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Developmental speech perception Werker, Janet 1978

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DEVELOPMENTAL SPEECH PERCEPTION by JANET FELDMAN WERKER B.A,, Harvard U n i v e r s i t y , 1974 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n THE FACULTY OF GRADUATE STUDIES (Department of Psychology) We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1978 @ Janet Feldman Werker, 1978 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m ' e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and stud y . I f u r t h e r a g r e e t h a t ' p e r m i s s i o n - f o r . - e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may b e g r a n t e d b y the H e a d o f my Department or b y h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t b e a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Psychology Department o f T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date i i ABSTRACT Previous research has indicated that infants have the a b i l i t y to c a t e g o r i c a l l y discriminate many of the d i s t i n c t i v e features of speech sounds regardless of t h e i r exposure to a language i n which such d i s -t i n c t i o n s are important, whereas adults of one language group may have d i f f i c u l t y d i s c r i m i n a t i n g l i n g u i s t i c features that are important i n a foreign language. This suggests a decline during development i n l i n g u i s -t i c perceptual a b i l i t i e s , during which the a b i l i t y to discriminate non-relevant features may be l o s t . This study was designed to be the f i r s t i n a s e r i e s of tests of such a decline and involved comparing E n g l i s h -speaking adults, Hindi speaking adults, and six-month o l d infants on th e i r a b i l i t y to discriminate foreign and native speech contrasts. Two p a i r s of Hindi sounds, and one p a i r of English sounds were i n -vestigated i n t h i s study, Infants were tested i n a " v i s u a l l y r e i n f o r c e d i n f a n t speech d i s c r i m i n a t i o n " (VRISD) paradigm. This i s a di s c r i m i n a t i o n paradigm i n which the infant i s conditioned to turn i t s head when there i s a change i n the auditory stimulus. A va r i a t e of t h i s paradigm was employed f o r the adult subjects using a button-press, rather than a head turn, as the c r i t i c a l behavioral response. This study y i e l d e d support f o r the notion that i n f a n t s have the a b i l i t y to c a t e g o r i c a l l y discriminate d i s t i n c t i v e features of speech sounds regardless of exposure to a language i n which such d i s t i n c t i o n s are important. Some support was also given f o r the idea that there may be a decline i n speech perceptual a b i l i t i e s with e i t h e r age/or l i n g u i s t -i c experience, but th i s f i n d i n g was only s i g n i f i c a n t with one of the two Hindi sound p a i r s . i i i Two explanations are offered for these r e s u l t s . I t i s suggested that the English population may have had someexperience with the non-s i g n i f i c a n t Hindi contrast. A l t e r n a t i v e l y , i t i s suggested that d i f f e r -e n t i a l perceptual distance may have accounted for the differences between the two Hindi sound p a i r s . Two l e v e l s of processing, acoustic and l i n g u i s -t i c , are then invoked i n t h i s explanation. i v TABLE OF CONTENTS Page ABSTRACT l i TABLE OF..CONTENTS ........ i v LIST OF TABLES ........ ,v • LIST OF APPENDIX A TABLES . . . v j LIST OF FIGURES ........ v i i LIST OF APPENDIX A FIGURES v i i i ACKNOWLEDGEMENTS ..... . . . i x INTRODUCTION 1 .METHOD . 19 RESULTS 29 DISCUSSION > 36 CONCLUSIONS 44 REFERENCES ........ 45 APPENDIX A . . . . , , 53 APPENDIX B . . . . . .i. . 58 V LIST OF-TABLES Page TABLE 1 Hindi Stop Consonants ....... 7 TABLE 2 F r i c a t i v e Discrimination by Age ....... 10 TABLE 3 Analysis of Proportions f o r Retror-flex/Dental Contrast' .,„.... 30 TABLE 4 Analysis of Proportions f o r Voice-less Aspirated/Breathy Voiced Contrast ' 30 TABLE 5 Mult i p l e Comparisons,on Retroflex/ Dental Contrast 31 TABLE 6 Multiple Comparisons on Voiceless Aspirated/Breathy Voiced Contrast ^ TABLE 7 Infant Mean Number of T r i a l s on Speech Contrasts 33 TABLE 8 C e l l Means and Standard Deviations For Number of T r i a l s to C r i t e r i o n ,. 35 TABLE 9 Source Table for Number of T r i a l s to C r i t e r i o n ; Analysis of Variance 35 v i LIST OP APPENDIX A TABLE Page TABLE 1 The Prime Features 56 v i i LIST OF FIGURES page FIGURE 1 Mean Number of Sucks Per Minute ..... 17 FIGURE 2 Arrangement of the Experimental Site ..... 21 FIGURE 3 Infant During Control T r i a l 2 2 FIGURE 4 Infant During Experimental T r i a l ...... v i i i LIST OF-APPENDIX A FIGURES Page FIGURE 1 Overlap of A r t i c u l a t o r y Features ...... 54 FIGURE 2 Abbreviated "d" Spectograms \ 54 ACKNOWLEDGEMENTS I would l i k e to give s p e c i a l thanks to Dr, Richard Tees, Dr. John G i l b e r t , and Keith Humphrey f o r giving so much assistance and encouragement throughout'the project. Thanks are also due to Dr.'Robert Fremder and Dr. Tannis MacBeth Williams for t h e i r w i l l r -ing assistance during c r i t i c a l stages of t h i s project. 1 1 INTRODUCTION' This study was designed to be a f i r s t step i n . t e s t i n g the following hypothesis t Humans are born with the a b i l i t y to discriminate the univ e r s a l set of d i s t i n c t i v e l i n g u i s t i c features, Through development, there i s a decline i n t h i s a b i l i t y as ,the perceptual space becomes organized to approximate the phonemic categories used i n the na^ t l v e language, This idea (that some perceptual c a p a b i l i t i e s decline with age) con<-f l i c t s with most approaches to perceptual development. According to Gibson (1967) f o r example, perceptual capacity becomes i n c r e a s i n g l y d i f -f e r e n t i a t e d and ref±ned through ontogeny, Perceptual learning r e s u l t s i n an Increase i n a b i l i t y to acquire information from the environment as a r e s u l t of experience with the array of s t i m u l i provided by the environment. Thus only those s t i m u l i present i n the environment lead to refinements i n perceptual.capacity. A d d i t i o n a l l y , perceptual learning i s seen as an increase, rather than a decrease, i n discriminatory a b i l i t y , Other contemporary•theories of perceptual development also support the notion of increasing d i f f e r e n t i a t i o n as a r e s u l t of experience.' For example Hebb and Piaget would both view perceptual development as r e f l e c t -ing the construction of "schemata" as organizations of the lelements of sensory input. The schema i s then capable of being modified with further experience and i s thought to influence the perception of objects by "guiding" the i n d i v i d u a l to c e r t a i n d e t a i l s and by aiding i n c l a s s i f y i n g and understanding the sensory input (e.g., c f . Tees, 1976), Somewhat s i m i l a r l y , perception has been regarded as a process of category b u i l d i n g 2 and inference drawing (Bruner, 1957). As more categories are b u i l t , perception becomes l e s s dependent upon the d e t a i l s of the sensory input, and more on the categories. Through development the categories become more accessible so that fewer d e t a i l s are necessary for c l a s s i f y i n g an input. On the other hand, behaviorists such as M i l l e r (1948) view perceptual development as r e s u l t i n g from p o s i t i v e feedback from the environment. A chance response to an appropriate stimulus r e s u l t s i n p o s i t i v e feedback, and t h i s motivates the i n d i v i d u a l to discriminate that stimulus from others a second time, etc. Although these theories deal adequately with many facets of p'ercep<-t i o n , they do not deal d i r e c t l y with d i s c r i m i n a t i o n . According to S-.S'. Stevens (1939), discrimination i s the fundamental cognitive act. , The a b i l i t y to discriminate the fundamental features of speech i s the necessary f i r s t step i n language learning. 0n the basis of elementary discriminations, then, we make our f i r s t rudimentary classes and i n doing so we have the f i r s t step toward ge n e r a l i z a t i o n . (Sevens, 1939, p. 58). One, perhaps unique aspect of speech p e r c e p t i o n i s the accumulation of evidence suggesting that "categorization" of speech sounds i s an innate propensity of the human organism, That i s , rather.than having t o . l e a f n to d i f f e r e n t i a t e phoneiic features and then organize them into categories, human infants seem to respond from the beginning, to speech sounds accord-ing to phonemic categories. This kind of a b i l i t y would enable the infant to break the continuous auditory input of speech into d i s c r e t e segments, thus s t a r t i n g the process of the eventual i d e n t i f i c a t i o n of meaningful seg-ments. For example, when given synthesized speech sounds varying along 71) Before proceeding with t h i s section i t i s necessary to understand the basic research i n experimental psychology concerning the decoding of speech sounds and the r e a l i t y of d i s t i n c t i v e features. Interested readers are r e f e r r e d to Appendix A. 3 a continuum, infants as young as 1 month of age show evidence of d i s c r i -minating the acoustic cues which d i f f e r e n t i a t e phonemes, but do not r e -spond to within category v a r i a t i o n s , ( e . g . , Elmas,Siqueland, Jusczyk, & Vigo r i to ,1971). In each natural language only a subset of the u n i v e r s a l set of phonetic d i s t i n c t i o n s i s u t i l i z e d to d i f f e r e n t i a t e meaningful sound seg^ ments (phonemes). In an i n d i v i d u a l language, phoneme categories may broaden to .include more than a single phonetic s p e c i f i c a t i o n (allophonic v a r i a t i o n ) . For example, i n English, a s p i r a t i o n does not connote d i f f e r -ences i n meaning. Thus i f an English speaker pronounced " p i l l " with an aspirated or an unaspirated v o i c e l e s s stop consonant, other English speak-, ers-..would understand the word to be " p i l l " and would ignore the i r r e l e v a n t phonetic v a r i a t i o n s , It can be seen then, that iri terms of learning one's own language, perceptual development can be viewed as a process of groupr-irig i n i t i a l l y d i s t i n c t speech sounds into broader categories, thereby esr-t a b l i s h i n g the required set or class of phonemes relevant to one's native language. In addition to allophonic variations,, speakers of a , p a r t i c u l a r language may omit a subset of phonetic vfeatures from use. There i s some evidence that adult l i s t e n e r s have d i f f i c u l t y d i s c r i m i n a t i n g those features when hearing them f o r the f i r s t time i n a l i n g u i s t i c context (Lisker & Abramson, 1968). The s i g n i f i c a n c e of the discovery that young in f a n t s can discriminate some l i n g u i s t i c a l l y relevant d i s t i n c t i v e features of speech does not nec e s s a r i l y imply a conscious recognition of speech sounds as language, although Eimas (1975) has stated that t h i s discriminatory a b i l i t y "indicates •: 4 • that infants have some knowledge of the phonetic structure.of language, s p e c i f i c a l l y , they must have knowledge of at l e a s t some of the phonetic features." (p. '214). It i s unfortunate, however^ that at present there i s no way t o . d i f f e r e n t i a t e s t r i c t l y acoustic from phonetic knowledge. In any event demonstration of discriminatory a b i l i t i e s that r e f l e c t phonemic features suggests that infants'have at l e a s t the necessary f i r s t response c a p a b i l i t i e s to begin organizing t h e i r l i n g u i s t i c input into a f i n i t e set of categories. Whether the infant has knowledge of the phonetic structure becomes•irrelevant. Michael Laine, i n h i s Introduction to Structuralism (1970) stated that when people use t h e i r own language "...they c o n s i s t e n t l y and constantly apply i t s phono-l o g i c a l laws ( i t s structure, i n other words) i n t h e i r speech. They w i l l not, unless they are versed i n l i n g u i s t i c s , be consciously aware of them. Nor, i f asked, would they be able to supply those laws....... What the observer sees i s not the structure, but simr-p l y the evidence and product of the structure, ..... There i s i n man an innate, g e n e t i c a l l y transmitted and determined mechanism that acts as a s t r u c t u r i n g force., Moreover, t h i s inherent q u a l i t y or capacity i s so de-signed as to l i m i t the possible range of ways of s t r u c -turing, (Caine, 1970, p. 15) Thus the response c a p a c i t i e s of the human infant would l i m i t the range of categories used f o r l i n g u i s t i c input, . The hypothesis that speech perceptual development may proceed from the u n i v e r s a l to .a more l i m i t e d set of categories does not o r i g i n a t e with t h i s study. Similar speculations have been made by other researchers (Eimas, 1976; G i l b e r t , 1975; P i s o n i , 1977, Trehub, 1976). I t i s necessary, however, to a c t u a l l y test whether or not infants can discriminate non-native speech contrasts with greater ease than adults i n a s i n g l e , properly designed study, 5 In order to examine t h i s hypothesis, infants and adults were tested on two p a i r s of Hindi speech contrasts, JandLO'ne,pal'r of English speech^con-t r a s t s i n two very s i m i l a r d i s c r i m i n a t i o n paradigms. The English p a i r used was the common /ba//da/. These are both voiced stop consonants d i f f e r i n g only In place of a r t i c u l a t i o n ( b i l a b i a l vs. a p i c a l ) . This i s a r e l a t i v e l y common d i s t i n c t i o n across natural languages and has been previously studied using i n f a n t s . The f i r s t Hindi p a i r was the unvoiced, unaspirated r e t r o f l e x vs, dental stop /Ta/'/.ta/ where place of a r t i c u l a t i o n i s the c r i t i c a l dimension. Retro-f l e x consonants are produced by c u r l i n g the tongue back and placing i t pos^-t e r i o r to the alv e o l a r ridge. In contrast, dentals are produced by plac i n g the t i p or blade of the tongue against the back of the upper front t e e t h . Dental i s a common place of production i n En g l i s h (and i n most natural languages) whereas r e t r o f l e c t i o n does not carry phonemic information i n English. A d d i t i o n a l l y , r e t r o f l e x consonants are uncommon across natural languages and t h e i r contextual d i s t r i b u t i o n i s r e s t r i c t e d even i n those languages i n which they have import. The second Hindi p a i r was the unvoiced aspirated, dental stop vs. the murmured dental stop /t*V/d*V i n which a differ e n c e i n voice onset time i s the c r i t i c a l d i s t i n c t i o n . Voice onset time i s a combination of the state of the g l o t t i s during an a r t i c u l a t i o n and the presence or absence of a period of voicelessness during and a f t e r the release of an a r t i c u l a t i o n . In English only two categories of voice onset time a r e ' d i f f e r e n t i a t e d ; — voiced (the vocal words are nearly together so that they vibrate) and voi c e l e s s (vocal cords are so f a r apart that they cannot vibrate at a l l ) , There are two a d d i t i o n a l categories i n Hindi; v o i c e l e s s unaspirated and 6 brea thy v o i c e d (murmured) s tops , (See Table 1 ) , As can be seen, bo th p a i r s of H i n d i sounds i n v o l v e d i s t i n c t i o n s b e -tween ca t ego r i e s that do not e x i s t at a l l i n E n g l i s h and are r e l a t i v e l y u n -common to n a t u r a l languages. Evidence has been p rov ided (Singh &"Black , 1966) tha t these p a i r s would thus be among the hardest f o r E n g l i s h speakers to d i s c r i m i n a t e . A d d i t i o n a l l y , S . E . B lums te in suggested tha t i n ga the r ing p i l o t data f o r the s t u d y . o f r e t r o f l e x stop consonants (Stevens & B l u m s t e i n , 1975), E n g l i s h - s p e a k i n g subjec ts d i d seem todemonstrate d i f f i c u l t y i n d i s ^ c r i m i n a t i n g the unvoicedr-unaspirated d e n t a l v s , r e t r o f l e x stop consonants (personal communication, February , 1978), The d i s c r i m i n a t i o n paradigm used f o r the i n f a n t s i s c a l l e d " v i s u a l l y A r e i n f o r c e d speech d i s c r i m i n a t i o n " (VRTSD).• A v a r i a t e of t h i s paradigm was used f o r the a d u l t s . VRISD was f i r s t developed as a v a r i a n t of the c l a s s i c "p l ay audiometry" o f D i x and H a l l p i k e (1947) , i n which a c h i l d was condir^ t i o n e d through a s s o c i a t i o n to, push a bu t ton i n response to a sound source to e l i c i t the p r e s e n t a t i o n o f a p leasan t p i c t u r e . Suzuk i and Ogiba (1960) modi f i ed the response to a s imple headr-turn i n order to t e s t the hea r ing a b i l i t y of c h i l d r e n under 3 , c a l l i n g i t v i s u a l re inforcement audiometry (VRA). Al though Suzuki and Ogiba (1961) repor ted low success r a t e s f o r i n f a n t s one year and younger, more, recent work ( W i l s o n , L e e , Owen & Moore, unpubl i shed manuscr ip t ) i n d i c a t e d tha t 90% of i n f a n t s as young as age 5r- l /2 months can be t e s t ed w i t h t h i s paradigm. More r e c e n t l y researchers have begun us ing t h i s paradigm i n speech d i s c r i m i n a t i o n s t u d i e s ( E i l e r s & M i n i f i e , 1975; E i l e r s , W i l s o n & Moore, 1977; H i l l e n b r a n d , M i n i f i e & Edwards, 1977; K u h l , 1976, 1977; M i n i f i e , 1976) . In these s t u d i e s the i n f a n t was. cond i t i oned to t u rn h i s / h e r head toward a sound source when he/she de tec ted 7 Table 1 Hindi Stop Consonants Voiceless unaspirated Voiceless aspirated Voiced Breathy voiced . b i l a b i a l dental r e t r o f l e x post-alveolar a f f r i c a t e v e l a r p a l (take care of) * TA f (mode of singing) t a l (postpone) t f a l (gS) kan (ear) p a l (edge of knife) h ** £ an ( r o l l of cloth) t h a l (place f o r buying wood) t f a l (deceit) k an (mine) bal (hair) J? hal (forehead) h ** (charity) (paddy) dal d h a l (branch) (shield) d 3 a l (water) gan (song) - h , a l , (glimmer) h g an (Kind of bundle) = comparison Retroflex/Dental ** = comparison Voiceless Asp/Breathy Voiced 8 a change i n the s t i m u l u s , and was rewarded w i t h the appearance of a f l a s h -i n g , no i s e -p roduc ing toy a n i m a l . Not o n l y cou ld i n f a n t s as young as f i v e months perform s u c c e s s f u l l y i n t h i s paradigm, .but they a l s o show the a b i l i t y to t r a n s f e r t h i s " l e a r n i n g , r s e t " to new s t imulus p a i r s ( K u h l , p e r s o n a l communicat ion) . In fan t Research Al though speech researchers are u n i t e d i r i t h e i r b e l i e f tha t by age 2 months i n f a n t s demonstrate a s o p h i s t i c a t e d a b i l i t y to make phone t ic d i s c r i -mina t ions , , (Eimas , 1974, 1975a,b; E i l e r s & M i n i f i e , 1975; K u h l , 1976; M o f f i t , 1971; Trehub, 1973, 1976; W i l l i a m s , , i n p r e p a r a t i o n ) , the meaning of t h i s d i s c r i m i n a t o r y a b i l i t y i s debated. Accord ing to the a c o u s t i c cue h y p o t h e r -s i s , these .apparent "phonet ic d i s c r i m i n a t i o n s " , are based on lower, order a u d i t o r y d i s c r i m i n a t i o n s . a n d are viewed as no d i f f e r e n t from non^-speech a u d i t o r y p e r c e p t i o n (Stevens & K l a t t , 1974) . In c o n t r a s t , proponents o f the l i n g u i s t i c cue hypothes i s c l a i m tha t speech sounds are heardo. s p e c i f i c c a l l y as speech (Eimas ,• 1974; G i l b e r t , 1971; M o f f i t , 1971; Morse , 1976; Trehub, 1973), and tha t speech d i s c r i m i n a t i o n i s an inna te b i o l o g i c a l a b i l i ^ -t y important i n the process o f language a c q u i s i t i o n , (Eimas, S i q u e l a n d , Jusczyk & V i g o r i t o , 1971). A d d i t i o n a l elements of the l i n g u i s t i c cue hypo-t h e s i s i n c l u d e the f o l l o w i n g : (1) p e r c e p t i o n o f consonantr-vowel sounds i s c a t e g o r i c a l and l i n g u i s t i c a l l y r e l e v a n t , (2) speech p e r c e p t i o n i s non^-developmenta l , i . e . , i n f a n t s respond to phone t ic s t i m u l i i n the same way as a d u l t s , (3) non-speech sounds,are not pe rce ived c a t e g o r i c a l l y and (4) hu^ mans are the on ly spec ies tha t can pe rce ive speech sounds c a t e g o r i c a l l y . Whi le there i s some evidence to suggest tha t i n f a n t s and a d u l t s can p e r c e i v e some nonspeech sounds c a t e g o r i c a l l y ( Juscyk, Rosner & C u t t i n g , 9 1977), that other animals can show c a t e g o r i c a l perception f o r phonetic features (Kuhl & M i l l e r , 1975), and that within category perception i s C2) possible under, extreme conditions (Samuel, 1977), the c r i t i c a l issues for the present study are whether or not perception of consonant-vowel sounds i s organized according to phonemic categories and whether infants . can respond to phonetic s t i m u l i i n the same way as adults. Several studies have already been undertaken to examine these two c r i t i c a l Issues. Two measures have been used extensively i n these studies; heart rate deceleration (HRD) and high amplitude sucking (HAS) (both have been discussed extensively by Morse (1974), HRD i s based on the assumption that heart rate decelerates i n response to a novel stimulus. In contrast HAS involves a behavioral response by the infant (sucking), Both HRD and HAS are used i n a habxtuation^dishabituation design, contingent upon rein<-f o r c i n g properties of the speech s t i m u l i . Both have the following weaknesses. (1) Tt i s d i f f i c u l t to i n t e r p r e t negative .results. I t i s never known whether th e , c h i l d was unable to make a dis c r i m i n a t i o n or did not f i n d the s t i m u l i i n t r i n s i c a l l y r e i n f o r c i n g . (2) I t i s impossible tocompare data across i n d i v i d u a l s . (3) There i s about a 65% rate of incompletion, that i s , data can only be reported on about 35% of the sample. In addition, the HAS paradigm can only be used with infants up to 12 months of age. The HRD can be further c r i t i c i z e d f o r i t s s e n s i t i v i t y to both the state of the infant and the c h a r a c t e r i s t i c s of the speech s t i m u l i (Morse, 1974). In s p i t e of the problems Eimas et a l . (197.1), using a HAS paradigm, were able to provide answers r e l a t i n g to the fundamental questions. For example, i n an experiment i n which voice onset time (VOT) was varied by (2) ~ T" "~ ~ 'These findings are a l l taken as evidence that there i s both a l i n g u i s t i c and an acoustic stage i n processing, but do not negate.the psychological r e a l i t y of c a t e g o r i c a l perception i n a l i n g u i s t i c context. 10 I n t e r v a l s o f 20 m s e c , i n f a n t s aged 1-4 months were shown to d i s c r i m i n a t e between the v o i c e d and v o i c e l e s s stop consonants / b / and / p / a long the same phonemic boundary as a d u l t s ; tha t i s , they showed bo th ' c a t e g o r i c a l d i s c r i m i n a t i o n and l i n g u i s t i c a l l y r e l evan t p e r c e p t i o n . I n a d d i t i o n to c a t e g o r i c a l d i s c r i m i n a t i o n along the VOT continuum, c a r e f u l l y designed fo l low-up s t u d i e s have demonstrated tha t i n f a n t s can c a t e g o r i c a l l y d i s c r i -minate the / r / - / l / d i s t i n c t i o n (Eimas,' 1975b), stop consonants i n f i n a l p o s i t i o n (Eimas, 1 1974) ,• p l ace o f a r t i c u l a t i o n ( J i i sczuk , 1977a) , most o f the f r i c a t i v e s ( E i l e r s & M i n i f i e , 1975) , some vowels (Trehub, 1973) , g l i d e s i n i n i t i a l and media l p o s i t i o n ( Jusczyk , Copari & Thompson, 1977) , and n e a r l y every o the r fea ture on which they have been t e s t e d . Not a l l the a v a i l a b l e evidence i s suppor t ive of the c e n t r a l hypothe^ s i s o f t h i s s tudy . TMrre -eisl.£Someiesugge_s:t-io:nmthat f r i c a t i v e p a i r s may be d i f f i c u l t fo r young i n f a n t s to d i s c r i m i n a t e ( E i l e r s & M i n i f i e , 1975; E i l e r s , W i l s o n & Moore, 1977) . Us ing v i s u a l l y r e i n f o r c e d i n f a n t speech d i s c r i m i n a t i o n (VRISD) , i n f a n t s aged 6"8 and 12r-14 months o f age were compared on t h e i r a b i l i t y to d i s c r i m i n a t e n a t u r a l p a i r s o f both F i / 9 i and F u / 8 a . T h e i r r e s u l t s are summarized i n Table 2, A s i g n i f i e s the i n ^ fan ts cou ld make the d i s c r i m i n a t i o n , and a " - " s i g n i f i e s tha t they cou ld n o t . Table 2 F r i c a t i v e D i s c r i m i n a t i o n by Age 6-8 mos, 12-14 mos. F i / 0 i r-.. + Fu/0a 11 E i l e r s suggests tha t these f i n d i n g s show tha t "improvement" does occur w i t h age i n f r i c a t i v e d i s c r i m i n a t i o n because the 6-8 month i n f a n t s f a i l e d both p a i r s , w h i l e the 12-14 month i n f a n t s passed the F i / 9 i d i s c r i m i n a t i o n . E i l e r s et a l . (1977) concluded tha t t h e i r f i n d i n g s c a l l i n t o q u e s t i o n the u n i v e r s a l i t y o f phonemic d i s c r i m i n a t o r y a b i l i t i e s i n young i n f a n t s and suggest i n s t e a d a more complex p i c t u r e of p e r c e p t u a l development i n c l u d i n g bo th a u d i t o r y c a p a c i t y and l e a r n i n g , T h i s " n e g a t i v e " evidence i s not uncha l l enged , however, Us ing the same paradigm (VR1SD), Holmberg, Morgan and K u h l (1977) have found evidence of Fa /0a d i s c r i m i n a t i o n i n a study o f 6-month o l d i n f a n t s , Holmberg et a l . suggest exper imenta l c o n d i t i o n s may»account f o r the d i f f e r e n c e between t h e i r r e s u l t s and those obta ined b y . E i l e r s et_ al_, (1977) i n tha t the l a t t e r r e q u i r e d tha t i n f a n t s show evidence of d i s c r i m i n a t i o n w i t h i n o n l y s i x t r i -a l s . F a i l u r e to do so was i n t e r p r e t e d as i n a b i l i t y to make the d i s c r i m i n a -t i o n . Holmberg et a l . c l a i m tha t s t a t e f l u c t u a t i o n and v a r i a t i o n s 1 i n a t t en t i venes s may make the s i x t r i a l requirement too s t r i n g e n t f o r younger i n f a n t s . In any event , i t should a l so be po in ted out tha t f r i c a t i v e s have been shown to be d i f f i c u l t to d i s c r i m i n a t e whether i n n a t u r a l or syn the-s i z e d forms i n the case o f the a d u l t s ( M i l l e r & N i c e l y , 1955) and c h i l d r e n (Abbs & M i n i f i e , 1969), Proponents of the a c o u s t i c cue hypo thes i s i n t e r p r e t f i n d i n g s such as those presented by E i l e r s e_t al_ (1977) as evidence tha t d i s c r i m i n a t i o n i s p u r e l y a u d i t o r y , not l i n g u i s t i c a l l y r e l e v a n t and thus sub jec t to l e a r n i n g . They suggest tha t the c a t e g o r i c a l d i s c r i m i n a t i o n of consonants i s an a r t i -f ac t of the p a r t i c u l a r s t i m u l i used . For example, i n VOT s t u d i e s , i t has been suggested tha t the c r u c i a l cue i s the presence o r absence of the f i r s t 12 formant t r a n s i t i o n r a t h e r than the r e l a t i v e amount of v o i c i n g ( e . g . , Stevens & K l a t t , 1974), However, M o f f i t (unpublished) i n v e s t i g a t e d t h i s s p e c i f i c ques t i on i n astudy o f c a t e g o r i c a l p e r c e p t i o n of b i l a b i a l stop c o n -sonants . Us ing f o u r , p a i r s of s y n t h e t i c a l l y produced s t i m u l i , two p a i r s d i f f e r i n g m u l t i ^ d i m e n s i o n a l l y and two p a i r s d i f f e r i n g i n v o i c i n g o n l y , M o f f i t found that i n f a n t s aged 30-60 days were able to make l i n g u i s t i c a l l y r e l e v a n t d i s c r i m i n a t i o n s wi thou t the a c o u s t i c cue of presence or absence of the f i r s t formant t r a n s i t i o n . Kuh l (persona l communication^ i s i n v e s t i g a t i n g the s p e c i f i c dimensions of speech d i s c r i m i n a t i v e a b i l i t i e s i n i n f a n t s u s i n g a paradigm which i s r e -l a t i v e l y . n e w to i n f a n t speech p e r c e p t i o n r e sea r ch , the p e r c e p t u a l constancy paradigm ( s i m i l a r to VRXSD), v i s u a l l y r e i n f o r c e d i n f a n t speech d i s c r i m i n a -t i o n . She has demonstrated that i n f a n t s can more q u i c k l y l e a r n to organize ' t h e i r l i n g u i s t i c c a t ego r i e s acco rd ing to phone t ic fea tures w h i l e d i s r e g a r d -i n g v a r i a t i o n s i n bo th speaker and i n t o n a t i o n than they can l e a r n to o rgan-i z e c a t ego r i e s acco rd ing to these l a t t e r dimensions d i s r e g a r d i n g phone t ic f ea tu re s . Fu r the r support fo r the two c r i t i c a l i s sues of the l i n g u i s t i c hypothe-s i s (as o u t l i n e d p r e v i o u s l y ) i s found i n c r o s s - c u l t u r a l s t u d i e s . Babies of K i k u y u , Spanish and E n g l i s h speaking parents have been shown to d i s c r i m i n a t e l i n g u i s t i c fea tures tha t are not r e l evan t i n t h e i r n a t i v e languages (Lasky , Lasky & K l e i n , 1975; S t r e e t e r , 1976; Trehub, 1973, 1976) . A d u l t Research In con t r a s t to the r e s u l t s of r esea rch w i t h i n f a n t s , s t u d i e s o f adu l t speech d i s c r i m i n a t i o n have r e s u l t e d i n obse rva t ions tha t adu l t s have d i f f i -c u l t y d i s c r i m i n a t i n g phonemes tha t are not used i n t h e i r n a t i v e language. 13 Japanese adults have been shown to have d i f f i c u l t y d i s c r i m i n a t i n g the English / r / - / l / . In a study by Miyawaki, Strange, Verberge, Liberman & Fujimura (1975), 21 Japanese and 39 United States adults were tested on a d i s c r i m i n a t i o n task using synthesized versions of /ra/ and / l a / i n which the c r i t i c a l perceptual cue was s t a r t i n g frequency and t r a n s i t i o n of the t h i r d formant (F3). The r e s u l t s f o r i d e n t i f i c a t i o n and d i s c r i m i n a t i o n tasks with mature English speaking subjects from the United States, showed t h e i r perception to be nearly c a t e g o r i c a l . On the other hand, native-. Japanese speaking adults were able to discriminate only s l i g h t l y above the l e v e l of chance. A comparison of these same two groups on discrimination of non-speech counterparts of /ra/ and / l a / (F3) same as i n speech token, but F l and F2 amplitudes set at zero) yielded a d i f f e r e n t r e s u l t . Both groups showed equally successful discrimination of a l l comparison p a i r s . Miyawaki et a l , concluded that experience with language a f f e c t s l i n g u i s t i c , but not acoustic perceptual a b i l i t i e s . Studies with English speaking adult subjects have shown that they.ex-perience d i f f i c u l t y i n discriminating test tokens that span a non-English lead boundary i n VOT (Lisker & Abramson, 1968). Discrimination data for adult l i s t e n e r s (Lisker & Abramson, 1970) shows that Spanish speakers can only d i s t i n g u i s h between two categories of v o i c i n g . In contrast, data pre-sented by Lasky, Lasky and K l e i n (1975)^ ind i c a t e that infants being reared i n Spanish speaking environments can discriminate three v o i c i n g d i s t i n c t i o n s . A d d i t i o n a l l y , Trehub (1976) has suggested that adults have d i f f i c u l t y disv criminating the d i s t i n c t i v e feature, + stridency, as exemplified i n , f o r example, the Czech /za/ /ra/.-14 I t has been suggested that since English speakers have only, two cate-gories for prevocalic stop consonants they may lose the a b i l i t y to d i s c r i -minate sounds inv o l v i n g three and four categories. (Ladefoged, 1975), For-example, the Eastern Armenian;- language has three categories for prevocalic stops, and Hindi has four categories, Ladefoged's suggestion has been sup-ported i n the l i t e r a t u r e . For example, 'Singh and Black (1966) tested adult . Japanese, Hindi> English and Arabic speakers le s s than a month a f t e r they arri v e d iri the United States, A f t e r being traiiied for one hour'on a serie s of consonant-vowel sounds, the subjects 'were asked to i d e n t i f y those same sounds i n w r i t i n g . A l l l i s t e n e r s i d e n t i f i e d the sounds o f ' t h e i r native language best, The Hindi s t i m u l i used i n the present study were p a r t i c u -l a r l y d i f f i c u l t f o r non-Hindi speakers to i d e n t i f y . , It should be noted, however, .that(jmemoryj requirements may confound these r e s u l t s . I d e n t i f i c a t i o n paradigms (such as used by Singh and Black) involve the use of short-term memory f o r l a b e l s and are thus inadequate fo r t e s t i n g pure di s c r i m i n a t i o n a b i l i t i e s . Since many of the cross-language adult findings are based on i d e n t i f i c a t i o n studies they could be misleading. . In the studies reported by Trehub (1976) and Miyawaki et _al. (1975) d i s c r i -mination paradigms were used, and the adults s t i l l demonstrated d i f f i c u l t y with the non-English discriminations. It can be argued that r e s u l t s of tests of perceptual a b i l i t i e s can be misleading under conditions of low motivation because subjects w i l l be i n -c l i n e d to use "everyday" categories. With greater motivation, however, sub-j e c t s may be able to make f i n e r d i s c r i m i n a t i o n (see Brown & Lenneberg, 1958), Although many studies i n adult speech perception have ignored t h i s problem, research i n psychophysical acoustics suggests that motivation i s 15 c r i t i c a l . Samuel (1977) has shown that w i t h t r a i n i n g (and thus feedback) , a d u l t s may be able to d i s c r i m i n a t e w i t h i n category speech s t i m u l i w i t h shor t onset t ime . Al though he c i t e s t h i s as e v i d e n c e ' f o r p e r c e p t i o n i n bo th a phone t i c ( c a t e g o r i c a l ) and a c o u s t i c (cont inuous) mode, i t may be i n t e r p r e -ted as evidence for . the importance of .mot iva t ion . i n summary, a rev iew o f the l i t e r a t u r e suggests that i n f a n t s may have g rea te r d i s c r i m i n a t i v e speech a b i l i t i e s than adu l t s and tha t exper ience w i t h language may narrow d i s c r i m i n a t i o n a b i l i t i e s . To da te , however, t h i s ques t i on has not been examined p r o p e r l y i n a s i n g l e s t u d y . w i t h i d e n t i c a l tokens and w i t h procedures that a l l o w f o r comparable i n d i v i d u a l da t a . I n f a n t / A d u l t Research , Trehub (1976) desc r ibed a s e r i e s of ..four d i f f e r e n t experiments that were grouped fo r a n a l y s i s that most c l o s e l y address the hypo thes i s of t h i s study i n tha t she t r i e d to compare r e su l t s , of i n f a n t and adu l t exper iments . In experiments I and I I , Eng l i sh -Canad ian i n f a n t s aged 5-17 weeks were t e s t e d i n a HAS paradigm f o r t h e i r a b i l i t y to d i s c r i m i n a t e the o r a l n a s a l vowel d i s t i n c t i o n which occurs on ly i n French and P o l i s h /pa//f>a/, and the d i s t i n c t i v e fea ture o f s t r i d e n c y e x e m p l i f i e d by the Czech / z a / / r a / . The group r e s u l t s suggested that i n f a n t s cou ld d i s c r i m i n a t e these fea tures (see F igu re I ) . Trehub then employed a change-no change paradigm to d e t e r -mine whether E n g l i s h - s p e a k i n g adu l t s cou ld d i s c r i m i n a t e the Czech p a i r . A s i g n a l d e t e c t i o n a n a l y s i s i m p l i e d s u b s t a n t i a l confus ion f o r the two Czech sounds (d '=,83 compared wfth d '=1.00 fo r the common E n g l i s h p a i r / b a / / d a / ) . Trehub then compared the adu l t da ta to the i n f a n t data o f Experiment I I , and to, some 1972 / b a / / d a / i n f a n t da t a . The two se t s of i n f a n t da ta were analyzed by an a n a l y s i s o f v a r i a n c e (group x the suck ing r a t e i n the 5 p o s t -decrement minutes x language),. There was no s i g n i f i c a n t i n t e r a c t i o n between 16 experimental and control groups and language suggesting equal discrimina-. t i o n a b i l i t i e s f o r English and Czech contrasts. When compared to the adult data t h i s suggests English infants have greater d i s c r i m i n a t i o n a b i l i -t i e s than the adults. As Trehub h e r s e l f points out, however, the use of d i f f e r e n t paradigms i n d i f f e r e n t labs makes such comparisons only specula-t i v e . A d d i t i o n a l l y , the infant findings were based on group (HAS) data; responses had to be averaged over the postdecrement time period whereas adult r e s u l t s were based on di s c r e t e i n d i v i d u a l data (although grouped f o r an a l y s i s ) . P o t e n t i a l l y relevant findings have also been reported very b r i e f l y by . Bower (1977). When l i s t e n i n g to the speech of t h e i r own language, adults perform a "dance" of subtle body movement which r e f l e c t s the d i s c r e t e units of the continuous speech input (Condon & Ogsten, 1971). Without giving any.experimental d e t a i l s , Bower, claims that while adults perform t h i s "dance".onlyhinsresponse to t h e i r native language^ i n f a n t s "dance" to the speech of any language. Indirect evidence supporting the hypothesis that i n f a n t s may be better able to discriminate non-native sounds than adults i s provided by studies of second-language learning i n c h i l d r e n . The b i o l o g i c a l argument of the s t r i c t - c r i t i c a l - p e r i o d hypothesis as put f o r t h by P e n f i e l d and Roberts (1959) and by Lenneberg (1967) suggests that the c r i t i c a l period for language a c q u i s i t i o n l a s t s from about age two u n t i l puberty, and is.due to the lack of complete hemispheric s p e c i a l i z a t i o n . Although t h i s hypothesis has been c r i t i c i z e d from the point of view of age of l a t e r a l i z a t i o n (Kimura, 1967) and on the basis of B u r s t a l l ' s hypothesis of a l a t e r optimum age for language learning ( i n McLaughlin, 1977), the evidence for a c r i t i c a l period 17 F i g . 1 Mean number of sucks per minute, as a percentage of the maximum predecrement sucking rate, for 5 minutes before and a f t e r the decrement c r i t e r i o n . 18 with respect to accent i s strong. I t has been found that the younger the ' c h i l d , the more perfect the prdriounciation i n learning a second language (Asher & Garcia, 1969). A d d i t i o n a l l y , .case studies of b i l i n g u a l c h i l d r e n reveal that younger ch i l d r e n seem to do better on the acquistion of phono-l o g i c a l features (McLaughlin, 1977), demonstrating a greater perceptual f l e x i b i l i t y i n younger than i n older c h i l d r e n . F i n a l l y , recent speech per-ception data of adult b i l i n g u a l s suggests t h e i r perception of acoustic con-tinua r e f l e c t s the phonetic categories of both languages ' (Carramazza, Yeni-Komshian, Z u r i t & Carbone, 1973; Williams,.1975). The hypothesis examined i n t h i s study i s a c t u a l l y intermediate to the l i n g u i s t i c and the acoustic cue hypothesis, According to the present hypo-th e s i s , the infant has the a b i l i t y to respond to the universal set of phonemic d i s t i n c t i o n s at b i r t h . Whether t h i s a b i l i t y i s purely acoustic or l i n g u i s t i c i s not important. What i s important i s that since the i n -fants can discriminate the u n i v e r s a l set of l i n g u i s t i c features, they are able to break the continuous flow of speech input into i t s d i s c r e t e fcap-tures, and thus begin segmenting the meaningful aspects of l i n g u i s t i c i n r -put.. This predisposes infants to acquire t h e i r native language'with greater ease than i f they.had to learn to discriminate the l i n g u i s t i c fea^ tures. The purpose of t h i s study was to test the hypothesis that through development the individualsbbegin t o o r g a n i z e t h e i r speech perception cate-gories to moire and more c l o s e l y approximate, the phonetic categories used i n t h e i r own language. This a b i l i t y may be purely auditory at b i r t h and be-come encoded l i n g u i s t i c a l l y through ontogeny, or i t may,be a s p e c i f i c language a b i l i t y at b i r t h , as some neuropsychological ( G l a n v i l l e , Levenson & Best, 1977; Kimura, 1967) and anatomical (Witelson & P a i l l i e , 1973) e v i -dence suggests. 19 METHOD Subjects Four groups of volunteer- subjects were tested i n a d i s c r i m i n a t i o n paradigm (described i n the next section) on two pairs of Hindi speech con-trasts . Group T consisted of f i v e Hindi speaking adults (three, males, two females) aged 22-35. The subjects were rec r u i t e d through advertising and word-of-mouth from the Vancouver community. Group IX consisted of f i f t e e n infants ( s i x males, nine females) rang-ing in,age from 6 months,' 7 days to 1 months, 23 days,.with an average age of 6 months, 28 days. The infants were re c r u i t e d from the community by adv e r t i s i n g i n newspapers,, at well-baby c l i n i c s , and by telephoning people. l i s t e d i n b i r t h announcements. Although English was the p r i n c i p l e language spoken i n a l l the infant homes, ad d i t i o n a l languages were spoken i n four of the homes. Groups I I I and TV each consisted of ten English-speaking adults ( s i x males, four females i n each group) aged 22-35 re c r u i t e d from the. Uni v e r s i t y of B r i t i s h Columbia campus, As i t w a s ' d i f f i c u l t to f i n d adults with no foreign language t r a i n i n g , notes were taken on formal t r a i n i n g and on i n f o r -mal exposure for each adult. Group ITT consisted of "naive" adults, whereas Group TV was given l i m i t e d feedback i n the di s c r i m i n a t i o n paradigm to make t h e i r task more comparable to^thec.ihfantatask. Procedure and Apparatus The procedure and apparatus for the t e s t i n g of the infants i s outlined i n some d e t a i l as i t i s not widely available i n the l i t e r a t u r e . This pro-cedure i s c a l l e d v i s u a l l y reinforced infant.speech d i s c r i m i n a t i o n (VRISD). 20 As the adult procedure was designed to approximate t h i s infant procedure as nearly as p o s s i b l e , i t w i l l only be described b r i e f l y . . In the present study, the experimental set-up consisted of a sound-attenuated room with a one-way observationwindow adjoining the control room i n which the experimenter arid l o g i c system were situated. The sound attenur-ated room contained one'small table, i n the middle foreground of the room., A chair was d i r e c t l y behind the table on which the parent and infant were seated with t h e i r backs to the experimenter. A second chair was located across the table and s l i g h t l y to the l e f t from the parent/infant on which the a s s i stant was seated. A speaker,was located i n the back r i g h t corner of the room,.and a v i s u a l r e i n f o r c e r was located at a 45 degree angle from the c h i l d ' s l e f t side (See Figure 2), To avoid i n f l u e n c i n g the i n f a n t , the assistant and parent both wore sound attenuating earphones (see Figures 3 & 4). The v i s u a l r e i n f o r c e r was an e l e c t r i c a l l y activated toy animal conv tained iri a smoked p l e x i g l a s s box. The smoked glass made i t po s s i b l e to see the animal orily when the v i s u a l r e i n f o r c e r was activated and l i g h t s i n -side the box came on. A c t i v a t i o n of the r e i n f o r c e r also made the animal s t a r t moving and producing noise .(toy bear drums, chimpanzee claps cymbals). In the VRJSD system, the experimenter presented a sound which did or did not change. The experimenter and assistant both voted as to whether the infant responded to a change. If both voted that the i n f a n t had resporided within the required i n t e r v a l , a r e i n f o r c e r was presented to the i n f a n t . More s p e c i f i c a l l y , , the e n t i r e VRISD system was c o n t r o l l e d by a l o g i c -system to ensure maximum experimental control i n the test paradigm throughout the test period. Sound I (e.g., ba) was f i r s t played through the speaker at 2 sec. i n t e r v a l s . When the experimenter activated the l o g i c system, the FIGURE 2 Arrangement of the Experimental S i t e A TABLE I P OBSERVATION WINDOW -EQUIPMENT, E A = Assistant S = Speaker VR = V i s u a l Reinforcer I = Infant P = Parent E = Experimenter FIGURE 3. Infant O r i e n t a t i o n During Control T r i a l ro FIGURE 4. Infant O r i e n t a t i o n During Experimental T r i a l ro LO 24 vote button held by the assistant l i t up to indic a t e that a response i n -t e r v a l was.beginning. The experimenter then selected e i t h e r track.A (con-t r o l track, no change i n stimuli) or t r a c t B (experimental track, i n which the s t i m u l i changes, e.g.,1 to 4 tokens of da) according to a predetermined randomized schedule. An adjustable timerwas set at 4-1/2 sec and activated. During t h i s 4-1/2 sec i n t e r v a l , i f the infant turned' i t s head toward the sound source, and i f both the experimenter and the ass i s t a n t independently pressed t h e i r vote buttons the di s c r i m i n a t i o n was assessed to have been made, arid the v i s u a l r e i n f o r c e s was activated f o r 4 sec. I t was necessary that both the experimenter and the assistant vote within the s p e c i f i e d time i n -t e r v a l , and that track B had been chosen for the v i s u a l r e i n f o r c e r to be activated. I f any of those conditions were not met, the r e i n f o r c e r did not come on, (A manual override was also included i n the system which made i t possible to activa t e the v i s u a l r e i n f o r c e r at any time to allow for f l e x i -b i l i t y during the conditioning stages of the VRA paradigm), The VR1SD procedure began with a request to the mother to s i t behind the table with the infant on her lap. The mother was given headphones de-l i v e r i n g music to prevent her from hearing the speech s t i m u l i . The a s s i s t -ant (who was also wearing headphones) sat across the table to the c h i l d ' s r i g h t side and showed the c h i l d a s e r i e s of toys to keep him/her happy and occupied during the t e s t i n g session. The assistan t ' s r o l e was extremely important to the paradigm, as i t was necessary to,keep the c h i l d passively interested i n the toys, but not so interested that he/she would disregard changes i n the speech s t i m u l i . When the infant was atte n t i v e and calm, with his head facing the toys, the experimenter began a t r i a l by se l e c t i n g e i t h e r " s t a r t " track A (control) or track B (change) according to a prede-25 termined random schedule. The conditioning portion of the paradigm proceeded as follows. A serie s of one s y l l a b l e sounds ( i . e . , Ba) was played over the speaker. When the assistant indicated the infant was i n a state of readiness (by pressing a s i l e n t foot button to activate a l i g h t that the experimenter' could see), the experimenter changed to Track 2, and Da was played over the speaker. Immediately following the f i r s t token of Da, the toy animal was activated. Upon.activation, l i g h t s came on i n the p l e x i g l a s box, and the toy animal started performing. The noise of the animal attracted the infant's atten-t i o n , and a head turn response was made to see the toy animal (see Figures 3 and 4).' This procedure of presenting the sound stimulus and a c t i v a t i n g the r e i n f o r c e r was repeated for 2 to 3 more t r i a l s ; The experimenter then waited u n t i l a f t e r the second token of "Da" before a c t i v a t i n g the r e i n f o r c e r ' to give the infant the a d d i t i o n a l seconds to respond. I f no head turn r e -sponse:, was made, the en t i r e procedure was repeated. As soon as one head turn response was made upon presentation of-the sound change before a c t i v a -t i o n of the r e i n f o r c e r , a c t i v a t i o n of the toy animal became contingent upon the i n f a n t making a head turn within 4-1/2 seconds a f t e r a changed stimulus, and the paradigm was taken over by the l o g i c system. Sixty-eight percent of the infants formed the association within an average of. nine conditioning t r i a l s . Two to four sessions were required to complete the t e s t i n g of each i n -fant. Parents were requested to bring t h e i r infants on days when they had. no evidence of colds or ear i n f e c t i o n s . Care was taken to ensure that each infant was comfortable i n the experimental room before t e s t i n g began, and observations were made on the. infants a b i l i t y to respond to a sudden onset of sound (they a l l d i d ) . On the f i r s t day of restin g the infant was condi-26 tioned to one or the other of the Hindi sound pa i r s chosen on a random-• 3 -U - (3) lzed b a s i s . Testing on the other Hindi sound p a i r was then completed on day 1, or one of the next three testing sessions. Infants that did not condition on the f i r s t day were given a second.day of t r a i n i n g . I f they did not be-gin to condition within the f i r s t f i v e minutes of t e s t i n g on' the second day, they were switched to the common English p a i r /Ba//Da/, I f they did not learn with that p a i r during the session, they were not continued iri the study. (Mothers would not continue bringing a baby out to an experi-ment t h e i r baby would not succeed a t ) , F a i l u r e to respond to a new sound change was followed i n the,same session by r e t e s t i n g the infant on a pre-v i o u s l y tested contrast. This was done to tr y to determine whether the sound p a i r , or the state of the i n f a n t , was responsible for the negative r e s u l t s . Procedures as s i m i l a r as possible to these were used with the adult subjects. The,experimental set-up was nearly i d e n t i c a l , with the subject s i t t i n g at the table ^'facing the loud speaker. When the subject indicated readiness, the experimenter would begin the t e s t i n g session. The subject's task was to push the vote button on a "vote" box when a change i n stimulus was detected. The-visual r e i n f o r c e r contained the toy animal, and was ac-tiva t e d upon a correct vote i n an experimental t r i a l . The c r i t e r i o n f or d i s c r i m i n a t i o n was set at 8 out of 10 correct r e -sponses for change t r i a l s ; The mode of presenting c o n t r o l t r i a l s v aried -?ln t h e - l n l t r a l ^desigriZsre• had« planned/to 'cohditioh^infants on /Ba//Da/ and then trans f e r them to the Hin d i . p a i r s . Several problems arose. Most importantly, our mothers, t i r e d of making the long t r i p to.UBC would make up reasons not to return a f t e r the 3rd or 4th session. As i t was pr i m a r i l y important to have a within group comparison ori the 2 p a i r s of Hindi speech sounds, data was therefore c o l l e c t e d on /Ba//Da/ only when po s s i b l e . s l i g h t l y between the infants and the adults. As i n d i c a t e d e a r l i e r , the assistant indicated the infant's readiness by s i l e n t l y ' a c t i v a t i n g a l i g h t for the experimenter to see, During the period the l i g h t was activated, a l l head turn,responses (including f a l s e p o s i t i v e s ) were recorded. At l e a s t four times during each seri e s of ten change t r i a l s , the experimenter would not change the s i g n a l . During the other times the s i g n a l would be changed between 1 and 8 sec.after a c t i v a t i o n of the "readiness" l i g h t i n a random fashion. The a s s i s t a n t never knew i f a change t r i a l would occur and would never know when i n the observation period that change would occur. The actual c r i t e r i o n was. therefore at l e a s t 12 out of 14. For adults, change t r i a l s occurred i n an i r r e g u l a r fashion ranging from 8 to 30 sees. A l l f a l s e p o s i t i v e s were counted, so again the 8 out of 10 c r i t e r i o n i s not an accurate i n d i c a t o r of the l e v e l of performance since guessing could have occurred a f t e r every token (every two sec). The c r i t e r i o n for infants and adults i s defined i n terms of experimenter delimited observation periods, rather than i n absolute performance. A second group of English adults was tested with l i m i t e d feedback to provide a procedure more comparable to that of the i n f a n t s . In t h i s group, subjects were runii.as i n a conditioning paradigm, with the sound change paired with a c t i v a t i o n of the r e i n f o r c e r f o r the f i r s t X t r i a l s (where X was the average number of t r i a l s to c r i t e r i o n fori:the i n f a n t s ) . A l l adults were tested i n one session. Stimuli Three stimulus p a i r s , one English /Ba//Da/, and two Hindi /ta//Ta/ h h and/t //d /, were used. The vowel (a) was used for a l l s t i m u l i as i t i s common i n both Hindi and English and i s one of the most frequent vowels to 28 appear with r e t r o f l e x consonants (Stevens & Blumsteln, 1974). ; A l l tones were made inthe Phonetics laboratory at the Uni v e r s i t y of B r i t i s h Columbia. Each tape contained 8 natural exemplars of each sound ', This was to ensure that v a r i a t i o n s i n duration, fundamental frequency and information would be randomized both within and between categories. 29 RESULTS Each i n d i v i d u a l i n each group was recorded as having e i t h e r reached or not reached the 8 out of 10 c r i t e r i o n on the two Hindi p a i r s . An analysis of proportions was then performed on this data (see Tables 3 and 4). This analysis i s based on the Scheffe theorem (Marascuillo, 1966). I t i s used to compare', discrete, data i n which the proportions of i n d i v i d u a l s f a l l i n g into given categories is- compared. The n u l l hypothesis was that there would be "no s i g n i f i c a n t difference among the proportion of i n d i v i d u a l s reaching c r i t e r i o n i n the four groups." The r e j e c t i o n l e v e l f o r this•hypothesis was set at p = ,05. For the f i r s t comparison (the Hindi'contrast Retroflex/Dental) the o v e r a l l Chi-square obtained had a p r o b a b i l i t y of le s s than ,05 (p = .0000016) and thus enabled r e j e c t i o n of the n u l l hypothesis. A s e r i e s of multiple comparisons between each p a i r of groups yielded the r e s u l t s outlined i n Table 5. There was no s i g n i f i c a n t difference between the proportion of Hindi adults and infants reaching c r i t e r i o n , nor was there a s i g n i f i c a n t d i f f e r e n c e between the naive and the trained English speaking adults. A l l other com-parisons ' (Hindi vs. each English group and infants vs. each Adult English group) were s i g n i f i c a n t . Eor the second comparison (the Hindi contrast unvoiced, aspirated dental vs. breathy-voiced dental), the o v e r a l l chi-square obtained was not s i g n i f i c a n t (p .05, p = .0580), so r e j e c t i o n of the n u l l hypothesis was not possible. However, since the p_ value was so close to .05, a s e r i e s of multiple comparisons was performed to comb the data for trends. The r e -su l t s are summarized i n Table 6. 30 Table 3 A n a l y s i s of P r o p o r t i o n s f o r R e t r o f l e x / D e n t a l Cont ras t Group 1 Group I I Group I I I Group IV ( H i n d i A d u l t s ) ( In fan ts ) (Naive Eng. (Tra ined Eng. A d u l t s ) adu l t s ) Reached c r i t e r i o n 5 Did not reach cfi€?^rXy:> A ttribif T o t a l N 5 11 1 *12 1 9 10 0 10 10 Table 4 A n a l y s i s of P r o p o r t i o n s f o r V o i c e l e s s a s p i r a t e d / Breathy v o i c e d Cont ras t Group I Group• I I Group 111 Group IV Reached c r i t e r i o n D i d not reach c r i -t e r i o n T o t a l N 10 *12 10 10 A l t o g e t h e r , 15 i n f a n t s were ^ t e s t e d i n a l l , b u t 3 would not c o n d i t i o n to the paradigm, even w i t h the E n g l i s h Ba/ba sound p a i r . The remaining 12 cond i t i oned and 9 passed both speech sound p a i r s . 31 Table 5 M u l t i p l e Comparisons on R e t r o f l e x / D e n t a l Cont ras t Comparison Confidence I n t e r v a l , P rob . of No D i f f e r e n c e 2 - 1 -0.306 to 0,140 .779 3- 1 -1 .165 to -0 .635 *..000 3- 2 -1 .163 to -0 .470 *.000 4- 1 -1 .163 to -0 .470 *.000 4-2 -1 .140 to -0.694 *,000 4-3 -0.365 to 0.165 ,774 Table 6 ' M u l t i p l e Comparisons on V o i c e l e s s A s p i r a t e d / ' Breathy Voiced C o n t r a s t ' Comparison Confidence I n t e r v a l Prob , o f No D i f f e r e n c e x 1 - - v V ' • i. v . 2- 1 -0 .436 to 0.102 .494 3-1 -0 .987 to 0.213 *,002 3- 2 -0 ,905 to 0.038 .153 4- 1 -0 .662 to 0,062 .232 4-2 -0 .585 to 0.318 .909 4-3 -0 .230 to 0,830 ,572 32 The only s i g n i f i c a n t d i f f e r e n c e occurred between the Hindi adults and the naive English adults. The comparison between the infants and the naive English adults was the next closest to being a s i g n i f i c a n t d i f f e r e n c e but s t i l l had a 15% p r o b a b i l i t y of being due e n t i r e l y to chance.'" Since the VRISD paradigm i s a conditioning paradigm, i t can be c r i t i -cized f o r allowing the infants a chance to "learn 1' the di s c r i m i n a t i o n during the t e s t i n g session. As outlined i n the method section, Group XV (adults with training) was included to address t h i s type of c r i t i c i s m . A d d i t i o n a l l y , two other sources of data were c o l l e c t e d to t r y to understand the r e l a t i v e contribution of "learning" within the t e s t i n g session. The f i r s t source was the i n c l u s i o n of the common.English /Ba/ vs. /Da/ sound p a i r whenever p o s s i -b l e i n infant t e s t i n g . The second source was a comparison of the number of t r i a l s to e i t h e r c r i t e r i o n or stopping f o r each of the four groups. It was only possible to collect./Ba/- /Da/' data on four infants^ two of whomwere tested on,the Hindi,contrasts, and two of whom were only tested on the English contrasts. Since the two who were only .tested on the English contrasts were never tested on the Hindi.sounds, and since other-infants who were tested on the Hindi sounds f a i l e d to reach c r i t e r i o n or were not tested on the Ba/Da, no chi-square comparisons were made., These data were analyzed i n terms of mean number of t r i a l s to shaping and to c r i t e r i o n as summarized i n Table 7. Only i n d i v i d u a l s who reached c r i t e r i o n were included i n computing these means. T-tests for correlated data were then performed comparing the means l i s t e d i n Table 7. No s i g n i f i c a n t d i f -ferences were found among the three d i f f e r e n t sound p a i r s i n ei t h e r number of t r i a l s to shaping, or number of t r i a l s to reaching c r i t e r i o n . Since the N was so small, a 2-group, one-tailed t - t e s t was performed to compare 33 Table 7 Mean Number of Infant T r i a l s on Speech Contrasts Infants . Trial to shaping Trials; to passing N = 4 Ba/Da 5,5 20.2 N = 11 Ret/Dent 10,9 26,5' N = 10 Un/ASD 8,1 22,36 34 /Ta/ / t a / and /Ba/ /Da/. Although the d i f f e r e n c e between the means on number of t r i a l s to c r i t e r i o n was c l e a r l y not s i g n i f i c a n t , the d i f f e r e n c e on number of t r i a l s to shaping almost reached s i g n i f i c a n c e at p .05 l e v e l b h (p = .06), A s i m i l a r analysis on / t / /d / vs. /Ba//Da/ did not approach s i g n i f i c a n c e . An analysis of variance was run on the number of t r i a l s to c r i t e r i o n Cor s t o p p i n g ) f o r the four groups on the two p a i r s of Hindi sounds. C e l l means are shown i n Table 8, and the r e s u l t s of the analysis of v a r i -ance are shown i n Table 9. As can be seen, the main e f f e c t s for both Group (I-TV) and Sound P a i r were s t a t i s t i c a l l y s i g n i f i c a n t . Using Tukey's method of planned comparisons, i t was found that the group main e f f e c t could be accounted for iby a . s i g n i f i c a n t d i f f e r e n c e between the Group 1 (Hindi adults) and a l l other groups on number of t r i a l s to c r i -t e r i o n . No s i g n i f i c a n t differences emerged between Groups T l , I I I and IV. The other main e f f e c t was simply that o v e r a l l , the unvoiced, unaspir-ated/unvoiced aspirated sound p a i r was easier than the r e t r o f l e x / d e n t a l . ' (Ba//Da/ could not be included i n the ANOVA as i t would not f i t into a repeated measures design). Tnfarits and adults were run as long as possible during a t e s t i n g session i n the hope that they would reach c r i t e r i o n , Whenever an infant became overly fussy, or sleepy during a t e s t i n g session, we would stop.' Conversely when an adult started s i g n a l l i n g he/she was fatigued we would stop.' A d d i t i o n a l l y , t e s t i n g of adults who f a i l e d to show any recognition of the sound change was terminated a f t e r 25 t r i a l s . 35 Table 8 C e l l Means (M) and Standard D e v i a t i o n s (SD) f o r Number of T r i a l s to C r i t e r i o n Group I Group I I G r o u p . I l l Group IV M SD M SD M SD M SD Ta/ta 10.4 .548 27.58 9.65 25,6 10.38 27.7 3.498 T h / D h 10.2 .447 22.5 11.31 18.5 5.60 1 9 . 3 ' 5.056 Table 9 Source Table f o r Number o f T r i a l s to C r i t e r i o n ; A n a l y s i s of Var i ance Sum of Squares Degrees of Freedom MS F r a t i o Between Group 2247.099 3 749.03 13,307* E r r o r 1857.516 33 56.29 Sound P a i r 446.842 1 446.84 6.797* Grp x S n d p a i r 160,814 3 53.61 0.815 W i t h i n Groups 2169.508 33 65.74 • • • \ • • 36 DISCUSSION The r e s u l t s of t h i s study y i e l d support for the hypothesis: ^Humans are born,with the a b i l i t y to discriminate.the universal set of d i s t i n c t i v e l i n g u i s t i c features. Through development there i s a decline i n t h i s a b i l i t y as the per-ceptual space becomes organized to approximate the phone-mic categories used i n the native language". There was no d i f f e r e n c e between the infants and the Hindi adults, or be-tween the two groups of English speaking adults, but there were s i g n i f i -cant differences i n discriminatory a b i l i t i e s between a l l other p a i r s of groups for the r e t r o f l e x / d e n t a l d i s t i n c t i o n , A higher proportion of the infants and the Hindi adults could discriminate t h i s Hindi contrast than could e i t h e r group of English speaking adults, English adults with l i m i -ted t r a i n i n g performed no differentafrom English adults without t r a i n i n g , showing that minimal t r a i n i n g with adults did not f a c i l i t a t e the d i s c r i -mination. I n t e r e s t i n g l y , the one adult English speaker who was able to discriminate the contrast reported that seven years p r i o r to his being tested on the Hindi contrast he had spoken T w i f o r a period of three months, Retroflex/Dental i s used i n Twi to d i f f e r e n t i a t e phonemic cate- , gories (Fromkin, 1974), This subject, l i k e the Hindi speakers, reported the contrast as being very obvious, and was surprised others could not discriminate the difference, Results from the comparison of the four groups on the other Hindi h h sound p a i r , /d / and / t / were les s c l e a r , Although the analysis of proportions did not quite reach s i g n i f i c a n c e planned comparisons were performed to try to determine whether there was any pattern to the pos- 1 s i b l e difference between the four groups. ' The only s i g n i f i c a n t d i f f e r e n c e 37 was between the Hindi adults and the naive English adults. I t should be pointed out that two infants out of-twelve f a i l e d to perform t h i s d i s -crimination. One.of'the i n f a n t s , however, was very c l e a r l y able to make th i s d i s c r i m i n a t i o n , but simply f a i l e d to perform the required task. Dur-r ing the t e s t i n g session, she would turn her eyes toward the speaker when-ever the sound changed, but she would, not perform a f u l l head turn. Eye movements were not r e i n f o r c e d , nor could they be counted as correct r e -sponses. Had we been able to count them, however, t h i s infant would have reached c r i t e r i o n , .arid the o v e r a l l Chi^square for the comparison would have reached s i g n i f i c a n c e (p = .02). In a d d i t i o n , the i n f a n t vs. naive adults comparison would have reached s i g n i f i c a n c e . (p = .03).; The compari-son;- between the E n g l i s h adults with t r a i n i n g , and both the Hindi adults and English infants would s t i l l not have been s i g n i f i c a n t , however. Thus, at best, the i n c l u s i o n of t h i s infant i n the analysis would have lent only l i m i t e d support to the main hypothesis; In an attempt to determine whether the Hindi. contrasts required a greater number of t r i a l s to c r i t e r i o n than did the E n g l i s h contrast /Ba/ /Da/, t - t e s t s were performed on the. i n f a n t data. Although the means were greater f o r the Hindi contrasts (see Table 7), t h i s d i f f e r e n c e did not reach s i g n i f i c a n c e i n a correlated one-tailed t - t e s t . This f i n d i n g was. s u r p r i s i n g since i t was predicted that the English contrast would,be somewhat easi e r , at l e a s t i n shaping t r i a l s , sirice many of the i n f a n t s were already r e p e a t i n g /ba/'s and /da/'s i n both t h e i r i m i t a t i v e and spontaneous babbling. This lack of s i g n i f i c a n c e suggests that even though some language appropriate sounds have entered the i n f a n t s ' productive 38 r e p e r t o i r e , f l e x i b i l i t y may s t i l l be ma in ta ined ,a t the p e r c e p t u a l l e v e l . An a n a l y s i s of v a r i a n c e conducted on number o f t r i a l s to c r i t e r i o n y i e l d e d two s i g n i f i c a n t e f f e c t s . "Groups" and "Sound P a i r s " . Planned comparisons showed o n l y the d i f f e r e n c e between H i n d i a d u l t s and a l l o ther groups t o . b e ' s i g n i f i c a n t . ' This i s not s u r p r i s i n g g iven that H i n d i adu l t s performed s i m i l a r l y to E n g l i s h speakers i n a p i l o t experiment con-ducted u s i n g E n g l i s h con t r a s t s as s t i m u l i , That i s , they reached p e r f e c t scores almost immediately on n a t i v e c o n t r a s t s . Of more i n t e r e s t , how-eve r , i s the l a c k of s i g n i f i c a n c e between p a i r s of the o the r three groups. The i n f a n t s may have faced a more d i f f i c u l t t ask than the a d u l t s f o r three reasons.' (1) The i n f a n t s had to c o n t i n u a l l y d i v i d e t h e i r a t t e n t i o n between the toys be ing manipulated by the a s s i s t a n t and the speech sounds. The adu l t s on the o ther hand, always had t h e i r a t t e n t i o n d i r e c t e d a t . t h e speech sounds, (2) Al though the v i s u a l r e i n f o r c e r may have been more•rewarding to the i n f a n t s than to the a d u l t s , presumably the fear o f f a i l u r e was not as s t r o n g . (Green and Swets, 1966) have suggested tha t fear o f f a i l u r e may be equa l t o monetary re inforcements as a m o t i v a t i n g f o r c e fo r a d u l t s . C e r t a i n l y , the a p o l o g i e s , r a t i o n a l e s , and compla in ts o f f e r e d by each adu l t sub jec t who d i d not reach c r i t e r i o n onthese c o n t r a s t s y i e l d e d s u b j e c t i v e support f o r t h i s n o t i o n ! (3) Infants are desc r ibed as be ing more a f f ec t ed by s t a t e f l u c t u a -t i o n s (E i senberg , 1976) than adu l t s and should thus be expected to make more e r r o r s on an e q u a l l y easy task due to these s t a t e f l u c t u a t i o n s . That i s , be ing t i r e d , hungry, e t c , . , i s desc r ibed as i n t e r f e r i n g much more 39 with an infant's attention to a task than would s i m i l a r f l u c t u a t i o n s i n an adult. A d d i t i o n a l l y , day to day differences i n q u a l i t i e s such as s o c i a b i l i t y , excitement, fear of strange places, etc, a f f e c t an i n -fant ' s perf ormance i n a c o n t r o l l e d experimental s e t t i n g . ' The e f f e c t s of such factors on thel performance of adults i s assumed to be minimal. Since there was no s i g n i f i c a n t difference between the number of t r i a l s to c r i t e r i o n (or stopping) for adults and i n f a n t s , . i t cannot be argued that.the infants were simply given a greater number of t r i a l s to " l e a r n " the contrasts. Thus the hypothesis'that infants can discriminate non-native sounds with l i t t l e or no learning although adults may not be able t o d o so was substantiated, There i s some question as to whether VRTSD should continue to be considered a conditioning paradigm or whether,it should be reconceived as a d i s c r i m i n a t i o n paradigm with feedback. Since the monkey iri a box can hardly.be seen as a potent adult r e i n f o r c e r , one could/argue.. ^that fear offfailure.wastthe -motivating!:foreeDbehirid^adult^pefformahce^. A d d i t i o n a l l y , infant behavior suggested some kirid of "competence" motiva-t i o n rather than a.direct stimulus r e i n f o r c e r as being primary. Once an infant had "learned" to perform a head turn response upon a change i n the. background stimulus the r e i n f o r c i n g value of the toy seemed to' be diminished, A f t e r several t r i a l s , i n fants would t y p i c a l l y concentrate on the assistant manipulatirig toys, would then swing t h e i r head around toward the speaker and back again when the speech sound changed and continue watching the assistant rather than the r e i n f o r c e r , ' I t seemed as i f infants only wanted to know they could acti v a t e the toy animal, 40 but did not p a r t i c u l a r l y care to watch i t . In addition, i t would be hard to argue that subjects could " l e a r n " which acoustic signals they should heed given the multiple natural tokens and the l i m i t e d number of t r i a l s . The.second main e f f e c t "Sound P a i r s " was a t t r i b u t a b l e to / t ^ / / d ^ / taking f e w e r . t r i a l s to discriminate for a l l groups,, Such a r e s u l t i s consistent with the r e s u l t s from both the Analysis of Porportions and from the t - t e s t s i n that both these s t a t i s t i c a l analyses gave some siip^ port f o r the notion that /t*V/d*V was-intermediate i n d i f f i c u l t y between the common English /Ba//Da/ and the, more rare Hindi /Ta//ta/ contrasts. Two explanations could be offered for t h i s d i fference, (1) A "language experience" confound could have been possible for two reasons.' F i r s t , v o i c e l e s s , aspirated vs. breathy voiced stops are used phonemically across a wider range of natural languages'than i s the r e t r o f l e x vs. dental place of a r t i c u l a t i o n d i s t i n c t i o n . Thus adults, and even i n f a n t s , would be more l i k e l y to have had exposure to t h i s sound contrast. Second, there i s controversy as to the correct d e s c r i p t i o n of the four categories of voice onset time used iri Hindi, Although many l i n : r • guists(e.g., Ladefoged, 1975) assert that breathy v o i c i n g must be desr-cribed as a unique category of voice onset time, some l i n g u i s t s have described breathy v o i c i n g as being a voiced, aspirated stop, ' I f t h i s l a t t e r d e s c r i p t i o n i s correct, one could argue that the.voiceless vs. voiced d i s t i n c t i o n could provide English l i s t e n e r s with a p a r t i a l cue to the d i s c r i m i n a t i o n . (English d i f f e r e n t i a t e s voice vs. v o i c e l e s s un^ aspirated stops). 41 C2) An explanation based on the notion of "perceptual distance" i s also p o s s i b l e . Tt may be that although the human ear can nec e s s a r i l y discriminate a l l phonemic d i f f e r e n c e s , the perceptual d i s s i m i l a r i t y of some'of these differences i s greater f o r some feature d i s t i n c t i o n s than i t i s for others. In this regard a s t r i c t l y phonological d e s c r i p t i o n (based on meaningful articulat'ory differences) may not always be complet The r e l i a n c e on such a d e s c r i p t i o n i n t r a d i t i o n a l l i n g u i s t i c s rather than oh a phonetic d e s c r i p t i o n (based more on acoustic differences) may have been misleading. That i s , a s i n g l e feature d i f f e r e n c e i s a useful t o o l f o r explaining phenomena that y i e l d a perceptual (and meaningful) invar i a n t but not an acoustic one. This does not, however, imply pere ceptual (or acoustic) equality among a l l feature differences,' A perceptual distance explanation i n i t i a l l y appears to involve an acoustic rather than a l i n g u i s t i c , speech perception mechanism. On clo s e r examination however, a more complex picture emerges, suggesting p o s s i b l e p a r a l l e l l e v e l s of processing with d i f f e r e n t i a l access to an acoustic or a l i n g u i s t i c l e v e l depending upon the most'effective strateg for the task. In summary, the infants were found to discriminate a l l sound pa i r s according to phonemic category with comparable ease (with a s l i g h t sugr gestion that the Hindi /Ta//ta/ was more d i f f i c u l t to shape), Tt was, also shown that Hindi adults could discriminate, a l l sound p a i r s , whereas English adults could not discriminate /Ta//ta/ at a l l , and only some h h h h English adults could discriminate / t //d /', O v e r a l l , the ft //d / d i s -crimination appeared to be easier than the /Ta//ta/ d i s c r i m i n a t i o n . An important a d d i t i o n a l piece of information concerns the categorizing phenomenon.observed, That i s , i n d i v i d u a l s whocould perform to. c r i -t e r i o n for a sound p a i r would continue to perform at that l e v e l through-out a t e s t i n g session without an increase i n f a l s e p o s i t i v e rate, (In-fants would t i r e a f t e r an a d d i t i o n a l 10 t r i a l s or so). Once a c r i t e r i o n was established, the i n d i v i d u a l s did not return to p r e - c r i t e r i o n l e v e l s of performance. ' Because natural tokens were used, there were obvious differences between each token within a speech sound category, Those d i f -ferences were only responded to by i n d i v i d u a l s who could not reach c r i -t e r i o n on a sound pair i . Individuals who categorized the sounds (reached c r i t e r i o n at the phoneme l e v e l ) did not respond to within category v a r i a t i o n , although they could hear differences when asked. If i t i s accepted that neither Hindi sound p a i r involved tokens that are used phonemically i n English ( i . e . , i f the language experience con-found explanation i s discovered) recourse to a categorizing explanation based on experience with a language i s not po s s i b l e . The explanation 1 would l i k e to o f f e r i s thus based on the notion of twor-level of proces-sing, an acoustic and a l i n g u i s t i c l e v e l , much as suggested by Wood (1974). When possibl e , people seem to employ a l i n g u i s t i c l e v e l of pro-cessing, and respond to the speech sounds i n a c a t e g o r i c a l manner d i s r e -garding within category differences, When t h i s strategy f a i l s , they employ an acoustic l e v e l of processing, An acoustic phonetic analysis of the speech sounds chosen for t h i s studysupports such an explanation. The phonological and phonetic des-c r i p t i o n s of r e t r o f l e x vs. dental sounds are i d e n t i c a l . The phonetic d e s c r i p t i o n of v o i c e l e s s aspirated vs., breathy voiced i s d i f ferent, howr, ever, from the phonological d e s c r i p t i o n . That i s , although these sounds 43 d i f f e r i n only a s i n g l e phonemic feature, the voice onset time d i f f e r -ence may be at l e a s t two steps apart on a continuum. This i s because the Hindi murmured stops are neither voiced nor aspirated, Tt could be assumed' that they a c t u a l l y d i f f e r i n at le a s t two ways from vo i c e l e s s aspirated stops (Ladefoged, 1975), Tt could then be argued that the per-il h ceptual distance between ft / and/d / i s greater than.that f o r /Ta//ta/. Thus employing an acoustic l e v e l of processing would be more successful for t h i s sound p a i r , and could lead to more accurate d i s c r i m i n a t i o n by non-native speakers. Since-the data suggested that phonemic discrimina-t i o n of /t*V/d*V was easier (required fewer t r i a l s to reach c r i t e r i o n ) for a l l groups than /Ta//ta/, a l i n g u i s t i c l e v e l of processing can also be invoked enabling l i s t e n e r s to ignore acoustic differences that' are i r r e l e v a n t to natural languages. 44 CONCLUSIONS This study yielded d e f i n i t e support for the:idea that infants possess the propensity to discriminate the universal set of l i n g u i s t i c , features. The checks b u i l t into the study make i t d i f f i c u l t to argue that infants were simply learning these contrasts i n a very few t r i a l s . The r e s u l t s therefore support the view that i n f a n t s actively* impose'a structure (but a structure constrained by b i o l o g i c a l perceptual capar b i l i t i e s ) on continuous'auditory input, ;, Such an innate.constraint would allow the infant to segment the continuous input of speech into the units used to convey,meaningful differences within the language •. environment to which the infant i s exposed. Some support was given for the idea that there may be a decline i n speech perceptual a b i l i t i e s with "either age/or l i n g u i s t i c experience. The f i n d i n g that t h i s decline was more evident with one than the other Hindi sound p a i r makes i n t e r p r e t a t i o n more d i f f i c u l t , . Two explanations were offered f o r these r e s u l t s . It. was suggested that the Non-Hindi h h population may not have been naive with respect, to the / t //d / c o n t r a s t . 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Consonant cue p e r c e p t i o n by twenty^ t o ' t w e n t y - f o u r week o l d i n f a n t s . ; C h i l d Development, 1971, 42, 717-731. M o f f i t , A . R , C a t e g o r i c a l d i s c r i m i n a t i o n among the -acoust ic cues fo r b i l a b i a l -stop consonants by young i n f a n t s . (Unpublished m a n u s c r i p t ) . Moore, J . M , , W i l s o n , W , R . , & Thompson, G. V i s u a l re inforcement o f head-t u r n . responses i n i n f a n t s under twelve months of a g e . J o u r n a l o f  Speech arid Hear ing D i s o r d e r s , 1976. Morse, P . A . Infant speech p e r c e p t i o n : A p r e l i m i n a r y model and review o f the l i t e r a t u r e . I n R . L , S c h i e f e l b u s h and L . L . L l o y d (Eds , ) Language p e r s p e c t i v e s - a c q u i s i t i o n , r e t a r d a t i o n , and i n t e r v e n t i o n . B a l t i m o r e : U n i v e r s i t y Park, P r e s s , 1974. P e n f i e l d , W. , & Robe r t s , L . Speech arid b r a i n mechanisms.. P r i n c e t o n : P r i n c e t o n U n i v e r s i t y P r e s s , 1959. 50 Piaget,. J." • The o r i g i n s of i n t e l l i g e n c e i n c h i l d r e n . New York: Inter-national U n i v e r s i t i e s Press, 1952. P i s o n i , D.P. Speech perception. In Status Report, Haskihs Laboratories, . 1977. P r a t t ; K.C. The neonate. In L. Carmichael (Ed.), Manual of c h i l d psy- chology. New.York: John Wiley & Sons, Inc., 1960, Pp. 215-291. : Samuel, A.G. The e f f e c t of d i s c r i m i n a t i o n t r a i n i n g on' speech perception: . Noncategorical perception. Perception and Psychophysics, 1977, 22., (4), 321-330. Singh,,S., & Black, J.W. Study of twenty-six i n t e r v o c a l consonants as spoken and recognized by four language groups, Jourrial' of the Ac o u s t i c a l Society of America, 1966, 39,; 371r-387. Stern, H.H. Optimal age: Myth or r e a l i t y ? The Canadian Modern Language Review, 1976, 32(3), 283-294. Stevens, K.N., & K l a t t , D.H. Role of formant t r a n s i t i o n s i n the voiced-vo i c e l e s s d i s t i n c t i o n f o r stops. Journal Of the A c o u s t i c a l Society of America, 1974, 55_, 653-659. Stevens, K.N., & Blumstein, S.E. Quantal aspects of consonant productiori and perception; A study of r e t r o f l e x stop consonants. Journal.of Phonetics, 1975, 3, 215-233. Stevens, S.S. Psychology and the science of science, Psychological B u l l e t i n , 1939, 36_, 221-263. Streeter, L.A. Language perception of two-month-old i n f a n t s shows e f f e c t s of both innate mechanisms and experience. Nature, 1976, 25,9, 39-41. 51 Suzuki, T. & Ogiba, Y, A technique of pure tone audiometry f o r . c h i l d r e n under 3 years of age? Conditioned o r i e n t a t i o n r e f l e x (C.O.R.) audiometry. Review of Laryngology, 1960, 81, 33, Suzuki, T., & Ogiba, Y, Conditioned o r i e n t a t i o n r e f l e x audiometry. Archives of Otolaryngology, .1961, 74, 192-198, Tees; R.C. ' Perceptual development i n mammals, ' In C, G o t t l i e b (Ed,),' Studies on the development of behavior and the nervous system: Neural and behavioral s p e c i f i c i t y . New York: Academic Press, 1976j *:PpS 1281-326. Trehub, S.E, A u d i t o r y - l i n g u i s t i c s e n s i t i v i t y i n i n f a n t s . Doctoral d i s s e r -t a t i o n . M c G i l l U n i v e r s i t y , Montreal, 1973, . Trehub, S.E, The d i s c r i m i n a t i o n of foreign speech contrasts by infants and adults. C h i l d Development, 1976, 47(2), 466-472. Williams, L,. Speech perception and production as a function of exposure  to a second language. Unpublished Doctoral D i s s e r t a t i o n , Harvard Uni v e r s i t y , 1974. Williams, L. Infant d i s c r i m i n a t i o n of synthetic speech s t i m u l i contrast-ing i n place of a r t i c u l a t i o n with and without a release burst. Manuscript i n preparation. Wilson, W.R. Assessment of auditory a b i l i t i e s i n i n f a n t s . Paper pre-sented as a.short course at American speech and Hearing Association, Western Regional Convention, May, 1976. . Wilson, W.R., Lee, K.H., Owen, G., & Moore, J.M. Instrumentation for operant infant auditory assessment. Ch i l d Development and ..Mental Retardation Center, U n i v e r s i t y of Washington, Undated manuscript. 52 Witelson, S.F., & P a l l i e , W, L e f t hemisphere s p e c i a l i z a t i o n f o r language i n the Newborn: Neuroanatomical evidence of asymmetry. Brain, 1973, 96^ , 641-646. Wood, .CO.. P a r a l l e l processing at auditory- and phonetic information i n speech and di s c r i m i n a t i o n . Perception and Psychophysics, 1975, 15,-501-508. 53 APPENDIX A Background i n Speech Decoding and i n D i s t i n c t i v e Features It i s now well established that the cochlea,,is completely formed by 26 weeks i n utero, and that by t h i s time both the middle and inner ear structures have reached f u l l adult s i z e . (Eisenberg, 1976). Auditory nerve f i b e r s begin to myelinate during the. s i x t h month i n utero, so that by b i r t h even.the auditory cortex i s myelinated i n the- normal f u l l - t e r m infant (Eisenberg, 1976). Although i t was once believed that the i n f a n t ; could not make any d i f f e r e n t i a l r e s P o n s e s associated with the complex c h a r a c t e r i s t i c s of auditory s t i m u l i (Pratt, I960), i t i s now 'well docun mented that most newborns, even premature babies and those with abnormali-t i e s of the c e n t r a l nervous system can discriminate sounds according to various acoustic variables (Eisenberg, 1976). Several acoustic parameters r e l a t e d to the decoding of speech have been explored. Each of the parameters which may be p a r t i c u l a r l y impor-tant i n speech has been shown to be within the auditory c a p a b i l i t i e s of the newborn: (1) duration, or the t o t a l amount of time consumed by a s t i r -mulus; (Eisenberg, 1976)5 (2) frequency, i n Hertz (hz), or the number of sine wave r e p e t i t i o n s per second i n a pure tone s i g n a l (Trehub, 1973); (3) sound pressure l e v e l , or the ph y s i c a l i n t e n s i t y of the s i g n a l . i n decibels with reference to acoustic zero (Eisenberg, 1976), (4) dimen-s i o n a l i t y , or the kind and amount of variance within a complex auditory stimulus (Eisenberg, 1976). Unfortunately, speech sounds cannot be e a s i l y analyzed i n terms of t h e i r constituent parts for three main reasons. 54 (1) Speech i s continuous, thus acoustic cues are highly overlapping, as shown by the diagram below. | ^ j | g TIME Figure l i Schematic diagram showing how the overlap of a r t l c u l a t o r y features produced encoding i n the conversion to sound, From Liberman, 1967), (2) Phonetic segments do not have inva r i a n t properties. For example, the /d/'s i n the continuum from / d i / to /du/ would each be perceived as a /d/ sound, but the acoustic dimensions of these /d/ portions would be e n t i r e l y d i f f e r e n t as i l l u s t r a t e d i n the abbreviated spectograms below. (From Liberman, 1967). 3000 1800 0 Idi de d9 da d) do du Figure 2. Abbreviated "d M spectograms, In addition, accents, voice q u a l i t y , whispering, etc, a l l create v a r i a t i o n i n the acoustic s i g n a l , but do n o t a l t e r a l i s t e n e r ' s i n v a r i a n t perception. (3) Phonetic segments do not stand i n a one-to-one r e l a t i o n to the acoustic s i g n a l , i n most non-speech and "unencoded" speech sounds, i t i s possible to judge the manner i n which the energy of the sound i s d i s t r i -buted, whereas i n encoded speech sounds, i t i s impossible to judge the 55 a c o u s t i c cues u n d e r l y i n g the s i g n a l , ' Al though so f a r i t has proved imposs ib l e to demonstrate i n v a r i a n t a c o u s t i c cues u n d e r l y i n g segments o f speech, there are (as i n d i c a t e d above) p e r c e p t u a l i n v a r i a n t s . That i s , many speech sounds (except vowels and f r i c a t i v e s ) are pe rce ived i n a c a t e g o r i c a l f a sh ion when presented i n a l i n g u i s t i c con t ex t . Thus a l though a speech s i g n a l may ..vary . a long an a c o u s t i c continuum, i t w i l l not be p e r c e i v e d as a new ca tegory u n t i l i t c rosses a phoneme boundary. The meaning o f ' t h i s p e r c e p t u a l invar iance . i s a mat ter of cons ide rab l e debate. Some i n v e s t i g a t o r s p o s i t a s p e c i f i c l i n g u i s t i c p r o c e s s e s ' ( E i m a s , 1976) , whereas o thers c l a i m i t to be a s imple a c o u s t i c p rocessor more s e n s i t i v e t o ' t h e c o m p l e x i t i e s of m u l t i d i m e n s i o n a l s i g n a l s (Stevens- & K l a t t , 1974), ' A d d i t i o n a l l y , the f i n d i n g o f w i t h i n -category d i s c r i m i n a t i o n under s p e c i a l c i rcumstances has l ead some i n v e s -t i g a t o r s to p o s i t two p a r a l l e l modes o f p r o c e s s i n g , a c o u s t i c and phone t i c (Wood, 1974) . In an attempt to understand t h i s pe rcep tua l i n v a r i a n c e , t r a d i t i o n a l l i n g u i s t i c s desc r ibes a s t r u c t u r a l a n a l y s i s of the r e g u l a r i t y between phonemes and a r t i c u l a t i o n , and p o s i t s a u n i v e r s a l set of phonemes i n terms of a r t i c u l a t o r y f e a t u r e s . S e v e r a l c l a s s i f i c a t i o n schemes have been developed, some i n terms o f o n l y phonemic d e s c r i p t i o n (Jakobson & H a l l e , 1956), and o thers i n c l u d i n g r u l e s to account fo r recombina t ion i n t o mor-phemes (Chomsky & H a l l e , 1968). An example of fea tu re d e s c r i p t i o n i s g iven i n . T a b l e 1. As can be seen i n Table 1, each phoneme can be d e s c r i b e d i n terms o f a r t i c u l a t o r y fea tures arid phonemic c o n t r a s t s can be de sc r i bed i n terms *A s t imulus dimension i s cons idered to be p e r c e i v e d c a t e g o r i c a l l y i f the spac ing of s i g n a l s a long that dimension i s found to be the same i n d i s c r i m i n a t i o n experiments as i n i d e n t i f i c a t i o n exper iments . T a b l e 1 Tho prime features. 56 Feature Abbreviated definition Phonological Exemplification name of physical scale terms symbols language word gloss % value 1 Glottalic Rate of upward movement [cjectivel t' Uduk f t lick 100 of the glottis (pulmonic) t Uduk ter collect 50 [implosive] d" Uduk dek lift 0 2 Velaric Degree of suction of air in [ + click] 1 Zulu lata climb 100 mouth (-c l ick] t Zulu tatii third 0 3 Voice Degree of approximation of the (glottal stop] ? Javanese buka> open 100 arytenoid cartilages [laryngealized] b Hausa be:rd: rat 80 (voice) b llausa be:ra girl 60 [murmur] b f t Hindi br.al forehead 20 (voiceless) P Hindi pal take care of 0 4 Aspiration Time of onset of voicing with [aspirated] P" Thai p»a: split 100 respect to release of the [unaspirated] P Thai pa: forest 50 articulation [voiced] b Thai ba: shoulder 0 5 Place Distance from the glottis to the [bilabial) P Ewe e(3e Ewe 100 first constriction of the [labiodental] v Ewe tvt two 95 vocal tract [dental) I Malayalam .kutti stabbed 90 [alveolar] t Malayalam kutti peg 85 [retroflex] t Malayalam kutti child 80 [palato-alveolar] 1 English Jip sheep 75 (palatal) c Quechua caka bridge 70 [velar] k Qucchua kara expensive 60 [uvularl q Quechua qara skin 50 [pharyngeal] h Arabic had someone 30 [glottal] > Arabic 'alia God 0 6 Labial Degree of approximation of ( + labial) Igbo akpa bag 100 the centers of the lips (-labial] k Igbo aka hand 0 7 Stop Degree of approximation of (stop] t English tat tie 100 the articulators [fricative] s English sai sigh 90 [approximant] h English hai high 0 8 Nasal Degree of lowering of the ( +nasal) n English noo know 100 soft palate [-nasal] d English doo dough 0 9 Lateral Amount of airstream flowing ( +lateral) 1 English loo low 100 over the side of the tongue [-lateral] d English doo doe 0 10 Trill Degree of vibration of an [ +trill] r Spanish pero dog 100 articulator [- tr i l l ] r Spanish pero but 0 (11 Tap) Rate of articulator^ [ + tap] r Tamil srsm saw 100 movement? [-tap] j Tamil a:j3m depth 0 11 Sonorant Amount of acoustic (•fsonorantl, i English ' s A n i a r sunnier 80 energy [ — sonorant] j English Vnjan onion 70 13 Sibilant Amount of high frequency [ +sibilant] s English stn sin 100 (over 3000 Hz.) energy [-sibilant] e English Oin thin 20 14 Grave Ratio of low to h i g h [ +grave) f English pin, kin pin, kin 90 frequency energy (-grave) 0 English tin tin 60 15 Height Inverse of frequency of the [4 height] i Danish vi:6a know 95 first formant 13 h e i g h t ] e Danish ve:6a wheat 65 [2 height] c Danish VE:ds wet 50 •t [1 height] X Danish wade 10 16 Back Difference between frequency of I + back) u English hu who 80 formant two and formant one [-back] i English hi he 5 17 Round Inverse of distance between (4-round] y French ly read 90 corners of the lips ( — round) i French Ii bed 0 18 Wide Degree of advancement of [ + wide] i Igbo obi heart 100 tongue root I-wide] i Igbo ybj poverty 20 19 Rhotacized Lowering of the frequency of [ +rhotacized] 31 English bsjd bird 100 the third formant I — rhotacized) I English bid bid 0 20 Syllabic (No agreed physical scale) [ +syllabic] n English SAdn sudden 100 ( - syllabic] n English SAn sun 0 of feature d i f f e r e n c e s . Support for such a system was presented by M i l l e r and Nicely (1955) i n a now c l a s s i c study which demonstrated that under masking conditions, errors i n perceptual responses increased as the number of feature differences decreased. Similar .pairs (phonemes d i f f e r i n g i n only one a r t i c u l a t o r y feature) were judged to be the hardest to discriminate,; An example of a h i g h l y s i m i l a r p a i r of sounds would be /b/ and /p/; the only a r t i c u l a t o r y feature difference iri v o i c i n g • ( v o i c -ing i s then c a l l e d the " d i s t i n c t i v e feature"), Most current speech per-, ception research involves phoneme p a i r s which d i f f e r i n only one d i s - . t i n c t i v e feature. 58 APPENDIX B : C o n s e n t Forms A d u l t , ' ^ C o n s e n t Form THE UNIVERSITY OF BRITISH COLUMBIA 2075 Wesbrook Mall Vancouver, B.C., Canada V6T 1W5 Department of Psychology CONSENT FORM This experimental procedure has been requested by I have been informed of the procedures and understand them. I also understand that the procedures may be terminated at any time at my request. PROCEDURE: This is a study in speech perception. You will be sitting on a chair facing a loud speaker in the testing chamber. A series of one syllable speech sounds will be played over the speaker. Your task will be to press a button when-ever you detect a change in the speech sounds. Every correct dis-crimination response will be signalled by flashing lights. A record of all your responses will be kept. If at any time you desire, there will be a break in, or ter-mination of, the testing session. My signature below certifies that I consent to the experimental procedure which has been described and which is to be conducted on the following d?-te: in the following place: • and designated in the following manner: Date: . Name: Signature: 59 I n f a n t C o n s e n t Form THE UNIVERSITY OF BRITISH COLUMBIA 2075 Uesbrook Mall Vancouver, B.C., Canada V6T 1W5 Department of Psychology CONSENT FORM This experimental procedure has been requested by I have been informed of the procedures and understand them. I also understand that the procedures may be terminated at any time at my request. PROCEDURE: The infant will be held on his/her guardian's lap in the testing chamber. He or she will see a series of toys, and will hear a series of one syllable speech sounds. The infant will be watched by the experimenter in the adjoining room, and by the assistant in the testing chamber. Whenever the infant turns to-ward the loud-speaker during a test trial, the experimenter and the assistant will press a button. If this head turn has occurred when there is a change in the speech stimuli, a toy animal inside the dark plexiglass box will begin performing. A record of all the baby's responses to the speech sounds will be kept. The baby will be held by, and will be under the control of, the guardian at all times. Whenever the guardian desires, there will be a break in or termination of the testing session. My signature below certifies that I consent to the experimental procedure which has been described and which is to be conducted on the following date: • In the following place: and designated in the following manner: . Date: Name: SignaTUre: 

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