Auditory Illusions and Confusions

These failures of perception are studied because they isolate and

clarify sonle fundamental processes that normally lead to accurac.

of perception and appropriate Interpretation of ambiguous sound.

For more than a century visu al illu-sions have been of particular inter-est to students of perception. AI-

though they are in effect misjudgmentsof the l'eal world, they apparently reBectthe operation of fundamental perceptualmechanisms, and they serve to isolateand clarify visual processes that are nor-mally inaccessible to investigation. Audi-tory illusions, on the other hand, havereceived little scientific attention. Until

recently the Beeting nature of auditorystimuli made it difficult to create, control

and reproduce sound patterns as readilyas visu al ones. The tape recorder made iteasy to manipulate sounds, and yet fora time there was little examination of

auditory illusions, perhaps because therewas no historical tradition to build on-

no puzzles inherited from the experi-mental psychologists of the past cen-tury, as there were in the case of opticalillusions. Some new investigations, how-ever, have led to the discovery of illu-sions in hearing that help to explain thehuman ability to extract informationfrom Beeting patterns of sound. Theseinvestigations have also led to the iden-

tification of confusions in hearing thathelp to explain some limitations of thatability.

Consider for a moment that you are ata convention banquet. \Vhile you

are still finishing your dinner the after-dinner speeches begin. The clatter ofdishes masks some of the speech sounds,as do occasion al coughs from your neigh-bors and your own munching. Nonethe-less, you may be able to understand

what the speaker is saying by utilizingthe information that reaches you duringintervals that are relatively free of theseinterfering noises. ln order to understandhow speech perception functions in thepresence of transient noises, we and

Charles J.Obusek did some experiments

30

by Richard M. Warren and Roslyn P. Warrcn

last year in our laboratory at the Univer-sity of 'Wisconsin at Milwaukee. First werecorded the sentence "The state gover-nors met with their respective legisla-tures convening in the capital city."Then we carefully cut out of the tape re-cording of the sentence one phoneme, orspeech :;ound: the first "s" in "Iegisla-tures." We also cut out enough of thepreceding and following phonemes toremove any transition al eues to the iden-tity of the missing speech sound. Final-Iy, we spliced the recorded sound of acough of the same duration into the tapeto replace the deleted segment.

\Vhen this doctored sentence was

played to listeners, we found that wehad created an extremely compelling il-lusion: the missing speech sound washeard as clearly as were any of the pho-nemes that were physically present. Wecalled this phenomenon "phonemic res-toration." Even on hearing the sentenceagain, after having been told that asound was missing, our subjects couldnot distinguish the ilIusory sound fromthe real one. One might expect that themissing phoneme could be identified bylocating the position of the cough, butthis strategy was of no help. The coughhad no clear location in the sentence; it

seemed to coexist with other speechsounds without interfering with theirintelligibility. Phonemic restoration alsooccurred with other sounds, such as abuzz or tone, when these sounds were asloud as or louder than the loudest sound

in the sentence. Moreover, phonemicrestorations were not limited to singlespeech sounds. The en tire syllable "gis"in "Iegislatures" was heard clearly whenit was replaced by an extraneous soundof the same duration.

We did find a condition in which the

missing sound was not restored. \Vhena silent gap replaced the "s" in "legisla-tures," the gap could be located within

the sentence and the missing sound idtified. ln visual terrns, it was as iferasure of a letter in a printed text couÏd'~be detected, whereas an opaque blot']over the same symbol would ;esult iJi~

iIlusory perception of the obliterated let-'ter, with the blot appearing as a trans-îparent smear over another portion of the!text [see top illustration on pages32 and!33]. Of course, in vision a blot can 001

localized readily, and even the mor~j1 . " f d ' .

11. " i!

e USlve proo rea el' 5 1 USIOns can ueliminated when the reader is told in ad]vance just where the error in the text J1'

curs. With phonemic restorations, holever, knowledge of the nature of tIjextraneous sound and of the identitybl,~.,the missing phoneme does not preventclear perception of the missing sound!:even when the stimulus is played to thc~;Jlistener as many times as he wÎôhes. :t:

The inability to localize an extraneo~jsound in a sentence was first reported2J1960 by the

,

British workers Peter L

I'

foged and Donald E. Broadbent. S'they employed brief intrusive 50(clicks and short hisses) and took

that no phoneme was obliterated, Pnemic restorations did not arisc. Sn .

short, nonmasking extraneouS 50were later used by a group at the,sachusetts Institute of Technology

included Jerry A. Fodor, Merrill F. -rett and Thomas Bever. They have:

ported that systematic errors in localthe clicks are caused by various fealof sentence structure, and they have';the errors to explore those featureS.

perceptual synthesis of the ?h

~

'

is accomplished on the basI.s ~fbal context. ln the case of the rnlSSIll

in "legislatures" the context pri~rabsent sound suffices for identifi,vVhat about a sentence so const

that the context necessary to idenobliterated sound does not co

..........

TORY ILLUSIONS are investigated in the authors' laborato-le subject, listening through headphones to a stimulus signal

generated by the equipment in the background and reproducedby the tape recorder, reports to the experimenter on what he hears.

31

aTIJe governors metstate

b~ ~ ~--

with legislatures conveningtheir respective in the capital---------- -------------

The governorsm~ with ~~ir_- - respect~~~~~I-atu~~~-~~~~~~~~-g___~-~h~_- ~i~~'

state

PHONEMIC RESTORATION is an illu,ion that ,how, the im-

portance of context in determining what sound is heard. A sentcneewas recorded on tape (a). Then the first "s" in "Iegiolatures" was

]ater? \Vith the symbo] " representing aloue! cough that replaces a speech sound,consider a spoken sentence bcginning,"It \Vas found that the" ee] was on the

_." The context provided by the lastword in the sentence shou]d resolve the

ambiguity and de termine the appropri-ate phonemic restoration, Among the\\'ords that eould complete the sentenceare "axJe," "shoe," "orange" and "tab]e."Each implies a e!ifj'erent speech soundfor the preceding \\"OH] fragment, re-spectivelv "wheel," "hec]," "pecJ" am]"mea1." PrcJiminary studies by Cary

H!GH TONE EUZZ

=00MILLISECONDS

one 7 th rée

<E 200MILLISECONDS

7>

excised and a cough of the same duration (black rectangle) wasspliced in its pla,'e (b L Wh en the altered sentence was played tsuhject" the mi",ing "s" was heard clearly Ic) and localization 07

Sherman in our laboratorv have indi-

cated that the listener e!oes experieneethe appropriate phonemie restoration,apparent]y by storing the ineomp]ete in-formation until the neccssary context issuppliee! so that the required phonemel'an he synthesizee!. \Ve are still im'esti-gating the influence of such factors asthe e!uration of extraneous sounds in re-

lation to the e!uration of the missingphoneme and the maximum temporalseparation bel\veen the ambiguous \\'ore!fragment and the resolving context thatwill still permit phonemic restoration.

LOIN TONE HISS

The use of subsequent context for Cor-reding errors hae! been suggested On]ogiea] groune!s by George A. l\JilIer ofRoekefeJJer University. He reasoned thatunless some sueh strategy were avaj].able, a mistake once made while Hsten-ing to spoken diseourse wauld cause

errors in interpreting the foJJowing par.tions of the message ta pile up, until the".

entire system eventuaJJy staJJed. The,long delays in museu]ar acth'jty that'have been observee! in the skilled tran-

scription of an ineoming message a]sosuggést that storage of ineaming ]an-:

HIGH TONE BU

'.IVVV~VWVVVV\MI.

7eight 7two 70ne

TEMPORAL CONFUSION was o]!'cncd "hen a high tone, a huzz,a low tone and a hiss (repre,ented here ,('hcmati('ally " eaeh la'ting

200 milli,c('on(b, werc l>re,ented repeatcdly (top). Subjects rouI

not report the sequcnec of the sounds "roperly whetber they tri

e e e e e e e e e e e 100 0 0 0 0 0 0 0 0 01i i i i i i i i i i i i i i i i i i ii i i il U'U U U U U U U U U u le e e e e e e

( 200 >MILLISECONDS

eeeeeeee 00000000

'<E 150 ,;>1~5071MILLISECONDS

i iiiiiiiiiiiiiiii UUUUUUUU", ,~ ~ "

e e e e e e e'e

FOUR VOWEL SOUNDS were used in another experim"nt ontemporal confusion. When the vowel sound, of "beet," "boot," "bit"

and "hut" wcre presented at a sustained level for 200 JO.

thcir scquen('e ('ould not hl' detcrmined (top), De]e

32

governors met with their respective legi latures ,convening

\Jecough wai' indefinite; "hen required to gue" the loeation, suh.

,;erlsgenerally mis,ed the corren pOi'ition hy ,everal phonemes, a,~dicated 1gray area). \Vheu a ,ileut gap, rather than a eough, re.

,uageinformation is assoeiateù \\'ith;rforcorrection, ln the 11)90's \\TilliamBryan,mù i'\oble I-Luter noted that high-

o/skilledteJegraphers Jistening to \[orsetildedid not transeribe the auùitory sig-naisthat constituteù a worù unlil .Ionieil ta 12 \Vords after the signaIs wnekard. If subsequent portions of themessagecould not pro vide helpflll con-lext,as in the case of stock qllotations or,lra~smissionsin cipher, the telegrapherslehanged their strategy and folloll'ed

[

fuemessage mllch more closel\' in time,

Telegraph coll1panies charged highcr

liONE HISS

'WWVWVW

~one

in the capital city.

plaeed the "s," the gaI' eould hl' loeated and the mi"ing sound

eould he identilied id J. This illustration, like those that fo!lolr, is

neeei'sarily an approximate representation o[ an auditor) dIee!.

rales for selllJing such messages precisel)'heeause thev lacked redundant conlcxl.\\ erc lherdore much more difficulllo re-ceive and had to he transmitted moreslowl\'.

This tclegrapher's technique ilIus-trates a surprising relalion that one en-COllnters again and again in perception:The development of an extremely com-plex procedure for data processing isnecessary lo achie\'e the deceptive im-pression of an "eas)'" perceptual task,FrolI1 time to time other \nJrkers 11<1\'e

noted the delay het\Veen language input

HIGH TOèJE BUZZ

, ~ three ~eight

so vcrhally or h)' onlering [our ('anl,. caeh reprc,<,nting a

Wh en ~ounds lasted :WOmillise('onds. suhjeeb ('ould order

and motor response, ln 192,,) \\'i1liamBook observed the similarit)' hct\\ecnt)'pe\Vriting and code transcription, rc-porting that in the case of an cxpertlypist "attention \Vas Pllshed ahead ofthe hands as far as possible (Llsllally fouror fi\'e \l'ords).''

Inahilit\. to locate the positioll of ex-trancous sounds in sentences repre-

.lents a failure in the ùelectioll of tem-

poral orùer. Il mighl he thollght llwlthis temporal cOllfusion resnlts l'rom aconflict bet\\'cen \'erbal and lion \'erbal

LOW TO'",=: HISS

~two s.

tltem with eards ImiddlcL When 'pokcn digit, wcre ,uh,titntcd [or

'OlllHb, it was ea~y for snhjeeb to report their order (bollOm).

iiiiiiiii u u u u u UU U

s of eaeh sound and replaeing it witlt ,ilence (middle) al.half of the ,ubje"b to determine the ,equenee. The ,e.

quenee was readily determined when vowels were gin>n normal

(Jualitie, o[ graduaI onset and de('ay. suggested by eurves 1bollom).

33

a

~

. .tres st r e ss t re s st re s stress t re s st re s s t re s s t re s s t r es s t r e s st r es s t re s st r e s s t r es st r e s st r e s st re s s t r e s s t re ss t re~st re

~ .......-..---

b

"

tress tress tress tress tress tress tress tress stress stress stress stress stress stress stress stress stress dress:tli~-- : ';~j'.",'

' ---

.dress dress dressdr~ss floris florls flor~s floris floris florist floris~ florist .florist florist Joyce. Joyce Joyce JOYC~

VERBAL TRANSFORMATION EFFECT is noted "hen suhjectsliotcn to a distinct recording of a single word repeated on a loop of

modes of perception. Recent ohserva-tions in our laboratory haye indicated,however, that inability to detect se-quence is not restricted to verhal-non-verhal interactions. ln 1968, during anexperiment on loudness, we IlOted ta oursurprise that listeners could not tell theorder of three successive sounds repeat-cd over and over \Vithout pauses. Thesounds-a hiss, a tone and a huzz-eat:hlastt'd a fifth of a second (200 millisec-

onds) and were recorded on a tape thatwas then spliced to form a loop. Theduration of each sound was qnite longcompared with the 70- ta 80-milliset:ondaverage for a phoneme in speet:h and\Vas weil \Vithin the temporal range usedin music for the successive notes of melo-

dies; the hiss, tone and buzz could each

be heard clearly. Yet it was impossible toteH the order of the sounds. The patternswirled by, the temporal structure tan-talizingly just beyond one's grasp.

It might he thought that a little ad-Yance planning \\'ould make the taskeasy. It should be po~sible, for example,to t:ollcentrate on one of the sounds (saythe hiss) and then decide \\'hether thesound that follows it is a tone or a buzz;

this single decision wou Id fix the thirdsound in the remaining slot and solvethe probJem. ln practice, however, thesingle det:ision cannot be made withaccuracy. Out of 50 listeners we found

that only 22 named the order correctly-slightly fewer than the 50 percent cor-

rcct ans\\"Crs that wou Id be expccted byt:hallt:e aJone,

This seemed at first ta contradict the

findings of earlier studies. Results re-ported by Ira Hirsh of the St. Louis Cen-

trai Institute for the Deaf and by othershad indicated that temporal resolution ofsu ch sounds as tones, hisses and buzzes

should be possible down to a separationof about 20 milliseconds-even less time

than is required for accurate temporalordering of the sounds forming speech ormusic. These values, however, had been

based on pairs of sounds. The subjectslistened to a single pair (such as atone

34

tape (a). One might expect a kind of reversaI effect, with the stim.

ulus "treos" perceiveù sometimes as "reol." Insteaù lack of context

and a hiss) and reported their order. It\Vas possible, we reasoned, that subjectscould say which sound came first and

which last not by actuaHy perceiving thetemporal order as such hut by detectingwhich of the sounds occurred at eitherthe onset or the termination of the stim-

ulus pair. ln 1959 Broadbcnt and Lade-foged had suggested that the ability oftheir subjects ta order pairs of sonndsmight be based on the "quality" of thepair as a whole. Could that "quality" bedctermined by which sound was prescntat the onset and/or the tennination of

the brief pair?With thresho]d judgments of this kind,

\\.hen subjects are \\'orking at the limitof their ability, introspection as ta howthey make their decisions is particularlvdiffieult; they simply cannot say. To de-termine what criteria are actually beingused one must reJy on experiments. \Vereturned ta our recvcled 200-millisecond

stimuli (hiss, tone, buzz) that could notbe ordered, but this time we inserted athree-second interval of silence between

successive presentations of the three-sound sequence. ~Iost listeners couldnow identify the first and last items inthe series correctly, somewhat more ac-curately in the case of the last sound.This supported our suspicion that "se-quence perceptjon" \Vith pairs of soumIsrepresents a special case and is reallyperception of onset and termination.

1n Ol'der to examine further the percep-tion of temporal order in the absence

of onset and termination cues, we em-

p]oyed a variety of repeated four-itemsequences. The chance of guessing theorder correctly, stm"ting \\'ith whicheversound one chooses, is one in six. \Vith a

sequence consisting of a high toue (afrcquency of 1,000 hertz, or 1,000 cy-cles peI' second), a buzz (-lO-hertz squarewa\'e), a low tone (796 hertz) and ahiss (2,000-hertz octave band of noise),

each lasting 200 milliseconds, correct re-sponses were only at the level of chance.lt was necessary ta increase the duration

of each item to between about 300 and700 milliseconds (the exact value de-

pending on practice and the responseprocedure) ta obtain a correct identifi-cation of sequence from half of the sub-jects tested. For durations of 300 milli-seconds or more, calling out the order ofthe sounds resulted in more error~; than

arranging four cards, each bearing thename of one sound, in the appropriatesequence.

\Ve noticed a curious feature of the

four-item sequences: listeners frequentlycould not tell at first how many differentsounds were present in the series. Theapparent disappearance of one or some-limes even two items could be minimized

by telling the listener the number ofsounds there were and by 6rst intro-ducing each sound aJone. This iIIusoryabscnce of stimuli eau Id not aeeaunt

completely for the inability ta perceivesequence, however: ev en people whoI!t'ard the four sounds clearly c()uld notreport their sequence. \Ve also foundthat repetition was not in itself a barrierto sequence perception, \Vhen four spa-ken digits, each lasting 200 milliseconds,were recorded separately (ta avoid tran-sitional cues), spliced into a loop andrepeated over and over, the subjectsperceived the order at once and withcertainty.

This great difference bet\\'een thetemporal perception of verbal and ofnonverbal stimuli suggested that ",acould use perception of sequence in anefFort to establish which attributes of

sounds are responsibJe for speechl.ik,ccharacteristics. \Ve cut four 200-mllh-

.! d tate-second seaments out of extenue 5 Jbd .fixe

ments of separate vowels hel at.l .leyel for several seconds. \Vhen these

1. d

' ta a ]ooPtape segments were sp lce 111 -'

1 "rd a rC '

and played back, the listener 1e" Isd VOWC

jpeated sequence of four stea y .following one another without paus~... . .bly chang4Smce no speaker can pOSSI ,. this waY'jIrom one vowel to another !Il .

.tl t 't

'P

'll 'S{' the s~WI JOu a tranSI IOn or a,..' ..

. 'al'quence sounded curiously arufici ~-

~--~ ~-~--- 0 --~---------- ~ o--_o------

té .. 0

~~"S t re s st re s s t res s t res st res st r es st r e s st r e s st res st r es st re s st re s s t res st r es st re s s t re sst re s st re sst r es st re s st res s..",-,- ~-_o o- -- ---___0___0 ono --on _0 0_- -- -- 0 0 - 0__0___-

dress dress dress dress tress tress tress tress tress tress Joyce Joyce Joyce Joyce Joyce Joyce dress

dress stress stress stress stress stress dress dress dress dress dress purse purse purse purse purse 0 -.

hasa more profound efIect: most subjects experience ilIusory,. changesinvolving substantial distortion of the stimulus. A man lis.

crudeattempts to synthesize speechsoundselectronicallv-

Our subjects did no better th anchancethe first time they attempted 10

judgethe order of the sounds. By delet-iuga SO-millisecond portion of each sus-tainedvowel and replacing it with a si-lentgap, we made the sequence soundmorelike normal speech, and then iden-tificationof order was possible for halfofa new group of subjects. The subjectsapproached a perfect score only whenwepresented vowels of the same dura-lion(ISO milliseconds separated by 50m11liseconds of silence) but recorded

wilhthe normal qualities of vocal onsetanddecay that are characteristic of sep-arateshort utterances of vowel sounds.

Itappears, in short, that accurate per-ceptionof temporal order may be possi-bleonly for sequences that resemblethose encountered in speech and inmusic-special sequences in which thecomponent sounds are linked together,following specific mIes, into coherentpassages.

During the 19S0's Colin Cherry of theImperial College of Science and Tech-nologyin London \Vrote about the "cock-tail-party problem," the task of attend-ingto one chosen conversation amongseveral equally audible conversations.Apparently such cu es as voice qualityandspatial Jocalization help the listenerlakeep fixed on a single voice amongl!1a~y.\Vhen a person attends to one oftheseverbal sequences, he excludes theothers, so that presumably it would not!Jepossible for him to relate the tem-

~oralposition of a phoneme in one con-versation (or other extraneous sounds

5uehas coughs) to the temporal positionofphonemes in the attended conversa-

tiou.Such observations lead us to specu-kte that the inability to perceive the cor-rect order of stimuli that do not form

hJtegrated sequences of speech or music!)jaynot represent a Haw or defect of our:pereeptual skills. Rather, this restriction

i~ftemporal pattern perception may be~~essential step in the continuaI process

tening to "tress" repeated 360 times in three minutes heard 16chauges involving eight different words, some illustrated here (b1.

ofextracting intelligible signals from theubiquitous background of noise.

JYlusical and verbal passages have anorganization based on the temporal

order of their sounds; this organizationfurnishes a context for the individual

sounds. Verbal context, as we pointedout above, can determine completely thesynthesis of illusory speech sounds; pho-nemic restorations are heard when the

context is clear but part of the stimulusis absent. Another illusion m-ises whenthe stimulus is clear but the context is

absent. If one listens to a clear recordingof a word or phrase repeated over andover, having only itself as context, il-lusory changes occur in what the voiceseems to be saying. Any word or phraseis subject to these illusory changes, usu-ally \\lith considerable phonetic distor-tion and frequently \\lith semantic link-ages. These illusory words are 11eardquite clearly, and listeners find it diffi-cuIt to believe they are hearing a singleauditory pattern repeated on a loop oftape. As an example of the kind ofchanges heard, a subject listening to"tress" repeated without pause hearddistinctly, within the course of a fewminutes, such illusory forms as "dress,""stress," "Joyce," "Horis," "Horist" and"purse." This illusion, which we calI theverbal transfOlmation effect, has provid-ed unexpected glimpses of hitherto un-explored perceptual mechanisms for 01'-ganizing speech sounds into words andsentences.

The implications of the verbal tr-ans-formation illusion were not appreciatedfully in 1958, when one of us (Richard-Warren) and Richard L. Gregory firstreported the discovery of "an auditoryanalogue of the visual reversible figure."\Ve had been looking for an auditoryillusion resembling the one observed insuch ambiguous figures as the Neckercube, whose faces seem to pop into elif-ferent perspective orientations as onelooks at it. \Ve reasoned that ambiguousauditory patterns would undergo similar

iJIusory shifts; for example, the word"rest" repeated clearly over and overwithout pause should shift to "tress,"tben back to "rest" and so on. \Ve did

find such closed-Ioop shifts but we alsofound some other illusory changes-to"dress" and "Estber," for instance- At the

time, although we noted that perceptualdistortion of tbe stimulus had occurred,

we considered it only a curious sideeitect.

Further study b:--'the present authorshas drawn attention to basic differences

bet\\-een the visual and auditory illu-sions, however. Tbe auditory effect is notlimited to ambiguous patterns; any wordor phrase will do. Changes are impos-sible to predict, varv greatly from indi-vidual to individual and often involveconsiderable distorhon of the stimulus

pattern. A subjeet listening to the word"see" repeated over and over may hear aphrase as far remoyed fI.om the stimulusas "Iunchtime," particularly if the lime isabout noon! Changes occur frequently:when a single word is repeated twice asecond for three minutes, the averageyoung adult hears about 30 changes in-volyjng about six different forms.

There are some remarkable effects ofage on the frequency of verbal trans-

formations and the types of illusorvchanges. These age differences seem (0reHect basie changes in the way in whicha person processes \-erbal input over alife-span. Children at the age of five ex-perience either very few or no verbaltransformations. At six half the children

tested heard illusory changes, and thosewho did experienced them at the rapidrate charaeteristic ofolder children. 13)'the age of eight ail the children testedheaI'd verbal transformations. The rate

of illusory changes apparently remainsapproximately constant into the twentiesand then declines slowly during the mid-dIe years; for listeners over 65 the ratewas founel to be on Iv a fifth the rate for

young adults and was approximatelyequal to the rate for five-year-olds. This

35

decrease after middle age is not due di-rectly to any decrease in auditory acuitywith aging. Actually the aged are gener-;1l1ymore accurate in this task than theyoung, reporting common English stimu-lus words correctly and continuing ta re-

spond ta the stimulus as it actuaIJy is-the same word repeated over and overwithout change. J\Joreover, if youngadults hear a word pJayed indistinctly

against a background of noise (whichshould simula te a decrease in acuit)'),

they still hear manv more illnsorvchanges than the aged.

Besides counting the nnmber of

changes, we have examined the group-ings of speech sounds ta determine theunits of perceptual organization at dif-ferent ages. Children respond in tennsof the sounds of English but may groupthem in ways not found in the language.For example, with the ward "tress" re-

peatecl over and over, a l'hi]cl mightreport "sreb" even though the initia]"sr" sequence is not found in English\Vords. Young adults group speechsounds onl)' in ways that are permittedin English, but they do report nonsenses)'IJab]es: given the stimulus "tress," thevmight report "tresh" as one of the soumIsthey hear. Olcler people, on the otherhand, report on])' meaningfnl wonls.Presented \Vith "tress," they tend to hear"tress" continuous]y, and \\.hen infre-(lnent changes do occur, they usnally areto such close!y re]atecl forms as "dress."If an older person is presented with arepeated nOllsense syllable, there is an

50 ~_.

40-

interesting l'l'suIt. If "flime" is the stimu-lus, for example, the o]cler listener gen-erally distorts the ward into a phoneticaJ-ly close English word su ch as "slime"and tends to stay with the sense-making(bnt ilIusory) \Vord throughout.

Our observations with verbal transfor-

mations have suggested that as peoplegrow aIder thev employ diHerent per-cep tuai mechanisms appropriate to theirfamiliarity with language ancl their fune-tional capacities, both of which changewith age. We believe specific mecha-nisms associated with the skilled use of

verbal context unclerlie the age differ-ences in the frequency ancl nature of \'er-bal transformations. Repeatecl words donot How past us as normal eomponentsin the stream of language do; like a vor-tex, they move ,,'ithout progressing. lnthe absence of the semantic and gram-matical confirmation ordinarily provicleclby verbal context, perception of repeatedwords becomes unstable for ail but the

very young ancl the olcl. And since eachsuccessive perceptual organization is sub-jcct to the same lack of stabilizing con-text, it suffers the fate of its predecessor.

The absence of illusory changes atagefive suggests that young children havenot )'et reached the stage in languagedevelopment where storage with skilIeclreorganization comes into play. The Jossof susceptibility in alert ancl healthyelderly listeners suggests that they nolonger have the funetional capacity forthis mechanism. It is rather weil estab-

lished that short-term memory is less ef-

50

m m_m m ~'-- 40-

1-Zw

ii 30w0...

>-uzw:=J ,,0..awcrLL

10-

0

1-Zw

ii 30w0..

>-UZw:=J 20-awcrLL

10-

2-3 47

NU~IBER OF CHANGES

0

fective in the aged when interveningactivity is requirecl between input andretrieval. Concurrent processes of cod.

ing, storing, comparing and reorganizingmav the l'l'fore not be possible, sa that theoptimum strategv is to employ onk thepast context of the message as an "icl taorganization of the l'urrent input. Thefact that in the presence of repeated

stimuli the agecl report only meaningfulwords is consistent with this view. If thisinterpretation is correct, one would ex-pect that phonemic restoration for eider.Iy people wou]cl be limitecl to replace-ment of speech sounds identified by priorcontext; the use of subsequent o)]1text, in ~the manner of young adults, wou]clnotbe possible. \Ne plan to do experimentstesting this prediction.

ln summary, it appears that phonemicrestorations and verbal transforma-

tions provide new techniques for study-ing the perccptual organization of Leardspeech, particularly the grouping ofspeech sounds, the correction of the lis-teller's errors and the reso]utioll of acous-

tic ambiguities. The observations wehave descrihed for the perception ofauditory se(luence indicate that specialperceptual trcatment of the sOèmds ofspeech (and music) allow us to extractonler and meaning from what wouldotherwise be a world of auclitory chaos.

1t is curious that in studying illusions andconfusions we encounter mechanisms

that ensure accurate perception and theappropria te interpretation of ambiguities.

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2 3-4 58 9-16

NUMBER OF DIFFERENT WORDS, . tests

ber of different forms (right) perceived during three-mlnute v'j.by subjects 18 to 25 (gray) and 62 to 86 years old (bl,Jck). 1ferences reflect changes in the perceptual processing of spe

AGE DIFFERENCES in the freqnency of verbal transformations

are shown for two of the age groups tested. The bars indicate thenumber of changes from one form to another (le/tl and the num-

36