fo
r the
It/.
Clea
rly, r
espo
nse
stren
~' h
gro
ws
fast
er fo
r the
It! i
nIs
ikrt
l tha
n fo
r the
It! i
n Ig
ldAt!;
pic
king
an
arbi
trary
thre
shol
d of
.9 fo
rresponse initiation, we find that the
It!
in Is
ikrt
l rea
ches
crit
erio
n ab
out
3 cy
cles
or 7
5 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
repo
rted
an e
xper
imen
t tha
t dem
onst
rate
s th
e ex
iste
nce
ofle
xica
l effe
cts i
n ph
onem
e m
onito
ring
for p
hone
mes
com
ing
at la
ter p
oi~t
sin
wor
ds. F
or p
hone
mes
com
ing
at th
e be
ginn
ing
of a
wor
d or
at t
he e
ndof
the
first
sylla
ble,
he
foun
d no
faci
litat
ion
for p
hone
mes
in w
ords
rel-
TRAC
E M
OD
EL
IN.l*
,,,~
U
-1,1
II I
;.., 1.
:=:
:.0 0.
111
!:
40-
Q.. ~ 0.
MC
CLE
LLAN
D A
ND
ELM
AN
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
Ilarg
ll ilnd II
(gs/.
Th
e v.
:rlic
al li
n.:s
indi
cale
the
peak
s on
Ihe
feal
ure
paue
rns
corre
spon
ding
10
!he
succ
essiv
.: ph
on.:m
.:s o
f Ihe
pres
eRle
d w
ord.
-Lar
l-L-
-Lar
. I-L-
-Lar
l-L-
ms
adva
ntag
e co
mpa
red
to c
orre
spon
ding
pos
ition
s in
non
words. This
com
pare
s qui
te c
lose
ly w
ith th
e va
lue
of a
bout
75
ms w
e ob
tain
ed fo
r the
Isik
r t/-
ld'tl
exa
mpl
e. A
t the
end
s of e
ven
long
er w
ords
, the
wor
d ad
-va
ntag
e in
crea
sed
in si
ze to
185 ms. Marslen-
Wils
ons
resu
lt Ih
us c
on-
firm
s tha
t the
re a
re' in
deed
lexi
cal e
ffect
s in
pho
nem
e m
onilo
ring-
even
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 pho
nem
es w
hose
pro
cess
ing
can
be c
ompl
eted
long
bef
ore
lexi
cal i
nflu
ence
s wou
ld h
a\:,e
a c
hanc
e to
show
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. fo
r the
stre
am Is
ik..
.1 ("
secr
e., and
Id'
guld
ut" )
. Ver
tical
line
s in
dica
te th
e pe
aks
of th
e in
put p
atte
rns
corre
spon
ding
10
Ihe
succ
essiv
e ph
onem
es in
eith
er sl
ream
.
IIIm
m
B I
100
.!:.... ~ 0.
III 1.0
.... en
0.
III g 0.
III III02
0
-Lr-
s- -Lr-a-
s- -L
r-a-
e-FIG. 9. Stale of Ihe ltace al three di
ffere
nt p
ainl
s dur
ing
the
proc
essin
g of
the
wor
dta
rgel
(/tar
gt/!
an
d th
e no
nwor
d "t
rugu
s " (/
trsf
),
ativ
e to
pho
nem
es in
non
wor
ds (i
n fa
ct th
ere
was
a n
on w
ord
adva
ntag
efo
r the
se e
arly
targ
et c
ondi
tions
). Fo
r tar
gets
occu
rring
at t
he e
nd o
f the
seco
nd sy
llabl
e of
a tw
o-sy
llabl
e w
ord
(like
"se
cret
thou
gh th
e st
imul
iin
this
par
ticul
ar e
xper
imen
t wer
e D
utch
) Mar
slen
- Wilson found an 85-
- -- ----
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
The
TRA
CE m
odel
and
Mar
slen-
Wils
ons C
OH
ORT
mod
el (M
arsle
n-W
ilson
& T
yler
, 198
0; M
arsle
n-W
ilson
& W
elsh
, 1978) offer fairly similar
inte
rpre
tatio
ns o
f lex
ical
effe
cts i
n ph
onem
e m
onito
ring,
Bot
h m
odel
sac
coun
t for
the
grow
th in
the
effe
ct a
s a
func
tion
of p
ositi
on in
the
wor
d,A
s in
COH
ORT
, lex
ieal
effe
cts i
n TR
ACE
dep
end
on th
e po
int a
t whi
chth
e pa
ttern
of a
ctiv
atio
n at
the
wor
d le
vel b
egin
s to
spec
ify th
e id
entit
ies
of the ph
onem
es, I
nC
OH
OR
T, th
ere
is a
dis
cret
e m
omen
t whe
n th
isoc
curs
-whe
n th
e co
hort
of it
ems c
onsis
tent
with
the
inpu
t is r
educ
edto a single item. In T~R
ACE,
thin
gs a
re n
ot q
uite
so
disc
rete
, How
ever
,it
will
still
gen
eral
ly b
e th
e ca
se in
TR
ACE
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," th
e po
int a
t whi
chth
e bo
ttom
-up
inpu
t rem
ains
con
siste
nt w
ith o
nly
a si
ngle
wor
d, H
ow-
ever, since Marslen-
Wils
ons
expe
rimen
ts w
ere
perfo
rmed
with
Dut
chw
ords
, we
have
not
bee
n ab
le to
sim
ulat
e hi
s exp
erim
enta
l dem
onstr
atio
nof
this
effe
ct in
det
ail.
TRA
CE a
nd C
OH
ORT
mak
e sim
ilar p
redi
ctio
ns in
som
e sit
uatio
ns,
but n
ot in
all.
In th
e ne
xt se
ctio
n, w
e co
nsid
er a
phe
nom
enon
whi
chTR
ACE
acc
ount
s for
,via
the
sam
e m
echa
nism
s it u
ses t
o ac
coun
t for
the
lexi
cal e
ffect
s we
have
bee
n co
nsid
erin
g. H
ere,
the
grad
ed fe
edba
ck fr
omth
e w
ord
leve
l to
the,
pho
nem
e le
vel a
llow
s TRA
CE to
acc
ount
for a
nef
fect
that
wou
ld n
ot b
e pr
edic
ted
by C
OH
ORT
, unl
ess a
dditi
onal
as-
sum
ptio
ns w
ere
mad
e,
Are
PlrO
llOto
ctic
Rille
Ejfe
ct.f
the Res"lt of a Co1lspiracy?
Rec
ently
, Mas
saro
;;tn
d C
ohen
(198
3) h
ave
repo
rted
evid
ence
they
take
as s
uppo
rt fo
r the
use
of p
hono
tact
ic ru
les
in p
hone
me
iden
tific
atio
n. In
one
expe
rimen
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
iffer
ent c
onte
xts.
In o
ne c
on-
text (fLi/)
Irl
is permissible in English, but
III
is no
t. In
ano
ther
con
text
(/5-i/) /11
is permissible in English but
Irl
is not. In a third context
(/Li/)
both are permissible, and in a fourth
(/v_ i
/) ne
ither
is p
erm
issi
ble.
Mas
saro
and
Coh
en fo
und
a bi
as to
per
ceiv
e ambiguous segments as
Irl
whe
n Irl
was permissible or as
III
whe
n 11
/ w
as p
erm
issib
le. N
o bi
as a
ppea
red
inei
ther
of t
he o
ther
two
cond
ition
s.W
ith m
ost o
f the
se st
imul
i, ph
onot
actic
acc
epta
bilit
y is
conf
ound
edwith the actual lexica1 status of the item; thus
/nil
and
ffril
flee"
and
free
) are both words, as is
Itril
bul not
Illil,
In the
Is_il
co
ntex
t, ho
w-
ever. neither Islil or
Isril
ar
e w
ords
, yet
Mas
saro
and
Coh
en fo
und
a bi
asto hear the ambiguous segment as
III,
in accordance with phonotactic
rule
s. It tu
rns o
ut th
at T
RACE
pro
duce
s the
sam
e ef
fect
, eve
n th
ough
it la
cks
phon
otac
tlc ru
les,
The
reas
on is
that
the
ambi
guou
s stim
ulus
pro
duce
s
parti
al a
ctiv
atio
ns o
f a n
umbe
r of w
ords
('~s
leep" and "sleet" in the
mod
el' s
lexi
con;
it w
ould
also
act
ivat
e "s
leev
e,
" "
sleek
,an
d ot
hers
ina
mod
el w
ith a
fulle
r lex
icon
). N
one
of th
ese
wor
d un
its g
ets a
s act
ive
as it
wou
ld if
the
entir
e w
ord
had
been
pre
sent
ed, H
owev
er, a
ll of
them
(in th
e sim
ulat
ion,
ther
e ar
e on
y tw
o, b
ut th
e pr
inci
ple
still
appl
ies)
are
parti
ally
act
ivat
ed, a
nd a
ll co
nspi
re to
geth
er a
nd c
ontri
bute
to th
e ac
ti-vation of
III.
This feedback support for the
III
allo
ws i
t to
dom
inat
e th
eIrl
, just as it would if
Islil
w
ere
an a
c~ua
l wor
d, a
s sho
wn
in F
ig, 1
2,Th
e hy
poth
esis
that
pho
nota
ctic
rule
effe
cts a
re re
ally
bas
ed o
n w
ord
activ
atio
ns le
ads t
o a
pred
ictio
n: th
at w
e sh
ould
be
able
to re
vers
e th
ese
effe
cts i
f we
pres
ent i
tem
s tha
t are
supp
orte
d str
ongl
y by
one
or m
ore
lexi
cal i
tem
s eve
n if
they
vio
late
pho
nota
ctic
rule
s, A
rece
nt e
xper
imen
tby
Elm
an (1
983)
con
firm
s thi
s pre
dict
ion,
In th
is ex
perim
ent,
ambi
guou
sphonemes (for example, halfway between
Ibl
and
Id/)
wer
e pr
esen
ted
inth
ree
diffe
rent
type
s of
con
text
s, In
all
thre
e ty
pes,
one
of t
he tw
o (in
this
case, 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
illega
l ite
m w
as v
ery
cI()s
e to
a w
ord
("bw
acel
et"
dwac
elet
"). I
n a
third
cas
e, n
eith
er it
em
EiIT
llJIIT
rntil
ltil
l
9tIJ
JE!
l. 1
;..1
- 5
S J
1- -51- -81- -5
FIG
. 12.
Sta
te (I
f the
1i'a
ce a
t sev
eral
poi
nts i
n pr
oces
sing
a se
gmen
t am
bigu
ous b
etw
een
111
and
Irl,
in the context
Is_i
/. Th
e un
its fo
r "sle
ep" I
Islip
/) an
d "s
leet
" (/sl
it/) a
re b
oxed
toge
ther
sinc
e th
ey ta
ke o
n id
entic
al a
ctiv
atio
n va
lues
.
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
was
par
ticul
arly
clo
se to
a w
ord
("bw
ime
dwim
eRe
sults
of
th
eex
perim
ent a
re s
how
n in
Thble 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 bet
wee
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) w
as o
ne fe
atur
e aw
ay fr
oma
parti
cula
r lex
ical
item
("br
acel
et" )
, sub
ject
s te
nded
to h
ear t
he a
mbi
g-uo
us it
em in
acc
ord
with
the
sim
ilar l
exic
al it
em (t
hat i
s, a
s a
Ibl)
even
thou
gh it
was
pho
nota
ctic
ally
inco
rrect
.. To determine whether the model w
ould
also
pro
duce
such
are
vers
alof
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 ph
onot
actic
ally
acc
epta
ble
in th
is co
ntex
t, bu
tIt
I in
this
con
text
mak
es a
n ite
m th
at is
ver
y cl
ose
to th
e w
ord
" tru
ly,
The results
of
this
run,
at t
wo
diffe
rent
poi
nts d
urin
g pr
oces
sing,
are
show
n in
Fig
. 13,
Ear
ly o
n in
pro
cess
ing,
ther
e is
a s
light
bia
s in
favo
rof
th
e Ip
l over the
Itl,
because at first a large number
of
Ipll
wor
ds a
reslightly more activated than any words beginning with
Itl,
Late
r, th
ough
,th
e It
I get
s th
e up
per h
and
as th
e w
ord
" tru
ly" c
omes
to d
omin
ate
at th
eword level. Thus, by the end
of
the
wor
d or
shor
tly th
erea
fter,
the
clos
est
wor
d ha
s be
gun
to p
laya
dom
inat
ing
role
, cau
sing
the
mod
el to
pre
fer
the phonotactically inappropriate interpretation
of
the
ambi
guou
s in
itial
segm
ent.
Of c
ours
e, 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 se
gmen
t is n
otambiguous, 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,
Trad
ing
Rel
atio
ns a
nd C
ateg
oriL
'al P
erc'
eptio
nIn
the
sim
ulat
ions
con
side
red
thus
far,
phon
eme
iden
tific
atio
~ is
intlu
-enced by two different kinds
of
fact
ors,
feat
ural
and
lexi
cal.
Whe
n on
eso
rt of
in
form
atio
n is
lack
in~,
the
othe
r can
com
pens
ate
for i
t. Th
e 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, Th
e TR
ACE
mod
el e
xhib
its th
i-s sa
me
flexi
bilit
y, a
s we
deta
ilsh
ortly
.But there is something
of
a pa
rado
x, W
hile
the
p(:rc
eptu
al m
echa
nism
sex
hibi
t gre
at fl
exib
ility
in th
e cu
es th
at th
ey re
ly o
n fo
r pho
nem
e id
enti-
ficat
ion,
they
also
app
ear t
o be
qui
te "
cate
goric
al" i
n na
ture
. Tha
t is
they
pro
duce
muc
h sh
arpe
r bou
ndar
ies b
etw
een
phon
etic
cat
egor
ies t
han
we
mig
ht e
xpec
t bas
ed o
n th
eir s
ensit
ivity
to m
ultip
le cu
es; 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 ins
tanc
es
of
the
sam
e ph
o-ne
me. In th
is se
ctio
n, w
e ill
ustra
te th
at in
TRA
CE, j
ust a
s in
hum
an sp
eech
. per
cept
ion,
flex
ibili
ty in
feat
ure
inte
rpre
tatio
n-sp
ecifi
cally
, the
abi
lity
to trade one feature
of
a ph
onem
e of
f aga
inst
ano
ther
-coe
xist
s w
ith a
stron
g te
nden
cy to
war
d ca
tego
rical
per
cept
ion.
For t
hese
sim
ulat
ions
, the
mod
el w
as st
rippe
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 tra
dc-
n:::u
u:n
JIT!
iI:TI
!a:it
Lnu:
:r::il
l
fillJ
8iam
u I
I U I
i -f I
I I
P r
a r i
P r
,,
TABL
E 4
Perc
enla
ge C
hoic
e of
Pho
nola
clic
ally
Irre
gula
r Con
sona
nt
Stim
ulus
type
Lega
l wor
d/ill
egal
non
wor
d Le
gal n
on w
ord/
illeg
al n
onw
ord
Lega
l non
wor
d/ill
egal
nea
rwor
d
Exam
ple
dwin
dle/
bwin
dle
dwim
e/bw
ime
dwac
elel
/bw
acel
el
Perc
enta
ge o
f ide
nlifi
clili
ons
as "
illeg
al" p
hone
me
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 se
gmen
lfollowed by Ilulil
TRAC
E M
OD
EL. M
C C
LELL
AND
AN
D E
LMAN
100
150 300
seve
ral c
ateg
o~ic
al p
erce
ptio
n stu
dies
of V
OT
cont
inua
(usin
g Ig
/-/k/
.Id
/-/tl.
or
Ib
/-/pl
sti
mul
i) ha
ve c
ovar
ied
both
VO
T an
d FI
OF.
if o
nly
beca
use
FIO
F te
nds t
o co
vary
with
VO
T W
hl.ll
real
istic
stim
uli a
re u
sed
(e.g
.. Pi
soni
& L
azar
us. 1
974: Samuel. 1977), Though the simulations us
eIg
/-/kl
co
ntin
uum
. we
cons
ider
seve
ral c
ateg
oric
al p
erce
ptio
n ex
peri-
ments using
Id/-/
tl an
d Ib
l-lpl
co
ntin
ua. s
ince
the
sam
e di
men
sions
can
diffe
rent
iate
the
two
mem
bers
of b
oth
of th
ese
othe
r pai
rs, W
e al
so c
on-
sider
dat
a ob
tain
ed in
exp
erim
ents
on o
ther
con
tinua
. usin
g ot
her c
ues,
We
coul
d ea
sily
have
repe
ated
the
simul
atio
ns w
ith o
ther
sets
of c
ontin
ua; .
how
ever
. the
gen
eral
qua
litat
ive
form
of t
he re
sults
wou
ld b
e th
e sa
me,
Wha
t wou
ld v
ary
from
cas
e to
cas
e w
ould
be
the
mag
nitu
de o
f the
effe
ctof
a s
tep
alon
g a
give
n di
men
sion
,Th
e pa
ttern
of e
xcita
tory
inpu
t to
the
VO
T an
d FI
OF
dete
ctor
s pro
-duced by the canonical mock speech
Igl
and
Ikl
used
in th
e si
mul
atio
nsar
e illu
stra
ted
in F
ig. 1
5,
Trad;"g relat;OIu,
TRAC
E qu
ite n
atur
ally
tend
s to
pro
duce
trad
ing
rela
tions
bet
wee
n fe
atur
es. s
ince
it re
lies o
n th
e w
eigh
ted
sum
of t
heex
cita
tory
inpu
ts to
det
erm
ine
how
stro
ngly
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 str
ongl
y ac
tivat
ed th
anan
y ot
her,
and
will
ther
efor
e be
the
mos
t lik
ely
resp
onse
whe
n a
choi
cem
ust b
e m
ade
betw
een
one
phon
eme
and
anot
her,
Sinc
e th
e ne
t bot
tom
-up input is just the sum of all of the inputs, no one input is necessarily
deci
sive
in th
is re
gard
,G
ener
ally
, exp
erim
ents
dem
onstr
atin
g tra
ding
rela
tions
bet
wee
n tw
o or
.m
ore
cues
man
ipul
ate
each
of t
he c
ues
over
a n
umbe
r of v
alue
s ra
ngin
gbe
twee
n a
valu
e m
ore
typi
cal o
f one
of t
wo
phon
emes
and
a v
alue
mor
ety
pica
l of t
he o
ther
, Sum
mer
field
and
Hag
gard
did
this
for V
OT
and
FIO
F, a
nd fo
und
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 the
val
ue o
f VQ
T ne
eded
.fo
r 50%
cho
ices
of I
k/. U
nfor
tuna
tely
; the
y di
d no
t pre
sent
full
curv
esre
latin
g ph
onem
e id
entif
icat
ion
to th
e va
lues
use
d on
eac
h of
the
two
dim
ensio
ns, I
n lie
u of
this,
we
pres
ent c
urve
s in
Fig,
16
from
a c
lass
ictra
ding
rela
tions
exp
erim
ent,
by D
enes
(195
5), S
imila
r pat
tern
s of
resu
ltsha
ve b
een
repo
rted
in o
ther
stud
ies,
usin
g ot
her c
ues (
e,g" Massaro.
1981
, Fig
s. 4
and
5), t
houg
h th
e tra
nsiti
ons a
re o
ften
som
ewha
t ste
eper
(see
bel
ow fo
r a d
iscus
sion
of th
e is~
ue o
f ste
epne
ss).
We
have
cho
sen
to p
rese
nt th
e sh
allo
wer
cur
ves r
epor
ted
by D
enes
bec
ause
in th
em w
ese
e cl
early
.that
ther
e ar
e ca
ses i
n w
hich
a c
ue th
at fa
vors
one
of t
he tw
oph
onem
es to
a m
oder
ate
degr
ee w
ill g
ive
rise
to th
e pe
rcep
tion
of th
eot
her p
hone
me
whe
n pa
ired
up w
ith a
stro
ng c
ue th
at fa
vors
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
rhon
emel
evel
ther
e w
ere
only
three phonemes.
tal. Ig/.
and
Ik/,
plus silence
(I-I).
Fr
om th
ese
four
item
s.inputs and percepts of the form
ga-
and
ka-
coul
d be
con
struc
ted.
. The
follo
win
g ad
ditio
nal c
onst
rain
ts w
ere
impo
sed
on th
e fe
atur
e sp
eci-
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 t
he a
ctiv
atio
ns o
fth
e Ig
l an
d Ik
l ph
onem
e un
its w
here
they
ove
rlapp
ed w
ith th
e co
nson
ant:
(2)
Igl
and
Ikl
wer
e id
entic
al o
n fiv
e of
the
seve
n di
men
sions
. and
diff
ered
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)
and
the
()nse
t fre
quen
cy o
f the
fitst
form
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 the
oth
er si
mul
atio
ns, F
igur
e 14
illu
strat
es h
ow F
IOF
tend
s to
incr
ease
as
voic
e on
set t
ime
is d
elay
ed.
Sum
mer
field
and
Hag
gard
(197
7) h
ave
show
n th
at su
bjec
ts ar
e se
nsiti
vebo
th to
VaT
and
to F
IOF
and
that
it is
pos
sible
to tr
ade
one
of th
ese
cues off against the other. Thus. the boundary between
Igal
an
d Ik
al
shift
sto
long
er V
OTs
whe
n FI
star
ts of
f low
er ra
ther
than
hig
her,
Cat
egor
ical
per
cept
ion
and
tradi
ng 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 fo
cus o
n th
e V
OT
and
FIO
F fe
atur
es. a
sexemplified by the
Igal
-/kal
co
ntin
uum
. bec
ause
ther
e is
data
on
trade
-of
fs b
etw
een
thes
e cu
es (S
umm
erfie
ld &
Hag
gard
, 197
7). a
nd b
ecau
se
2000
1500
i'510
00IiI
. 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 '(lO
Pcu
rvel
is e
nerg
ized
by
aper
iodi
c no
ise so
urce
s. an
d FI
is "
cut b
ack"
(the
noi
se so
urce
has
liUle
or n
o en
ergy
in th
is ra
ngel
. Bec
ause
of t
he fa
ct th
at F
t ris
es o
ver t
ime
afte
r syl
labl
eon
set (
as th
e vo
cattr
uct m
oves
from
a sh
ape
cons
isten
t with
the
cons
onan
t int
o a.
sha
peco
nsis
tent
with
...he
vow
ell.
its fr
eque
ncy
at th
e on
set o
f voi
cing
is h
ighe
r for
late
r val
ues
of V
OT.
Par
amet
ers u
sed
in c
onstr
uctin
g th
is sc
hem
atic
sylla
ble
are
deriv
ed fr
om K
ewle
y-!'o
rt's
(198
21 a
naly
sis
of th
e pa
ram
eter
s of
form
ants
. in
natu
ral s
peec
h. a
nd a
re s
imila
r to
thos
e us
ed in
man
y pe
rcep
tual
exp
erim
ents
,
....
..5 0.
:5 0,
I.. U) 0
.
....
..5 075
:5 0.
till
s.. en 025
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
Ioo
~80
I!i 4
9
, ~20
r 0
III 12
345 Ikl
I .
Voic
e O
nset
Tim
e10
0 20
0FR
ICA
TIO
N D
URA
TIO
N (M
SEC)
FIG
. .16
. Res
ulls
of a
n ex
perim
enl d
emon
slra
ling
Ihe
Irade
-off
belw
een
IWO
cue
s 10
Ihe
identity of
Isl
and
Iii.
Dala from Denes, 1955
, fill
ed b
y th
e m
odel
of M
assa
ro a
nd C
ohen
,1977. e. so ms; 0, 100 ms; 8, ISO ms; A
, 200
ms,
Repr
inle
d w
ilh p
erm
issio
n fro
m M
assa
roan
d C
ohen
(197
7).
1.00
1&1
1234
5 Ik
l
trade
-off
curv
es a
s ha
ve b
een
gene
rally
repo
rted,
we
gene
rate
d a
set o
f25
inte
rmed
iate
pho
netic
segm
ents
mad
e up
by
pairi
ng e
ach
of fi
ve d
if-fe
rent
inte
rmed
iate
pat
tern
s on
the
VO
T di
men
sion
with
eac
h of
live
diffe
rent
inte
rmed
iate
pat
tern
s on
the
FIO
F di
men
sion
. The
dilf
cren
tfe
atur
e pa
ttern
s use
d on
eac
h di
men
sion
are
show
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
sions
, the
inte
rmed
iate
segm
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 st
imul
i. pr
eced
ed b
y sil
ence
(I-I)
and followed by
la-I.
In th
is an
d al
l sub
sequ
ent s
imul
atio
ns w
e re
port
in th
is pa
per.
the
peak
of t
he in
itial
sile
nce
phon
eme
occu
rred
at T
ime
Slic
e 6
in th
e in
put.
and
the
peak
s of s
ucce
ssiv
e ph
onem
e se
gmen
ts o
c-curred at six sli
ce in
terv
als.
Thus
. for
thes
e sti
mul
i. th
e pe
ak o
n th
ein
term
edia
te p
hone
tic se
gmen
t occ
urre
d at
Slic
e 12
. the
pea
k of
the
fol-
low
ing
vow
el o
ccur
red
at S
lice
18. a
nd ~
he p
eak
of th
e fin
al si
lenc
e oc
-cu
rred
at S
lice
24. F
or e
ach
inpu
t 'pr
esen
ted.
the
inte
ract
ive
activ
atio
npr
oces
s w
as a
llow
ed to
con
tinue
thro
ugh
a to
tal o
f 60
time
slic
es. w
ell
past
the
end
of th
e in
put.
The
stat
e of
the
Trac
e at
var
ious
poi
nts
inpr
oces
sing.
for t
he m
ost/g
/~Iik
e of
the
25 st
imul
i, is
show
n in
Fig
. 17.
At
the
end
of th
e 60
th ti
me
slice
. we
reco
rded
the
activ
atio
n of
the
units
for
Ig/
and
Ikl
in T
ime
Slic
e 12
and
the .
probability of choosing
Igl
base
d on
thes
e ac
tivat
ions
, (It
mak
es n
o di
ffere
nce
to th
e qu
alita
tive
appe
aran
ceof
the
resu
lts if
a d
iffer
ent d
ecis
ion
time
is us
ed; e
arlie
r dec
ision
tim
esar
e as
soci
ated
with
smal
ler d
iffer
ence
s in
rela
tive
activ
atio
n be
twee
n th
eIg
I an
d Ik
l ph
onem
e un
its. a
nd la
ter o
nes w
ith la
rger
dift
eren
ces.
but t
hege
nera
l pat
tern
is th
e sa
me,
Ft Onset Frequency
FIG
. 15.
Can
onic
al fe
atur
e-level inpul for Ig! and I
kI,
on Ih
elw
o di
men
sions
Ihal
disl
ingu
ish .
them
. and
Ihe
palle
rns
used
for t
he li
ve in
lerm
edia
le v
alue
s us
ed in
the
Iradi
ng re
lalio
nssi
mul
atio
n, A
long
Ihe
absc
issa
of e
ach
dim
ensi
on Ih
e ni
ne u
nils
for t
he n
ine
dil1
eren
l val
uerdnges of the dimension are armyed. The curves labeled Ig! and
Ikl
jndi
cale
Ihe
rela
live
slren
glh
of th
e ex
cita
tory
inpu
llo e
ach
i,)f I
hese
uni
ls, p
rodu
ced
by Ih
e in
dica
led
phon
eme.
The
cano
nica
l cur
ves a
lso in
dica
le Ih
e slr
engl
hs o
f the
feat
ure-
la- p
hone
me
conn
eclio
ns fo
rIg
!. an
d Ik
l on
Ihes
e di
men
sions
. Tha
i is.
Ihe
cano
nica
l inp
ut p
alle
rn fo
r eac
h ph
onem
eex
aclly
mal
ches
Ihe
slren
glhs
of I
he c
orre
spon
ding
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 Ira
din.
: rel
alio
nssim
ulal
ion.
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 thr
ough
the
mid
dle
of th
eir r
ange
, 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 se
e if
TRA
CE w
ould
sim
ulat
e th
e ba
sic tr
ade-
off e
ffect
obt
aine
d by
Sum
mer
field
and
Hag
gard
. and
to se
e if
it w
ould
prd
duce
the
sam
e sh
ape
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
~ 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 V
aT n
eede
d to
ach
ieve
50%
pro
babi
lity
ofre
porti
ng Ik
/. w
e ca
n se
e th
at th
e V
aT n
eede
d in
crea
ses a
s the
FIO
Fde
crea
ses,
just
as th
ese
inve
stiga
tors
foun
d.
Cue
trade
-offs
in p
hone
me
iden
tific
atio
n ar
e ac
coun
ted
for i
n de
tail
byth
e fe
atur
e in
tegr
atio
n m
odel
ofO
den
and
Mas
saro
(197
8; M
assa
ro. 1
981;
Mas
sarQ
and
Ode
n. I
980a
. 198
0b);
Whi
le w
e ha
ve sh
own
how
TRA
CEca
n ac
coun
t for
the
basic
trad
e-of
f effe
ct a
nd th
e ge
nera
l for
m o
f the
trade
-off
curv
es. w
e ha
ve n
ot y
et a
ttem
pted
the
kind
s of
det
aile
d fit
s th
atM
assa
ro, O
den,
and
col
labo
rato
rs h
ave
repo
rted
in a
num
ber o
f stu
dies
,H
owev
er. t
he m
odel
s are
qui
te si
mila
r. so
it se
ems r
athe
r unl
ikel
y th
atcu
e tra
de-o
ff da
ta w
ould
be
able
to d
iScr
imin
ate
betw
een
them
, And
bot
hm
ake
spec
ial a
ssum
ptio
ns a
bout
lack
of i
nvar
ianc
e of
cue
s to
phon
eme
iden
tity
acro
ss c
onte
xts,
O
ne a
ppar
ent d
issim
ilarit
y be
twee
n th
e m
odel
s des
erve
s com
men
t.W
here
as c
ue st
reng
ths a
re c
ombi
ned
mul
tiplic
ativ
ely
in th
e de
term
inat
ion
of re
spon
se st
reng
ths i
n th
e fe
atur
e in
tegr
atio
n m
odel
. the
y ar
e co
mbi
ned
addi
tivei
y in
the
botto
m-u
p in
puts
to th
e un
its in
TR
ACE,
How
ever
, in
TRA
CE, t
wo
furth
er c
ompu
tatio
nal s
teps
take
pla
ce b
efor
e th
ese
inpu
tsresult in resp
onse
stre
ngth
s. Fi
rst,
the
inte
ract
ive-
activ
atio
n process en-
hanc
es d
iffer
ence
s bet
wee
n co
mpe
ting
units
, Sec
ond,
the
resu
lting
uni
tac
tivat
ions
are
sub
ject
ed to
an
expo
nent
ial t
rans
form
atio
n. J
ust t
his
. second step by i
tself
wou
ld tr
ansf
orm
influ
ence
s tha
t hav
e ad
ditiv
e ef
fect
son
uni
t act
ivat
ions
into
influ
ence
s tha
t. ha
ve m
ultip
licat
ive
effe
cts o
n re
-sp
onse
stre
ngth
. Thu
s, th
e m
odel
s w
ould
be
mat
hem
atic
ally
equ
ival
ent
if th
e in
tera
ctiv
e ac
tivat
ion
proc
ess 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 clo
sely
rela
ted
to th
e on
es w
e us
e(G
ross
berg
, 197
8), w
hat t
he in
tera
ctiv
e ac
tivat
ion
proc
ess d
oes i
s sim
ply
resc
ale
the
unit
activ
atio
ns, p
rese
rvin
g th
e ra
tios
of th
eir b
otto
m-u
pac
tivat
ion
but k
eepi
ng th
em b
ound
ed. T
houg
h ou
r ver
sion
of th
ese
equa
-tio
ns d
oes n
ot d
o th
is ex
actly
, the
way
s in
whi
ch it
dev
iate
s fro
m th
isw
ould
be
diffi
cult
to u
se a
s the
bas
is fo
r an
empi
rical
dist
inct
ion
betw
een
the
TRA
CE a
ppro
ach
and
the
feat
ure
inte
grat
ion
mod
el" T
hus,
up
to a
poin
t, w
e ca
n se
e TR
ACE
as (a
ppro
xim
atel
y) im
plem
entin
g th
e co
mpu
-ta
tions
spec
ified
in a
den
and
Mas
saro
s m
odel
. The
mod
els
diffe
r,th
ough
, in
that
TRA
CE is
dyn
amic
and
in th
at it
inco
rpor
ates
feed
back
to th
e ph
onem
e le
vel.
This
allo
ws T
RACE
to a
ccou
nt fo
r cat
egor
ical
perc
eptio
n in
a d
iffer
ent w
ay.
Categorical perception.
In s
pite
ofth
e fa
ct th
at T
RAC
E is
qui
te fl
exib
lein
the
way
it c
ombi
nes i
nfor
mat
ion
from
diff
eren
t fea
ture
s to
dete
rmin
ethe identity of a ph
onem
e, th
e m
odel
is q
uite
categorical in its overt
resp
onse
s, Th
is is
illus
trate
d in
two
way
s: fir
st. th
e m
odel
show
s a m
uch
shar
per t
rans
ition
in it
s cho
ices
of r
espo
nses
as w
e m
ove
from
Ig/ to
Ikl
07+
- g
II..
g 04
~ 03
5;!.
0 I
Xn"
-X.
.- -X
a- +
2 -X
..- +.
1'10
. 17,
The
sta
te o
f the
'/i'a
ce a
t var
ious
poi
nts
durin
g an
d af
ter t
he p
rese
ntat
ion
of a
sylla
hle
cuns
istil
fg (,
f the
mos
t IgI
-lik
e ot
the
2S in
term
edia
te se
gmen
ts us
ed in
the
tradi
ngrelations experiment. represented by
I'!(/.
preceded by silence and followed by
lal,
then
anot
her s
ilenc
e.
Resp
onse
pro
babi
litie
s wer
e co
mpu
ted
usin
g th
e fo
rmul
as g
iven
ear
lier
for c
onve
rting
act
ivat
ions
to re
spon
se st
reng
ths a
nd st
reng
ths i
nto
prob
-ab
ilitie
s, Th
e re
sulti
ng re
spon
se p
roba
bilit
ies,
for e
ach
of th
e 25
con
di-
tions
of t
he e
xper
imen
t, ar
e sh
own'
in F
ig, 1
8. T
he p
atte
rn o
f res
ults
isqu
ite si
mila
r to
that
obt
aine
d in
Den
es (1
955) experiment on the
1st-
cont
inuu
m. T
he c
ontri
butio
n of
eac
h cu
e is
app
roxi
mat
ely
linea
r and
addi
tive
in th
e m
iddl
e of
the
rang
e; b
ut th
e cu
rves
flat
ten
out a
t the
extre
mes
, as i
n th
e D
enes
(195
5) e
xper
imen
t. M
ore
impo
rtant
ly, t
he m
od-
el's
beh
avio
r exh
ibits
the
abili
ty to
trad
e on
e cu
e of
f aga
inst
anot
her.
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) th
e ne
utra
lva
lue
of th
e VO
T di
men
sion
cou
pled
with
the
mos
t Ik/
-like
val
ue o
n th
e1'
101'
dim
ensi
on: (
2) th
e ne
utra
l val
ue o
n th
e FI
OF
dim
ensi
on c
oupl
edw
ith th
e m
ost I
k/-li
ke v
alue
of t
he V
aT d
imen
sion;
and
(3) t
he so
mew
hat
...;' '- 060-
Yoke Olisel.Tirne
FI(L III, Simulated prob;lbility of choosing
Ik/ll
t Ti
me
Slic
e 1i
0, fo
r eac
h of
the
25 s
timul
ius
ed in
'he
tradi
ng re
latio
ns si
mul
atio
n ex
perim
ent.
Num
bers
nex
t to
each
cur
ve re
fer t
oth
e in
term
edia
te p
;llIe
rn o
n,th
e FI
OF
cont
inuu
m u
sed
in th
e fiv
e st
imul
i con
tribu
ting
toea
ch c
urve
, Uig
her n
umbe
rs c
orre
spon
d to
hig
her v
alue
s of
FIO
F.
:.., ::=
040
-
020
a.. 0,
0 I
3, 4
6
7 8
\I 10 II 12
Stim
ulus
Num
ber
FIG
. 20.
Effe
cts o
f com
petit
ion
on p
hone
me
activ
iltio
ns. T
he fi
rst p
anel
show
s rel
ativ
eamounts of bollom-up excitatory input to
Igl
and
IkJ
produced by each of the II sti
mul
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
Cycl
e 60
, Stim
uli 3
and
9 c
orre
spun
d 10
Ihe
cano
nica
l/gl a
ndIk
/, re
spec
tivel
y.
of th
e un
its fo
r /g/
and
/k/ a
t the
end
of 6
0 cy
cles
of p
roce
ssin
g. T
he sl
ight
diffe
renc
es 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 t
rans
ition
than
the
rela
tive
botto
m-u
p ex
-ci
tatio
n cu
rves
. Th
ere
are
two
reas
ons 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
prim
ary
reas
on is
competitive inhibition.
The
effe
ct o
f the
com
petit
ive
inhi
bitio
n at
the
pho-
nem
e le
vel i
s to
grea
tly 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 e
asy
to se
e w
hy th
is ha
ppen
s. O
nce
one
phon
eme
is sli
ghtly
mor
e str
ongl
y ac
tivat
ed th
an th
e ot
her.
it ex
erts
a st
rong
er in
hibi
tory
influ
ence
on
the
othe
r tha
n th
e ot
her c
an e
xert
onit.
The
net
resu
lt is
that
"th
e ric
h ge
t ric
her," This general property of
com
petit
ive
inhi
bitio
n m
echa
nism
s was
disc
usse
d by
McC
lella
nd a
nd R
u-m
elha
rt (1
981)
, fol
low
ing
earli
er o
bser
vatio
ns b
y G
ross
berg
(see
Gro
ss-
berg, 1978, f
or a
disc
ussio
n) a
nd L
evin
(197
6); i
t is a
lso w
ell k
now
n as
one
poss
ible
bas
is' o
f edg
e en
hanc
emen
t effe
cts i
n lo
w le
vels
of v
isual
TRAC
E M
OD
EL
alon
g th
e V
aT a
nd F
IOF
dim
ensio
ns th
an w
e w
ould
exp
ect f
rom
the
sligh
t cha
nges
in th
e re
lativ
e ex
cita
tion
of th
e /g
/ and
/kI u
nits.
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 t
he sa
me
phon
eme,
whi
le sh
arpe
ning
diff
eren
ces b
etw
een
inpu
ts as
signe
d to
diff
eren
t cat
egor
ies,
We
will
con
sider
eac
h of
thes
etw
o po
ints
in tu
rn, a
fter w
e de
scrib
ethe
stim
uli u
sed
in th
e simulations.
Elev
en d
iffer
ent c
onso
nant
feat
ure
patte
rns w
ere
used
, em
bedd
ed in
the
sam
e sim
ulat
ed /-
/ context as in the trading relations simulation,
The
stim
uli v
arie
d fro
m v
ery
low
val
ues
of b
oth
VaT
and FIOF, more
extre
me
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 on
the
VaT
and
FIO
F di
men
sion
s, T
he lo
catio
nsof
the
peak
act
ivat
ion
valu
es o
n ea
ch o
f the
se tw
o co
ntin
ua a
re sh
own
in F
ig, 1
9,
Figu
re 2
0 in
dica
tes
the
rela
tive
initi
al b
otto
m-u
p ac
tivat
ion
of th
e /g
/, a
nd /k
/ pho
nem
e un
its fo
r eac
h of
the
II stimuli used in the simulation.
The
first
thin
g 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
iffer
onl
y sli
ghtly
, For
exa
mpl
e, th
e ca
noni
cal f
eatl,
Jre
patte
rn fo
r /g/
send
s 75%
as m
uch
exci
tatio
n (0
/g/ a
s it s
ends
to /k
/, Th
efe
atur
e pa
ttern
two
step
s to
war
d/g/
from
/k/ (
Stim
ulus
5),
send
s 88%
as
muc
h ac
tivat
ion
to /g
/ as
to /k
/.Th
e fig
ure
also
indi
cate
s, in
the
seco
nd p
anel
, the
resu
lting
act
ivat
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
Voic
e O
nsel
Tim
e
/s//k
/1
2 3
4 5
6 7
8 9
1011
0 2 F
t Onsel Frequency
FtG
. t9.
Loc
atio
ns o
f pea
k ac
tivat
ions
alo
ng Ih
e V
aT a
nd F
tOF
dim
ensio
ns. l
or e
ach
ofth
e II
stim
uli u
sed
in th
e ca
tego
rical
per
cept
ion
simul
atio
n.
MC
CLE
LLAN
D A
ND
ELM
AN
/8/
/k/
...
1'2
Stim
ulus
Num
ber
/s//k
/
TRAC
E M
OD
EL:4
6M
C C
LELL
AND
AN
D E
LMAN
/81
Ikl
This
obvi
ously
brin
gs o
ut th
e fa
ct th
at th
e ap
pare
nt st
eepn
ess o
f 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 fac
tors
(Lan
e, 1
965)
, Whe
ther
an
empi
rical
or s
imul
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
perim
ente
r or m
odel
er, H
owev
er, i
t is w
orth
not
ing
that
the
steep
-ne
ss o
f the
iden
tific
atio
n fu
nctio
n is
inde
pend
ent o
f the
pre
senc
e of
tradi
ng re
latio
ns, a
t lea
st in
the
simul
atio
n m
odel
, Tha
t is,
if w
e ha
d us
edm
ore
wid
ely
sepa
rate
d ste
ps a
long
the
VO
T an
d FI
OF
dim
ensio
n, w
ew
ould
hav
e ob
tain
ed m
uch
steep
er id
entif
icat
ion funct1Qns. The additivity
of e
xcita
tory
inpu
ts w
ould
still
app
ly, a
nd th
us it
wou
ld st
ill b
e po
ssib
leto trade cues off against e~ch other,
In T
RACE
, the
cat
egor
ical
out
put o
f the
mod
el c
omes
abo
ut o
nly
afte
ran interactive competition process that greatly sharpens the differences
in the activation of the detectors for the relevant units, This interactive
proc
ess t
akes
tim
e. In
the
simul
atio
n re
sults
repo
rted
here
, we
assu
med
that
subj
ects
wai
ted
a fix
ed ti
me
befo
re re
spon
ding
. But
, if w
e as
sum
e, t
hat s
ubje
cts a
re a
ble
to re
spon
d as
soon
as t
he re
spon
se st
reng
th ra
tiore
ache
s som
e cr
iteria
lleve
l, w
e w
ould
find
that
subj
ects
wou
ld b
e ab
leto
resp
ond
mor
e qu
ickl
y to
stim
uli n
ear t
he p
roto
type
of e
ach
cate
gory
than
they
can
to s
timul
i nea
r the
bou
ndar
y, T
his
is ex
actly
wha
t was
foun
d by
Piso
~i a
nd T
ash
(197
4).
The
shar
peni
ng th
e m
odel
impo
ses o
n th
e id
entif
icat
ion
func
tion,
co
njun
ctio
n w
ith th
e fa
Ct th
at it
can
trad
e on
e fe
atur
e of
f aga
inst
anot
her,
show
s how
the
mod
el, l
ike
hum
an p
erce
iver
s of
spe
ech,
can
be
both
flexi
ble
and
deci
sive
at th
e sa
me
time,
The
se a
spec
ts of
TRA
CE a
resh
ared
with
the
feat
ure
inte
grat
ion
mod
el (M
assa
ro, 1
981)
,. How
ever
, the
TRA
CE m
odel
's de
cisiv
enes
s ext
ends
eve
.1 fu
rther
than
we
have
ob-
serv
ed th
us fa
r: fe
edba
ck fr
om th
e ph
onem
e to
the
feat
ure
leve
l ten
ds to
.ca
use
the
mod
el to
obl
itera
te th
e di
ffere
nces
bet
wee
n in
put f
eatu
re p
at-
tern
s tha
t 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 sha
rp id
entif
icat
ion
func
-tio
ns, b
ut a
lso
for t
he fa
ct th
at d
iscr
imin
abilit
y of
spee
ch so
unds
is fa
rpo
orer
with
in c
ateg
orie
s tha
n it
is be
twee
n ca
tego
ries.
Stric
tly s
peak
ing,
at l
east
as
defin
ed b
y Liberman, Cooper, Shank-
wei
ler,
and
Stud
dert-
Kenn
edy
(196
7), t
rue
cate
goric
al p
erce
ptio
n is
onl
yex
hibi
ted
whe
n th
e ab
ility
to d
iscrim
inat
e di
ffere
nt so
unds
is n
o be
tter
than
. cou
ld b
e ex
pect
ed 'b
ased
on
the
assu
mpt
ion
that
the
only
bas
is a
liste
ner h
as fo
r disc
rimin
atio
n is
the
cate
goric
al a
ssig
nmen
t of t
he st
im-
ulus
to a
par
ticul
ar p
hone
tic c
ateg
ory,
How
ever
, it i
s con
cede
d th
attru
e" c
ateg
oric
al p
erce
ptio
n in
this
sem
o: is
nev
er in
fact
obs
erve
d(S
tudd
ert-
Ken
nedy
, Lib
erm
an, H
arris
, & C
oope
r, 19
70),
Whi
le it
is tr
ueth
at th
e di
scrim
inat
ion
of so
unds
is m
uch
bette
r for
soun
ds w
hich
per
-
info
rmat
ion
proc
essin
g, A
seco
nd c
ause
of t
he sh
arpe
ning
of t
he a
ctiv
a-tio
n cu
rves
is th
e ph
onem
e-to
-feat
ure
feed
back
, whi
ch w
e co
nsid
er in
deta
il in
a m
omen
t. Th
e id
entif
icat
ion
func
tions
that
resu
lt fro
m a
pply
ing
the
Luce
cho
ice
rule
to th
e ac
tivat
ion
valu
es sh
own
in th
e se
cond
pan
el o
f Fig
, 20
are
show
n in
Fig
. 21 along with the
lBX
di
scrim
inat
ion
func
tion,
whi
ch is
disc
usse
d be
low
. The
iden
tific
atio
n fu
nctio
ns a
re e
ven
shar
per t
han
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
/ ins
tead
of /
g/ fo
r Stim
ulus
5, f
or w
hich
/k/ r
ecei
ves
88%
as
muc
hbo
ttom
-up
supp
ort a
s /g/
, The
in~r
ease
d sh
arpn
ess i
s due
to th
~ pr
oper
ties
of th
e re
spon
se s
treng
th a
ssum
ptio
ns. T
hese
ass
umpt
ions
ess
entia
lly im
-pl
emen
t the
not
ion
that
the
sens
itivi
ty o
f the
deci
sion
mec
hani
sm, i
nterms of
d'
for c
hoos
ing
the
mos
t stro
ngly
. act
ivat
ed o
f tw
o un
its, i
s alin
ear f
unct
ion
of th
e di
ffere
nce
in a
ctiv
atio
n of
the
two
units
, Whe
n th
eactivations are far enough apart,
d'
)Viii
be s
uffic
ient
to e
nsur
e ne
ar-lO
O%
corre
ct p
elfo
rman
ce, e
ven
thou
gh b
oth
units
hav
e gr
eate
r tha
n 0
activ
a-tio
n, O
f cou
rse,
the
.am
ount
of s
epar
atio
n in
the
activ
atio
ns th
at is
nec
-es
sary
for a
ny g
iven
leve
l of p
erfo
rman
ce is
a m
atte
r 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 thi
s par
amet
er in
the
pres
ent
sim
ulat
ions
(10)
was
the
sam
e as
that
use
d in
all
othe
r cas
es w
here
we
trans
late
act
ivat
ion
into
resp
onse
pro
babi
lity,
incl
udin
g th
e tra
ding
:rela
-tio
ns si
mul
atio
n.
Som
e re
ader
s may
be
puzz
led
as to
why
TRA
CE II
exh
ibits
a sh
arp
iden
tific
atio
n fu
nctio
n in
the
cate
goric
al p
erce
ptio
n ex
perim
ent,
but
show
s a
muc
h m
ore
grad
ual t
rans
ition
bet
wee
n /g
/ and
/k/ i
n th
e tra
ding
rela
tions
sim
ulat
ion,
The
reas
on is
sim
ply
that
fine
r ste
ps a
long
the
VO
Tan
d FI
OF
cont
inua
wer
e us
ed in
the
tradi
ng re
latio
ns si
mul
atio
n, A
ll of
the stimuli for the tl1ading relations s
imul
atio
n lie
bet
wee
n St
imul
i 6 a
nd4
in th
e ca
tego
rical
per
cept
ion
simul
atio
n.
~ 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
ABX
ta
sk.
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
ceiv
ers a
ssig
n to
diff
eren
t cat
egor
ies t
han
for s
ound
s the
y as
sign
to th
esa
me
cate
gory
, the
re is
als
o at
leas
t a te
nden
cy fo
r dis
crim
inat
ion
to b
eso
mew
hat b
ette
r tha
n pr
edic
ted
by th
e id
entif
icat
ion
func
tion,
eve
n be
-tw
een
stim
uli w
hich
are
alw
ays a
ssig
ned
to th
e. s
ame
cate
gory
. TRA
CEII
prod
uces
this
kind
of a
ppro
xim
ate
cate
goric
al p
erce
ptio
n.Th
e 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; as
they
bec
ome
activ
e, th
ey b
egin
to c
ompe
te, a
nd o
ne g
radu
ally
com
es to
dom
inat
e th
eot
hers
, Thi
s 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. Th
us, a
s a p
artic
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
stro
ng a
s tim
e go
es o
n, si
nce
the
feat
ure
inpu
t onl
y ex
cite
s th
e fe
atur
e un
its v
ery
brie
fly; t
he o
rigin
al p
at-
tern
of a
ctiv
atio
n pr
oduc
ed b
y th
e ph
onem
e un
its is
, the
refo
re, g
radu
ally
repl
aced
by
the
cano
nica
l pat
tern
impo
sed
by th
e fe
edba
ck fr
om th
e ph
o-" n
eme
leve
l, Th
e re
sult
is th
a~ th
e pa
ttern
of a
ctiv
atio
n re
mai
ning
at t
hefe
atur
e le
vel a
fter 6
0 cy
cles
of p
roce
ssin
g ha
s bec
ome
assim
ilate
d to
the
prot
otyp
e, In
this
way
, fea
ture
pat
tern
s for
diff
eren
t inp
uts a
ssig
ned
toth
e sa
me
cate
gory
are
rend
ered
nea
rly in
dist
ingu
isha
ble,
An
impr
essio
n of
the
mag
nitu
de o
f thi
s effe
ct is
illu
strat
ed in
Fig
, 22,
whi
ch sh
ows h
ow d
iffer
ent t
he fe
atur
e pa
ttern
s of a
djac
ent s
timul
i are
at
the
end
of 6
0 cy
cles
of p
roce
ssin
g. T
he m
easu
re o
f diff
eren
ce is
sim
ply
I -
"b'
whe
re
"b
stand
s for
the
corre
latio
n of
the
patte
rns p
rodu
ced
bysti
mul
i an
d b,
O
nly
the
two
dim
ensio
ns w
hich
act
ually
diff
er b
etw
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
rrela
tion
cons
ider
s onl
y th
e fe
atur
e pa
ttern
on
the
feat
ure
units
in T
ime
Slic
e 12
, rig
ht a
t the
cen
ter o
f the
inpu
t spe
cific
atio
n. If
all
dim
ensio
ns a
re c
onsid
ered
, the
val
ues o
f the
diff
eren
ce m
easu
re a
re re
-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.To
rela
te th
e di
ffere
nce
betw
een
two
stim
uli ~
o pr
obab
ility
corre
ctchoice performance in the
ABX
ta
sk g
ener
ally
use
d in
cat
egor
ical
per
-ce
ptio
n ex
perim
ents
, we
once
aga
in u
se th
e Lu
ce (1
959)
choice model.
The
prob
abilit
y of
iden
tifyi
ng sti
mul
us
with alternative
in is given
by Ix
=,,)
II.(
whe
re S
ax is the "st
reng
th" o
f the
sim
ilarit
y between (/ and
x.
This
isgiven 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 re
quire
d to
tran
s-la
te c
orre
latio
ns, r
angi
ng fr
om +
Ito
- I, i
nto
posit
ive
valu
es, s
o th
atLu
ces
ratio
rule
can
be
used
. The
sam
e tra
nsfo
rmat
ion
is u
sed
for t
rans
-la
ting
activ
atio
ns in
to re
spon
se st
reng
ths i
n id
entif
icat
ion
task
s.) Here
is th
e pa
ram
eter
that
scal
es th
e re
latio
n be
twee
n co
rrela
tions
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 ide
ntifi
catio
n re
spon
ses,
The
resu
lting
resp
onse
pro
babi
litie
s,for one choice of the parameter
,.
(5) a
re sh
own
in F
ig; 2
1 (th
e ex
pone
n-tiation parameter
,.
is different than the parameter
used
in g
ener
atin
gid
entif
icat
ion
prob
abili
ties f
rom
act
ivat
ions
bec
ause
cor
rela
tions
and
ac-
tivations are not on equivalent scales),
Basic
ally
, the
figu
re sh
ows t
hat t
he e
ffect
of f
eedb
ack
is to
mak
e th
efe
atur
e pa
ttern
s for
inpu
ts w
ell w
ithin
eac
h ca
tego
ry m
ore
simila
r tha
nth
ose
for i
nput
s nea
r the
bou
ndar
y be
t~ee
n categories. Differences be-
twee
n sti
mul
i nea
r the
pro
toty
pe o
f the
' sam
e ph
onem
e ar
e al
mos
t obl
i-te
rate
d. W
hen
two
stim
uli s
tradd
le 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
rimin
atin
g sti
mul
i with
in a
pho
nem
e ca
tego
ry is
muc
h lo
wer
Ihan
Ihe
prob
abili
ty o
f disc
rimin
atin
g sti
mul
i in
diffe
rent
cat
egor
ies.
The
proc
ess o
f "ca
noni
caliz
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 lim
e, 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
rives
the
repr
esen
tatio
n to
war
d th
e pr
otot
ype,
is b
uild
ing
up. I
n th
e sim
ulat
ions
,w
e al
low
ed a
con
sider
able
am
ount
of t
ime
for t
hese
pro
cess
es b
efor
e
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/-ik
i co
ntin
uum
use
d fo
r pro
duci
ng th
e id
entif
i-ca
tion
func
tions
show
n pr
evio
usly
in F
ig. 2
1. T
he d
iffer
ence
mea
sure
is th
e co
rrela
tion
ofth
e tw
o pa
ttern
s, su
btra
cted
from
1.0
; thu
s, if
the
two
patte
rns c
orre
late
d pe
rfect
ly, t
heir
difference would be O.
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
L~ '
com
putin
g sim
ilarit
ies o
f diff
eren
t act
ivat
ion
patte
rns t
o ea
ch o
ther
, Ob-
viou
sly. i
f we
had
left
less
tim
e. th
ere
wou
ld n
ot h
ave
been
as m
uch
ofan
opp
ortu
nity
for t
hese
forc
es to
ope
rate
. Thu
s, TR
ACE
is in
agr
eem
ent
with 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
rre
spon
ses o
n ju
dgm
~nts
of th
e sim
ilarit
y of
stim
uli s
pace
d cl
osel
y to
-ge
ther
in ti
me
(Piso
nl&
Laz
arus
, 197
4).
It sh
ould
be
note
d th
at it
wou
ld b
e po
ssib
le to
acc
ount
for c
ateg
oric
alpe
rcep
tion
in T
RACE
with
out i
nvok
ing
feed
back
from
the
phon
eme
leve
lto
the
feat
ure
leve
l, A
ll w
e w
ould
nee
d to
~o
is as
sum
e th
at th
e fe
atur
ein
form
atio
n th
at g
ives
rise
to p
hone
me
iden
tific
atio
n is
inac
cess
ible
, as
. pro
pose
d by
the
mot
or th
eory
of s
peec
h pe
rcep
tion
(Lib
erm
an e
t ai"
1967
). or
is ra
pidl
y lo
st a
s pr
opos
ed b
y th
e "d
ual-c
ode"
mod
el (F
ujisa
ki&
Kaw
ashi
ma,
196
8; M
assa
ro. 1
975, 1981; Pisoni, 1973, 1975,) T
he d
ual-
code
mod
el, w
hich
has
had
con
sider
able
succ
ess a
ccou
ntin
g fo
r cat
egor
-ic
al p
erce
ptio
n da
ta, a
ssum
es th
at p
hone
me
iden
tific
atio
n ca
n be
bas
edei
ther
on
prec
ateg
oric
al in
form
atio
n or
on
the
resu
lts o
f the
pho
nem
eid
entif
icat
ion
proc
ess,
Sinc
e it
is as
sum
ed th
at fe
atur
e in
form
atio
n de
cays
rapi
dly
(esp
ecia
lly fo
r con
sona
nt fe
atur
es-s
ee b
elow
), re
spon
ses
mus
tof
ten
be b
ased
sole
ly o
n th
e ou
tput
of t
he p
hone
me
iden
tific
atio
n pr
oces
s,w
hich
is a
ssum
ed to
"rov
ide
a di
scre
te c
ode
ofth
e se
quen
ce o
f pho
nem
es.
This
inte
rpre
tatio
n ac
coun
ts fo
r muc
h of
the
data
on
cate
goric
al p
erce
p-tio
n qu
ite w
ell.
Inde
ed, i
t is
fairl
y di
fficu
lt to
find
way
s of d
istin
guish
ing
betw
een
a fe
edba
ck f!
1ode
l and
one
that
attr
ibut
es c
ateg
oric
al p
erC
eptio
nto
a lo
ss o
f inf
orm
atio
n fro
m th
e fe
atur
e le
vel c
oupl
ed w
ith a
relia
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 sho
w le
ss o
f a te
nden
cy to
war
d ca
t-eg
oric
al p
erce
ptio
n th
an c
onso
nant
s (Fr
y, A
bram
son,
Eim
as, &
Lib
-er
man
, 196
2; P
ison
i, 19
73).
It is
sim
ply
nece
ssar
y to
ass
ume
that
vow
elfe
atur
es a
re m
ore
pers
isten
t tha
n co
nson
ant f
eatu
res (
Crow
der,
1978
,19
81; F
ujisa
ki &
Kaw
ashi
ma,
196
8; P
isoni
, 197
3, 1
975)
, How
ever
, the
two
clas
ses o
f int
erpr
teta
tions
do
diffe
r in
one
way
, The
feed
back
acc
ount
seem
s to
diffe
r mos
t cle
arly
from
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
cat
egor
y, b
ut st
ill w
ithin
it H
ere,
TRA
CE te
nds t
o sh
owgr
eate
r disc
rimin
atio
n th
an it
show
s bet
wee
n sti
mul
i squ
arel
y in
the
mid
dle
of a
cat
egor
y,
Stan
dard
inte
rpre
tatio
ns o
f cat
egor
ical
per
cept
ion
can
acco
unt f
or in
-cr
ease
s in
~lo
;crim
inab
ility
near
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
RAC
E ca
n ac
coun
t 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. In
TRA
CE, t
he re
ason
for t
his i
ncre
ase
in d
iscrim
-in
abilit
y is
that
the
activ
atio
n of
the
appr
opria
te it
em a
t the
pho
nem
ele
vel i
s ,w
eake
r, an
d th
eref
ore
the
feed
back
sign
al is
wea
ker,
than
it is
whe
n th
e in
put o
ccur
s nea
r the
cen
ter o
f the
category. For example,
Stim
ulus
I in
our
sim
ulat
ions
falls
bel
ow th
e ca
noni
cal/g
/ stim
ulus
, and
ther
efor
e ac
tivat
es th
e Ig
/ pho
nem
e de
tect
or le
ss s
trong
ly th
an s
timul
icloser to the canonical
Ig/,
A similar thing happens with the
Ik/.
This
resu
lts in
less
"ca
noni
caliz
atio
n" o
f the
ext
rem
e sti
mul
i, an
d pr
oduc
es a
-sha
ped
disc
rimin
atio
n fu
nctio
n, a
s sho
wn
in F
ig. 2
2,Th
ere
is so
me
evid
ence
bea
ring
on th
is as
pect
of T
RACE
's a
ccou
nt o
fca
tego
rical
per
cept
ion,
Sam
uel (
1977) has reported
ABX
di
scrim
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 co
ntin
uum
, Ind
eed,
Sam
uel's
acc
ount
of t
his e
ffect
, tho
ugh
not c
ouch
ed in
term
s of i
nter
ac-
tive
activ
atio
n pr
oces
ses,
has a
gre
at d
eal o
f sim
ilarit
y to
wha
t we
see
inTR
ACE
; he
sugg
ests
that
nea
r-can
onic
al it
ems a
re m
ore
stron
gly
assim
-ila
ted
to th
e ca
noni
cal p
atte
rn, U
nfor
tuna
tely
the
effe
ct w
e se
ek is
fairl
ysu
btle
, and
so it
will
be
diffi
cult
to se
para
te fr
om n
oise
. In
Sam
uel'
expe
rimen
t., th
e ef
fect
is fa
irly
clea
r-cut
at b
oth
extre
mes
of t
he V
OT
cont
inuu
m in
thre
e ob
serv
ers a
t the
end
of e
xten
sive
train
ing,
as s
how
nin
Fig
, 23,
and
eve
n un
prac
ticed
subj
ects
tend
to sh
ow th
e ef
fect
tow
ard
the high end of the VOT continuum, well past the prototype for
It/.
In su
mm
ary,
TRA
CE a
ppea
rs to
pro
vide
a fa
irly
accu
rate
acc
ount
of
the
phen
omen
a of
cue
trad
e-of
fs a
nd c
ateg
oric
al p
erce
ptio
n of
spee
chso
unds
, It a
ccou
nts
for c
ateg
oric
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
strac
t lev
el o
fpr
oces
sing;
it a
ssum
es in
stead
that
the
feat
ure
leve
l, lik
e ot
her l
evel
s of
the
syste
m, i
s sub
ject
to fe
edba
ck fr
om h
ighe
r lev
els
whi
ch a
ctua
llych
ange
s the
repr
esen
tatio
n as
it is
bei
ng re
tain
ed in
mem
ory,
pus
hing
to
war
d a
cano
nica
l rep
rese
ntat
ion
of th
e ph
onem
e m
ost s
trong
ly a
ctiv
ated
by th
e in
put.
Oth
er P
heno
men
a at
the
Phon
eme
Leve
lTh
e lit
erat
ure
on p
hone
me
perc
eptio
n in
clud
es s
ever
al fu
rther
find
ings
we
have
not
yet
bee
n ab
le to
con
side
r in
deta
il. T
he n
ext f
ew. p
arag
raph
sco
nsid
er o
ne o
f the
se 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
ursim
ulat
ions
of t
radi
ng re
latio
ns, w
e ha
ve sh
own
that
the
crite
rial v
alue
need
ed o
n on
e di
men
sion
of st
imul
us v
aria
tion
can
be a
ffect
ed b
y ot
~er
dim
ensio
ns. T
hus,
whe
n th
e on
set o
f FI i
s rel
ativ
ely
high
, sho
rter v
oici
ngla
tenc
ies a
re n
eede
d to
per
ceiv
e a
soun
d as
unv
oice
d, O
ther
fact
ors a
lsoin
nuen
ce th
e ph
onem
e pe
rcei
ved
as a
resu
lt of
a p
artic
ular
feat
ural
inpu
t.
TRAC
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 MCB
0102
0504
0501
0101
0
'"'
MC
CLE
LLAN
D A
ND
ELM
AN
CONTROL GROUP
spea
ker p
aram
eter
s, O
ur m
ain
poin
t her
e is
that
con
nect
ion
mod
ulat
ion
is q
uite
a d
iffer
ent m
echa
nism
than
the
sim
ple
addi
tive
,com
bina
tion
ofex
cita
tory
influ
ence
s th
at u
nder
lies
the
way
TR
ACE
acco
O'nt
s for trade-
offs
am
ong
the
cues
to a
sin
gle
phon
eme
or fo
r the
effe
cts o
f top
-dow
nin
fluen
ces o
n th
e ph
onem
e bo
unda
ry,
Sum
mar
y of
Pho
nem
e Id
entif
icat
ion
Sim
ulat
iolls
We
have
con
sider
ed a
num
ber o
f 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, bo
th in
reac
tion
time
and
in re
spon
se c
hoic
e m
easu
res;
"pho
nota
ctic
rule" effects on ph
onem
eid
entif
icat
ion
and
the
role
of s
peci
fic le
xica
l ite
ms i
n in
fluen
cing
thes
eef
fect
s; th
e in
tegr
atio
n of
mul
tiple
cue
s to
phon
eme
iden
tity
and
the
cat-
egor
ical
nat
ure
of th
e pe
rcep
t tha
t res
ults
from
this
inte
grat
ion.
TR
ACE
inte
grat
es a
ll of
thes
e ph
enom
ena
into
a si
ngle
acc
ount
that
inco
rpor
ates
aspe
cts o
f the
acc
ount
s offe
red
for p
artic
ular
asp
ects
of th
ese
resu
lts b
yot
her m
odel
s, In
the
next
sec
tion,
we
show
how
TR
ACE
can
also en-
com
pass
a n
umbe
r of p
heno
men
a co
ncer
ning
the
reco
gniti
on o
f spo
ken
wor
ds,
. ,""
." \
. CGI
/ "
, ,..' "
. .. "
CG2
CG3
0 10 20 50 40 50 IiO
10
.0
THE
TIM
E C
OU
RSE
OF
WO
RD
REC
OG
NIT
ION
The
study
of s
poke
n w
ord
reco
gniti
on h
as a
long
his
tory
, and
man
ym
odel
s ha
ve b
een
prop
osed
, Mor
ton
s no
w-c
lass
ic lo
goge
n m
odel
(Mor
ton,
196
9) w
as th
e fir
st to
pro
vide
an
expl
icit
acco
unt o
f the
inte
-gr
atio
n of
con
text
ual a
nd se
nsor
y in
form
atio
n in
wor
d re
cogn
ition
. Oth
erm
odel
s of t
his p
erio
d (e
,g.,
Broa
dben
t, 1967) concentrated primarily on
effe
cts o
f wor
d fre
quen
cy, 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.
Seve
ral s
tudi
es b
y M
arsl
en-W
ilson
and
his
col
labo
rato
rs (M
arsl
en-
Wilson, 1973; Marslen-W
ilson
& T
yler
, 1975) and by Cole and hiscollab-
orat
ors (
Cole
, 197
3; C
ole
& Ja
kim
ik, 1
978, 1980) pioneered the in
vesti
-ga
tion
of th
is p
robl
em,
Mar
slen-
Wils
ons
CO
HO
RT
mod
el (M
arsl
en~W
ilson
& T
yler
, 198
0;M
!irsle
n-W
ilson
& W
elsh
, 197
8) o
f spe
ech
perc
eptio
n w
as b
ased
on
this
early
wor
k on
the
time
cour
se o
f spo
ken
wor
d re
cogn
ition
. The
CO
HO
RTm
odel
was
one
of t
he so
urce
s of i
nspi
ratio
n fo
r TRA
CE, f
or tw
o m
ain
reas
ons"
Firs
t, it
prov
ided
an
expl
icit
acco
unt o
f 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 re
al ti
me.
Sec
ond,
it a
ccou
nted
for
the
findi
ngs
of a
num
ber o
f im
porta
nt 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-fic
ienc
ies o
f the
CO
HO
RT m
odel
hav
e be
en p
oint
ed o
ut, a
s we
shal
l see
,Be
caus
e TR
ACE
was
mot
ivat
ed in
larg
e pa
rt by
a d
esire
to k
eep
wha
tis
good
abo
ut C
OH
ORT
and
impr
ove
upon
its w
eakn
esse
s, w
e be
gin
this
VO
ICE
ON
SET
TIM
E (m
ile)
FIG, 23. Identification (solid curves) and
ABX
di
scrim
inat
ion
data
(das
hed
curv
es) f
rom
Ihre
e pr
actic
ed a
nd th
ree
naiv
e su
bjec
ts. S
impl
ified
and
repr
inte
d, w
ith p
erm
issi
on, f
rom
Sam
uel( 1
977)
. Th
e id
entit
y of
pho
nem
es su
rroun
ding
a ta
rget
pho
nem
e, th
e ra
te o
fsp
eech
of a
, syl
labl
e in
whi
ch a
par
ticul
ar fe
atur
e va
lue
occu
rs, a
s w
ell a
sch
arac
teris
tics o
f the
spea
ker a
nd th
e la
ngua
ge b
eing
spok
en a
ll in
fluen
ceth
e in
terp
reta
tions
of f
eatu
res.
See
Repp
and
Lib
erm
an (1
984) for a dis-
cuss
ion
of a
ll of
thes
e so
rts o
f inf
luen
ces o
n th
e boundaries between
phon
emes
, It
has b
een
sugg
este
d by
Mill
er, G
reen
, and
Sch
erm
er (1
984)
and
by
Rep
p an
d Li
berm
an (1
984)
that
thes
e di
ffere
nt e
ffect
s m
ay h
ave
diffe
rent
sour
ces,
In p
artic
ular
, Mill
er e
t al.
(198
4) su
gges
t tha
t lex
ical
effe
cts 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
influ
ence
s suc
h as
spee
ch ra
te a
nd c
oarti
cula
tory
influ
ence
s due
to lo
cal p
hone
tic c
onte
xt.
The
assu
mpt
ions
we
have
inco
rpor
ated
into
TRA
CE m
ake
a si
mila
rdi
stinc
tion,
In T
RACE
I, w
e ha
ve a
ccou
nted
for e
ffect
s of p
hone
tic c
on-
text
by
allo
win
g ac
tivat
ions
of u
nits
to in
fluen
ce th
e fe
atur
e-to
- pho
nem
eco
nnec
tions
in a
djac
ent t
ime
slice
s (se
e El
man
& M
cCle
lland
, in
pres
s,fo
r det
ails)
. In
the
disc
ussio
n,w
e ' c
onsid
er w
ays o
f ext
endi
ng th
e co
n-ne
ctio
n m
odul
atio
n id
ea to
acc
omm
odat
e ef
fect
s of v
aria
tions
in ra
te a
nd
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
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 a
ssum
ptio
ns o
f the
mod
el, t
hen
cons
ider
its s
treng
ths a
ndw
eakn
esse
s. T
here
app
ear t
o be
four
bas
ic a
ssum
ptio
ns o
f the
CO
HO
RT
mod
el.
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-
plus
-vow
el) o
f the
wor
d to
det
erm
ine
whi
chw
ords
will
be
in a
n in
itial
coh
ort o
r can
dida
te se
t,2.
Onc
e th
e ca
ndid
ate
set i
s est
ablis
hed,
the
mod
el e
limin
ates
wor
dsfro
m th
e co
hort
imm
edia
tely
, as"
each
succ
essiv
e ph
onem
e ar
rives
, if t
hene
w p
hone
me
fails
to m
atch
the
next
pho
nem
e in
the
wor
d, W
ords
can
also
be
elim
inat
ed o
n th
e ba
sis o
f sem
antic
con
strai
nts,
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
redu
ced
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
soon
as t
here
are
no re
mai
ning
mem
bers
in th
e co
hort,
4. W
ord
reco
gniti
on c
an in
fluen
ce th
e id
entif
icat
ion
of ph
onem
es in
aw
ord
only
afte
r the
wor
d ha
s bee
n re
cogn
ized
,Th
ere
is a
cons
ide~
able
bod
y of
dat
a th
at su
ppor
ts va
rious
pre
dict
ions
of th
e CO
HO
RT m
odel
, It h
as b
een
obse
rved
in a
var
iety
of pa
radi
gms
thai
lexi
cal i
nflu
ence
s on
phon
eme
iden
tific
atio
n re
spon
ses a
re m
uch
grea
ler l
aler
in w
ords
than
at t
heir
begi
nnin
gs (B
agle
y, 1
900;
Col
e an
dJakimik, 1978, 1980; Marslen-Wilson, 1980; Marslen-Wilson and Welsh,
1978
). W
e co
nsid
ered
som
e of
this
evid
ence
in ea
rlier section~.. A
noth
er
impo
rtant
find
ing
suJi)
porti
ng C
OH
ORT
is th
e fa
ct th
at th
e re
attio
n tim
eto
dec
ide
that
an
item
is a
non
wor
d is
cons
tant
, whe
n m
easu
red
from
the
occu
rrenc
e of
the
first
pho
nem
e th
at ru
les
out t
he la
st re
mai
ning
wor
d in
the
coho
rt (M
arsl
en-W
ilson
, 198
0),
Perh
aps t
he m
ost d
irect
supp
ort f
or th
e ba
sic w
ord
reco
gniti
on a
s-su
mpt
ions
of C
OH
ORT
com
es fr
om th
e ga
ting
para
digm
, int
rodu
ced
first
by G
rosje
an (1
980)
, In
this
para
digm
, sub
ject
s are
requ
ired
to g
uess
the
iden
t it y
of a
wor
d af
ter h
earin
g su
cces
sive
pres
enta
tions
of t
he w
ord,
The
first
pre
sent
atio
n is
cut
ofT
so that the subject hears only the first
(N
= 30
to 5
0 in
diff
eren
t stu
dies
). La
ter p
rese
ntat
ions
are
succ
essiv
ely
leng
then
ed in
N-m
s inc
rem
ents
until
eve
ntua
lly th
e w
hole
wor
d is
pre-
sent
ed. T
he d
urat
ion
at w
hich
hal
fthe
subj
ects
corre
ctly
iden
tify
the
wor
dis
calle
d th
e "i
sola
tiQn
poin
t. " C
onsi
dera
bly
mor
e in
put i
s re
quire
d be
fore
subjects 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 ini
tial s
tudy
con
firm
ed m
any
basic
pre
dict
ions
of C
OH
ORT
, tho
ugh
it al
so ra
ised
a fe
w d
iffic
ultie
s for
it (s
ee b
elow
). In
a m
ore
rece
nt st
udy
usin
g th
e sa
me
met
hod,
Tyl
er an
dW
esse
ls (1
983)
car
ried
out a
ver
y cl
ose
anal
ysis
of th
e re
latio
n be
twee
nth
e em
piric
ally
det
erm
ined
isol
atio
n po
int a
nd th
e po
int a
t whi
ch th
e in
put
the
subj
ect h
as re
ceiv
ed is
con
sist
ent w
ith o
ne a
nd o
nly
one
rem
aini
ngite
m, t
he p
oint
at w
hich
reco
gniti
on 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
reco
gniti
on p
oint
, stro
ngly
supp
ortin
g th
e ba
sicimmediacy assumptions of the COHORT model,
It sh
ould
be
note
d th
at th
e ga
ting
task
is n
ot a
tim
ed ta
sk, a
nd so
itdo
es n
ot. p
rovi
de a
dire
ct me
asure of what the su
bjec
t kno
ws a
s the
spee
ch in
put i
s unf
oldi
ng, H
owev
er, i
t is n
ow in
fairl
y w
ide
use,
and
Cotton and Grosjean (1984) have established that the basic patterns of
resu
lts o
btai
ned
in G
rosje
ans (
1980
) pio
neer
ing
gatin
g ex
perim
ent d
o no
tde
pend
on
the
pres
enta
tion
of s
ucce
ssiv
ely
long
er a
nd lo
nger
pres
enta
-
tions
of t
he sa
me
stim
ulus
.A dilemma for COHORT,
Thou
gh th
e CO
HO
RT m
odel
acc
ount
s for
ala
rge
body
of d
ata,
ther
e ar
e se
vera
l diff
icul
t:"s w
ith it
. We
cons
ider
firs
tth
e on
e th
at se
ems t
he m
ost s
erio
us: a
s st
ated
, CO
HO
RT
requ
ires
ac-
cura
te, u
ndist
orte
d 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
nun
less
the
initi
al c
onso
nant
clu
ster p
lus v
owel
is h
eard
. and
they
ar~
discarded from it as soon as a ph
onem
e co
mes
alo
ng th
at th
ey fa
il to
mat
ch. N
o ex
plic
it pr
oced
ure
is de
scrib
ed fo
r rec
over
ing
wor
ds in
to th
eco
hort
once
they
hav
e be
en e
xclu
ded
from
it, o
r whe
n th
e beginning of
the
wor
d is
not
acc
urat
ely
perc
eive
d du
e to
noi
se o
r elis
ion,
Thes
e as
pect
s of C
OH
ORT
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 hav
e be
en re
plac
edby
noi
se (S
aJas
so &
Piso
ni, 1
985)
. Fro
m a
com
puta
tiona
l poi
nt o
f vie
w,
this
mak
es th
e m
odel
an
extre
mel
y br
ittle
one
; in
parti
cula
r it f
ails
to d
eal
with
the
prob
lem
of n
oise
and
und
ersp
ecifi
catio
n w
hich
is so
cru
cial
for
reco
gniti
on o
f rea
l spe
ech
(Tho
mps
on. 19
84),
The
reco
gniz
abili
ty o
f dist
orte
d ite
ms l
ike
"dwib
ble"
might be taken
as su
gges
ting
that
wha
t we
need
to d
o is
liber
aliz
e th
e cr
iterio
n fo
r en-
terin
g an
d re
tain
ing
wor
ds in
the
coho
rt. T
hus,
the
coho
rt co
uld
be d
e-fin
ed a
s th
e se
t of w
ords
con
sist
ent w
ith w
hat h
as b
een
hear
d or
mild
(e,g" one or two fe
atur
es) d
evia
tions
from
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. It
wou
ld a
lso a
llow
the
mod
el to
cop
e w
ith c
ases
whe
re th
e be
ginn
ing
of th
e w
ord
is un
ders
peci
fied;
in- t
hese
cas
es. t
hein
itial
coh
ort w
ould
sim
ply
be la
rger
than
in th
e ca
se w
here
the
inpu
tde
arly
spec
ified
the
initi
al p
hone
mes
.H
owev
er. t
here
is st
ill a
pro
blem
. Som
etim
es w
e ne
ed to
be
able
toru
le o
ut it
ems w
hich
mism
atch
the
inpu
t on
one
or tw
o di
men
sion
s an
dso
met
imes
we
do n
ot. C
onsid
er th
e ite
ms "
plea
sant" and "
blac
elet
." In
the
first
case
. we
need
to ex
clude "
pres
ent" from the cohort, so the
TRAC
E M
OD
ELMC CLELLAND AND ELMAN
sligh
t diff
eren
ce b
etw
een
III a
nd Ir
l mus
t be
suffi
cien
t to
rule
it o
ut; i
n th
ese
cond
cas
e, w
e do
not
wan
t to
lose
the
wor
d " b
race
let, "
sinc
e it
pro-
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 ru
le a
wor
d ca
ndid
ate
out.
Thus
the
dile
mm
a: o
n th
e on
e ha
nd, w
e w
ant a
mec
hani
sm th
at w
ill be
able
to s
elec
t the
cor
rect
wor
das
soo
n as
an
undi
stor
ted
inpu
t spe
cifie
sit
uniq
uely
, to
acco
unt f
or th
e Ty
ler a
nd W
esse
ls re
sults
. On
the
othe
rha
nd, w
e do
not
wan
t the
mod
el to
com
plet
ely
elim
inat
e po
ssib
ilitie
sw
hich
mig
ht la
ter t
urn
out t
o . b
e co
rrect
, We
shal
l sho
rtly
see
that
TR
ACE
prov
ides
... w
ay o
ut o
f thi
s dile
mm
a.
Another problem for COHORT.
Gro
sjean
(198
5) h
as re
cent
ly p
oint
edou
t ano
ther
pro
blem
for C
OH
ORT
, nam
ely,
the
poss
ibili
ty th
at th
e su
b-je
ct m
ay b
e un
certa
in a
bout
the 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 not
alw
ays p
ossib
le to
kno
w in
adv
ance
whe
re o
new
ord
star
ts a
nd th
e ne
xt w
ord
ends
. As
we
disc
usse
d in
the
intro
duct
ion,
acou
stic
cue
s to
junc
ture
are
not
alw
ays
relia
ble,
' and
in th
e ab
senc
e of
acou
stic
cues
, eve
n an
opt
imal
ly e
ffici
ent m
echa
nism
~an
not a
lway
s, know th
at it
has
hea
rd th
e en
d of
one
wor
d un
til it
hea
rs en
ough
of t
hene
xt to
rule
out
the
poss
ible
con
tinua
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 CO
HO
RT'
succ
esse
s, an
d ov
erco
me
thes
e tw
o im
porta
nt d
efic
ienc
ies,
The
next
two
sect
ions
show
that
TRA
CE d
oes q
uite
wel
l on
both
cou
nts.
The
first
ofth
ese
sect
ions
exa
min
es T
RACE
' s b
ehav
ior i
n pr
oces
sing
wor
ds w
hose
begi
nnin
gs a
nd e
ndin
gs a
re c
lear
ly d
elin
iate
d fo
r it b
y th
e pr
esen
ce o
fsil
ence
, The
seco
nd c
onsid
ers t
he p
roce
ssin
g 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 se
ctio
n w
e se
e ho
w T
RACE
reso
lves
the
dile
mm
a fa
cing
CO
-H
ORT
, in
that
it is
imm
edia
tely
sens
itive
to n
ew in
form
atio
n bu
t is
still
able
to c
ope
with
und
ersp
ecifi
ed o
r dist
orte
d w
ord
begi
nnin
gs, W
e al
soco
nsid
er h
ow th
e m
odel
acc
ount
s for
the
pref
eren
ce fo
r sho
rt-w
ord
re-
spon
ses e
arly
in p
roce
ssin
g a
long
wor
d, T
he se
ctio
n co
nclu
des w
ith a
disc
ussio
n of
way
s the
mod
el c
ould
be
exte
nded
to a
ccou
nt fo
r wor
dfre
quen
cy a
nd c
onte
xtua
l inf
luen
ces,
Com
petit
ion
~'S
bottom-lip inhibition.
TRA
CE d
eals
with
CO
HO
Rrs
dile
mm
a by
usin
g co
mpe
titio
n. ra
ther
than
pho
nem
e-to
-wor
d in
hibi
tion.
The
esse
nce
of 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
Trac
e , it
send
s.
exci
tatio
n to
all
the
wor
d un
its c
onsis
tent
with
that
pho
nem
e in
that
slic
e.Th
e w
ord
units
then
com
pete
with
eac
h ot
her;
item
s tha
t con
tain
eac
hsu
cces
sive
phon
eme
dom
inat
e al
l oth
ers,
but i
f no
wor
d "m
atch
es p
er-
fect
ly, a
wor
d th
at p
rovi
des a
clo
se ti
t to
the phoneme sequence can
even
taul
ly w
in o
ut o
ver w
ords
that
pro
vide
less
ade
quat
e m
atch
es. T
heex
act m
etric
of "
clos
enes
s of f
it " d
epen
ds. o
f cou
rse.
on
a la
rge
num
ber
of d
etai
ls, In
the
abse
nce
of su
ch a
met
ric, a
sim
ple
coun
t of t
he n
umbe
rof
aco
ustic
feat
ures
diff
erin
g be
twee
n a
lexi
cal i
tem
. and
a p
rese
nted
stim
-ul
us c
an p
rovi
de a
use
ful f
irst a
ppro
xim
atio
n. b
ut o
ther
fact
ors s
uch
asst
ress
, loc
atio
n of
diff
eren
ces
with
in th
e w
ord,
and
dis
crim
inab
ility
of th
edi
fferin
g fe
atur
e~. w
ill of
cou
rse
com
e into play.
Cons
ider
, fro
m th
is po
int o
f vie
w, o
ur tw
o ite
ms "
plea
sant
" and
"bl
ace-
let"
aga
in, I
n th
e fir
st in
stanc
e. "
plea
sant
" will
rece
ive
mor
e bo
ttom
-up
exci
tatio
n th
an "
pres
ent,"
and so w
ill w
in o
ut in
the
com
petit
ion.
We
have
alre
ady
seen
, in
our a
naly
sis
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 th
e jo
int e
ffect
s of c
ompe
titio
n an
d fe
edba
ck. B
ut th
ere
al b
eaut
y of
the
com
petit
ion
mec
hani
sm is
that
this
actio
n is
cont
inge
nton
the
activ
atio
n of
oth
er w
ord
cand
idat
es, T
hus,
in th
e ca
se o
f "bl
ace-
let"
, sin
ce th
ere
is no
wor
d "b
lace
let
" "
brac
el~t
" will
not
be
SlIp
-pr
esse
d, In
itial
ly, i
t is t
rue,
wor
ds li
ke "
blam
e " and "
blat
ant"
will tend
t~ d
omin
ate
"bra
cele
t," but since the input matches "
brac
elet
" bet
ter
than
any
oth
er w
ord,
"br
acel
et" wjll eventually co
me
to d
omin
ate
the
other possibilities,
This
beha
vior
of t
he m
odel
is . i
llustr
ated
usin
g ~x
ampl
es fr
om it
s re-
stric
ted
lexi
con
in F
ig. 2
4. In
one
cas
e. th
e in
put i
s "le
gal,"
and
the
wor
dre
gal"
is c
ompl
etel
y do
min
ated
by
"leg
al."
In the other case. the input
is "l
ugge
d," a
nd th
e w
ord
"rug
ged"
eve
ntua
lly d
omin
ates
, bec
ause
ther
eis
no w
ord
" lug
ged"
(pro
noun
ced
to rh
yme
with
"ru
gged
"th
e w
ord
lug"
is n
ot in
the
mod
el' s
lexi
con)
, Her
e "r
ugge
d~' m
ust c
ompe
te w
ithot
her p
artia
l mat
ches
of "
lugg
ed,"
of c
ours
e, a
nd it
is le
ss e
ffect
ive
inth
is re
gard
than
it w
ould
be
if th
e in
put ,
exac
tly m
atch
ed it
, but
it d
oes
win
out
in th
e en
d.
It sh
ould
be
note
d th
at th
e de
tails
of w
hat w
ord
will
be
mos
t stro
ngly
activ
ated
in su
ch c
ases
dep
end
on a
num
ber o
f fac
tors
, inc
ludi
ng, i
npa
rticu
lar,
the
disti
nctiv
enes
s of m
ismat
chin
g ph
onem
es. A
lso, i
t is p
os-
sible
to fi
nd c
ases
in w
hich
a w
ord
that
cor
rect
ly sp
ans a
par
t of a
long
erst
ring
dom
inat
es a
long
er w
ord
that
spa
ns th
e w
hole
strin
g bu
t miss
esou
t on
a ph
onem
e in
one
pla
ce o
r ano
ther
. 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
rtant
thin
g m
ight
not
turn
out
to b
e w
inni
ng a
nd lo
sing,
but
rath
er th
e fa
ct th
atbo
th te
nd to
stay
in th
e ga
me,
Suc
h ne
olog
ism
s ca
n su
gges
t a p
oetic
...
TRAC
E M
OD
ELM
C C
LELI
,-AN
D A
ND
ELM
AN
~Jj
fITCl
J
tEH
'.=-f1
tITiI
q;-
EliT
Ia:
:w
- Jig
~ I
- I
i g
I' a
. . I i g - 1-
- I I
g - I
-llg~l- +2
phon
emes
, In
this
sect
ion,
we
exam
ine
how
wel
l TRA
CE e
mul
ates
the
COH
ORT
mod
el, i
n ca
ses w
here
the
inpu
t is a
n un
disto
rted
repr
esen
ta-
tion
of so
me
parti
cula
r wor
d. In
par
ticul
ar, w
e w
ante
d to
see
how
clo
se.
TRAC
E w
ould
com
e to
beh
avin
g in
acc
ord
with
CO
HO
RT'
s ass
umpt
ion
that
inco
rrect
wor
ds a
re d
ropp
ed fr
om th
e co
hort
of a
ctiv
e ca
ndid
ates
as
soon
as
the
inpu
t div
erge
s fro
m th
em,
To e
xam
ine
this
pro
cess
, we
cons
ider
ed th
e pr
oces
sing
of th
ew
ord
"pro
duct
" (/p
rad"
ct/).
Fig
ure
25 s
how
s th
e st
ate
of th
e Th
ace
atva
rious
poi
nts i
n pr
oces
sing
this
' wor
d, a
nd F
ig. 2
6 sh
ows
the
resp
onse
stren
gths
of s
ever
al u
nits
rela
tive
to th
e str
engt
h of
the
wor
d "p
rodu
ct"
itsel
f, as
a fu
nctio
n of
tim
e re
lativ
e to
the
arriv
al o
f the
succ
essiv
e ph
o-ne
mes
in th
e in
put.
In th
is fig
ure,
the
resp
onse
stre
ngth
of "
prod
uct"
issim
ply
set t
o 1,
0 at
eac
h tim
esl
ice
and
the
resp
onse
stre
ngth
s of
uni
tsfo
r oth
er w
ords
are
plo
tted
in te
rms o
f the
ratio
of t
heir
stren
gth.
div
ided
by th
e str
engt
h of
"pr
oduc
t." T
he c
urve
s sho
wn
are
for t
he w
ords
!'tro
t,po
ssib
le," priest,
" "
prog
ress
," and "
prod
uce
; the
se w
ords
diff
erfro
m th
e w
ord
"pro
duct
" (ac
cord
ing
to th
e sim
ulat
ion
prog
ram
s st
ress
-le
ss e
ncod
ing
of th
em!)
ir, th
e 1s
t, 2n
d, 3
d, 4
th, a
nd 5
th p
hone
mes
, re-
spec
tivel
y, F
igur
e 26
show
s tha
t the
se it
ems b
egin
to d
rop
out o
f "co
n-te
ntio
n" ju
st af
ter e
ach
succ
essiv
e ph
onem
e co
mes
in, O
f cou
rse,
ther
eis
noth
ing
hard
and
fast
or a
bsol
ute
abou
t dro
ppin
g a
cand
idat
e in
TRAC
E. W
hat w
e se
e in
stea
d is
that
mis
mat
chin
g ca
ndid
ates
sim
ply
begi
n to
fade
as t
he in
put d
iver
ges f
rom
them
in fa
vor o
f som
e ot
her
cand
idat
e. T
his i
s jus
t the
kin
d of
beh
avio
r the
CO
HO
RT m
odel
wou
ld
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
tIl81
11tr
~ ~I
u 91
- p
r ad
- kr 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 "'eg
a'" a
nd "
'ugg
ed.
conj
unct
ion
of m
eani
ngs,
if us
ed ju
st rig
ht: "
He
wal
ked
brisk
ly d
own
the
stre
et, p
uffin
g hi
s vi
gore
tte.
Tim
e C
Ollr
.fe of w( ird recognition in
TRA
CE.
So fa
r we
have
sho
wn
how
TRA
CE o
verc
omes
a d
ificu
lty w
ith th
e CO
HO
RT m
odel
in c
ases
whe
re th
e be
ginn
ing
of a
wor
d ha
s bee
n di
storte
d. In
ear
lier s
ectio
ns o
nph
onem
e pr
oces
sing
,som
e of
the
simul
atio
ns il
lustr
ate
that
the
mod
el is
capa
ble
of re
cogn
izin
g w
ords
with
und
ersp
ecifi
ed (i
, e" a
mbi
guou
s) in
itial
prad
~kl-
-pra
d-kl
- -pr
ad~k
l- -p
rad-
kl-
FIG, 25. State of th
elhl
ce a
t var
ious
poi
nts i
n pr
oces
sing
the
wor
d "p
rodu
ct" (/prad'kt
/'.
12 1
8 24
30
38 4
2 48
!i4
80 8
8 Pr
oces
sing
Cycl
es
FIG
. 26.
Res
pons
e st
reng
ths
of tt
~ u
nits
for s
ever
al w
ords
rela
tive
to th
e re
spon
se s
treng
thof
the
unit
for "
prod
uct"
(/pr
ad- k
t/). a
s a fu
nctio
n of
tim
e re
lativ
e to
the
peak
of t
he fi
rst
phon
eme
that
fails
to m
atch
the
wor
d, T
he s
ucce
ssiv
e cu
rves
com
ing
off o
f the
hor
izon
tal
line
repr
esen
ting
the
norm
aliz
ed re
spon
se st
reng
th o
f "pr
oduc
t" a
re fo
r the
wor
ds "
Irot." ,
poss
ible
," "
prie
sl,
" "
prog
ress
, " and "
prod
uce." respectively. In our lexicon they are
, rendered as
Itnil/
, Ip
asI/,
Ipris
t/, Ip
ragr
s/, a
nd Ip
radu
s/, r
espe
ctiv
ely.
.... ~
2.~
1.
.... VJ 1
.80
~ 1.
S 1. 10
0Q
) ,D::: 0.
Q) 0
.~
0.'ii
' 0.
D::: 0.
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
We
wer
e at
firs
t som
ewha
t dist
urbe
d by
this
aspe
ct o
f the
mod
el's
beha
vior
, but
it tu
rns o
ut to
cor
resp
ond
quite
clo
sely
with
resu
lts o
btai
ned
in e
xper
imen
ts by
Gro
sjean
(198
0) a
nd C
otto
n an
d G
rosj
ean
(l9H
4) u
sing
the
gatin
g pa
radi
gm, B
oth
pape
rs fo
und
that
subj
ects
hear
ing
the
begi
n-ni
ngs o
f wor
ds li
ke "
capt
ain "
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 so
und
quite
a b
it lik
e " c
ap" followed by silence, In
TRA
CE, t
his s
ilenc
e w
ould
act
ivat
e sil
ence
uni
ts at
the
phon
eme
and
wor
d le
vels
, and
the
wor
d-le
vel s
ilenc
e un
its w
ould
com
pete
with
uni
tsfo
r wor
ds th
at e
xten
d in
to th
e si
lenc
e. It
will
rein
forc
e th
e pr
efer
ence
of
the
mod
el fo
r sho
rt-w
ord
inte
rpre
tatio
ns, b
ecau
se th
e de
tect
ion
of th
esil
ence
will
inhi
bit t
he d
etec
tor f
or th
e lo
nger
wor
d, T
hus,
ther
e ar
e ac
-tu
ally
two
reas
ons w
hy T
RACE
mig
ht fa
vor s
hort-
wor
d in
terp
reta
tions
over
long
-wor
d in
terp
reta
tions
in a
gat
ing
expe
rimen
t. W
heth
er h
uman
subj
ects
show
a re
sidua
l pre
fere
nce
for s
horte
r int
erpr
etat
ions
ove
r lon
ger
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 y
et c
lear
from
ava
ilabl
e da
ta,
We
shou
ld p
oint
out
that
the
expe
rimen
tal l
itera
ture
indi
cate
s tha
t the
adva
ntag
e of
sho
rter w
ords
ove
r lon
ger o
nes
hold
s on
ly u
nder
the
spec
ial
circ
umsta
nces
of g
ated
pre
sent
atio
n an
d th
en o
nly
with
ear
ly g
ates
, whe
nsh
orte
r wor
ds a
re re
lativ
ely
mor
e co
mpl
ete
than
long
er o
nes w
ould
be.
It ha
s bee
n w
ell k
now
n fo
r a lo
ng ti
me
that
long
er w
ords
are
gen
eral
lym
ore
read
ily re
cogn
ized
than
sho
rter o
nes
whe
n th
e w
hole
wor
d is
pre
-se
nted
for i
dent
ifica
tion
agai
nst a
bac
kgro
und
of n
oise
(Lic
klid
er &
Mill
er, 1
951)
, Pre
sum
ably
, the
reas
on fo
r thi
s is s
impl
y th
at lo
nger
wor
dsge
nera
lly p
rovi
de a
larg
er n
umbe
r of c
ues t
han
shor
ter w
ords
do
and
henc
e ar
e sim
ply
less
con
fusa
ble.
Frequency a"d context effects,
Ther
e ,a
re, o
f cou
rse ,
oth
er fa
ctor
sw
hich
influ
ence
whe
n w
ord
reco
gniti
on w
ill o
ccur
bey
ond
thos
e w
e ha
veco
nsid
ered
thus
far,
Two
very
impo
rtant
one
s are
wor
d fre
quen
cy a
ndco
ntex
tual
pre
dict
abilit
y, T
he li
tera
ture
on
thes
e t)o
Vo
fact
ors g
oes b
ack
to the turn of the century (Bagley, 1900).\ M
orto
ns (
1969
) log
ogen
mod
elef
fect
ivel
y de
als w
ith se
vera
l im
porta
nt a
spec
ts of
this
huge
lite
ratu
rethough not with the time course of these effects,
We
have
not
yet
incl
uded
eith
er w
ord
frequ
ency
or h
ighe
r lev
el c
on-
text
ual i
nflu
ence
s in
TRA
CE, t
houg
h of
cou
rse
we
belie
ve th
ey a
re im
-po
rtant
.Wor
d fre
quen
cy e
ffect
s cou
ld b
e ac
com
mod
ated
, as t
hey
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
sting
act
ivat
ion
leve
l of w
ord
units
, or i
n te
rms o
f var
iatio
nin
the
stren
gth
of p
hone
me-
to-w
ord
conn
ectio
ns. C
onte
xtua
l inf
luen
ces
can
be th
ough
t of a
s sup
plyi
ng a
ctiv
atio
n to
wor
d un
its fr
om e
ven
high
erle
vels
of p
roce
ssin
g th
an th
e w
ord
leve
l. In
this
way
, bas
ic a
spec
ts of
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,
Ther
e is
one
asp
ect o
f TR
ACE'
s beh
avio
r whi
ch d
iffer
s fro
m th
aI o
fCO
HO
RT: a
mon
g th
ose
wor
ds th
at a
re c
onsis
t~nt
with
the
inpu
t up
to a
parti
cula
r poi
nt in
tim
e. T
RACE
show
s a b
ias i
n fa
vor o
f sho
rter w
ords
over
long
er w
ords
, Thu
s, " p
riest"
has
a sl
ight advantage before the
Ial
com
es in
, and
"pr
oduc
e" is well ahead of "pr
oduc
t" u
ntil
the
tlcom
esin
(in
phon
emes
, "pr
oduc
e." i
s one
shor
ter t
han
" pro
duct
"Th
is ad
vant
age
for s
horte
r wor
ds is
due
to th
e co
mpe
titio
n m
echa
nism
,Re
call
that
wor
d un
its c
ompe
te w
ith e
ach
othe
r in
prop
ortio
n to
the
over
lap
of th
e se
ts of
tim
e sli
ces s
pann
ed b
y ea
ch o
f the
wor
ds, O
verla
pis,
of c
ours
e, sy
mm
etric
al, s
o lo
ng a
nd sh
ort w
ords
inhi
bit e
ach
othe
r to
an e
qual
ext
ent.
But l
onge
r wor
ds s
uffe
r mor
e in
hibi
tion
from
oth
er lo
ngw
ords
than
shor
t 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"
and
"pr
oduc
e." T
hus
units
for l
onge
r wor
ds a
re g
ener
ally
subj
ecte
d 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 so
they
tend
tosu
ffer i
n co
mpa
rison
to sh
ort w
ords
as a
resu
lt.3
The
data
repo
rted
by T
yler
and
Wes
sels
actu
ally
app
ears
to in
dica
te a
n e,ven more
imm
edia
te d
rop-
off t
han
is se
en in
this
simul
atio
n. H
owev
er, i
l sho
uld
be re
mem
bere
d t h
atth
e cu
rves
show
n in
Fig
. 26
are
on- li
ne re
spon
se st
reng
th c
urve
s, an
d th
us re
nec 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. "I
f the
i npu
t is'
sim
ply
turn
edof
f at t
he p
eak
of e
ach
phon
eme
s inp
ut sp
ecifi
catio
n, a
nd th
en a
llow
ed to
run
free
for a
few
cyc
les,
the
drop
out p
oint
shift
s eve
n ea
rlier
.
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
thes
e tw
o ki
nds o
f inn
uenc
es c
an b
e ca
ptur
ed. W
e le
ave
it to
futu
rere
sear
ch. h
owev
er. t
o de
term
ine
to w
hat e
xten
t the
se el
abor
atio
ns o
fTR
ACE
wou
ld p
rovi
de a
det
aile
d ac
coun
t of t
he d
ata
on th
e ro
les
ofth
ese
fact
ors,
For
now
. we
turn
to th
e pr
oble
m o
f det
erm
inin
g w
here
one
wor
d en
ds a
nd th
e ne
xt o
ne b
egin
s,
we
can
say
eith
er it
em in
a w
ay th
at m
akes
it so
und
like
a si
ngle
wor
dor
like
two
wor
ds, t
here
is a
n in
term
edia
te w
ay o
f say
ing
them
so th
atth
e fir
st se
ems t
o be
two
wor
ds a
nd th
e se
cond
seem
s lik
e on
ly o
ne.
To se
e w
hat T
RACE
II w
ould
do
with
sing
le- a
nd m
ultip
le-w
ord
inpu
ts,w
e ra
n sim
ulat
ion
expe
rimen
ts w
ith e
ach
indi
vidu
al w
ord
in th
e m
ain
2 I 1
-w
ord
lexi
con
prec
eded
and
follo
wed
by
sile
nce,
and
then
with
2 I
I pai
rsof
wor
ds, w
ith a
sile
nce
at th
e be
ginn
ing
and
at th
e en
d of
the
entir
est
ream
. The
pai
rs w
ere
mad
e by
sim
ply
perm
utin
g th
e le
xico
n tw
ice
and
then
abu
tting
the
two
perm
utat
ions
so
that
eac
h' w
ord
occu
rred
once
as
the
first
wor
d an
d on
ce a
s the
seco
nd w
ord
in th
e en
tire
set o
f 211
pai
rs,
We
stres
s, of
cou
rse,
that
real
spee
ch w
ould
tend
to c
onta
in c
ues t
hat
wou
ld m
ark
wor
d bo
unda
ries i
n m
any
case
s; th
e ex
peri
men
t is
sim
ply
desig
ned.
to sh
ow w
hat T
RACE
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
RAC
E m
ade
no m
ista
kes-
that
is, b
y a
few
slic
es a
fter t
he e
nd o
f the
wor
d, th
e w
ord
that
span
ned
the
entir
ein
put w
as m
ore
stron
gly
activ
ated
than
any
oth
er w
ord,
An
exam
ple
ofthis is shown using the item
Ipar
til
in Fig. 27. The stream
Ipar
til
mig
ht b
eei
ther
one
wor
d ("
party
) or t
wo
("par tea" or "par tee
the
mod
elknows of only one word pronounced
Iti/).
At
ear
ly p
oint
s in
'pro
cess
ing
the
wor
d, "
par" dominates over "
party
" and other longer words, for
reas
ons d
iscus
sed
in th
e pr
evio
us se
ctio
n, B
y th
e tim
e th
e m
odel
has
had
a ch
ance
to p
roce
ss th
e en
d of
the
wor
d, ho
wever, "
party
" comes to
dominate. .
Why
doe
s a si
ngle
long
er w
ord
even
tual
ly w
in o
ut o
ver t
wo
shor
ter
Lexi
cal B
as;. ~
(~r W
OI:d
Seg
men
tatio
nH
ow d
o w
e kn
ow w
hen
one
wor
d en
ds a
nd th
e ne
xt w
ord
begi
ns?
This
is b
y no
mea
ns a
n ea
sy ta
sk. a
s w
e no
ted
in th
e in
trodu
ctio
n, T
o re
cap
our e
arlie
r arg
umen
t. th
ere
are
som
e cu
es in
the
spee
ch st
ream
. but
as
seve
ral i
nves
tigat
ors h
ave
poin
ted
out (
Cole
& Ja
kim
ik. 1
980;
Gro
sjea
n& Gee. 19
84: T
hom
pson
. 198
4), t
hey
are
not a
lway
s suf
ficie
nt. p
artic
u-la
rly in
flue
nt sp
eech
, It w
ould
thus
app
ear t
hat t
here
is a
n im
porta
nt ro
lefo
r lex
ical
kno
wle
dge
to p
lay
in d
eter
min
ing
whe
re o
ne w
ord
ends
and
the
next
wor
d be
gins
; as
wel
l as
in id
entif
ying
the
obje
cts
that
resu
lt fro
mthe process of segmentation. Indeed. as Re
ddy
(197
6) h
as su
gges
ted,
segm
enta
tion
and
iden
tific
atio
n m
ay b
e jo
int r
esul
ts of
the
mec
hani
sms
of word recognition.
Col
e an
d Ja
kim
ik (1
980)
dis
cuss
thes
e po
ints
and
pre
sent
evi
denc
e th
atse
man
tic a
nd sy
ntac
tic c
onte
xt c
an g
uide
segm
enta
tion
in c
ases
whe
reth
e le
xico
n is
cons
is~en
t with
two
read
ings
("ca
r go"
vs "
carg
o).
Our
pres
ent m
odel
lack
s ~yn
tact
ic a
nd se
man
tic le
vels.
so it
can
not m
ake
use
of th
ese
high
er le
ver c
onstr
aint
s; bu
t it c
an m
ake
use
of it
s kn
owle
dge
about words, not only to identify individual w
ords
in is
olat
ion,
but
topi
ck o
ut a
sequ
ence
of w
ords
in c
ontin
uous
stre
ams o
f pho
nem
es. W
ord
iden
tific
atio
n an
d se
~men
tatio
nem
erge
toge
ther
from
the
i"te
riJct
ive~
ac-
tivat
ion
proc
ess,
as
part
and
parc
el o
f the
pro
cess
of w
ord
activ
atio
n,Th
is se
ctio
n co
nsid
ers s
ever
al a
spec
ts of
the
way
in w
hich
wor
d se
g-
men
tatio
n em
erge
s f~o
m th
e in
tera
ctiv
e-ac
tivat
ion
proc
ess,
as o
bser
ved
in si
mul
atio
ns w
ith T
RACE
II, B
efor
e 'w
e co
nsid
er th
ese,
it is
wor
thre
callin
g th
e de
tails
elf
som
e of
the
assu
mpt
ions
mad
e ab
out t
he b
otto
m-
up a
ctiv
atio
n of
wor
d' u
nits
and
abou
t com
petit
ive
inhi
bitio
n be
twee
n w
ord
units
. Firs
t, th
e ex
tent
to w
hich
a p
artic
ular
pho
nem
e ex
cite
s a p
artic
ular
wor
d un
it is
inde
pen d
ent o
f the
leng
th o
f the
wor
d, S
econ
d, th
e ex
tent
to w
hich
a p
artic
ular
wor
d un
it in
hibi
ts an
othe
r wor
d un
it is
prop
ortio
nal
to th
e te
mpo
ral o
verla
p of
the
two
wor
d un
its. T
his
mea
ns th
at w
ords
whi
ch d
o no
t ove
rlap
in ti
me
will
not
inhi
bit e
ach
othe
r, bu
t will
gan
g up
on o
ther
wor
ds th
at p
artia
lly o
verla
p ea
ch o
f the
m. T
hese
two
assu
mp-
tions
form
mos
t of t
h~ b
asis
of th
e ef
fect
s we
obse
rve
in th
e sim
ulat
ions
,
..,.
11/e bollndary
~ ill th
e ea
r of t
he "
behe
Ol'e
I",
Firs
t, w
e co
nsid
er th
eba
sic fa
ct th
at th
e nu
mbe
r of w
ords
we
hear
in a
sequ
ence
of p
hone
mes
can
depe
nd o
n ou
r kno
wle
dge
of th
e nu
mbe
r of w
ords
the
sequ
ence
mak
es. C
onsid
er th
e tw
o ut
tera
nces
, "sh
e ca
nt"
and
"se
cant
". T
houg
h
ili:IT
I:nili
:ITI:n
m.u
II r
aft I
ItP
~IT
JJ
iIJID
iIJID
II r t
II r
i -
u I P
u I
pllrti- -pB
rti- -
pBrl'
- -
pBrli
-Fl
o. 2
7. T
he s
tate
of t
he 'lh
tce
at v
ario
us p
oint
s du
ring
proc
essin
g of
Ipar
ti/,
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
m:IT
rnffi
:WilJ
Jim
B
m::!
LDa r l
m::u
:rni!!
IIDilJ
Ju:
:nliJ
ll -
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 c
anga
ng u
p on
a th
ird e
ach
over
laps
with
par
tly, a
nd d
rive
it ou
l.Th
ese
rem
arka
bly
simpl
e m
echa
nism
s 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 any
sylla
bifi-
catio
n, st
ress
, pho
netic
wor
d bo
unda
ry c
ues,
or se
man
tic a
nd sy
ntac
ticconstraints. 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
rrect
par
se, i
n th
e se
nse
that
no
othe
r wor
d w
as m
ore
activ
e th
an e
ither
of t
he tw
o w
ords
that
had
bee
npr
esen
ted,
Som
e of
the
failu
res o
f the
mod
el o
ccur
red
in c
ases
whe
re th
ein
put w
as a
ctua
lly c
onsis
tent
with
two
pars
es, e
ither
a lo
nger
span
ning
wor
d ra
ther
than
a si
ngle
wor
d (a
s in
" par
ty) o
r a d
iffer
ent p
arse
into
two
wor
ds, a
s in
" part rust" f
or "
par trusl." In such cases T
RACE
tend
sto
pre
fer p
arse
s in
whi
ch th
e lo
nger
wor
d co
mes
firs
t. Th
ere
wer
e, h
ow-
ever
, som
e ca
ses i
n 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 re
pres
ents
com
plet
e co
vera
ge o
f the
inpu
t hy
a se
tof
non
over
lapp
ing
wor
ds. F
or e
xam
ple,
con
side
r the
inpu
t Ipa
rki/.
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,
This
aspe
ct o
f TRA
CE II
' s b
ehav
ior i
ndic
ates
that
the
pres
ent v
crsi
onof
the
mod
el is
far f
rom
the
final
wor
d on
wor
d se
gmen
tatio
n. A
com
plet
em
odel
wou
ld a
lso e
xplo
it sy
llabi
ficat
ion,
stre
ss, 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 TRA
CEII'
s si
mpl
e ph
onem
e st
ream
s, T
he' a
ctiv
atio
n an
d co
mpe
titio
n m
echa
-ni
sms i
n TR
ACE
II a
re s
uffic
ient
to d
o qu
ite 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
perfe
ctly
in a
ll ca
ses
with
out t
he a
id ' o
f other cues.
Som
e re
ader
s may
be
troub
led
by a
mec
hani
srr t
hat d
oes
not i
nsis
tup
on a
par
se in
whi
ch e
ach
phon
eme
is co
vere
d by
one
and
onl
y on
ew
ord,
Act
ually
, tho
ugh,
this
char
acte
ristic
of t
he m
odel
is o
ften
a vi
rtuc,
since
in m
any
case
s the
last
phon
eme
ofh
wor
d m
ust d
o do
uble
dut
y as
the
first
phon
eme
of th
e ne
xt, a
s in
"hou
nd d
og" o
r "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 whe
n str
ings
with
mul
tiple
inte
rpre
tatio
ns a
re u
sed
as st
imul
i. Fo
rex
ampl
e, a
n ut
tera
nce
inte
nded
as
'no
notio
n" w
ill so
met
imes
be
hear
das
"kn
own
notio
n" (N
akat
ani &
Duk
es, 1
977)
. The
mod
el is
not
incl
ined
to su
ppre
ss a
ctiv
atio
ns o
f par
tially
ove
rlapp
ing
wor
ds, e
ven
whe
n a
non-
over
lapp
ing
pars
e is
avai
labl
e. T
his b
ehav
ior o
f TRA
CE is
illu
strat
ed w
ithIb
Asta
pl ("
bus top" or "
bus
stop
) in
Fig.
29.
In th
is ca
se, h
ighe
r lev
els
coul
d pr
ovid
e an
add
ition
al so
urce
of i
nfor
mat
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
RAC
E? T
here
are
two
mai
n re
ason
s, F
irst o
f all,
a lo
nger
wor
dev
entu
ally
rece
ives
mor
e bo
ttom
-up
supp
ort t
han
eith
er s
horte
r 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 wor
d. T
he se
cond
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 th
e tim
e th
e Iti
l is
com
ing
in, t
heword "
party
" is w
ell e
noug
h es
tabl
ished
that
it k
eeps
Itil
from
get
ting
asst
rong
ly a
ctiv
ated
as
it w
ould
oth
erw
ise,
as
illus
trate
d 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 l
onge
r wor
ds sh
ould
not
get
as s
trong
ly a
ctiv
ated
as s
horte
rw
ords
com
ing
earli
er in
the
long
er w
ord.
Thi
s pre
dict
ion
coul
d be
teste
dus
ing
the
gatin
g pa
radi
gm, o
r a c
ross
-mod
al p
rimin
g pa
radi
gm su
ch a
sth
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 o
f the
mod
el c
an b
e ov
errid
den
if th
ere
is b
otto
m-u
p in
form
atio
n fa
vorin
e th
etw
o-w
ord
inte
rpre
tatio
n, C
urre
ntly
, thi
s ca
n on
ly h
app~
n in
TRA
CEth
roug
h th
e in
serti
on o
f a b
rief s
ilenc
e be
twee
n th
e "p
ar" and the "te
a.A
s sho
wn
in F
ig, 2
8, th
is re
sults
in "
par"
and
"te
a" d
omin
atin
g al
l oth
erword candidates,
Wha
t hap
pens
whe
n th
ere
is no
long
wor
d th
at sp
ans t
he e
ntire
stre
am,
as in
Ibar
til?
In th
is ca
se, t
he m
odel
settl
es o
n th
e tw
o-w
ord
inte
rpre
tatio
nba
r tea
," a
s sho
wn
in F
ig, 2
8. N
ote
that
oth
er w
ords
, suc
h as
"ar
t,th
at sp
an a
porti
on o
f the
inpu
t, ar
e le
ss su
ccessful than either "
bar " or
tea.
" The
reas
on is
that
the
inte
rpre
tatio
ns "
bar" and "
art" overlap
with
eac
h ot
her,
and
" art
" and
"te
a" o
verla
p w
ith e
ach
othe
r, bu
t "ba
r
part
i- ' +
3 -p
ar-t
1-+3
-bar
f j- +
3 -p
ark i- +3
FIG
. 28,
Sla
le o
f the
'lta
ce a
fter p
roce
ssin
a th
e str
eam
s /pa
rliJ,
/par
-tiJ,
/bar
liJ, u
nit I
park
i/.
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
~!'
fl~P -
- b
esta
blish
whe
re a
wor
d w
ill e
nd e
ven
befo
re i.
act
ually
doe
s end
, par
tic-
ular
ly in
the
case
of l
onge
r wor
ds o
r whe
n ac
tivat
ions
at t
he w
ord
leve
lar
e ai
ded
by sy
ntac
tic a
nd se
man
tic c
onstr
aint
s, H
owev
er, i
t is m
uch
hard
er to
esta
blish
the
end
of a
non
wor
d, si
nce
the
fact
that
it is
a n
on-
w()r
d m
eans
that
we
cann
ot e
xplo
it an
y kn
owle
dge
of w
here
it sh
ould
end
to d
oso
,Th
is fa
ct m
ay a
ccou
nt fo
r the
find
ing
of Fo
ss and Blank (1
980)
that
subj
ects
are
muc
h sl
ower
to re
spon
d 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 th
e en
d of
last
yea
r, th
e go
vern
men
t dec
ided
. . .
b-sl
ap- -
br-S
ap.
FIG. 29. State of the Trace at the end of the streams Ibustapl ("bus stop" o
r "bus top
and
Ibru
Sapl
("br
ush
shop
than
they
wer
e w
hen
the
wor
d pr
eced
ing
the
targ
et (i
n th
is ca
se g
over
n-m
ent)
was
repl
aced
by
a no
nwor
d su
ch a
s "gatabont." It should be noted
that
the
targ
ets
wer
e sp
ecifi
ed a
s w
ord-
initi
al se
gmen
ts, T
here
fore
, the
subj
ects
had
not 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
fell
at th
e be
ginn
ing
of a
wor
d, a
s, w
ell,
The
faef
that
reac
tion
times
wer
e fa
ster 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 k
now
ledg
e of
whe
re th
e w
ord
"gov
ern-
men
t" e
nds t
o he
lp th
em d
eter
min
e w
here
the
next
wor
d be
gins
,A
n ex
ampl
e of
how
TRA
CE a
llow
s one
wor
d to
hel
p es
tabl
ish w
here
its su
cces
sor b
egin
s is i
llustr
ated
in F
ig, 3
0; In
the
exam
ple,
the.
mod
elre
ceiv
es th
e st
ream
"possible target" or "
pagu
sle ta
rget
." and we
imag
ine
that
the
targ
et is
wor
d-in
itial
/t/. I
n th
e fir
st ca
se. t
he w
ord
"pos
-, s
ible
is cl
early
esta
blish
ed a
nd c
ompe
titor
s und
erne
atIJ
it h
ave
been
completely crushed by the time the initial
It I
in "
targ
et" b
ecom
es a
ctiv
eat
the
phon
eme
leve
l (se
cond
pan
el in
the
uppe
r par
t of t
he fi
gure
). so
there is no ambiguity about the fact that this
It I
is a
t the
beg
inni
ng o
f the
next
wor
d, (T
he d
ecisi
on m
echa
nism
wou
ld. o
f cou
rse.
be
requ
ired
tono
te th
at th
e m
odel
had
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 o
f. di
ffere
nt p
lace
s. in
clud
ing
som
e th
at o
verla
p w
ith th
elocation of the
Itl,
are
partl
y ac
tivat
ed, T
hus.
the
subj
ect w
ould
hav
e to
wai
t unt
il he
is w
ell i
nto
the
wor
d "t
arge
t" b
efor
e it
beco
mes
cle
ar th
atthe first
It I
in ta
rget
is in
fact
a w
ord-
initi
al
It/.
In re
ality
, the
situ
atio
n is
prob
ably
not
as b
leak
for t
he p
erce
iver
as i
tap
pear
s in
this
exam
ple,
bec
ause
in m
any
case
s the
re w
ill b
e cu
es in
the
man
ner o
f pro
nunc
iatio
n an
d th
e sy
llabi
ficat
ion
of th
e in
put t
hat w
ill h
elp
to in
dica
te th
e lo
catio
n of
the
wor
d bo
unda
ry. H
owev
er. g
iven
'the
im-
prec
ision
and
freq
uent
abs
ence
of s
uch
cues
. it i
s not
surp
risin
g th
at th
e
The
sim
ulat
ions
we
have
repo
rted
show
that
the
wor
d ac
tivat
ion/
com
-pe
titio
n m
echa
nism
can
go
a lo
ng w
ay to
war
d pr
ovid
ing
a co
mpl
ete
in-
terpretation of the input stream as a seq,u
ence
of w
ords
, As a
wor
d is
begi
nnin
g to
com
e in
. the
mod
el te
nds
to p
refe
r sho
rter w
ords
con
sist
ent
with
the
inpu
t stre
am o
ver l
onge
r one
s. A
s the
input unfolds through
time.
how
ever
. the
mod
el te
nds t
o pr
efer
to in
terp
ret s
treams of pho-
nem
es a
s sin
gle
long
er w
ords
rath
er th
an a
s a se
quen
ce o
f sho
rt w
ords
;an
d it
tend
s to
find
pars
es th
at a
ccou
nt fo
r eac
h ph
onem
e on
ce. B
ut it
does
not
insi
st u
pon
this
. and
will
occa
sion
ally
pro
duce
an
inte
rpre
tatio
nth
at le
aves
par
t of t
he st
ream
of p
hone
mes
una
ccou
nted
for o
r whi
chac
coun
ts fo
r par
t of t
he s
tream
of p
hone
mes
twic
e, O
ften
enou
gh, i
t will
also
leav
e an
alte
rnat
ive
to it
s "pr
efer
red
paise
" 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
.Th
us fa
r in
this
sect
ion,
we
have
con
sider
ed th
e ge
nera
l pro
perti
es o
fth
e w
ay in
whi
ch T
RACE
use
s lex
ical
info
rmat
ion
to se
gmen
t a sp
eech
stre
am in
to w
ords
. but
we
have
not
con
side
red
muc
h in
the
way
of e
m-
piric
al d
ata
that
thes
e as
pect
s of t
he m
odel
shed
ligh
t on,
How
ever
. the
rear
e tw
o fin
ding
s in
the
liter
atur
e w
hich
can
be
inte
rpre
ted
in a
ccor
danc
ew
ith T
RAC
E's h
andl
ing
of m
ultiw
ord
spee
ch st
ream
s,W
here
doe
s 1I 1I00lword elld?
A n
umbe
r of i
nves
tigat
ors (
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 ide
n-tit
y ca
n be
use
d to
det
erm
ine
whe
re it
end
s and
ther
efor
e w
here
the
next
wor
d be
gins
. In
TRA
CE. t
he in
tera
ctiv
e ac
tivat
ion
proc
ess c
an o
ften
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
a s -
as-
a s -
ElD
as-b
lifa
. '
tl!.!!
J!..:
tgi
iII2
ili 8
H,j,
.. -
II
- p
- b
u I
r -'I
:0 ~
r 8
or "
tarn
ished
" or o
ne o
f sev
eral
oth
er p
ossib
ilitie
s, It
is on
ly a
fter m
orc
time
has
pass
ed. a
nd w
e ha
ve p
erce
ived
eith
er a
sile
nce
or e
noug
h of
the
next
wor
d to
rule
out
any
of t
he c
ontin
uatio
ns o
f Ita
rl, th
at w
e ca
n de
cide
we
have
hea
rd th
e w
ord
"tar
, " T
his s
ituat
ion.
as i
t aris
es in
TRA
CEw
ith th
e sim
ple
utte
ranc
e Ita
rbak
sl ("
tar b
ox) is illustrated in Fig. 31.
Though "
tar"
is so
mew
hat m
ore
activ
e th
an th
e lo
nger
wor
d " t
arge
twhen the
Irl
is co
min
g in
. it i
s onl
y w
hen
the
wor
d "b
ox" emerges as
the
inte
rpre
tatio
n of
the
phon
emes
follo
win
g " t
ar" t
hat t
he ri
val "
targ
et"
final
ly fa
des a
s a se
rious
con
tend
er,
With
long
er w
ords
the
situa
tion
is di
ffere
nt. A
s we
have
alre
ady
seen
in a
noth
er e
xam
ple.
by
the
time
the
end
of a
long
er w
ord
is re
ache
d it
is
pas'b
-Ilar
l-~-
pas-
b-Ila
rl-l-
pas-
b-Ila
rl-l-
IITD
...-r!
i;-~I
COI
ar:w
!i:I!:
D!!J
!Dj
s a
iE!!l
lllI
a rb
. ra
k
Pili
Pil
II I
u I !
!~
IIII
- p' .
Elii.
'!Eb
Enlli
!!i!::
iEE
TIl
W!i.
!- s
t:-
. -
fii.i4
P:~=
:. '-
II -
. . 1111
i2ili
9L__
_.Ci
Ll1
- s
- P a
. -
r d j
a S
a
-larb
aka-
-Iarb
,ka-
-Iarb
,",-
-I,rb
ak,-
pal-s
-llar
,-I- -
P"I-s-
Ilarg
-t- -
pal-
s-lls
rl-l-
FIG
. 30,
Sta
te o
f the
Tra
ce a
t sev
eral
poi
nts d
urin
g Ih
e pr
oces
sing
of "
poss
ible
targ
et" a
ndpa
gusl
e ta
rget
.
rjb- ;
' ., S
)fC
ITiI
u::L
fi
11m
iITID
I, ~i
liliE
!!I a k
a r
s -a
k
u I
u I P
II I
.iad
-
. lex
ical
stat
us o
f one
par
t of a
spee
ch st
ream
pla
ys a
n im
porta
nt ro
le 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
feat
ure
ofsp
eech
is th
e fa
ct th
at it
is n
ot a
lway
s po
ssib
le to
identifya word un-
ambi
guou
sly u
ntil
one
has h
eard
the
wor
d af
ter i
t. Co
nsid
er. 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 b
ox. " 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 sa
y un
equi
voca
lly th
at th
e w
ord
" tar
" will
not
turn
out
to b
e " t
arge
t,-I
arba
k,-
I-Iar
b,",-
I-I,rb
,k.-
I-Iar
baks
-Ft
G. 3
1. S
iale
of I
he T
race
al s
ever
al p
oint
s in
pro
cess
ing
"tar b
ox" and "
guita
r box
,
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
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
poss
ible
to h
ave
enou
gh in
form
atio
n to
iden
tify
the
wor
d un
ambi
guou
sly w
ell b
efor
e th
e en
d of
the
wor
d. A
n ill
ustra
tion
of th
is s
ituat
ion
is p
rovi
ded
by a
simulation using the utterance "
guita
rbo
x" Ig
tarb
aks/,
By
the
time
the
Irl h
as re
giste
red,
"gu
itar " is clearly
dom
inan
t at t
he w
ord
leve
l. an
d ca
n be
unai11biguously identified without
furth
er a
do.
Rece
ntly
, an
expe
rimen
t by
Gro
sjean
(198
5) h
as d
emon
strat
ed th
ese
sam
e ef
fect
s em
piric
ally
, Gro
sjean
pre
sent
ed su
bjec
ts w
ith lo
ng o
r sho
rtw
ords
follo
wed
by
ase
cond
w()r
d an
d m
easu
red
how
muc
h of
the
wor
dan
d its
succ
esso
r the
subj
ect n
eede
d to
hea
r to
iden
tify
the
targ
et. W
ithlo
nger
wor
ds, s
ubje
cts c
ould
usu
ally
gue
ss th
e w
ord
corre
ctly
wel
l bef
ore
the
end
of th
e w
ord,
; and
by
the
end
of th
e w
ord
they
wer
e qu
ite s
ure
ofth
e w
ord'
s ide
ntity
, With
mon
osyl
labi
c w
ords
, on
the
othe
r han
d, 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 t
he b
egin
ning
of t
he o
ne a
fter,
AsGrosjean (1985) points out, a m
~or r
easo
n fo
r thi
s is s
impl
y th
at th
esp
oken
inpu
t ofte
n do
es n
ot u
niqu
ely
spec
ify th
e id
entit
y of
a s
hort
wor
d.In
suc
h ca
ses,
the
perc
eptu
al s
yste
m is
ofte
n fo
rced
to p
roce
ss th
e sh
ort
wor
d, a
nd it
s suc
cess
or, a
t the
sam
e tim
e.RecoRllizilll: the words
ill
a short selltellce,
One
last
exam
ple
ofTR
ACE
II's
perfo
rman
ce in
seg
men
ting
wor
ds is
illu
strat
ed in
Fig
, 32,
The
figur
e sh
ows
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 th
e en
d, th
e w
ords
of t
he p
hras
eSh
e sh
ut a
box
, " w
hich
fils
the
inpu
t per
fect
ly w
ith n
o ov
erla
p, d
omi-
nate
all
othe
rs. .
This
exam
ple
illus
trate
s how
far i
t is s
omet
imes
pos
sible
to g
o in
pars
ing
a st
ream
of p
hone
mes
into
wor
ds, w
ithou
t eve
n co
nsid
erin
g sy
n-ta
clic
and
sem
antic
'(on
stra
ints
, or s
tress
, syl
labi
ficat
ion,
and
junc
ture
cues
to w
ord
iden
tific
atio
n. T
he e
xam
ple
also
illu
strat
es th
e di
fficu
lty th
em
odel
has
in p
erce
ivin
g sh
ort,
unstr
esse
d w
ords
like
". T
his
is, o
fco
urse
, jus
t an
extre
me
vers
ion
of th
e di
fficu
lty th
e m
odel
has
in p
ro-
cess
ing
mol
1osy
llabi
c w
ords
like
"ta
r," a
nd is
con
siste
nt w
ith G
rosje
anda
ta o
n th
e di
fficu
lty su
bjec
ts ha
ve w
ith id
entif
ying
shor
t wor
ds. I
n fa
ct,
Gro
sjean
and
Gee
(198
4) re
port
pilo
t dat
a in
dica
ting
that
thes
e di
fficu
lties
are
even
mor
e se
vere
with
func
tion
wor
ds li
ke "
" and "
of. " It should
be n
oted
that
TRA
CE m
akes
no
spec
ial d
istin
ctio
n be
twee
n co
nten
t and
func
tion
wor
ds, p
er se
, and
nei
ther
do
Gro
sjean
and
Gee
, How
ever
, fun
c-tio
n w
ords
are
usu
ally
uns
tress
ed a
nd c
onsid
erab
ly sh
orte
r tha
n co
nten
tw
ords
. Thu
s, it
is no
t nec
essa
ry to
poi
nt to
any
spec
ial m
echa
nism
s for
clos
ed v
ersu
s ope
n cl
ass m
orph
emes
to a
ccou
nt fo
r Gro
sjean
and
Gee
resu
lts.
m:n
IDJ
IH&
fnJiJ
EEJJ
5 I
s -
p u
s u
II i
S \I
-SIS
-l-ba
ks-
SiS-
t-bak
s-Si
S-l-b
aks-
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-bak
s-Si
S-l-b
llks-
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
tream
ISis
Tbak
sl ("
She
shut
8 b
ox
,.
Sum
mar
y of
Wor
d Id
emiji
catio
n Si
mul
atio
nsW
hile
pho
nem
e id
entif
icat
ion
has
been
stu
died
for m
any
year
s, d
ata
from on-lin
e stu
dies
of w
ord
reco
gniti
on is
just
begi
nnin
g to
acc
umul
ate;
Ther
e is
an o
lder
lite
ratu
re o
n ac
cura
cy o
f wor
d id
entif
icat
ion
in n
oise
.bu
t it h
as o
nly
been
qui
te re
cent
ly th
at u
sefu
l tec
hniq
ues h
ave
been
de-
velo
ped
for s
tudy
ing
wor
d re
cogn
ition
in re
al ti
me.
Wha
t evi
denc
e th
ere
is. th
ough
indi
cate
s the
com
plex
ity o
f the
wor
d
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
iden
tific
atio
n pr
oces
s, W
hile
the
wor
d id
entif
icat
ion
mec
hani
sm is
sen-
sitiv
e to
eac
h ne
w in
com
ing
phon
eme
as it
arri
ves,
it is nevertheless
robu
st en
ough
to re
cove
r fro
m u
nder
spec
ifica
tion
or d
istor
tion
of w
ord
begi
nnin
gs. A
nd it
app
ears
h..
be c
apab
le o
f som
e sim
ulta
neou
s pro
cess
ing
of su
cces
sive
wor
ds in
the
inpu
t stre
am, T
RACE
app
ears
to c
aptu
re th
ese
aspe
cts o
f the
tim
e co
urse
of w
ord
reco
gniti
on. I
n th
ese
resp
ects,
it im
-pr
oves
upo
n th
e CO
HO
RT m
odel
, the
onl
y pr
evio
usly
ext
ant m
odel
that
prov
ides
an
expl
icit
acco
unt o
f the
on-
line
proc
ess
of w
ord
reco
gniti
on,
And
the
mec
hani
sms i
t use
s . to
acco
mpl
ish th
is ar
e th
e sa
me
ones
that
itus
ed fo
r the
sim
ulat
ions
of t
he p
roce
ss o
f pho
nem
e id
entif
icat
ion
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 a
n in
itial
pre
fere
nce
for
shor
ter w
ords
rela
tive
to lo
nger
wor
ds, b
ut e
vent
ually
a se
quen
ce o
fph
onem
es th
at m
atch
es a
long
wor
d pe
rfect
ly w
ill b
e id
entif
ied
as th
atw
ord,
ove
rturn
ing
the
initi
al p
refe
renc
e fo
r the
shor
t-wor
d in
terp
reta
tion.
Thes
e as
pect
s of
the
mod
el, a
re c
onsi
sten
t with
hum
an d
ata
from
gat
ing
expe
rimen
ts.7,
Tho
ugh
the
mod
el is
hea
vily
influ
ence
d by
wor
d be
ginn
ings
, it c
anre
cove
r fro
m u
nder
spec
ifica
tion
or d
isto
rtion
of a
wor
d's
begi
nnin
g.S,
The
mod
el c
an u
se it
s kno
wle
dge
of th
e le
xico
n to
par
se se
quen
ces
of p
hone
mes
into
wor
ds, a
nd to
esta
blish
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 su
bjec
ts, th
e m
odel
som
etim
es c
anno
t ide
ntify
a w
ord
until
it h
as h
eard
par
t of t
he n
ext w
ord,
Also
like
hum
an su
bjec
ts. it
can
bette
r det
erm
ine
whe
re a
wor
d w
ill b
egin
whe
n it
is pr
eced
ed b
y a
wor
dra
ther
than
a n
onw
ord,
10. T
he m
odel
doe
s not
dem
and
a pa
rse
of a
pho
nem
e se
quen
ce th
atin
clud
es e
ach
phon
eme
in o
ne a
nd o
nly
one
wor
d, T
his a
llow
s it t
o co
pegr
acef
ully
with
elis
ion
. of p
hone
m~s
at w
ord
boun
darie
s. It
will
ofte
npe
rmit
seve
ral a
ltern
ativ
e pa
rses
to re
mai
n av
aila
ble
lor h
ighe
r lev
el in
-flu
ence
s to
choo
se a
mon
g,
In a
dditi
on to
thes
e ch
arac
teris
tics o
bser
ved
in th
e pr
esen
t pap
er, o
ursim
ulat
ions
with
TRA
CE I
show
seve
ral f
urth
er c
orre
spon
denc
es b
e-tw
een
the
mod
el a
nd h
uman
spee
ch. p
erce
ptio
n, M
ost i
mpo
rtant
of t
hese
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 th
e Tr
ace
to a
djus
t the
con
nect
ion
stren
gths
det
erm
inin
g w
hich
feat
ures
will
act
ivat
e w
hich
pho
nem
es in
adj
acen
t par
ts of
the
Trac
e. In
this WaY, the m
odel
can
adj
ust a
s hum
an su
bjec
ts do
to co
artic
uh.it
ory
influ
ence
s on
the
acou
stic
prop
ertie
s of p
hone
mes
(Fow
ler.
1984
; Man
n&
Rep
p, 19
80).
Ther
e is
, of c
ours
e. m
ore
data
on
som
e of
thes
e po
ints
than
oth
ers.
IIw
ill b
e ve
ry in
tere
sting
to se
e ho
w w
ell r
RACE
will
hol
d up
aga
inst
the
data
as f
urth
er e
mpi
rical
stud
ies a
re c
arrie
d ou
l.
ENER
AL
DIS
CUSS
ION
Sum
ma,
.y o
f TRA
CE' ~
' Suc
cess
esIn
this
artic
le, w
e ha
ve se
en th
at T
RACE
can
acc
ount
for a
num
ber o
fdi
ffere
nt a
spec
ts of
hum
an sp
eech
per
cept
ion.
We
begi
n by
list
ing
the
maj
or c
orre
spon
denc
es b
etw
een
TRA
CE a
nd w
hat w
e kn
ow a
bout
the
hum
an sp
eech
und
ersta
ndin
g pr
oces
s.
I, TR
ACE
, lik
e hu
man
s, us
es in
form
atio
n fro
m o
verla
ppin
g po
rtion
sof
the
spee
ch w
ave
to id
entif
y su
cces
sive
phon
emes
,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
affe
cted
by
man
y of
the
sam
e pa
ram
eter
s whi
ch af
fect
the
degr
ee o
f cat
egor
ical
per
cept
ion
show
n by
hum
an su
bjec
ts; in
par
ticul
ar.
the
exte
nt to
whi
ch p
erce
ptio
n w
ill be
cat
egor
ical
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 d
ifter
ent
dim
ensio
ns, a
nd e
xhib
its c
ue tr
ade-
offs
in p
hone
me
iden
tific
atio
n. T
hese
char
acte
ristic
s of h
uman
spee
ch p
erce
ptio
n ha
ve b
een
dem
onstr
ated
in a
very
hirg
e nu
mbe
r of s
tudi
es,
4, T
he m
odel
aug
men
ts in
form
atio
n fro
m th
e sp
eech
stre
am w
ith fc
ed-
back
from
the
lexi
cal l
evel
in re
achi
ng d
ecisi
ons a
bout
the
iden
tity
ofph
onem
es, T
hese
lexi
cal i
ntlu
ence
s on
pho
nem
e id
entif
icat
ion
occu
r in
cond
ition
s si
mila
r to
thos
e in
whi
ch le
xica
l effe
cts
have
bee
n re
porte
d,bu
t do
not o
ccur
in c
ondi
tions
in w
hich
thes
e ef
fect
s hav
e no
t bee
n ob
-
~~. .
5, L
ike
hum
an su
bjec
ts th
e m
odel
exh
ibits
app
aren
t pho
nota
ctic
rule
effe
cts o
n ph
onem
e id
entif
icat
ion.
thou
gh it
has
no
expl
icit
repr
esen
tatio
nof
the
phon
otac
tic ru
les,
The
tend
ency
to p
refe
r pho
nota
ctic
ally
regu
lar
inte
rpre
tatio
ns o
f am
bigu
ous p
hone
mes
can
be
over
ridde
n by
par
ticul
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
Succ
es~'
es o
f TR
ACE
To w
hat d
oes t
he T
RACE
mod
el o
we
its su
cces
~ in
sim
ulat
ing
hum
ansp
eech
per
cept
ion'
! Som
e of
TRA
CE's
succ
esse
s sim
ply
depe
nd o
n its
abili
ty to
mak
e us
e of
the
info
rmat
ion
as it
com
es il
. For
exa
mpl
e. it
fails
to sh
ow c
onte
xt e
ffect
s onl
y w
hen
a re
spon
se m
ust b
e m
ade.
or c
an b
em
ade
with
hig
h ac
cura
cy. b
efor
e co
ntex
tual
info
rmat
ion
is a
vaila
ble.
Ther
e ar
e se
vera
l oth
er re
ason
s for
TRA
CE's
succ
ess,
One
, we
thin
k.is
the
use
of c
ontin
uous
act
ivat
ion
and
com
petit
ion
proc
esse
s in
plac
e of
/'"
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
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 d
egre
e an
d pr
otec
t TRA
CEfr~
m c
ata-
strop
hic
com
mitm
ent i
n m
argi
nal c
ases
. and
they
pro
vide
a n
atur
iif m
eans
for c
ombi
ning
man
y ~i
ffere
nt so
urce
s: of
info
rmat
ion,
Of c
ours
e. th
is fe
a-tu
re o
f the
mod
el is
shar
ed w
ith se
vera
l oth
er m
odel
s (e,
g.. M
orto
n. 19
69;
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 in
corp
orat
ed th
ese
kind
s of a
ssum
ptio
ns in
a m
odel
of.
the
time
cour
se o
f wor
d re
cogn
ition
.Pa
rt of
the
succ
ess o
f TRA
CE is
spec
ifica
lly d
ue to
the
use
of c
om-
petit
ive
inhi
bito
ry in
tera
ctio
ns in
stead
of b
otto
m-u
p (o
r top
-dow
n) in
hi-
bitio
n. C
ompe
titio
n al
low
s the
mod
el to
sel
ect t
he b
est i
nter
pret
atio
nav
aila
ble.
sell
ling
for a
n im
perfe
ct o
ne w
hen
no b
elle
r one
is a
vaila
ble.
but o
verri
ding
poo
r one
s whe
n a '
goo
d on
e is
at h
and,
The
se a
nd o
ther
virtu
es o
f com
petit
ive
inhi
bitio
n ha
ve b
een
note
d be
fore
(e,g
.. Fe
ldm
an& Ballard. 1982: G
ro~s
berg
. 197
3; L
evin
. 197
6: R
atlif
f. 19
65; v
on B
ekes
y.1967) in other co
ntex
ts. T
heir
usef
ulne
ss h
ere
atte
sts to
the
gene
ral u
tility
of th
e co
mpe
titiv
e in
hibi
tion
mec
hani
sm.
The
elim
inat
ion
of b
etw
een-
leve
l inh
ibiti
on fr
om th
e in
tera
ctiv
e ac
ti-va
tion
mec
hani
sm p
uts
us in
a v
ery
nice
pos
ition
with
resp
ect t
o on
ege
nera
l crit
ique
of i
nter
activ
e-ac
tivat
ion
mod
els.
It is
ofte
n sa
id th
at a
c-tiv
atio
n m
odel
s are
~oo
unc
onst
rain
ed a
nd to
o fle
xibl
e to
be
anyt
hing
mor
e th
an a
lang
uage
for c
onve
nien
tly d
escr
ibin
g in
form
atio
n pr
oces
sing,
We
are
now
in a
pos
ition
to su
gges
t tha
t a re
stric
ted
vers
ion
of th
e fra
me-
wor
k is
not
onl
y su
ffici
ent b
ut s
uper
ior.
Inte
ract
ive-
activ
atio
n m
odel
sco
uld
expl
oit b
oth
exci
tato
ry a
nd in
hibi
tory
con
nect
ions
bot
h be
twee
nan
d w
ithin
leve
ls, b
u~ in
the
orig
inal
inte
ract
ive-
activ
atio
n m
odel
of l
ette
rpe
rcep
tion.
onl
y in
hibi
tory
inte
ract
ions
wer
e al
low
ed w
ithin
a le
vel.
Inm
ore
rece
nt v
ersi
ons
of th
e vi
sual
mod
el (M
cCle
lland
. 1985, 1986),
and
in T
RACE
, we
have
gon
e ev
en fu
rther
, allo
win
g on
ly e
xcita
tory
conn
ectio
ns b
etw
een
leve
ls an
d on
ly in
hibi
tory
con
nect
ions
with
in le
vels.
From
our
exp
erie
nce,
i t a
ppea
rs th
at m
odel
s w
hich
adh
ere
to th
ese
con-
strai
nts w
ork
as w
ell a
s or b
ette
r tha
n m
embe
rs o
f the
mor
e ge
nera
l cla
ssth
at d
o no
t. W
e ha
sten
to a
dd th
at w
e ha
ve n
o pr
oof t
hat t
his
is tr
ue, W
eha
ve, h
owev
er. n
o re
ason
to fe
el th
at w
e co
uld
impr
ove
the
perfo
rman
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 of
the
succ
esse
s of T
RACE
dep
end
on it
s use
offe
edba
ckfro
m h
ighe
r to
low
er re
vels,
Fee
dbac
k pl
ays a
cen
tral r
ole
in th
e ac
coun
tsof
cat
egor
ical
per
cep t
ion.
lexi
cal e
ffect
s on
phon
eme
iden
tific
atio
n, a
ndph
onot
actie
rule" e
ffect
s,
We
do n
ot c
laim
that
any
of t
hese
phe
nom
ena,
take
n in
divi
dual
ly, r
e-qu
ire th
e as
sum
ptio
n ; o
f a fe
edba
ck m
echa
nism
, For
exa
mpl
e, c
onsid
erth
e ph
enom
enon
of t
ateg
oric
al p
erce
ptio
n. W
e us
e fe
edba
ck fr
om th
e
phon
eme
to th
e fe
atur
e le
vel t
o dr
ive
feat
ure
patte
rns c
lose
r to
the
pro-
totype of the ph
onem
e th
ey m
ost s
trong
ly a
ctiv
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 bet
ter d
iscrim
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
sugg
estin
g th
at su
bjec
ts 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 t
heph
onem
e id
entif
icat
ion
proc
ess.
Sim
ilarly
, lex
ical
effe
cts o
n ph
onem
eid
entif
icat
ion
can
be a
ccou
nted
for b
y as
sum
ing
that
subj
ects
(som
etim
es)
read
out
from
the
wor
d le
vel a
nd in
fer t
he id
entit
y of
pho
nem
es fr
om th
ele
xica
l cod
e (M
arsl
en-Wilson, 1980: Marslen-
Wils
on &
Wel
sh, 1
978;
Mor
ton.
1979), In the case of "ph
onot
actic
rule
" 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 su
bjec
ts us
e kn
owle
dge
of th
e ph
onot
actic
con
strai
nts.
per-
haps
cap
ture
d in
uni
ts sta
ndin
g fo
r leg
al p
hone
me
pairs
. and
that
it is
the
outp
ut o
f suc
h un
its th
at a
ccou
nts
for t
he in
fluen
ce o
f pho
nota
ctic
reg-
ularity on phoneme identification.
We
know
of n
o sin
gle
conv
inci
ng e
mpi
rical
reas
on to
pre
fer f
eedb
ack
acco
unts
to o
ther
pos
sibili
ties,
How
ever
, we
have
two
theo
retic
al re
ason
sfo
r pre
ferri
ng to
reta
in to
p-do
wn
as w
ell a
s bot
tom
-up
inte
ract
ions
in o
urac
tivat
ion
mod
els,
One
reas
on h
as to
do
with
the simplicity of the re-
sulti
ng d
ecisi
on m
echa
nism
s, Fe
edba
ck a
llow
s hig
herle
vel c
onsid
erat
ions
to in
fluen
ce 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
sider
atio
ns in
fluen
ce th
e ou
tcom
e of
pro
cess
ing
at h
ighe
r lev
els,
The
influ
ence
s of
lexi
cal a
nd o
ther
con
stra
ints
on
pho-
nem
e id
entif
icat
ion
need
not
be
push
ed o
ut o
f the
theo
ry o
f spe
ech
per-
cept
ion
itsel
f int
o de
cisio
n pr
oces
ses,
but a
re in
tegr
ated
dire
ctly
into
the
perc
eptu
al p
roce
ss in
a u
nifie
d w
ay, G
iven
top-
dow
n as
wel
l as
botto
m-
up p
roce
ssin
g, th
e de
cisio
n m
echa
nism
s req
uire
d fo
r gen
erat
ing'
ove
rtre
spon
ses t
hat r
eflectlexical and other contextual influences are g
reat
lysim
plifi
ed; n
o sp
ecia
l pro
visio
n ne
eds t
o be
m.,d
e fo
r com
bini
ng le
xica
lan
d ph
onet
ic o
utpu
ts in
the
deci
sion
mec
hani
sm,
A se
cond
reas
on fo
r ret
aini
ng fe
edba
ck c
omes
up
whe
n w
e co
nsid
erth
e pr
oble
m o
f lea
rnin
g. A
lthou
gh w
e ha
ve n
ot d
iscus
sed
how
lear
ning
mig
ht o
ccur
in T
RACE
, we
have
ass
umed
that
the
mec
hani
sms o
f spe
ech
perc
eptio
n ar
e ac
quire
d th
roug
h m
odifi
catio
n of
con
nect
ion
stren
gths
.V
ery
roug
hly,
in m
any
lear
ning
sche
mes
, 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
rticu
lar u
nit h
as b
een
tune
d" to
resp
ond
to a
par
ticul
ar p
atte
rn. i
t is d
iffic
ult t
o re
tune
it: i
tfir
es w
hen
its "
expe
cted
" pat
tern
is p
rese
nted
. and
whe
n it
fires
. its
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
tend
ency
to re
spon
d to
that
pat
tern
onl
y in
crea
ses.
Feed
back
pro
vide
s aw
ay to
bre
ak th
is vi
ciou
s cyc
le, I
f hig
her l
evel
s in
sist
that
a p
artic
ular
phon
eme
is pr
esen
t. th
en th
e un
it fo
r tha
t 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 p
hone
me
inste
ad; t
hen
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
lligen
cere
quire
d fo
r 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 w
hich
exh
ibit
this
inte
l-lig
ence
exp
licit.
As f
orm
ulat
ed h
ere.
thes
e m
echa
nism
s ar
e in
cred
ibly
sim
ple;
yet
they
app
ear t
o bu
y qu
ite a
lot w
hich
ofte
n ge
ts p
ushe
d in
toun
spec
ified
"de
cisio
n" and "postperceptual guessing" p
roce
sses
(e.
Forster. 1976),
Fina
lly. t
h~ .s
ucce
ss
of
TRA
CE a
lso d
epen
ds u
pon
its ar
chite
ctur
e,ra
ther
than
the
fund
amen
tal c
ompu
tatio
nal p
rinci
ples
' of a
ctiv
atio
n an
dcompetition. or the decision to include feedback, By
arc
hite
ctur
e, w
emean the organization
of
the Trace structure into layers consisting
of
units
corre
spon
ding
to it
ems o
ccur
ring
at p
artic
ular
tim
es w
ithin
the
utte
ranc
e,A
s we
note
d in
the
intro
ducL
ion.
this
arch
itect
ure
is on
e w
e de
cide
d up
ononly after several other kinds
of
arch
itect
ure
had
faile
d,Th
ere
are
thre
e pr
inci
ple
posi
tive
cons
eque
nces
of
th
e TR
ACE
arc
hi-
tect
ure.
Firs
t, it
keep
s stra
ight
wha
t occ
urre
d w
hen
in th
e sp
eech
stre
am,
Com
petit
ion
occu
rs o
nly
betw
een
units
com
petin
g to
repr
esen
t the
sam
eportion 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,
Furth
erm
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
segm
ent l
onge
r 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,
Se
cond
, the
arc
hite
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 the
mod
el is
toaccount for the fact that the identity
of
a ph
onem
e (o
r a w
ord;
War
ren
&Sh
erm
an, 1
974) can be influenced by w
hat c
omes
afte
r it a
s w
ell a
s w
hat
comes beforeiL Some kind
of
reco
rd
of
the
past
is ne
cess
ary
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' a
ndef
ficie
nLTh
ird, t
he T
race
stru
ctur
e pr
ovid
es a
n ex
plic
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 whi
ch c
arry
out
per
cept
ual p
roce
ssin
g an
d th
ose
whi
ch p
rovi
de a
wor
king
mem
ory
for t
he re
sults
of t
he p
erce
ptua
l pro
cess
. At o
ne a
ndth
e sa
me
time.
the
Trac
e 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 f
orih
e fa
ct th
atco
here
nt m
emor
y tra
ces
pers
ist l
onge
r tha
n in
cohe
rent
one
s. T
he c
o-he
rent
one
s re
sona
te th
roug
h in
tera
ctiv
e (th
at is
, bot
tom
-up
and
top-
dow
n) a
ctiv
atio
n. w
hile
inco
here
nt o
nes f
ail t
o es
tabl
ish a
reso
nanc
e an
dth
eref
ore
die
away
mor
e ra
pidl
y,Se
vera
l of
th
ese
aspe
cts o
f TRA
CE o
verla
p w
ith a
ssum
ptio
ns m
ade
inot
her m
odel
s, as
men
tione
d in
pre
viou
s sec
tions
; con
tinui
ty b
etw
een
wor
king
mem
ory
and
the
perc
eptu
al p
roce
ssin
g str
uctu
res h
as b
een
sug-
geste
d by
a n
umbe
r of o
ther
aut
hors
(e.g
,. Co
nrad
,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
stru
ctur
e ha
s pre
viou
sly b
een
advo
cate
d by
Cro
wde
r (19
78,
1981) and Grossberg (1978), Indeed, G
ross
berg
has
not
ed th
at re
sona
ting
activ
atio
n/co
mpe
titio
n pr
oces
ses
can
both
enh
ance
a p
erce
ptua
l rep
re-
sent
atio
n an
d in
crea
se th
e re
tent
ion
of a
repr
esen
tatio
n; h
is a
naly
sis
ofin
tera
ctiv
e-ac
tivat
ion
proc
esse
s in
perc
eptio
n an
d ap
emor
y ca
ptur
es th
eco
ntin
uity
of p
erce
ptio
n an
d m
emor
y as
wel
l as
man
y ot
her d
esira
ble
prop
ertie
s of
in
tera
ctiv
e-ac
tivat
ion
mec
hani
sms,
Som
e D
efic
ienc
ies
of T
RACE
. Alth
ough
TRA
CE h
as h
ad a
num
ber o
f im
porta
nt su
cces
ses,
it a
lso h
asa number of equally important deficiencies. A number
of these deficien-
cies
rela
te to
sim
plify
ing
assu
mpt
ions
of t
he si
mul
atio
n m
odel
. It i
s im
-portant to be clear that such deficiencies are not in
trins
ic to
the
basic
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
ersta
nd it
s bas
ic p
rope
rties
. 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 sa
lient
and
use
ful,
and
over
lap
an e
qual
amount from one phoneme to another-are no
t pre
sent
in T
RAC
E I.
Obv
ious
ly a
fully
real
istic
mod
el w
ould
take
acc
ount
of s
uch
dine
renc
es.
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 fre
quen
cy, a
nd so
me
mec
ha-
nism
s for
exp
loiti
ng a
vaila
ble
cues
to w
ord
boun
darie
s,Another deficiency
of
the
mod
el is
that
the
deci
sion
mec
hani
sms h
ave
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 fo
r ,de
cidi
ng w
hen
a no
nwor
d ha
s bee
npr
esen
ted.
Nor
hav
e w
e sp
ecifi
ed h
ow d
ecis
ion
proc
esse
s w
ould
act
ually
use
the
info
rmat
ion
avai
labl
e at
the
wor
d le
vel t
o lo
cate
wor
d-in
itial
pho
-ne
mes
, A re
late
d pr
oble
m is
the
lack
of a
n ex
plic
it pr
ovisi
on fo
r vari-
abili
ty in
the
activ
atio
n an
d/or
read
out p
roce
sses
. Inc
orpo
ratin
g va
ri-ab
ility
dire
ctly
into
a si
mul
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
TRAC
E M
OD
EL
abili
ty to
cap
ture
the
deta
iled
prop
ertie
s of
reac
tion
time
dist
ribut
ions
and
erro
rs (R
atcl
iff. 1
978)
.So far we have considered de
ficie
ncie
s whi
ch w
e w
ould
attr
ibut
e to
sim
plify
ing
assu
mpt
ions
ado
pted
to k
eep
TRAC
E as
sim
ple
and
trans
-pa
rent
in it
s beh
avio
r as p
ossib
le. H
owev
er. t
here
are
som
e pr
oble
ms t
hat
are
intri
nsic
to th
e ba
sic
stru
ctur
e of
the
mod
el,
One
fund
amen
tal d
efic
ienc
y of
TRA
CE is
that
fact
that
it requires
mas
sive
dupl
icat
ion
of u
nits
and
conn
ectio
ns. c
opyi
ng o
ver a
nd o
ver
agai
n th
e co
nnec
tion
patte
rns
thaI
' det
erm
ine
whi
ch fe
atur
es a
ctiv
ate
whi
ch p
hone
mes
and
whi
ch p
hone
mes
act
ivat
e w
hich
wor
ds. A
s w
~ al
-re
ady
note
d. le
arni
ng in
act
ivat
ion
mod
els (
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 c
onne
ctio
ns b
etw
een
units
dep
endi
ng o
n th
eir
sim
ulta
neou
s ac
tivat
ion,
Giv
en T
RAC
E's
arch
itect
ure.
suc
h le
arni
ngw
ould
not
gen
eral
ize
from
one
par
t of t
he T
race
to a
noth
er a
nd so
wou
ldno
t be
acce
ssib
le fo
r inp
uts a
risin
g at
diff
eren
t loc
atio
ns in
the
Trac
e, A
seco
nd p
robl
em is
that
the
mod
el. a
s is
. is
inse
nsiti
ve to
var
iatio
n in
glo
bal
para
met
ers,
such
as s
peak
ing
rate
, spe
aker
cha
ract
erist
ics a
nd a
ccen
t,an
d am
bien
t aco
ustic
cha
ract
erist
ics,
A th
ird d
efic
ienc
y is
that
it fa
ils to
acco
unt f
or th
e fa
ct th
at o
ne p
rese
ntat
ion
of a
wor
d ha
s an
effe
ct 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
rrent
ver
sion
of th
e m
odel
. sim
ply
exci
te s
epar
ate
toke
ns fo
r the
sam
e w
ord
in d
iffer
ent p
arts
of t
he T
race
,A
ll th
ese
defic
ienc
ies r
efle
ct th
e fa
ct, t
hat t
he T
RAC
E co
nsis
ts o
f ala
rge
set o
f ind
epen
dent
toke
ns o
f eac
h fe
atur
e. p
hone
me,
and
wor
d un
it,W
hat a
ppea
rs to
be
calle
d fo
r ins
tead
is a
mod
el in
whi
ch th
ere
is a
sin
gle
store
d re
pres
enta
tion
of e
ach
phon
eme
and
each
wor
d in
som
e ce
ntra
lrt;
pres
enta
tiona
l stru
ctur
e, If
this
struc
ture
is a
cces
sed
ever
y tim
e th
ew
ord
is p
rese
nted
, the
n w
e co
uld
acco
unt f
or re
petit
ion
prim
ing
effe
cts,
Like
wise
. if t
here
wer
e a
singl
e ce
ntra
l stru
ctur
e. le
arni
ng c
ould
occ
ur 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 cha
nges
in g
loba
l par
am~
eter
s or
spe
aker
cha
ract
eris
tics,
How
ever
. it r
emai
ns n
eces
sary
to k
eep
stra
ight
the
rela
tive
,tem
pora
llo
catio
n of
diff
eren
t fea
ture
. pho
nem
e. a
nd w
ord
activ
atio
ns. T
hus
it w
illnot do to simply abandon the Trace in favor of a single set of units
cons
istin
g of
just
one
copy
of e
ach
phon
eme
and
one
copy
of e
ach
wor
d,It
seem
s tha
t we
need
to h
ave
thin
gs b
oth
way
s: w
e ne
ed a
cen
tral
repr
esen
tatio
n th
at p
lays
a ro
le in
pro
cess
ing
ever
y ph
onem
e an
d ev
ery
wor
d an
d th
iit is
subj
ect t
o le
arni
ng, r
etun
ing.
and
prim
ing,
We
also
nee
dto
kee
p a
dyna
mic
trac
e of
the
unfo
ldin
g re
pres
enta
tion
of th
e sp
eech
stre
am. s
o th
at w
e ca
n co
ntin
ue to
acc
omm
odat
e bo
th le
ft an
d rig
ht c
on"
text
ual e
ffect
s.
MC
CLE
LLAN
D A
ND
ELM
AN
We
are
curre
ntly
beg
inni
ng to
dev
elop
a m
odel
that
has
thes
e pr
oper
-tie
s, ba
sed
on a
sche
me
for u
sing
a ce
ntra
l net
wor
k of
uni
ts to
tune
the
conn
ectio
ns b
etw
een
the
units
in th
e Tr
ace
in th
e co
urse
of p
roce
ssin
g.th
ereb
y ef
fect
ivel
y pr
ogra
min
g it
"on
the
fly,"
Sim
ilar i
deas
hav
e al
read
ybe
en a
pplie
d to
visu
al w
ord
reco
gniti
on (M
cCle
lland
, 198
5, 1
986)
. Our
hope
is th
at a
new
ver
sifJn
of th
e m
odel
bas
ed o
n th
ese
idea
s will
pre
serv
eth
e po
sitiv
e fe
atur
es o
f TRA
CE I
and
TRA
CE II
. whi
le o
verc
omin
g th
eir
principle deficiencies,
Som
e G
ener
al Is
sues
in S
peec
h an
d La
ngua
ge P
erce
ptio
nTh
ere
are
a nu
mbe
r of g
en~r
al is
sues
in sp
eech
and
lang
uage
' per
cep-
tion,
Fou
r que
stion
s in
parti
cula
r app
ear t
o lie
clo
se to
the
hear
t of o
urco
ncep
tion
of w
hat s
peec
h pe
rcep
tion
is al
l abo
ut. F
irst.
wha
t are
the
basic
uni
ts in
spee
ch p
erce
ptio
n? S
econ
d. w
hat i
s the
per
cept
. and
whi
chas
pect
s of t
he p
roce
ssin
g of
spok
en la
ngua
ge sh
ould
be
calle
d pe
rcep
tual
?Th
ird. w
hat i
s the
repr
esen
tatio
n of
ling
uisti
c ru
les?
Fou
rth. i
s the
re a
ny-
thin
g un
ique
or s
peci
al a
bout
spe
ech
perc
eptio
n? W
e co
nclu
de th
is a
rticl
eby
con
sider
ing
each
issu
e fro
m th
e pe
rspe
ctiv
e w
e ha
ve d
evel
oped
thro
ugh
the
cour
se o
f our
~xp
lora
tions
of T
RACE
.What is the perceptual "nit?
Thro
ugho
ut th
is ar
ticle
. we
have
con
sid-
ered
thre
e le
vels
of p
roce
ssin
g-fe
atur
e, p
hone
me,
and
wor
d. A
t eac
hle
vel,
indi
vidu
al p
roce
ssin
g un
its st
and
for h
ypot
hese
s abo
ut th
e fe
atur
es,
phon
emes
. and
wor
ds th
at m
ight
be
pres
ent a
t diff
eren
t poi
nts i
n th
e in
put
strea
m, I
t is w
orth
not
ing
that
mos
t asp
ects
of th
e m
odel
's pe
rform
ance
, are
inde
pend
ent o
f the
spec
ific
assu
mpt
ions
that
we
have
mad
e ab
out t
heun
its, o
r eve
n th
e le
vels.
Thu
s. if
we
repl
aced
the
phon
eme
leve
l with
demisyllables (Fujimura & Lovins, 1978) or
pho
nem
e tri
ples
(Wic
kelg
ren.
1969
), ve
ry li
ttle
of th
e be
havi
or o
f the
mod
el w
ould
cha
nge.
The
se u
nits
can
capt
ure
som
e of
the
coar
ticul
ator
y in
fluen
ces o
n ph
onem
e id
~ntit
y.an
d th
ey w
ould
redu
ce s
ome
of th
e w
ord-
boun
dary
am
bigu
ities
face
d by
the
curre
nt v
ersio
n of
the
mod
el, b
ut n
eith
er co
articulatory influences
nor w
ord
boun
dary
am
bigu
ities
wou
ld d
isap
pear
alto
geth
er (s
ee E
lman
& M
cCle
lland
. in
pres
s, fo
r fur
ther
dis
cuss
ion)
, In
fact
, int
erac
tive
activ
atio
n m
odel
s lik
e TR
ACE
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
slice
of T
RAC
E m
ight
be
repl
aced
by
adi
ffere
nt se
t of u
nits
whi
ch d
id n
ot h
ave
a on
e-to
-one
cor
resp
onde
nce
toph
onem
es. A
pho
nem
e w
ould
be
repr
esen
ted
by a
par
ticul
ar p
atte
rn o
fac
tivat
ion
over
the
set o
f uni
ts (e
ach
repr
esen
ting,
per
haps
. to
som
e co
n-ju
nctio
n of
low
er le
vel f
eatu
res)
rath
er th
an b
y a
singl
e un
it in
the
set.
Ther
e ar
e so
me
com
puta
tiona
l adv
anta
ges o
f dist
ribut
ed re
pres
enta
tion
com
pare
d to
our
"on
e un
it on
e co
ncep
t" assumption (Hinton, Mc-
""'
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
LMAN
Cle
lland
, & R
umel
hart,
in p
ress
), bu
t it i
s ve
ry d
iffic
ult t
o fin
d pr
inci
pled
way
s of d
istin
guish
ing
betw
een
loca
l and
dist
ribut
ed re
pres
enta
tiona
lsc
hem
es e
mpi
rical
ly, I
ndee
d, in
cer
tain
cas
es th
ere
is an
exa
ct m
appi
ngan
d, in
gen
eral
, it i
s pos
sible
to a
ppro
xim
ate
mos
t asp
ects
of th
e be
havi
orof
a lo
cal s
chem
e w
ith a
dist
ribut
ed o
ne a
nd v
ice
vers
a (S
mol
ensk
y,1986). In light of this, our u
se o
f loc
al a
s op
pose
d to
dis
tribu
ted
repr
e-se
ntat
ions
is n
ot p
erha
ps a
s si
gnifi
cant
as
it m
ight
app
ear a
t firs
t gla
nce.
Wha
t is e
ssen
tial i
s the
info
rmat
ion
that
the
repr
esen
tatio
n ca
ptur
es,
rath
er th
an w
heth
er it
doe
s so
via
dis
tribu
ted
or 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
) rep
rese
ntin
g a
mut
ually
exc
lusi
ve a
ltern
ativ
e m
akes
itm
uch
easie
r to
rela
te th
e sta
tes o
f the
pro
cess
ing
syste
m to
ove
rt re
spon
seca
tego
ries b
ut is
not
oth
erw
ise a
fund
amen
tal f
eatu
re o
f the
stru
ctur
e of
the
mod
el.
What is the percept?
At a
num
ber o
f poi
nts i
n th
is ar
ticle
, we
have
allu
ded
to w
ays i
n w
hich
our
con
cept
ion
of p
erce
ptio
n di
ffers
from
the
usag
e of
oth
er a
utho
rs, S
uch
conc
epts
as p
erce
ptio
n ar
e in
here
ntly
tied
to th
eory
, and
onl
y de
rive
thei
r mea
ning
with
resp
ect t
o pa
rticu
lar t
heo-
retic
al c
onst
ruct
s, W
here
doe
s th
e TR
ACE
mod
el p
lace
us,
then
, with
resp
ect t
o th
e qu
estio
n, w
hat i
s spe
ech
perc
eptio
n?Fo
r one
thin
g, T
RAC
E bl
urs
the
dist
inct
ion
betw
een
perc
eptio
n an
dother aspects of cognitive processing, T
here
is re
ally
no
clea
r way
inTR
ACE
to sa
y w
here
per
cept
ual p
roce
ssin
g en
ds a
nd c
once
ptua
l pro
-ce
sses
or m
emor
y be
gin,
How
ever
, fol
low
ing
Mar
rs (1
982)
def
initi
on o
fvi
sual
per
cept
.ion,
we
coul
d sa
y th
at s
peec
h pe
rcep
tion
is th
e pr
oces
s of
form
ing
repr
esen
tatio
ns o
f the
stim
ulus
-the
spea
kers
utte
ranc
e-at
seve
ral l
evel
s of d
escr
iptio
n, T
RACE
pro
vide
s suc
h a
set o
f rep
rese
nta-
tions
, as w
ell a
s pro
cess
es to
con
struc
t the
m. O
n th
is vi
ew, t
hen,
the
Trac
e is
the
perc
ept,
and
inte
ract
ive
activ
atio
n is
the
proc
ess o
f per
cep-
tion, A
spec
ts of
this
defin
ition
are
app
ealin
g. F
or e
xam
ple,
on
this
view
, the
perc
ept i
s a v
ery
rich
obje
ct, o
ne th
at re
fers
bot
h to
abs
tract
, con
cept
ual
entit
ies l
ike
wor
ds a
nd p
erha
ps a
t hig
her l
evel
s eve
n m
eani
ngs,
as
wel
las
to m
ore
conc
rete
ent
ities
like
aco
ustic
sign
als a
nd fe
atur
es, P
erce
ptio
nis
not r
estri
cted
to o
ne o
r a su
bset
of l
evel
s, as
it is
in c
erta
in m
odel
s(e
.g.,
Mar
slen
-Wils
on, 1
980;
Mor
ton,
1979
).O
n th
e ot
her h
and,
the
defin
ition
seem
s ove
rly li
bera
l, fo
r the
re 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 e
xper
imen
ts, b
oth
in sp
eech
(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 are
' at b
est a
cces
sed
only
with
ext
ra ti
me
or e
ffort.
On
this
evid
ence
, if p
erce
ptio
n is
to fo
rm re
p-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
RACE
, the
n pe
rcep
tion
is qu
ite in
depe
nden
t of t
he e
xper
ienc
e of
the
perc
eive
r and
of a
cces
s to
the
perc
ept.
Put 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 n
ot th
e pe
rcep
tual
"exp
eric
nce.
This
doe
s no
t 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 p
arts
of i
t may
be 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
view
, it w
ould
not
be
in-
cohe
rent
to s
uppo
se th
at re
pres
enta
tions
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 sep
arat
e fro
m th
e an
alys
is 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 o
fac
cess
to th
e Tr
ace.
In o
ur si
mul
atio
ns, w
e ha
ve a
ssum
ed th
at th
e de
ci-
sion
mec
hani
sm c
ould
be
dire
cted
with
equ
al fa
cilit
y to
all
leve
ls. b
ut th
ism
ay tu
rn o
ut to
be
an a
ssum
ptio
n th
at d
oes n
ot a
pply
in a
ll ca
ses.
HolY are rules represe~ted?
It is
com
mon
in th
eorie
s of l
angu
age
toas
sum
e w
ithou
t disc
ussio
n th
at li
ngui
stic
rule
s are
repr
esen
ted
"...'
SlIc
hin 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 d
iftic
ultie
sas
soci
ated
with
this
view
, Firs
t, it
:doe
s not
exp
lain
how
exc
eptio
ns a
reha
ndle
d; it
wou
ld se
em th
at fo
r eve
ry e
xcep
tion,
ther
e w
ould
hav
e to
be
a sp
ecia
l rul
e th
at ta
kes p
rece
denc
e ov
er th
e m
ore general formulation.
Seco
nd, i
t doe
s no
t exp
lain
asp
ects
of r
ule
acqu
isiti
on b
y ch
ildre
n le
ai'n
ing
lang
uage
, par
ticul
arly
the
fact
that
" rul
es a
ppea
r to
be a
cqui
red,
at l
east
to a
larg
e ex
tent
, on
a w
ord
by w
ord
basis
; acq
uisit
ion
is m
arke
d by
agr
adua
l spr
ead
of th
e ru
le fr
om o
ne le
xica
l ite
m o
r set
of l
exic
al it
ems t
oot
hers
. Thi
rd, i
t doe
s not
exp
lain
how
rule
s com
e ,in
to e
xiste
nce
histo
ri-ca
lly; a
s with
acq
uisit
ion,
it a
ppea
rs th
at ru
les s
prea
d gr
adua
lly o
ver t
hele
xico
n, It
is d
iffic
ult t
o re
conc
ile se
vera
lofth
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 l
ike
TRA
CE a
nd th
e in
tera
ctiv
e-ac
tivat
ion
mod
el o
f wor
d re
c-og
nitio
n ta
ke a
ver
y di
ffere
nt p
ersp
ectiv
e on
the
issue
of l
ingu
istic
rule
s,Th
ey a
re n
ot re
pres
ente
d as
suc
h, b
ut ra
ther
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
essin
g th
e pa
rticu
lar i
tem
s whi
ch e
mbo
dy th
ese
rule
s. Su
ch a
mec
h-an
ism a
ppea
rs to
avo
id th
e pr
oble
m o
f exc
eptio
ns w
ithou
t dift
icul
ty, a
ndto
hol
d ou
t the
hop
e of
acc
ount
ing
for t
he o
bser
vatio
n th
at ru
le a
cqui
sitio
nan
d ru
le c
hang
e ar
e st
rong
ly ti
ed to
par
ticul
ar it
ems
whi
ch e
mbo
dy th
eru
~.
Wha
t is
sped
t,! a
bollt
...'p
eech
? We dose by ra
ising
a q
ucsti
on th
at o
ften
TRAC
E M
OD
ELM
C C
LELL
AND
AN
D E
l ".'I
AN
REFE
REN
CES
Bagl
ey, W
. C. (
I~), The apperception o
r the
:spo
ken
sent
ence
: A st
udy
in th
e ps
ycho
logy
of language,
Am
eric
an Jo
llrnc
II of
P,fy
dlol
oR.",
12
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130.
Ballard. D. H.. Hinton, G. E,. &: Sejnowski, T. J. (1983). l'arallel visual computation.
Na-
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mea
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Und
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n G
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Sll"
Ole
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af;n
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ce,u;
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emor
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ustic
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e~ch
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G. (
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d I'O
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The
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h un
ders
tand
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m: A
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81).
Engl
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CoR-
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alke
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orth
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Identifying the speech codes.
CoRn
;I;,'e
P,f
ydw
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ss, D
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&: G
erns
bach
er. M
. A. (
1983
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rack
ing
the
dual
cod
e: T
owar
d a
unita
ry m
odel
of phoneme identification.
Jollr
nal o
f Ver
bal L
earn
;nR
and
Ver
bal B
ella
,';or
, 22
. 609
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3.
com
es u
p in
disc
ussio
ns o
f the
mec
hani
sms o
f spe
ech
perc
eptio
n. Is
spee
ch sp
ecia
l? If
so. i
n w
hat w
ays?
It h
as b
een
argu
ed th
at sp
eech
issp
ecia
l bec
ause
of t
he d
istin
ctiv
e ph
enom
enon
of c
ateg
oric
al p
erce
ptio
n;be
caus
e of
the
enco
dedn
ess o
f inf
orm
atio
n ab
out o
ne p
hone
me
in th
ose
porti
ons o
flhe
spee
ch st
ream
that
are
gen
eral
ly th
ough
t to
repr
esen
t oth
erph
onem
es; b
ecau
se th
e in
form
atio
n' in
the
spee
ch s
tream
that
indi
cate
sth
e pr
esen
ce o
f a p
artic
ular
pho
nem
e ap
pear
s not
to b
e in
varia
nt a
t any
obvi
ous p
hysic
al le
vel;
beca
use
Qf t
he la
ck o
f seg
men
t bou
ndar
ies.
and
for a
var
iety
of o
ther
reas
ons.
Ove
r the
last
seve
ral y
ears
, a n
umbe
r of e
mpi
rical
arg
umen
ts ha
ve b
een
put f
orw
ard
that
sugg
est t
hat p
erha
ps sp
eech
may
not
be
so sp
ecia
l, 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 d
omai
ns (M
edin
& B
arsa
lou,
in p
ress
).an
d a
larg
e nu
mbe
r of s
tudi
es h
ave
repo
rted
cate
goric
al p
erce
ptio
n in
othe
r mod
aliti
es (s
ee R
epp.
198
4. fo
r a d
iscus
sion)
, Com
puta
tiona
l wor
kon
pro
blem
s in
vis
ion
have
mad
e cl
ear t
hat i
nfor
mat
ion
that
mus
t be
extra
cted
from
vis
ual d
ispl
ays
is -o
ften
com
plex
ly e
ncod
ed w
ith o
ther
info
rmat
ion
(Bar
row
& T
enen
baum
; 197
8; M
arl'.
1982
), an
d th
e la
ck
clea
r bou
ndar
ies
bet;w
een
perc
ept m
il un
its in
visi
on is
not
orio
us (B
alla
rdet a!.. 1983: M
arr.
1982
), Th
us, t
he p
sych
olog
ical
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 sp
eech
per
cept
ion
is di
ffere
nt th
an th
e co
nste
llatio
n of
prob
lem
s fa
ced
in a
ny o
ther
par
ticul
ar c
ase.
but
mos
t of t
he in
divi
dual
prob
lem
s th
emse
lves
do
appe
ar to
hav
e an
alog
s in
oth
er d
omai
ns.
We
ther
efor
e pr
efer
to v
iew
spee
ch a
s an
exce
llent
test
bed
for t
hede
velo
pmen
t of a
n un
ders
tand
ing
of m
echa
nism
s whi
ch m
ight
turn
out
to h
ave
cons
ider
ably
bro
ader
app
licat
ion,
Spe
ech
is sp
ecia
l to
us, s
ince
it so
rich
ly c
aptu
res t
he m
ultip
licity
of t
he so
urce
s of c
onstr
aint
whi
chm
ust b
e ex
ploi
ted
in p
erce
ptua
l pro
cess
ing,
and
bec
ause
it so
cle
arly
indi
cate
s the
pow
erfu
l inf
luen
ces o
f the
mec
hani
sms o
f per
cept
ion
on th
eco
nstru
cted
per
cept
ual r
epre
sent
atio
n. W
e se
e th
e TR
ACE
mod
el a
s an
exam
ple
of a
larg
e cl
ass o
f mas
sivel
y pa
ralle
l. in
tera
ctiv
e m
odel
s tha
tho
lds g
reat
pro
mise
to p
rovi
de a
dee
per u
nder
stand
ing
of th
e m
echa
nism
sge
nera
lly u
sed
in p
erce
ptio
n,
Ackley, D.. Hinton. Goo & Sejnowski, T. (l9
8.'i)
, Bol
lzm
ann
mac
hine
s: C
onst
rain
t sat
isfa
c-tion networks thai learn.
C"N
n;I;I
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. 1\,
t 19771, Neural models with cognitive im
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atio
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n D
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Sam
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f('f;I
I re
"JillN
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cepl
i"n C
/IIJ
mm
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on.
Hm
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e,N
J: E
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TRAC
E M
OD
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C C
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AND
AN
D E
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l Re
,'iel
l', 7
6,1.
5.
Wol
f, J.
Joo
& W
oods
, W. A
. (19
781,
The
HW
IM sp
eech
understanding system. In W. A.
lea (Ed.
),
Tren
d.t i
n Sp
ttcll
rt~'C/
Rniti
(",.
Engl
ewoo
d Cl
iffs,
NJ:
Pren
tice-
Hal
l.(A
ccep
ted
July
2.5, 198.5)
Recommended