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The development of cross language speech perception : the influence of age, experience, and context on… Werker, Janet 1981

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THE DEVELOPMENT OF CROSS LANGUAGE SPEECH PERCEPTION: THE INFLUENCE OF AGE, EXPERIENCE, AND CONTEXT ON PERCEPTUAL ORGANIZATION by JANET FELDMAN WERKER B.A., Harvard U n i v e r s i t y , 1974 M.A., U n i v e r s i t y of B r i t i s h Columbia, 1979 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of Psychology) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA 1982 © Janet Feldman Werker, 1982 In 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 the requirements f o r an advanced degree at the 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 the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r re ference and s tudy . I f u r t h e r agree 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 copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department or by h i s o r her r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed 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 . Department of PSYCHOLOGY  The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date JULY 16, 1982 ABSTRACT Previous research (Werker, G i l b e r t , Humphrey, £ Tees, 1981) i n which we compared E n g l i s h i n f a n t s , E n g l i s h a d u l t s , and H i n d i a d u l t s 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 two p a i r s of H i n d i (non-English) speech co n t r a s t s i n d i c a t e d t h a t i n f a n t s without p r i o r s p e c i f i c language e x p e r i -ence can d i s c r i m i n a t e speech sounds according to phonetic c a t e g o r i e s , whereas a d u l t s may l o s e t h i s a b i l i t y as a f u n c t i o n of e i t h e r age and/or s p e c i f i c language experience. The present work was designed to answer s e v e r a l questions t h a t emerged from that e a r l i e r research. F i r s t , experiments focussed on d e l i n e a t i n g the time course of the " d e c l i n e " i n non-native speech d i s c r i m i n a t i o n a b i l i t i e s across childhood. Second, experiments examined the g e n e r a l i t y of developmental change between infancy and adulthood by l o o k i n g at cross-language speech perception of a new (Thompson, an I n t e r i o r S a l i s h Native Indian Language) non-English speech c o n t r a s t . T h i r d , speech perception performance was examined i n r e l a t i o n t o c o g n i t i v e and l i n g u i s t i c development t o t r y to determine why the d e c l i n e occurred at one r a t h e r than another point i n ontogeny. F i n a l l y , an attempt was made to c l a r i f y the nature and i m p l i c a t i o n s of the apparent l o s s of non-native speech perception a b i l i t i e s by v a r y i n g both the d i s c r i m i n a t i o n procedure and the perceptual set c o n d i t i o n s used i n adult t e s t i n g . The r e s u l t s of these experiments r e p l i c a t e our o r i g i n a l f i n d i n g s (Werker, et. a l . , 1981) showing that i n f a n t s can d i s c r i m i n a t e the u n i v e r s a l set of phonetic c o n t r a s t s , and that there i s a d e c l i n e i n t h i s a b i l i t y as a r e s u l t of s p e c i f i c l i n g u i s t i c experience. This d e c l i n e occurs w i t h i n the f i r s t year of l i f e . The data t e n t a t i v e l y support the notio n t h a t a c e r t a i n l e v e l of memory develop-ment (.enabling an e a r l y form of r e p r e s e n t a t i o n a l ability.;) . may be necessary before s p e c i f i c experience can modify i n i t i a l i n f a n t a b i l i t i e s . In a d d i t i o n , the r e s u l t s show a d i f f e r e n c e between phonetic and phonemic (meaning based) perception i n a d u l t s u b j e c t s , w i t h the phonemic being the most robust and the most e a s i l y demonstrated. I t i s suggested that phonemic pe r c e p t i o n may r e f l e c t the s t r u c t u r i n g of c o g n i t i v e / p e r c e p t u a l c a t e g o r i e s . Speculation as. to the form ( p r o t o t y p i c a l ) and the format ( i n i t i a l l y e n a c t i v e , l a t e r symbolic) of the r e p r e s e n t a t i o n of these categ o r i e s i s o f f e r e d . I i i TABLE OF CONTENTS ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF APPENDICES INTRODUCTION General T h e o r e t i c a l Issues Issues i n Speech Perception R e l a t i n g Language and Cognit i v e t o Speech Perception METHODS AND RESULTS Experiment I Experiment I I Experiment I I I A Experiment I I I B Experiment I I I C Experiment IV Experiment V SUMMARY OF RESULTS DISCUSSION Ou t l i n e of Proposed Model REFERENCES i i i i i v v i v i i 1 ..1 13 Development 41 48 62 76 80 84 89 95 104 105 125 132 i v TABLES Table 1 The Prime Features i g Table 2 A Chart of the E n g l i s h Consonants 31 Table 3 Summary of Infant Data 32 Table 4 O u t l i n e o f Experiments 47 Table 5 H i n d i Stop Consonants 50 Table 6 D i s c r i m i n a t i o n Performance on Two H i n d i Speech Contrasts 56 Table 7 P a i r - w i s e M u l t i p l e Comparisons on the H i n d i R e t r o f l e x / D e n t a l Contrast 57 Table 8 P a i r - w i s e M u l t i p l e Comparisons on the H i n d i V o i c i n g Contrast 59 Table 9 Thompson Consonantal System 64 Table 10 D i s c r i m i n a t i o n Performance on the Thompson Contrast 75 Table 11 Infant D i s c r i m i n a t i o n Performance on the non-English Speech Contrasts 79 Table 12 Performance on Priming P o r t i o n and Tes t i n g P o r t i o n i n Per c e p t u a l Set Conditions 10 2 v FIGURES Figure 1 P o s s i b l e e f f e c t s of e a r l y experience Figure 2. Two "d" spectograms i n d i f f e r e n t vowel contexts Figure 3 I l l u s t r a t i o n of the encoded and overlapping nature o f speech "Figure 4 C a t e g o r i c a l perception f u n c t i o n Figure 5 Spectograms of the F i r s t H i n d i Contrast Figure 6 Spectograms of the Second H i n d i Contrast Figure 7 Subjects reaching c r i t e r i o n on H i n d i Stop Consonants Figure- 8 Wave form o f the Thompson g l o t t a l i z e d v e l a r / u v u l a r contrast Figure 9 Arrangement of the Experimental S i t e Figure 10A Infant o r i e n t a t i o n during c o n t r o l t r i a l Figure 10B Infant o r i e n t a t i o n during experimental t r i a l Figure 11 P r o p o r t i o n of i n f a n t subjects reaching c r i t e r i o n on H i n d i and S a l i s h c o n t r a s t s Figure 12 D i s c r i m i n a t i o n performance of subjects i n the same/different (AX) procedure Figure 13 Waveform of the e j e c t i v e p r o t i o n of the Thompson g l o t t a l i z e d v e l a r / u v u l a r c o n t r a s t Figure 14 Neisser's perceptual c y c l e Figure 15 Schematic i l l u s t r a t i o n of proposed speech perception model v i APPENDICES Appendix A The r a t i o n a l e behind the use of m u l t i p l e n a t u r a l tokens Appendix B D e t a i l s of the HT procedure as implemented -|_52 i n v a r i o u s l a b o r a t o r i e s Appendix C l The Development of V i s u a l P u r s u i t and the Permanence of Objects Appendix C2 Sample examination record form -^g^ Appendix D Ingram's phonetic inventory s c o r i n g sheets Appendix DI C h i l d s y l l a b l e sheet j_g3 Appendix D2 Lexicon sheet Appendix D3 Item and r e p l i c a sheet ^g5 Appendix E Consent forms Appendix E l Infant speech pe r c e p t i o n task -^ gg Appendix E2 Infant c o g n i t i v e and l i n g u i s t i c t a s k s -^7 Appendix E3 Adult speech perception task -^ gg Appendix E4 Same/Different speech d i s c r i m i n a t i o n task ^gg v i i ACKNOWLEDGEMENTS I would l i k e to thank the many people who a s s i s t e d me with the various phases of t h i s research. Richard Tees, my research supervisor, provided endless help and encouragement at every phase of t h i s project. The combination of c a r e f u l attention together with unlimited independence created an optimal learning environment. The other members of my committee, Merry Bullock, John Gilbert., Anne Treisman, and Tannis MacBeth Williams also provided constructive input i n the design, the execution, and the writing of t h i s work. In addition, I want to thank Guy Carden f o r h i s very h e l p f u l suggestions, and f o r f i r s t introducing me to Haskins Laboratories. I want to extend my gratitude to everyone at Haskins just f o r being there, and f o r being so excited about t h e i r work. In p a r t i c u l a r , thanks go to A l Liberman f o r our long chats about the nature and pur-V pose of speech research, and to Bruno Repp, f o r his help with regard to p a r t i c u l a r experiments. • Thanks are also extended to Maggie Edwards, Kathy Searcy, and G a i l M i t c h e l l f o r a s s i s t i n g i n the c o l l e c t i o n and t r a n s c r i p t i o n of the data, and to Sue Tees for suggesting that I look more c l o s e l y at the infants around 1 year of age. I would not have been able to do portions of t h i s work without Yvonne Hebart, who trusted me enough to introduce me to the wonderful people associated with the Nicola Valley Indian Band Council. Special thanks go to Mary Coutlee f o r coming up with the Thompson words and sounds I used, and to Mary, Mabel Joe, Joe Pete Saddleman, Joseph Mischel, and Jim Toodlican f o r recording t h e i r native sounds. Thanks also to Mandy Jimmy and Sandra Coutlee f o r bringing t h e i r babies to Vancouver. x i i i For h i s cooperation and countless re-recordings of the H i n d i sounds, I want t o thank Tej B h a t i a . I a l s o want to express my a p p r e c i -a t i o n to Ken Bryant f o r h i s cooperation and a s s i s t a n c e i n f i n d i n g n a t i v e speakers, and t o Leigh L i s k e r f o r h e l p i n g me s e l e c t the f i n a l H i n d i sounds used i n t h i s research. To the many other people who were of such h e l p , Dale Kinkade, Pat Kuhl, Steve H o l l i d a y , David Ingram, Louis G o l d s t e i n , Doug Whalen, Carole Bawden, La r r y Ward, and Nancy Palmer, among ot h e r s , I extend my g r a t i t u d e . F i n a l l y , I want t o thank my husband Ken f o r a l l h i s l o v i n g h e l p , encouragement, and understanding and our two boys, Gregory and E r i c , f o r accepting t h i s new c h i l d named "Thesis" without too much j ealousy. i x 1 INTRODUCTION Theories of perceptual development vary widely both i n t h e i r scope and i n t h e i r p h i l o s o p h i c a l r o o t s . Much speech perception research has been done without reference t o these t h e o r i e s . In the f i r s t s e c t i o n , issues r e l a t i n g t o current t h e o r i e s of perc e p t u a l development w i l l be o u t l i n e d . The f o l l o w i n g s e c t i o n s w i l l d i s c u s s i s s u e s which are d i r e c t l y r e l e v a n t t o speech p e r c e p t i o n . General T h e o r e t i c a l Issues A concern of many researchers i s how the developing organism learns to appreciate important events i n h i s or her environment. E a r l y research i n the e m p i r i c i s t t r a d i t i o n assumed that the world of the i n f a n t c o n s i s t e d of a "buzzing, blooming, confusion" ( W i l l i a m James, 1890/1950) and only through l e a r n i n g d i d the i n f a n t come to be able to d i f f e r e n t i a t e the world i n t o p e r c e p t i b l e , d i s t i n g u i s h a b l e elements. G e s t a l t i s t s , (Kofkka, 1935; Kohler, 1938) reacted against t h i s t r a d i -t i o n , n o t i n g that c e r t a i n p r o p e r t i e s of the perceptual world such as p r i m i t i v e figure-ground d i s t i n c t i o n , u n i t y , closedness, e t c . may be "givens" i n the perc e p t u a l array. They suggested t h a t these "givens" are perceived as s t r u c t u r e s which could not be explained by t r a d i t i o n a l models of l e a r n i n g . This l e d the G e s t a l t i s t s t o view pe r c e p t i o n as the d i r e c t 'appreciation of an already s t r u c t u r e d environment and t o concen-t r a t e on d e s c r i b i n g the r e g u l a r i t i e s i n the world. The search f o r i n v a r i a n t p r o p e r t i e s d i r e c t l y a c c e s s i b l e t o the young i n f a n t has continued i n recent work from a Gibsonian (E. Gibson, 1982; J . Gibson, 2 1979) p e r s p e c t i v e . A somewhat d i f f e r e n t approach t o perception a r i s e s from the Kantian t r a d i t i o n i n which i t i s suggested that, some c o n s t r a i n t s may-e x i s t w i t h i n the p e r c e i v e r t h a t predispose the young i n d i v i d u a l t o be s e l e c t i v e l y s e n s i t i v e t o some p r o p e r t i e s i n the world. Theories i n t h i s t r a d i t i o n attempt to describe these c o n s t r a i n t s and to determine t h e i r consequences i n r e l a t i o n to perceptual development. In t h i s r egard, researchers have s p e c i f i e d the many competencies e x h i b i t e d by the young i n f a n t (Cohen, 1973; Fantz, Fagan £ Miranda, 1974; H a i t h , 1978; Maurer, 1974; Salapatek, 1975) and have attempted t o understand how these competencies i n f l u e n c e l e a r n i n g about the world (Brown, 1982; Gelman, 1982). Somewhat s i m i l a r l y , t r a d i t i o n a l l i n g u i s t i c t h e o r i e s ( i . e . Chomsky, 1965; 1979) suggest t h a t a l l systems r e l e v a n t t o language a c q u i s i t i o n are b u i l t i n and have some form of r e p r e s e n t a t i o n i n the u n d e r l y i n g , innate U n i v e r s a l Grammar (UG). The major concern i n l i n g u i s t i c s i s a formal d e s c r i p t i o n of the p r o p e r t i e s of the UG and of the s p e c i f i c grammar(s) which f u n c t i o n at various stages'" of develop-ment. Formal l i n g u i s t i c d e s c r i p t i o n s r e q u i r e that parameters be described and set i n such a manner that p a r t i c u l a r changes can be accounted f o r and p r e d i c t e d . L i t t l e a t t e n t i o n , however, i s given t o the process of change, as that process i s assumed t o be under the con-t r o l of the language a c q u i s i t i o n device (Chomsky, 1965). Given t h i s p e r s p e c t i v e , i t i s not s u r p r i s i n g that d i s c u s s i o n s of perceptual change and development are not considered i n t r a d i t i o n a l l i n g u i s t i c models of speech perception. Most t h e o r i e s of perceptual development focus on improvements during ontogeny i n the i n i t i a l l y rudimentary a b i l i t y to d i f f e r e n t i a t e stimulus events (.Brunei*, 1957; Gibson, 1969). The s t o r y w i t h respect to speech p e r c e p t i o n , may be c h a r a c t e r i z e d by a high l e v e l of i n i t i a l neonatal a b i l i t y f o l l o w e d by both improvements and d e c l i n e s during normal development. Although p e r c e p t i o n i n many other domains may a l s o evidence a high l e v e l of i n i t i a l a b i l i t y f o l l o w e d by s e l e c t i v e improve-ments (see B o r n s t e i n , 1981, f o r a d i s c u s s i o n of t h i s with regard t o col o u r v i s i o n , among other c a p a c i t i e s ) , d e c l i n e s comparable t o those i d e n t i f i e d i n speech perception are not common. Thus i t i s not sur-p r i s i n g that most e x i s t i n g t h e o r i e s of perc e p t u a l development do not adequately address the i s s u e of s e l e c t i v e d e c l i n e . Researchers i n neuroscience have r e c e n t l y begun t o consider the extent t o which most normal development may be c h a r a c t e r i z e d by f u n c t i o n a l l o s s as w e l l as gain (Greenough, 1978). Such a l o s s i s seen as b e n e f i c i a l i n that i t makes the organism s e l e c t i v e l y responsive t o the most important events i n i t s p a r t i c u l a r environment ( c f . Tees S Werker, 1981). These con-s i d e r a t i o n s are a l s o r e l e v a n t t o t h e o r i e s of perceptual development. I t has been found t o be u s e f u l t o c h a r a c t e r i z e the various models of pe r c e p t u a l development as e i t h e r d i f f e r e n t i a t i o n or enrichment t h e o r i e s . According t o d i f f e r e n t i a t i o n models (Gibson, 1969; Kofkka, 1935) p e r c e p t u a l c a p a c i t y becomes i n c r e a s i n g l y elaborated through ontogeny. Such models p r e d i c t an i n c r e a s i n g a b i l i t y to d i s c r i m i n a t e the components of events (e.g. speech sounds) as a f u n c t i o n o f percep-t u a l development (E. Gibson, 1953; J . Gibson 6 E. Gibson, 1955). According to J . Gibson's v e r s i o n of a d i f f e r e n t a t i o n model, behaviour and perception are inv o l v e d i n each perceptual a c t , and perception i s seen as f u n c t i o n a l , u n i t a r y , and h o l i s t i c . Furthermore, as i n a l l d i r e c t , r e a l i s t i c conceptions, "affordances" are there t o be perceived 4 and are not read i n t o events by the p e r c e i v e r . Since perception i s based on affordance, the i n v a r i a n t s i n the perceptual world need not be measurable events, r a t h e r they can be conceived i n terms of the generating mechanisms or the f u n c t i o n a l contexts from which they arose. Thus a h o r i z o n t a l surface which i s s u f f i c i e n t l y l a r g e , e t c . a f f o r d s w a l k a b i l i t y , r u n a b i l i t y , e t c . , and i t s i n v a r i a n t s are determined by the a c t i o n s i t " a f f o r d s " , r a t h e r than by i t s p h y s i c a l c h a r a c t e r i s t i c s . In t h e i r work, E. Gibson and colleagues have explored the extent t o which i n f a n t p e r c e p t i o n i s meaningful and u n i t a r y , and whether and how young i n f a n t s must l e a r n t o perceive affordances w i t h regard t o , f o r example, support surfaces (.Campos, H i a t t , Ramsay, Henderson, £ Svejda, 1978), g r a s p a b i l i t y (.Bruner £ Koslowski, 1972; F i e l d , 1977), d e f o r m a b i l i t y (Gibson, Owsley, Walker £ Megaw-Nyce, 1979), and motion (Gibson, Owsley, £ Johnston, 1978). This research provides strong support f o r the n o t i o n that i n v a r i a n t p r o p e r t i e s which are given i n the continuously transforming v i s u a l a r r a y are d i r e c t l y a c c e s s i b l e t o the young i n f a n t . However, t h i s need not be meaningful t o the i n f a n t , and t o the extent that the concept of:. affordance ;has'.many of i t s p h i l o s o p h i c a l r o o t s i n f u n c t i o n a l i s m (Gibson, 1979) one would expect t h a t the emphasis on the e v o l u t i o n a r y match between organism and environment would r e q u i r e that t h e o r i e s i n t h i s t r a d i t i o n describe at l e a s t some of the s p e c i a l s e n s i t i v i t i e s ( c o n s t r a i n t s ) w i t h i n the organism t h a t might guide perception. Some Gihsonians (e.g. Malcom, 1971; Turvey £ Shaw, 1979) argue, however, t h a t i t does not improve the p r e d i c t i v e power of the theory t o s p e c i f y the nature of i n i t i a l c o n s t r a i n t s . 5 In c o n t r a s t , refinement t h e o r i e s of perceptual development ( i . e . Bruner, 1957; Hebb 3 j 1949;. N e i s s e r , 1967) view perception as the l e a r n i n g of a s s o c i a t i o n s between s t i m u l i so th a t p r e d i c t i o n s about which kinds of s t i m u l i may go together are p o s s i b l e . In t h i s way, the p r e c e i v e r can become l e s s and l e s s dependent on the stimulus array and more dependent on the a s s o c i a t i o n s he or she has formed through'prev.ious' experience with the world. Such t h e o r i e s view perceptual development as i n v o l v i n g the c o n s t r u c t i n g of "schemas" (.as f i r s t used by B a r t l e t t , 1932) — as organ-i z a t i o n s of sensory input. As these "schemas" become more elab o r a t e d , they are thought t o i n f l u e n c e the perception of o b j e c t s by gu i d i n g the i n d i v i d u a l t o s p e c i f i c d e t a i l s and by a i d i n g i n c l a s s i f y i n g and under-standing new in f o r m a t i o n (.see Tees, 1976). There i s reason to argue t h a t , whether schemas are der i v e d from stimulus-stimulus a s s o c i a t i o n s (.i.e. Hebb, 1959) or v i a a c t i v e c o n s t r u c t -i n g (Bruner, 1957), t h e i r development should make i t i n c r e a s i n g l y d i f f i c u l t to d i s c r i m i n a t e w i t h i n category d e t a i l s . That i s , as a r e s u l t of experience c l a s s i f y i n g these d e t a i l s as part of the same category, t h e i r d i s t i n c t i v e n e s s should d i m i n i s h . Donderi, S e a l , and Covit (1973), f o r example, provided support f o r such an argument by showing that l e a r n i n g to a s s o c i a t e a group of f e a t u r e s as one complex shape a c t u a l l y decreased d i s c r i m i n a b i l i t y of the d i s c r e t e f e a t u r e s . I t has a l s o been shown th a t grouping i n i t i a l l y d i s t i n c t i v e shapes together made them be perceived l a t e r as more.similar than they were o r i g i n a l l y (Donderi, e t . a l , 1973; Tees 6 More, 1967). P o s s i b l e forms of r e p r e s e n t a t i o n Enrichment t h e o r i e s of perc e p t u a l development which address the perception of complex patterns r e q u i r e a s p e c i f i c a t i o n of the k i n d of 6 " r e p r e s e n t a t i o n " that may guide the p e r c e p t i o n . The nature and form of proposed r e p r e s e n t a t i o n s can'vary w i d e l y , (.as o u t l i n e d by Reed, 1978) as can the processes l e a d i n g t o that r e p r e s e n t a t i o n (Forman £ S i g e l , 1978). Reed o u t l i n e s s i x d i f f e r e n t p o s s i b l e forms of r e p r e s e n t a t i o n : template, f e a t u r a l , s t r u c t u r a l , a n a l y s i s - b y - s y n t h e s i s , t o p o l o g i c a l , and prototype models. Each of these w i l l be b r i e f l y discussed i n r e l a t i o n to speech perception research. Many i n v e s t i g a t o r s i n the f i e l d of speech perception have mis-t a k e n l y assumed th a t a l l models of r e p r e s e n t a t i o n must be e i t h e r template or f e a t u r a l i n which a p a t t e r n i s recognized only i f i t matches p r e c i s e l y an already e x i s t i n g i n t e r n a l l y represented form, or i f a c r i t i c a l number of i t s component p a r t s (or f e a t u r e s ) match i n t e r n a l l y represented "key" f e a t u r e s . Since speech cannot be e a s i l y broken down i n t o i n v a r i a n t f e a t u r e s , (see f u r t h e r d i s c u s s i o n below) i t seems reasonable t o argue that no s i n g l e " c a n o n i c a l form" can account f o r phonetic perception. However, while only Cole (1977; Cole £ S c o t t , 1974) has proposed a s t r i c t f e a t u r a l model t o account f o r speech p e r c e p t i o n , even f e a t u r a l models need not be s t a t i c . For example, the i n t e g r a l i t y / s e p a r a b i l i t y of the p a r t s of a p a t t e r n have been conceived o f as changing over time as a f u n c t i o n of p e r c e p t u a l l e a r n i n g (LaBerge £ Samuels, 1974; Treisman £ Gelade, 1980). While s t r u c t u r a l models are a l s o based on a f e a t u r a l a n a l y s i s , i t i s the r e a l t i o n s between the f e a t u r e s that i s most c r i t i c a l . In a d d i t i o n , f e a t u r a l and s t r u c t u r a l models can be more dynamically con-ceived by an a n a l y s i s - b y - s y n t h e s i s type of r e p r e s e n t a t i o n wherein both bottom-up and top-down processes f u n c t i o n simultaneously. These types of models have been proposed i n speech r e s e a r c h , and are i n t e r p r e t e d as suggesting that perception i s guided by a r e p r e s e n t a t i o n of the production 7 p o t e n t i a l (Liberman, Cooper, Shankweiler £ Studdert-Kennedy, 1967; Stevens £ H a l l e , 1967). In such models, the fea t u r e s that are s p e c i f i e d r e l a t e t o a r t i c u l a t o r y movements r a t h e r than a c o u s t i c i n f o r m a t i o n . In t o p o l o g i c a l models, the o v e r a l l o r g a n i z a t i o n of a p a t t e r n i s q u a n t i f i e d . Stevens 6 Blumstein (.1978) have described such a model to account f o r the perception of a c o u s t i c f e a t u r e s ; t h a t i s , the enve-lope of s p e c t r a l changes may be shown t o be p r e d i c t a b l e from a r t i c u l a t o r y movements f o r s p e c i f i c phonetic forms. F i n a l l y , a prototype form of r e p r e s e n t a t i o n i s p o s s i b l e . In such a model, a fuzzy set i s advocated i n t h a t the boundaries between ca t e g o r i e s are not always c l e a r l y d e f i n e d . Each category i s thought t o have an i d e a l i z e d modal exemplar, or "prototype", but no exemplar i s expected t o f u l l y conform t o t h i s i d e a l . Furthermore, no s i n g l e f e a t u r e i s n e c e s s a r i l y a d e f i n i n g one. Rather, a s e r i e s of s e v e r a l p o t e n t i a l l y c o n t r i b u t i n g (.and p o s s i b l y overlapping) f e a t u r a l s p e c i f i c a t i o n s i s conceived. Such models have been s u c c e s s f u l l y developed f o r d e s c r i b i n g person percep-t i o n (Wiggins, 1980), n a t u r a l c a t e g o r i e s (Rosch, 1977) and v i s u a l patterns (Posner £ Keele, 1968), and have more r e c e n t l y been con-s i d e r e d f o r speech pe r c e p t i o n ( B o r n s t e i n , 1981; Oden £ Massaro, 1978; Samuel, 19 82). As mentioned above, the process of forming r e p r e s e n t a t i o n s ( r e f e r r e d t o as r e p r e s e n t a t i o n a l format) can a l s o v a r y , e i t h e r as a f u n c t i o n of age (Bruner, Olver, £ G r e e n f i e l d , 1966) or of the p a r t i c u l a r context (.Kosslyn, 1978). I t has been suggested t h a t , over age, rep r e -s e t n a t i o n a l format changes from being p r i m a r i l y " e n a c t i v e " t o " i k o n i c " and then t o "symbolic" (Bruner, e t . a l . , 1966). Broadly conceived, en-', a c t i v e r e p r e s e n t a t i o n r e f e r s t o l e a r n i n g about something through doing i t , or through " a c t i v e l y t r y i n g to construct an understanding of i t . For example, we l e a r n to produce a p a r t i c u l a r phoneme, and when we know the sound, we know i t by the act of producing (or l i s t e n i n g to) i t . Because the r e p r e s e n t a t i o n was achieved through a c t i o n , i t can only be a p p l i e d and used, i n contexts which f a c i l i t a t e i t s being enacted (Bruner, 1973; P i a g e t , 1954). Such r e p r e s e n t a t i o n a l format i s commonly ass o c i a t e d with t h i n k i n g during the f i r s t 1% years of l i f e . Learning about an event through imagining i t i s known as i k o n i c r e p r e s e n t a t i o n . The r e s u l t i n g r e p r e s e n t a t i o n s are conceived as images which can provide a schema around which a c t i o n s can be performed. How-ever, the r e p r e s e n t a t i o n has l i m i t e d g e n e r a l i z a b i l i t y s i n c e u t i l i z a t i o n of the r e p r e s e n t a t i o n r e q u i r e s experiencing an event (or sound) s i m i l a r t o the r e p r e s e n t a t i o n of that event. Thus, the schema can be a p p l i e d to a phoneme when i t i s heard or produced, but cannot be a p p l i e d t o d i s s i m i l a r or u n f a m i l i a r sounds, or t o a b s t r a c t s i g n i f i e r s of those sounds (Bruner, 1973; K o s s l y n , 1978). F i n a l l y , symbolic r e p r e s e n t a t i o n a l format r e f e r s t o schemas which are formed by applying a set of r u l e s t o an event or to an a b s t r a c t s i g n i f i e r of t h a t event. Symbolic schemas can be a p p l i e d t o u n f a m i l i a r s i t u a t i o n s or sounds th a t do not n e c e s s a r i l y r e q u i r e s i m i l a r a c t i o n s (enactive) and do not n e c e s s a r i l y resemble the image ( i k o n i c ) of pre-v i o u s l y experienced s i t u a t i o n s . As such those-, r e p r e s e n t a t i o n s are the most f l e x i b l e and g e n e r a l i z a b l e (Bruner, 1964). D i f f e r e n t d e s c r i p t i o n s of the ontogeny of r e p r e s e n t a t i o n a l format have been suggested (see Bruner, 1964; Piaget 6 Inhelder, 1971; Vygotsky, 1962; Kagan, 1979) although most agree that t r u l y symbolic thought which i s not p e r c e p t u a l l y constrained i s not achieved u n t i l 9 l a t e childhood (ages 10-12). Piaget and Kagan have been p a r t i c u l a r l y -concerned w i t h infancy. Piaget claims that enactive Cor sensorimotor) schemas cannot f u n c t i o n as re p r e s e n t a t i o n s at a l l . In Piaget's use of the word, r e p r e s e n t a t i o n r e f e r s t o a memory image th a t can be evoked when not immediately cued. He r e f e r s to the e a r l y f l e e t i n g schemas as presentations (Piaget .'£ Inhelder, 1971). However, Kagan has data to suggest that the continuously developing enactive schemas may f u n c t i o n as • t r u e .representations, by the end of'.the f i r s t year of l i f e . . He has shown th a t by 8-12 months of age, the c h i l d has developed schemas which serve to ho l d events i n memory, f o r a longer p e r i o d of time, and enable the c h i l d to compare new events to past events (Kagan, 1979; Kagan ••& Hamburg, 1981). Kagan considers t h i s a b i l i t y t r u e ( a l b e i t f r a g i l e ) r e p r e s e n t a t i o n . D i f f e r e n t i a t i o n models most o f t e n a r i s e out of a d i r e c t r e a l i s t conception of p e r c e p t i o n , and many proponents of - these models sev e r e l y c r i t i c i z e the n o t i o n o f r e p r e s e n t a t i o n ( c f . A u s t i n , 1962). Although there i s a c e r t a i n appeal to c r i t i c i z i n g "schema" ..\ , models f o r r e q u i r i n g unnecessary h y p o t h e t i c a l c o n s t r u c t s , (Turvey £ Shaw, 1979) e x i s t i n g notions o f d i r e c t apprehension are, at b e s t , confusing. For example, Wilcox and Katz ( i n press) c l a i m t h a t there i s no need t o p o s i t any k i n d of i n t e r n a l schema t o i n f l u e n c e p e r c e p t i o n , because i t i s i l l o g i c a l t o conceive of memory as a stored mental r e p r e s e n t a t i o n . They argue t h a t events have both simultaneous and s e q u e n t i a l s t r u c t u r e , and the p e r c e i v e r can d i r e c t l y a p p r eciate how the past a f f e c t s the present and how the present a f f e c t s the past i n each p e r c e p t i o n . How-ever, Wilcox and Katz. ( l i k e J . Gibson) do not attempt to describe t h i s s t r u c t u r e i n the environment. Instead, they s t r e s s the n e c e s s i t y that the object t o be perceived must have e c o l o g i c a l v a l i d i t y t o the p e r c e i v e r . 10 0 I t i s d i f f i c u l t to comprehend how i t can be determined whether the object has e c o l o g i c a l v a l i d i t y without knowing something about the s t r u c t u r e of e i t h e r the p e r c e i v e r or the environment, u n l e s s , of course, e c o l o g i c a l v a l i d i t y i s c i r c u l a r l y defined as t h a t which the person can d i r e c t l y appre-c i a t e . In t h i s r e g a r d , a current theory of speech perception which i s most commonly a s s o c i a t e d w i t h the Haskins group could provide a way out of the dilemma. In t h i s model, the a r t i c u l a t o r y system, w i t h i t s i n -herent and w e l l - d e s c r i b e d c o n s t r a i n t s i s seen as the " e c o l o g i c a l l y v a l i d " s t r u c t u r e d source i n the environment. Since i t i s assumed t h a t the mechanisms f o r p e r c e i v i n g speech are represented w i t h those f o r pro-ducing speech i n t h i s model CStuddert-Kennedy, Liberman, H a r r i s , £ Cooper, 1970), i n i t s present form, the model cannot be encompassed by a d i r e c t r e a l i s t t h e r o e t i c a l viewpoint. The e f f e c t of e a r l y experience The nature of the e f f e c t of e a r l y experience on p e r c e p t u a l de-velopment has been an important concern f o r s c i e n t i s t s from many- d i s c i p l i n e s (Tees, 1967). Four p o s s i b l e i n f l u e n c e s of e a r l y experience on p e r c e p t u a l systems have been o u t l i n e d ( G o t t l i e b , 1976; Tees, 1976). Figure 1 shows how these can be modified to apply to speech perception. As shown i n Figure 1, (1) e a r l y experience may serve t o maintain the f u n c t i o n a l i n t e g -r i t y or a p r e - e x i s t i n g c a p a b i l i t y ; (2) e a r l y experience may f a c i l i t a t e development by r e f i n i n g and improving an already e x i s t i n g a b i l i t y ; (3) e a r l y experience may be necessary to induce the development of a p a r t i c u l a r a b i l i t y which was not f u n c t i o n a l at b i r t h ; and (M-) e a r l y experience may have no e f f e c t on the development of an a b i l i t y . In attempting t o describe the e f f e c t s of e a r l y experience, FIGURE 1 EFFECTS OF EARLY EXPERIENCE PRENATAL POSTNATAL A G E -Illustration of the major roles that early postnatal experience can play in mod-ifying the relative discriminability of speech sounds. Three general classes of theories are shown here to account for the development of speech-sound discrimination: universal theory, allune-ment theory and perceptual learning theory. (From As!in & P i son i , 1980) researchers have concentrated on showing how perceptual d e p r i v a t i o n can have d e t r i m e n t a l e f f e c t s on p h y s i o l o g i c a l and/or behavioural develop-ment. Much of t h i s research has examined the e f f e c t s of s p e c i f i c environmental c o n d i t i o n s on the development of the v i s u a l system (Wiesel £ Hubel, 1964; Tees, 1976; 1979). In a d d i t i o n , the r e s u l t s from infrahuman work have o f f e r e d p o s s i b l e c l a r i f i c a t i o n of the r o l e experience might play with regard t o human speech per c e p t i o n . M a r l e r , (.1977) has shown th a t s o c i a l l y i s o l a t e d white crowned sparrows exposed t o t h e i r s p e c i e s - s p e c i f i c song during a c e r t a i n " s e n s i t i v e " p e r i o d i n e a r l y l i f e are able e v e n t u a l l y t o develop a normal song upon reaching m a t u r i t y , using the template Cor r e p r e s e n t a t i o n ) formed i n e a r l y experience. How-ever, i f the sparrows are not exposed t o t h e i r s p e c i e s - s p e c i f i c song during t h a t developmental time p e r i o d , they do not develop a normal song, even i f exposed f o r much longer periods l a t e r i n l i f e . S i m i l a r r e s u l t s have emerged i n examinations of p e r c e p t i o n and production of species s p e c i f i c sounds i n other animal communication systems ( G o t t l i e b , 1978; 1979; King £ West, 1977; M a r l e r , Mundinger, Waser £ L u t j e n , 1972; Snowden, 1979). In some b i r d species while a r e l a t i v e l y normal general species song can develop without s p e c i f i c exposure, i n d i v i d u a l songs (each b i r d a l s o has an i n d i v i d u a l song) can be very a f f e c t e d . Emergent song patterns are t r u n c a t e d , and l a c k the complex p a t t e r n i n g common i n non-deprived b i r d s (Marler £ Peters, : 1981). This work provides support f o r the n o t i o n t h a t e a r l y experience can both maintain and f a c i l i t a t e f u r t h e r development. Marler has speculated that h i s r e s u l t s w i t h respect to the development of birdsong might suggest that l i s t e n i n g experience p r i o r t o language a c q u i s i t i o n may a l s o be necessary to enable the perceptual system t o maintain i t s s e n s i t i v i t y t o language sounds i n 13 humans. A s l i n and P i s o n i (1980) have attempted to account f o r the develop-ment of speech perception i n humans i n terms of the four p o s s i b i l i t i e s of e a r l y experience o u t l i n e d i n Figure 1. They argue that f u n c t i o n a l l o s s r e s u l t s from l i m i t e d e a r l y experience. Morse (1978) and Strange .£ Jenkins (1978) a l s o suggest that s p e c i f i c experience may be necessary t o maintain perceptual a b i l i t y . They c i t e evidence showing that r e t r a i n i n g a d u l t s t o d i s c r i m i n a t e non-native c o n t r a s t s has been l a r g e l y unsuccessful. In con-t r a s t , B o r n s t e i n , (19 70) has argued that e a r l y experience may not be necessary to maintain phonetic perception i n humans because phonetic perception i s so robust t h a t i t cannot be e a s i l y diminished. Work show-i n g that only l i m i t e d t r a i n i n g i s r e q u i r e d to f a c i l i t a t e r e l e a r n i n g of non-native v o i c i n g c o n t r a s t s ( A s l i n , P i s o n i , Walley, £ Murray, 1980.; Tees £ Werker, 1982; Werker, e t . a l . , 1981) provides some support f o r Bornstein's viewpoint. In recent experiments, we have data t o suggest t h a t i t may be easy t o r e t r a i n a d u l t s t o d i s c r i m i n a t e v o i c i n g d i s t i n c t i o n s , but that non-native place of a r t i c u l a t i o n c o n t r a s t s may be more r e s i s t a n t to r e t r a i n i n g (Tees £ Werker, 1982; Werker, e t . a l . , 1981). These f i n d i n g s would suggest t h a t r e s t r i c t e d e a r l y experience may l e a d t o a f u n c t i o n a l l o s s f o r place of a r t i c u l a t i o n c o n t r a s t s (as would be pre-d i c t e d by Morse, 1978) but not f o r v o i c i n g d i s t i n c t i o n s . Issues i n Speech Perception So f a r we have reviewed t h e o r e t i c a l issues i n perc e p t i o n and have attempted t o r e l a t e speech perception to these i s s u e s i n a general way. Speech perception has i t s own unique c o m p l e x i t i e s , however, which I w i l l attempt to c l a r i f y i n t h i s s e c t i o n . 14 The most i n t r i g u i n g aspect of speech perception i s t h a t although we never hear or produce e x a c t l y the same utterance more than once, we can decode speech a c c u r a t e l y . That i s , we somehow recognize and c a t e g o r i z e a l l the v a r y i n g r e p e t i t i o n s of a s i n g l e word as the same, be i t whispered or y e l l e d , and be i t spoken by a man, woman, or c h i l d i n one of an i n f i n i t e number of p o s s i b l e contexts. To do t h i s we have to recognize the i n v a r i a n t p r o p e r t i e s i n the s m a l l e s t segments that make up those words. In t h i s t h e s i s , the term "phonetics" w i l l r e f e r t o the set of speech sound combinations that could occur i n the languages of the world. "Phonemic" w i l l r e f e r t o the subset of those sounds that are used to d i f f e r e n t i a t e meaning i n a p a r t i c u l a r language. The same phoneme can be cued by very d i f f e r e n t formant t r a n s i -t i o n s depending on the vowel context (Figure 2). This i s because speech i s h i g h l y encoded and o v e r l a p p i n g , and i n f o r m a t i o n r e l a t i n g t o any s i n g l e phoneme i s spread out across the e n t i r e s y l l a b l e (see Figure 3). Thus a /b/ i n the context of "ag" would be d i f f e r e n t from a /b/ i n the context of " i g " or "ad". . In processing speech, we ignore a l l those d i f f e r e n c e s and perceive the sounds as "b's". Even though the a c o u s t i c cues f o r s p e c i f i c phonemes vary across context, research has shown that most stop consonants, l i q u i d s , vowels of short d u r a t i o n , and some f r i c a -t i v e and a f f r i c a t i v e sounds are perceived i n a c a t e g o r i c a l f a s h i o n . C a t e g o r i c a l perception i s defined as perception i n which i d e n t i f i c a t i o n f u n c t i o n s a c c u r a t e l y p r e d i c t d i s c r i m i n a t i o n f u n c t i o n s (Macmillan, Kaplan, £ Creelman, 1977). An i l l u s t r a t i o n o f an i d e a l i z e d 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 f u n c t i o n i s provided i n Figure 4. Speech research with a d u l t subjects has shown th a t l i s t e n e r s cannot r e l i a b l y d i f f e r e n t i a t e two consonant vowel (CV) speech sounds FIGURE 2 TWO "d" SPECTOGRAMS IN DIFFERENT VOWEL CONTEXTS Artificial spectograms for /di/ and /du/ showing the first and second formants. (From Liberman, Cooper, Shankwei1er, & Studdert-Kennedy, 1967). 16 FIGURE 3 ILLUSTRATION OF THE ENCODED AND OVERLAPPING NATURE OF SPEECH T I M E Schematic spectogram illustrating the simultaneous trans-mission of successive phonemic segments on the same part of the speech signal. (From Liberman, 1970 ). 1 2 3 4 5 6 7 8 STIMULUS NUMBER ALONG CONTINUUM F I G . H"? Idealized identification functions (left ordinate) and discrimina-tion function (right ordinate) to illustrate categorical perception of eight stimuli distributed at equal intervals along a physical continuum. 18 unless i t i s a l s o p o s s i b l e f o r them to apply d i f f e r e n t phonetic l a b e l s to those sounds, i . e . they show c a t e g o r i c a l perception. In a d d i t i o n , although speech sounds may be synthesized that vary i n steps of equal s i z e (e.g. 20 msec of VOT) along an a c o u s t i c continuum, any two of these sounds are not d i s c r i m i n a b l e unless they span a phonetic boundary (Eimas, 1963; Liberman, et. a l . , 1967; Liberman, H a r r i s , Hoffman £ G r i f f i t h , 1957; M a t t i n g l y , Liberman, S y r d a l , £ Halwes, 1971). Furthermore, e x p e r i -ments, usi n g synthesized speech have shown th a t although i t i s p o s s i b l e to manipulate one of many a c o u s t i c cues and create speech c o n t r a s t s which are perceived i n a c a t e g o r i c a l f a s h i o n , none of these cues seems t o be e s s e n t i a l f o r the percept. In i l l u s t r a t i o n , L i s k e r (1978) has reported 16 separate cues which can be used f o r d i s t i n g u i s h i n g /b/ from /p/. F i n a l l y , although speech i s dynamic since i t Is generated by a con-s t a n t l y v o c a l t r a c t , i t i s perceived as a d i s c r e t e s e r i e s of sounds. There has, as y e t , been no s u c c e s s f u l i d e n t i f i c a t i o n of a c o u s t i c i n v a r i a n t s which could l e a d to t h i s p e r c e p t u a l i n v a r i a n c e (Liberman, 1982; Liberman, e t . a l . , 1967), however, a r t i c u l a t o r y i n v a r i a n t s have been i d e n t i f i e d . That i s , each time a p a r t i c u l a r phoneme i s produced, i t appears that the a r t i c u l a t o r s act i n a r e g u l a r p r e d i c t a b l e f a s h i o n (see Ladefoged, 1975; P i c k e t t , 1980). A s t r u c t u r a l a n a l y s i s of t h i s phoneme/articulation r e g u l a r i t y y i e l d s a u n i v e r s a l set of phonemes i n terms of combinations of a r t i c u l a t i o n f e a t u r e s . An example of such a c l a s s i f i c a t i o n scheme i s given i n Table 1. The unique isomorphism between perception and production of speech sounds has l e d t h e o r i s t s t o develop models i n which speech i s described as being perceived i n terms of a r t i c u l a t o r y r e p r e s e n t a t i o n s . The c l a s s i c "motor theory" (Liberman, e t . a l . , 1967) and the " a n a l y s i s 19 Table 1 The prime features. Feature Abbreviated definition Phonological Exemplification name of physical scale terms symbols language word gloss 1 Glot ta l i c Rate of upward movement [ejective] t' U d u k f e l ick of the glottis [pulmonic] t U d u k ter collect [implosive] rf U d u k dek lift 2 Velar ic Degree of suction of air in [ + c l ick j 1 Z u l u lata c l imb mouth I - c l i c k ] t Z u l u tatu th i rd 3 Voice Degree of approximat ion of the [glottal stop] j Javanese buka> open arytenoid cartilages [laryngealized] b Hausa be:rd: rat [voice] b Hausa be:ra girl [murmur) H i n d i bf>al forehead [voiceless] P H i n d i pal take care o f 4 Aspi ra t ion T ime of onset of voic ing with [aspirated] P" T h a i p»a: split respect to release of the [unaspirated] P T h a i pa: forest art iculation [voiced] b T h a i ba: shoulder 5 Place Distance from the glottis to the [bilabial] P Ewe e(3e Ewe first constriction of the [labiodental] V Ewe eve two vocal tract [dental] I M a l a y a l a m k u i t i stabbed [alveolar] t M a l a y a l a m kut t i peg [retroflex] t M a l a y a l a m kut t i ch i ld [palato-alveolar] I English Jip sheep [palatal] c Quechua caka bridge [velar] k Qucchua kara expensive [uvular] q Quechua qara skin [pharyngeal] h A r a b i c had someone [glottal] j A r a b i c ' a l i a G o d 6 Labia l Degree of approximat ion of [ + labial] Igbo ifik bag the centers of the lips [ - l a b i a l ] k Igbo aka ' hand 7 Stop Degree of approximat ion o f [stop] t Engl i sh tai tie the articulators [fricative] s Engl ish sai sigh [approximant] h Engl ish hai high 8 Nasa l Degree of lowering of the [ + nasal] n Engl ish n o o know soft palate [ — nasal] d Engl ish d o o dough 9 Latera l A m o u n t of airstrearri f lowing [ +lateral] 1 Engl ish l o o low over the side of the tongue [ - l a t e ra l ] d Engl ish d o o doe 10 T r i l l Degree of vibrat ion of an [ + tr i i l] r Spanish pero dog articulator [ - t r i l l ] r Spanish pero but (11 Tap) Rate of articulatory [+.tap] f T a m i l srsm saw movement? [ - t a p ] i T a m i l a : jam depth 12 Sonorant A m o u n t of acoustic [ + sonorant] i Engl ish 'sAniar sunnier energy [ — sonorant] j Engl ish 'Anjsn onion 13 Sibilant A m o u n t of high frequency [ + sibilant] s Engl ish s in sin (over 3000 Hz . ) energy [ — sibilant] 8 Engl ish Oin thin 14 Grave Rat io of low to high [ +grave] f Engl ish p i n , k i n pin , k i n frequency energy [ -g r ave ] e English t in t in 15 Height Inverse of frequency of the [4 height] i Danish viroa know first formant [3 height] e Dan i sh ve:6a wheat [2 height] £ Danish VE : 6S wet [1 height] X Danish vae:d3 wade 16 Back Difference between frequency o f [ + back] u Engl i s l i hu who formant two and formant one [ - b a c k ] i Engl ish hi he 17 R o u n d Inverse of distance between [ + round] y French ly read corners of the lips [ — round] i French l i bed 18 Wide Degree of advancement o f [ +wide] i Igbo obi heart tongue root [ - w i d e ] i Igbo Obi poverty 19 Rhotacized Lower ing of the frequency o f [ +rhotacized] 31 Engl ish bsrd b i rd the third formant [ — rhotacized] I Engl ish b i d bid 20 Syllabic ( N o agreed physical scale) [ +syl labic] Engl i sh SAdp sudden [ — syllabic] n Engl i sh SAn sun (From Ladefoged, 1975) 20 by s y n t h e s i s model" (.Stevens 6 H a l l e , 1967) represent e a r l y versions of such models. Aco u s t i c and phonetic models of speech perception One of the key claims of the motor theory of speech perception i s t h a t speech i s " s p e c i a l " : t h a t i t i s perceived by a s p e c i f i c phonetic processor (Liberman, e t . a l . , 1967; Liberman, 1982). Considerable data c o l l e c t e d i n l a b o r a t o r y experiments i n the 1960s, and e a r l y 1970s.: sup-ported t h i s c laim. These data, and the r e s u l t a n t claims i n support of s p e c i a l i z e d phonetic processing were o u t l i n e d i n a paper by Wood (1976). The most important claims were: (.1) Speech perception i s " c a t e g o r i c a l " ; that i s , i t i s s i g n i f i c a n t l y e a s i e r t o d i s c r i m i n a t e sounds on e i t h e r s i d e of a phoneme boundary than i t i s t o d i s c r i m i n a t e sounds from w i t h i n a phoneme category. Since many speech experiments t e s t only d i s c r i m i n a -t i o n , t h i s e f f e c t i s more a c c u r a t e l y r e f e r r e d t o as the "phoneme boundary e f f e c t " (see Repp, 1981a). The "phoneme boundary e f f e c t " - h a s been found i n experiments studying both a d u l t s and i n f a n t s . (2) Sselective adaptation experiments show d i f f e r e n t e f f e c t s w i t h speech and w i t h non-speech s t i m u l i . The adaptation f u n c t i o n s f o r speech sounds y i e l d evidence c o n s i s t e n t w i t h p h o n e t i c a l l y based f e a t u r e d e t e c t o r s , w h i l e the adaptation f u n c t i o n s f o r non-speech s t i m u l i y i e l d adaptation func-t i o n s c o n s i s t e n t w i t h general a u d i t o r y f e a t u r e detectors (Eimas £ C o r b i t t , 1973). (3) Anatomical (Wada, 1975), p h y s i o l o g i c a l (Molfese £ Molfese, 1979), and p s y c h o l o g i c a l (Kimura, 1967) evidence suggests.that the l e f t hemisphere i s s p e c i a l i z e d f o r processing speech. Subsequent research has challenged each of Wood's c l a i m s . The f o l l o w i n g d i s c u s s i o n w i l l concentrate on challenges t o the "phoneme boundary e f f e c t " s i n c e that i s the c l a i m that i s the most r e l e v a n t to the issues r a i s e d i n t h i s t h e s i s . For a d i s c u s s i o n of challenges t o other aspects of h i s c l a i m , see Schouten (.1980). The most s i g n i f i c a n t challenge t o Wood's c l a i m was that the phoneme boundary e f f e c t has been shown to occur with complex non-speech sounds. I t has been shown w i t h v i o l i n pluck sounds (.Cutting £ Rosner, 1974) , with sounds d i f f e r i n g i n tone-onset time ( P i s o n i , 1977), and w i t h n o ise buzz sequences ( M i l l e r , Wier, Pastore, K e l l y , £ Dooling, 1976). Furthermore, there are data t o suggest that boundary e f f e c t s f o r non-speech sounds may r e f l e c t fundamental p r o p e r t i e s of the human a u d i t o r y system which would a l s o u n d e r l i e the apparently phonetic processing ( c f . P i s o n i , 1979). In a d d i t i o n , t h i s phoneme boundary e f f e c t has been shown i n primates' perception of human speech sounds (Morse £ Snowden, 197 5; Waters £ Wilson, 1974) and even i n c h i n c h i l l a s (Kuhl £ M i l l e r , 1975) . Although some speech sounds are perceived c a t e g o r i c a l l y , r e -search has suggested t h a t other speech sounds are perceived i n a more continuous manner (Healy £ Repp, 1982). Moreover, psychophysical experiments have i l l u s t r a t e d t h a t humans can be taught t o d i s c r i m i n a t e w i t h i n category, non-phonetic a c o u s t i c changes (Hanson, 1977; P i s o n i £ Lazarus, 1974; Samuel, 1977). Co n s i d e r a t i o n of these s t u d i e s makes i t d i f f i c u l t t o argue e i t h e r f o r or against a s p e c i f i c l i n g u i s t i c processor. That i s , i t i s conceiv-able t h a t speech i s processed i n a phonetic mode, but that other complex sounds may be perceived c a t e g o r i c a l l y i n an a c o u s t i c mode. However, i t i s e q u a l l y p l a u s i b l e t h a t i n i t i a l a c o u s t i c c o n s t r a i n t s form the b a s i s of a l a t e r developing s p e c i f i c phonetic processor. Both s y n t h e t i c and n a t u r a l tokens have been used i n speech perception work. Since s y n t h e t i c tokens o f t e n e l i m i n a t e much of the (.possibly important) non-changing i n f o r m a t i o n , i t i s conceivable that much of the psychophysical work has examined non-speech r a t h e r than speech per c e p t i o n . That i s , there i s no reason t o suppose t h a t , j u s t because a researcher claims t o be studying "speech" perception t h a t the subjects being t e s t e d neces-s a r i l y respond t o the s t i m u l i as speech. F i n a l l y , there i s some suggestion that non-human animals which c a t e g o r i z e human speech sounds may use s i m i l a r sound changes to d i f f e r e n t i a t e c a l l s w i t h i n t h e i r own language systems ( c f . Snowden, 1979). Even though data show our au d i t o r y system t o be very s i m i l a r t o that of other mammals, there i s no reason t o assume t h a t convergent s t r u c t u r a l e v o l u t i o n n e c e s s a r i l y i m p l i e s s i m i l a r f u n c t i o n a l use. Speech serves a h i g h l y a b s t r a c t com-municative f u n c t i o n i n humans, and not i n other animals. Given the d i f f e r e n c e i n f u n c t i o n , i t may not be u s e f u l t o compare speech percep-t i o n i n humans t o pe r c e p t i o n of sp e e c h - l i k e sounds i n other animals. In response to the above c h a l l e n g e s , data has been c o l l e c t e d which provides new support f o r the n o t i o n of a s e l e c t i v e speech pro-c e s s o r , at l e a s t i n the case of a'dult humans. This work has concentrated on t r a d i n g r e l a t i o n s , context e f f e c t s , and duplex p e r c e p t i o n . Research i n each area has supported the notio n o f some kind of "phonetic equivalence" (see Repp, 1981a) of d i f f e r e n t kinds of pe r c e p t u a l i n f o r m a t i o n across d i f f e r e n t c o n d i t i o n s . For example, Carden, L e v i t t , Jusczyk £ Walley (1981) showed that i d e n t i c a l a c o u s t i c changes l e d t o a d i f f e r e n t phonetic boundary when the sound was perceived as a stop consonant compared t o when i t was perceived as a f r i c a t i v e . "Trading r e l a t i o n s " i s the term used to describe c o n d i t i o n s i n which two or more a c o u s t i c cues can be interchanged without a f f e c t i n g 23 the phonetic percept. Research i n t r a d i n g r e l a t i o n s examines the d i s c r i m i n a t i o n o f sounds d i f f e r i n g i n a s i n g l e cue (.i.e. d u r a t i o n of s i l e n t c l o s u r e ) , c o n f l i c t i n g cues (.i.e. two a c o u s t i c dimensions vary so that one s i g n a l s a phonetic change and one does not) and cooperating cues (two a c o u s t i c cues vary so th a t both s i g n a l a phonetic change). C o n f l i c t i n g cues l e a d to changes t h a t are not d i s c r i m i n a b l e t o the l i s t e n e r whereas cooperating cues with p h y s i c a l d i f f e r e n c e s equal t o those of the c o n f l i c t i n g cues, l e a d t o changes which are d i s c r i m i n a b l e to the l i s t e n e r . Examples of p a i r s of cues which show t h i s t r a d i n g r e l a t i o n are f r i c a t i o n and v o c a l i c formant t r a n s i t i o n s i n f r i c a t i v e p e rception (Repp, 1981b; Whalen, 1981) and du r a t i o n of s i l e n t c l o s u r e and the onset frequency of formant t r a n s i t i o n s i n the perception of stop consonants ( F i t c h , Halwes, E r i c k s o n S Liberman, 1980). I t has been shown that when adult l i s t e n e r s hear ambiguous sounds as speech sounds, phonetic c a t e g o r i e s are a p p l i e d t o segment the s t i m u l i . I t has a l s o been shown that when l i s t e n e r s hear i d e n t i c a l sounds as non-speech, a u d i t o r y processing can be a p p l i e d , l e a d i n g t o a d i f f e r e n t segmentation. In a very c l e v e r study, Best, M o r o n g i e l l o , £ Robson (1981) examined the i n f l u e n c e of context e f f e c t s on perc e p t i o n of s i n e -wave analogs t o speech sounds. Some l i s t e n e r s perceived the analogs as funny speech, whereas others heard them as w h i s t l e s and c h i r p s . When cooperating phonetic cues were v a r i e d , the l i s t e n e r s who heard the sine-wave analogs as speech sounds showed a c l e a r phoneme boundary e f f e c t , whereas those l i s t e n e r s who heard the sounds as non-speech d i d not. S i m i l a r f i n d i n g s have emerged from s t u d i e s examining v a r i a -t i o n s i n context e f f e c t s . F i n a l l y , i n a study of duplex perception (simultaneous perception o f fused and non-fused components of d i c h o t i c 24 input) .Liberman, .and his'colleagues-' showed that perception of the fused d i c h o t i c input showed the phoneme boundary e f f e c t , whereas simultaneous p e r c e p t i o n of the non-fused " c h i r p " component was continuous (Liberman, Isenberg, 6 Rakerd, 1981; Liberman, 1982). Proponents of psychoacoustic explanations f o r speech perception respond to t h i s recent work by suggesting that speech, l i k e complex a c o u s t i c sounds, i s analyzed i n terms of r e l a t i o n a l components r a t h e r than i n terms of any s p e c i f i c ( i . e . phonetic) f e a t u r e s . They claim that the above f i n d i n g s can be explained by simple a u d i t o r y p r o c e s s i n g ; i . e . the a u d i t o r y system may be s t r u c t u r e d so that temporal and s p e c t r a l cues can trade (Blumstein & Stevens, 1980). In r e p l y , researchers arguing f o r the existence of a s e l e c t i v e phonetic processor c l a i m t h a t the kinds of a c o u s t i c t r a d i n g r e l a t i o n s that Blumstein & Stevens have i d e n t i f i e d do not begin t o account f o r the range of phonetic f e a t u r e s that can t r a d e , and thus that the a c o u s t i c model l a c k s g e n e r a l i z a b i l i t y . A c o u s t i c models of speech perception have most o f t e n been considered w i t h i n enrichment t h e o r i e s of p e r c e p t u a l development. Refinement models propose t h a t c e r t a i n psychoacoustic c a p a b i l i t i e s operate i n the young i n f a n t , and t h a t the i n f a n t c o n s t r u c t s l i n g u i s -t i c a l l y r e l e v a n t schemas from these as a r e s u l t of language. experience ( P i s o n i , 1979). Phonetic models have been conceptualized w i t h i n t h e o r i e s of p e r c e p t i o n which would be c o n s i s t e n t w i t h a d i f f e r e n t i a t i o n approach t o perceptual development. Recent attempts to l i k e n a d u l t speech perception to "event p e r c e p t i o n " or "affordance" (as i n J . Gibson, 1979) represent such a t r e n d (Liberman, et. a l . , 1979; Repp, 1981a). However, s e v e r a l independent processes have been combined i n these common c o n c e p t u a l i z a t i o n s which could be considered s e p a r a t e l y . By studying developmental processes i n speech p e r c e p t i o n , we should be able t o provide c l a r i f i c a t i o n about many of these processes. Such c l a r i f i c a t i o n i s needed to help i n c o r p o r a t e speech research i n t o more general t h e o r i e s of perceptual development. Infant a u d i t o r y a b i l i t i e s In the d i s c u s s i o n o f general t h e o r e t i c a l i s s u e s , i t was remarked t h a t researchers i n the Kantian t r a d i t i o n attempt to describe the i n -born c a p a b i l i t i e s of the young i n f a n t . This t r a d i t i o n has guided research i n i n f a n t speech and a u d i t i o n . S u b s t a n t i a l evidence shows tha t a u d i t o r y c a p a b i l i t i e s are w e l l developed at b i r t h (Eisenberg, 1976) and th a t young i n f a n t s can perceive and d i s c r i m i n a t e the a c o u s t i c parameters r e l a t e d t o speech. For example, the th r e s h o l d s f o r f r e -quency d i s c r i m i n a t i o n i n i n f a n t s 1-4 months of age are comparable t o those obtained f o r a d u l t s , (Berg, 1972; Schneider, Trehub, £ B u l l , 1979) e s p e c i a l l y i n the range used i n speech. Infants o l d e r than 1 week of age have been shown t o be almost as s e n s i t i v e t o v a r i a t i o n s i n i n t e n s i t y as a d u l t s through a v a r i e t y of beha v i o u r a l and e l e c t r o -p h y s i o l o g i c a l techniques (Eisenberg, 1976). In a d d i t i o n , b e h a v i o u r a l s t u d i e s have shown i n f a n t s t o respond d i f f e r e n t i a l l y t o v a r i a t i o n s i n the d u r a t i o n of sounds i n that the longer the sound ( i n the range from 300 msec to 5 sec) the greater the response (Eisenberg, 1976; L i n g , 1972). Unf o r t u n a t e l y , s t u d i e s o f sho r t e r durations which may be s i g n i f i c a n t i n speech perception are l a c k i n g . Since a d u l t subjects process a c o u s t i c v a r i a t i o n s t h a t occur w i t h i n 20-25 msec as a s i n g l e sound, and those o c c u r r i n g at i n t e r v a l s longer than that as two 26 successive sounds (Stevens and K l a t t , 1974), i t would be u s e f u l t o study i n f a n t p erception of d u r a t i o n .in t h i s range. U n t i l r e c e n t l y only a s i n g l e study had examined i n f a n t r e -sponses to r i s e and decay times by measuring heart r a t e responses. In t h i s study, i t was found that r a p i d r i s e times (30msec) were as s o c i a t e d w i t h an increase i n heart r a t e , w h i l e slower r i s e times (300 msec) were a s s o c i a t e d with"a d e c e l e r a t i o n i n heart r a t e (Berg, Berg £ Graham, 1971). Recently, however, data have i n d i c a t e d that i n f a n t s can respond t o r i s e times i n the range corresponding t o those found i n complex speech sounds. That i s , i n f a n t s can d i s c r i m i n a t e r i s e time d i f f e r e n c e s between 30 and 60 msec but they cannot d i s c r i m -i n a t e between 0 and 30 msec or between 60 and 90 msec (Jusczyk, Rosner, C u t t i n g , Foard £ Smith, 1977). Although f i n d i n g s such as these show i n f a n t s t o have the aud i t o r y c a p a b i l i t i e s t o perceive the parameters which may be import-ant i n speech p e r c e p t i o n , they do not address whether i n f a n t s respond to dimensional sounds (sounds d i f f e r i n g i n s e v e r a l parameters such as speech) s i m i l a r l y t o a d u l t s . Procedures f o r studying i n f a n t speech perception In i n v e s t i g a t i n g speech p e r c e p t u a l c a p a b i l i t i e s i n i n f a n t s , researchers have used three main paradigms; high amplitude sucking (HAS), heart-rate o r i e n t i n g response (HR), and the v i s u a l l y r e i n f o r c e d head-t u r n procedure (HT). In each of these t h r e e , i n f a n t s are presented w i t h a s i n g l e speech sound and/or a categp.ry of speech sounds f o r a pe r i o d of time. F o l l o w i n g t h i s i n i t i a l p r e s e n t a t i o n , a s e r i e s of novel sounds are presented and the i n f a n t ' s response i s monitored. In the HAS procedure, the i n f a n t i s presented w i t h r e p e t i t i o n s of a s i n g l e speech sound. Rate of p r e s e n t a t i o n i s contingent upon the i n f a n t ' s sucking r a t e . C h a r a c t e r i s t i c a l l y , sucking r a t e increases u n t i l the i n f a n t " h a b i t u a t e s " t o the sound. E i t h e r a c o n t r o l (no change) or an experimental t r i a l (sound changes) f o l l o w s f o r a p e r i o d of time during which sucking r a t e i s assessed. The HR pardigm i s a more c l a s s i c a l h a b i t u a t i o n paradigm i n which h e a r t - r a t e o r i e n t i n g response i s monitored. In young i n f a n t s , o r i e n t a t i o n to a stimulus i s u s u a l l y accompanied by a d e c e l e r a t i o n of heart r a t e (Sokolov, 1963). A f t e r h a b i t u a t i o n t o a sound, h e a r t - r a t e r e t u r n s t o a p r e - e s t a b l i s h e d base r a t e . Heart-rate can then be measured a f t e r " c o n t r o l " and "experimental" t r i a l s t o determine i f t h i n f a n t can d i s c r i m i n a t e the sounds. There are s e v e r a l problems with these two pardigms. Both procedures y i e l d data t h a t can only be analyzed according to the aver age score of a group of i n f a n t s s i n c e data from i n d i v i d u a l s i s unre-l i a b l e . Therefore, i t i s not p o s s i b l e t o determine whether any ( o r each) s i n g l e i n f a n t can d i s c r i m i n a t e a sound. More importantly the researcher has t o r e l y on the speech sounds themselves being i n t r i n -s i c a l l y i n t e r e s t i n g . That i s , i n f a n t s have t o be not only able t o d i s c r i m i n a t e a c o n t r a s t , but a l s o have to f i n d the sound change i n t e r e s t i n g enough t o show a change i n h e a r t - r a t e or r a t e of sucking. F a i l u r e t o o b t a i n a change may r e f l e c t e i t h e r perceptual or motiva-t i o n a l f a c t o r s or both, making i t impossible t o i n t e r p r e t the f a i l u r e F i n a l l y , the HAS pardigm i s only e f f e c t i v e with i n f a n t s up to 4 month of age. Although HR can be used across the l i f e span, d i f f i c u l t i e s i n comparing groups of subj ects of d i f f e r e n t ages e x i s t . For example 28 although a d e c e l e r a t i o n i n h e a r t - r a t e may i n d i c a t e o r i e n t a t i o n i n young i n f a n t s , an a c c e l e r a t i o n i s viewed as a s i g n of a t t e n t i o n i n s l i g h t l y o l d e r i n f a n t s (Campos S B r a c k b i l l , 1971). E r r o r i s a l s o introduced by " s t a t e " v a r i a t i o n s ( s l e e p y , f u s s y , a c t i v e ) s i n c e a c t i v i t y l e v e l i t s e l f has an i n f l u e n c e on h e a r t - r a t e . An a d d i t i o n a l problem i s that r e -searchers using the above two paradigms often report that 50-70% of the i n f a n t subjects need t o be discarded from any a n a l y s i s due to t h e i r f u s s i n e s s , f a l l i n g a s l e e p , or f a i l i n g t o respond t o the paradigm. Not only i s t h i s time consuming, such a drop-out r a t e could r e s u l t i n a non-representative sample of i n f a n t s being t e s t e d . The t h i r d paradigm, HT, i s an operant c o n d i t i o n i n g paradigm i n which the i n f a n t i s co n d i t i o n e d t o t u r n i t s head toward a sound source when there i s a change i n the background sti m u l u s . Correct head turns are r e i n f o r c e d w i t h the a c t i v a t i o n of an independent v i s u a l r e i n f o r c e r ( f o r a more d e t a i l e d d i s c u s s i o n , see Methods and Results s e c t i o n ) . A l -though t h i s paradigm cannot be used w i t h i n f a n t s l e s s than 5^ g months of age, comparable ve r s i o n s of i t can be used to t e s t subjects at d i f f e r -ent ages (with minor m o d i f i c a t i o n s ) through adulthood. Furthermore, i t y i e l d s data which can be understood f o r each i n d i v i d u a l i n f a n t , a l l o w i n g f o r analyses of i n d i v i d u a l as w e l l as group data. F i n a l l y , s i n c e a v i s u a l r e i n f o r c e r i s used, there i s no r e l i a n c e on the i n t r i n -s i c a l l y rewarding c h a r a c t e r i s t i c s of the t e s t s t i m u l i . I n f a n t speech research There i s an accumulation of evidence t h a t suggests t h a t c a t e g o r i z a t i o n of speech sounds- may be a n a t u r a l propensity of the human organism. That i s , r a t h e r than having s p e c i f i c a l l y t o l e a r n to 29 d i f f e r e n t i a t e phonetic f e a t u r e s and organize them i n t o c a t e g o r i e s , i n f a n t s seem to respond from a very e a r l y age t o speech sounds according t o c a t e g o r i e s t h a t w i l l serve as the b a s i s f o r a d u l t phonemic c a t e g o r i e s . (For a review, see Eimas, 1975a; Jusczyk, 1980; Morse, 1979). In a d d i t i o n , although i n f a n t s are able to detect d i f f e r e n c e s i n s t r e s s e d s y l l a b l e s (Spring £ Dale, 1977), i n t o n a t i o n contour, and speaker v a r i a t i o n (Holmberg, Morgan £ Kuhl, 1977), they c a t e g o r i z e sounds according t o phonetic boundaries i n fewer t r i a l s than they c a t e g o r i z e according t o those non-phonetic features (Homberg, e t . a l . , 1977; Kuhl, 1979). Furthermore, recent research has shown t h a t context e f f e c t s (e.g. d u r a t i o n of a s y l l a b l e ) i n f l u e n c e speech perception i n i n f a n t s (Eimas £ M i l l e r , 1980a). F i n a l l y , i n -f a n t s have been shown to c a t e g o r i z e speech sounds on the b a s i s of a b s t r a c t p h o n o l o g i c a l features such as p l a c e , manner, and vowel height ( M i l l e r £ Eimas, 1979). This s e n s i t i v i t y to phonetic d i f f e r -ences enables an i n f a n t t o break the continuous speech stream i n t o the d i s c r e t e segments t h a t are important i n the eventual i d e n t i f i c a -t i o n of meaningful u n i t s . The question of whether r e s u l t s from i n f a n t speech research support the n o t i o n of a s p e c i f i c phonetic or a general a c o u s t i c pro-cessor i s of concern i n i n f a n t speech work. Since that controversy i s not d i r e c t l y r e l e v a n t t o the hypotheses t e s t e d i n t h i s work, i t - w i l l not be d i s c u s s e d ' i n the I n t r o d u c t i o n . - I t , w i l l , be r a i s e d i n the D i s c u s s i o n . , The f o l l o w i n g s e c t i o n w i l l review the development of i n f a n t s ' d i s -c r i m i n a t i o n of consonant sounds. In p a r t i c u l a r , p erception of place of a r t i -c u l a t i o n and v o i c i n g d i f f e r e n c e s i n consonants across two manners of a r t i c u l a t i o n 30 (stops and f r i c a t i v e s ) w i l l be discussed. (See footnote 1 f o r a d e f i n i t i o n of these terms. ) Table 2 shows how the E n g l i s h consonants can be c l a s s i f i e d i n terms of place of a r t i c u l a t i o n , manner of a r t i c u l a t i o n , and v o i c i n g . A r e p r e s e n t a t i v e sample of phonetic d i s c r i m i n a t i o n research with young i n f a n t s i s shown i n Table 3. Consonant s t u d i e s are presented according to d i f f e r e n c e s i n p l a c e , manner and v o i c i n g . """Place of a r t i c u l a t i o n r e f e r s t o the p o s i t i o n i n the v o c a l t r a c t i n which the a i r f l o w i s obstructed before r e l e a s e . There are three places of a r t i c u l a t i o n i n E n g l i s h , and up to s i x i n other languages (see Table 1). When the v o i c i n g d i s t i n c t i o n i s discussed i n reference t o word-i n i t i a l stop consonants, a d i s t i n c t i o n i s made between the presence (voiced) and absence ( v o i c e l e s s ) of g l o t t a l v i b r a t i o n during the clo s u r e (Hockett, 1960). However, both voiced and v o i c e l e s s stops i n E n g l i s h may be produced without v o i c i n g during, the c l o s u r e ( L i s k e r S Abramson, 1964). Because of the i n c o n s i s t e n c i e s of such a phonetic a n a l y s i s , i t has become popular to describe v o i c i n g d i s t i n c t i o n s i n terms of voi c e onset time (VOT). VOT r e f e r s t o the time between the re l e a s e of a r t i c u l a t o r y c l o s u r e and the onset of p e r i o d i c v i b r a t i o n i n the v o c a l chords. The catego r i e s of v o i c i n g across n a t u r a l language can be approximated by d i f f e r e n c e s i n VOT. However, i t should be remembered that i n a d d i t i o n t o VOT, s e v e r a l other (up t o 16) a c o u s t i c cues have been i d e n t i f i e d which c o n t r i b u t e t o p e r c e p t i b l e d i f f e r e n c e s i n v o i c i n g ( L i s k e r , 1978). Nevertheless, s t u d i e s examining per c e p t i o n of v o i c i n g d i s t i n c t i o n s have c l a s s i c a l l y manipulated the exemplars along the VOT dimension ( c f . Eimas, et. a l . , 1971), although the o c c a s i o n a l study has examined v o i c i n g d i s c r i m i n a t i o n using f u l l y n a t u r a l exemplars (Trehub £ R a b i n o v i t c h , 1972). Manner of a r t i c u l a t i o n r e f e r s t o the way i n which a r t i c u l a t i o n i s produced, i . e . the way i n which the v o c a l t r a c t i s ( p a r t i a l l y or completely) c l o s e d or modified. Stop consonants are produced by a complete c l o s u r e of the a r t i c u l a t o r s and a sharp r e l e a s e of the a i r -flow (as the "b" i n buy). F r i c a t i v e s are produced by a narrowing of the distance between two a r t i c u l a t o r s , and thus the con t i n u i n g r e l e a s e of the a i r f l o w i s t u r b u l e n t (as the " f " i n f a s t ) . Other possible' manners of a r t i c u l a t i o n i n E n g l i s h are nasals and approximants. 31 Table 2 A Chart of the E n g l i s h Consonants Manner of a r t i c u l a t i o n b i 1 a b i a 1 a a 1 P 1 P 1 d d V a V a a e e e 1 e 1 V b n n o a o a e i t t 1 t 1 t 1 o a a a o a a a - 1 1 r - r 1 r n a s a l m n n stop P b t d k g f r i c a t i v e f V 0 3 s z ' 3 ( c e n t r a l ) approximant (w) r j w l a t e r a l (approximant)- 1 Whenever there are two symbols w i t h i n a s i n g l e c e l l , the one on the l e f t represents a v o i c e l e s s sound. A l l other symbols represent voiced sounds. (From Ladefoged, 1975). 32 TABLE 3 SUMMARY OF INFANT RESEARCH: DISCRIMINATION ALONG PHONETIC BOUNDARIES AGE CONTRAST PROCEDURE RESEARCHERS RESULTS I n i t i a l , n a t i v e speech c o n t r a s t s , Place of a r t i c u l a t i o n 2--3 months /dae//gae/ HAS Ei l e r s , 1 9 7 7 + 4--6 months /ba//ga/ HR Moffit,1971 + 6--9 weeks /ba//ga/ HAS Morse,1972 + 3--4 months /bu//gu/ HR M i l l e r , et.al.,1977 + »-6--12 weeks /da//ga/ HAS Williams £ Bush,1978 + 2--3 months /ba//da//ga/ HAS Eimas, 1974 + 3--4 months /da//ga/ HR M i l l e r £ Morse,1976 + 4--5 months /da//ga/ HR T i l l , 1976 + 2 months /d //g / HAS Jusczyk,1977 + 1--4 months /va//sa/ HAS E i l e r s £ Minifie,1975 + 1--4 months /sa//Sa/ HAS E i l e r s £ Minifie,1975 + 1--4 months / f ( a , i ) / / 0 ( a , i ) / HAS Ei l e r s , 1 9 7 7 -6--8 months /va//sa/ HT E i l e r s , et.al.,1977 + 6--8 months /f . ( a , i ) / / 9 ( a , i ) / H T E i l e r s , et.al.,1977 -6--8 months /sa//Sa/ HT E i l e r s , et.al.,1977 t 6--8 months / f i / / 6 i / HT(PC) Holmberg, et.al.,1977 + 6--8 months /sa//Sa/ HT(PC) Holmberg, et.al.,1977 + 2 months /fa//8a/ HAS Jusczyk, et.al.,1979 + 2 months /va//oa/ HAS Jusczyk, et.al.,1979 + 2 months /ba//da/ HAS Jusczyk, et.al.,1979 + jn- - i n i t i a l , n a t i v e speech c o n t r a s t s , Place of a r t i c u l a t i o n 2 months /daba//daga/ HAS Jusczyk £ Thompson,1978 + 2 months /ag//ad/ HAS Jusczyk,1977 + 2 months /bad//bag/ HAS Jusczyk,1977 + I n i t i a l , non-native speech c o n t r a s t s , Place of a r t i c u l a t i o n 6-8 months / t a / / t a / HT Werker, et.al.,1981 I n i t i a l , n a t i v e speech c o n t r a s t s , V o i c i n g 1-4 months /ba//pa/ HAS Eimas et.al.,1971 1-4 months /ba//pa/ HAS Trehub £Rabinovitch,1972 1-4 months /da//ta/ HAS Trehub £Rabinovitch,1972 1- 4 months /sa//za/ HAS E i l e r s £ Minifie,1975 6-12 weeks /ba//pa/ HR Roth £ Morse, 1975 6-8 months /pa//p na/ HT E i l e r s , et.al.,1979 2- 3 months /da//ta/ HAS Eimas,1975a + + + + + N o n - i n i t i a l , n a t i v e speech c o n t r a s t s , V o i c i n g 5--17 weeks /(k)apa//(k)aba/ (500 msec) HAS Trehub ,1976a + 5--17 weeks /(k)apa//(k)aba/ (300 msec) HAS Trehub ,1976a -1--4 months /a:t//a:d/ HT E i l e r s , et.al.,1977 -1--4 months /at//a:d/ HT E i l e r s , et.al.,1977 + 1--4 months /a:s//a:z/ HAS E i l e r s £ M i n i f i e , 1 9 7 5 -1--4 months /as//a:z/ HAS E i l e r s £ Minifie,1975 + I n i t i a l , non-native (and n a t i v e ) speech c o n t r a s t s , V o i c i n g 2-3 months /pa//p a//ba/ HAS Eimas,1965a 4-•6 months /ba//pa/ HR Lasky, et.al.,1975 + 2-•3 months /ba//pa/ HAS Streeter,1976 + 6-•8 months /pa//p a//ba/ HT E i l e r s , et.al.,1979 -,+ 0-•1 month /pa//p a//ba/ HAS B u t t e r f i e l d £ Cairns,1974 -» + 6- 8 months /pa//p a//ba/ HT A s l i n , et.al.,1979 + 6- 8 months /pa//p a//ba/ HT A s l i n , et.al.,1981 + I n i t i a l , n a t i v e speech c o n t r a s t s , Manner(" = shows context e f f e c t s ) 2-3 months 2-4 months 2-4 months 6-8 months / r a / / l a / HAS -/ba//wa/ HAS */ba//ma/ HAS /be//we//ue/ HT Eimas,1975b Eimas £ Mi l l e r , 1 9 8 0 + M i l l e r £ Eimas,1979 + H i l l e n b r a n d , et.al.,1979 + I n i t i a l , non-native speech c o n t r a s t s , Manner 5- 17 weeks / z a / / r a / HAS Trehub,1976b N o n - i n i t i a l , n a t i v e (and non-native) speech c o n t r a s t s , Manner 6- 8 months /awa//ara/ HT E i l e r s , et.al.,1978 Native speech c o n t r a s t s , Vowels 4--17 weeks / u / / i / HAS Trehub,1973 + 4--17 weeks / i / / a / HAS Trehub,1973 + 4--17 weeks /p a / / p i / HAS Trehub,1973 + 4--17 weeks / t a / / t i / HAS Trehub,1973 ' " + 4--16 weeks / a / / i / HAS Kuhl £ M i l l e r , 1 9 7 5 + 6 months /a//a/ HT(PC) Kuhl,1967;1977 + 6 months / i / / I / HT(PC) Kuhl,1976;1977 + 2 months / i / / I / HAS Swoboda, et.al.,1976 + 6--8 months / b l t / / b i t / HT E i l e r s , et.al.,1978 + Non-native speech c o n t r a s t s , Vowels 5-17 weeks /pa//pa/ HAS Trehub, 19 76 + 34 Within phonetic category d i s c r i m i n a t i o n s 6-8 months /ba//ba/ HT . A s l i n , et.al.,1981 + 6-8 months /pa//pa/ HT A s l i n , e t . a l . ,1981 + 6-8 months /pha//ph a/ HT A s l i n , et.al.,1981 + 1-4 months /ba//ba/ HAS Eimas, et.al.,1971 -1-4 months /ba//ba/ HAS Eimas, et.al.,1971 ' -2-3 months /da//da/ HAS Eimas, 1975a -2-3 months / t a / / t a / HAS Eimas, 1975a • -4-5 months /da//da/ HR T i l l , 1 9 7 6 -4-5 months /ga//ga/ HR T i l l , 1 9 7 6 -2 months / i / / i / HAS Swoboda, et.al.,1976 + 2 months m m HAS Swoboda, et.al.,1976 + on-speech sounds (.** = counterparts t o speech sounds) 2-3 months r i s e time HAS Jusczyk, et'.al.,1977 + 2-3 months onset time HAS Jusczyk, et.al.,1980 + * 2 months 2nd formant HAS Morse, 1972 -(/ba//ga/) t r a n s i t i o n s " 2-3 months 2nd formant HAS Eimas, 1974 -(/ba//da/) t r a n s i t i o n s " 4-5 months 2nd formant HR T i l l , 1976 -(/da//ga/) t r a n s i t i o n s " 2-3 months 3rd formant HAS Eimas, 1975 -(/ra//la/) t r a n s i t i o n s HR = Heart r a t e o r i e n t i n g response procedure HAS = High amplitude sucking procedure(s) HT = Head t u r n procedure(s) PC = Perceptual constancy: Grouping d i f f e r e n t s t i m u l i according t o a s p e c i f i e d category Native r e f e r s to c o n t r a s t s that are n a t i v e t o the subjects being t e s t e d . Non-native r e f e r s to c o n t r a s t s t h a t are'not n a t i v e t o the subjects, being t e s t e d . When voiced and v o i c e l e s s b i l a b i a l stops are tested., they are w r i t t e n as /ba//pa/. However, i f three c a t e g o r i e s of voice-onset time are t e s t e d , the sound corresponding most c l o s e l y t o the E n g l i s h sound i s w r i t t e n as /p^a/, w i t h the simultaneous onset sound w r i t t e n as /pa/. 35 There i s considerable evidence suggesting t h a t young i n f a n t s can d i s c r i m i n a t e both place of a r t i c u l a t i o n and v o i c i n g d i f f e r e n c e s i n stop consonants i n i n i t i a l p o s i t i o n according t o phonetic category. Morse (1972) used a HAS paradigm t o show that i n f a n t s aged 6-9 weeks: d i s -c r i m i n a t e the E n g l i s h place continuum /ba-/ . /ga/ according t o phonetic category and f a i l to respond t o w i t h i n category d i f f e r e n c e s . R e p l i c a -t i o n s have been provided by E i l e r s (1977), Eimas (.19740, and W i l l i a m s and Bush (1978). Following t h i s , other researchers using the HR paradigm showed a s i m i l a r p a t t e r n of d i s c r i m i n a t i o n ' r e s u l t s i n i n f a n t " c . . s t u d i e s ( L e a v i t t , Brown, Morse, £ Graham, 1976; M i l l e r £ Morse, 1976; Jusczyk, 1977; M o f f i t , 1971; T i l l , 1976). More r e c e n t l y , researchers using HAS have shown that i n f a n t s aged 2-3 months can d i s c r i m i n a t e stop consonants i n both medial (Jusczyk £ Thompson, 197 8; W i l l i a m s , 19 77) and f i n a l (Jusczyk, 1977) p o s i t i o n . R e s u l t s from experiments studying i n f a n t perception of v o i c i n g d i f f e r e n c e s i n stop consonants do not lend as c l e a r support f o r " p h o n e t i c a l l y organized" speech d i s c r i m i n a t i o n as do place of a r t i c u -l a t i o n s t u d i e s . Of p a r t i c u l a r relevance t o the issues r a i s e d i n the present work, i n f a n t s from any l i n g u i s t i c environment seem t o be able to d i s c r i m i n a t e speech sounds around the E n g l i s h VOT ( l a g ) boundary even i f they have not experienced a language which uses that boundary (Lasky, Lasky, £ K l e i n , 1975; S t r e e t e r , 1976) (with s l i g h t d i f f e r e n c e s i n the exact boundary across languages and across s t u d i e s ; c f . , W i l l i a m s , 1974). However, d i s c r i m i n a b i l i t y of the p r e v o i c i n g VOT (lead) boundary found i n some n a t u r a l languages, f o r example Thai and Spanish, i s more e q u i v o c a l . For example, i n a now c l a s s i c study, Eimas, Siqueland, Jusczyk, and V i g o r i t o (1971) showed i n f a n t s aged 1-4 months t o 36 d i s c r i m i n a t e the voiced and v o i c e l e s s stop consonants /b/ and /p/ along the same phonetic boundaries as E n g l i s h a d u l t s (the l a g VOT boundary). This f i n d i n g has been r e p l i c a t e d many times (see Table 2). In the s e v e r a l s t u d i e s examining perception of the l e a d VOT boundary (.Butter-f i e l d £ C a i r n s , 1974-; E i l e r s , Gavin £ Wilson, 1979; Eimas, 1975a,,to date, only two s t u d i e s provide c l e a r support that i n f a n t s can d i s -c r i m i n a t e t h i s d i s t i n c t i o n . ( A s l i n , Hennessy, P i s o n i , £ Perey, 1979; 1981). Sev e r a l methodological and conceptual problems make i n t e r p r e -t a t i o n of these i n c o n s i s t e n c i e s d i f f i c u l t . For example, E i l e r s e t . a l . (1979) have been c r i t i c i z e d f o r not g i v i n g the i n f a n t s a l a r g e enough number of t r i a l s w i t h i n which to perform the r e q u i r e d d i s c r i m i n a t i o n ( A s l i n £ P i s o n i , 1980). Studies of f r i c a t i v e c o n t r a s t s give s i m i l a r r e s u l t s : f r i c a t i v e place of a r t i c u l a t i o n but not VOT d i f f e r e n c e s appear t o be e a s i l y d i s c r i m i n a b l e by young i n f a n t s . For example, data from HAS s t u d i e s provide evidence t h a t i n f a n t s can d i s c r i m i n a t e the /va/ vs. /sa/ place d i f f e r e n c e , but not the /sa/ vs. /za/ v o i c i n g d i f f e r e n c e s at 1-4 months of age ( E i l e r s £ M i n i f i e s , 1975), whereas they can d i s c r i m i n a t e both sets of d i f f e r e n c e s by 6-8 months of age when t e s t e d i n the HT procedure ( E i l e r s , e t . a l . , 1977). These r e s u l t s must be i n t e r p r e t e d w i t h c a u t i o n , however, si n c e E i l e r s a l s o has data t o suggest that i n f a n t s from 1-12 months of age cannot d i s c r i m i n a t e / f ( a or i ) / vs. /0(a or i ) / whereas Holmberg, Morgan and Kuhl (1977) show that i n f a n t s can d i s c r i m i n a t e t h i s c o n t r a s t by 6-8 months of age. Although both sets of researchers employed the HT technique with the i n f a n t s 6 months and o l d e r , Holmberg, and h i s co-workers used n a t u r a l r a t h e r than s y n t h e t i c tokens, and they gave the i n f a n t s a greater number of t r i a l s (68 as opposed t o 6) t o 37 show evidence of d i s c r i m i n a t i o n . Cross-language speech research Experimental i n v e s t i g a t i o n of cross-language speech perception provides inform a t i o n about the nature of Innate a b i l i t i e s , and the e f f e c t of experience on perceptual development. I t has been p r e d i c t e d that young i n f a n t s can d i s c r i m i n a t e the u n i v e r s a l set of phonetic c o n t r a s t s , and t h a t there i s a d e c l i n e i n t h i s a b i l i t y as a f u n c t i o n of p a r t i c u l a r experience (Eimas, 1978; Morse, 1978; Werker e t . a l . , 1981). However, i t has a l s o been suggested that language experience may be necessary t o f a c i l i t a t e the p e r c e p t i o n of phonetic d i s t i n c t i o n s ( E i l e r s , e t . a l . , 1979). P o s i t i o n s intermediate to the above two have a l s o been promoted, wi t h some researchers p r e d i c t i n g t h a t experience might have a d i f f e r e n t e f f e c t on v o i c i n g than on 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 s (Trehub, B u l l , 6 Schneider, 1981), and other researchers c l a i m i n g that s e n s i -t i v i t y to phonetic boundaries i s so robust that experience cannot e f f e c t i t ( B o r n s t e i n , 1979). These p r e d i c t i o n s w i l l be explored i n the f o l l o w i n g s e c t i o n by examining cross-language speech perception research. Infant data w i l l be presented f i r s t , f o l l o w e d by a d i s c u s -s i o n of r e s u l t s from developmental s t u d i e s . Considerable evidence suggests that i n f a n t s can d i s c r i m i n a t e phonetic c o n t r a s t s they have not heard i n t h e i r n a t i v e language. This has been shown i n the case of c o n t r a s t s i n stop consonants d i f f e r i n g i n VOT ( A s l i n , e t . a l . 1979; Easky., ;et... a l . , 1.9754 :Streeter., ' . 1976), of s i b i l a n t s (Trehub, 1976b); vowels (Trehub, 1976b); l i q u i d s ( E i l e r s , O i l e r , £ Gavin, 1978) j and d i f f e r e n c e s i n place of a r t i c u l a t i o n (Werker, et. a l . , 1981). In o p p o s i t i o n t o these f i n d i n g s , E i l e r s and 38 her co-workers have r e c e n t l y provided data showing that Spanish i n f a n t s aged 6-8 months can d i s c r i m i n a t e the Spanish (lead) boundary i n VOT whereas i d e n t i c a l l y aged E n g l i s h i n f a n t s cannot ( E i l e r s , e t . a l . , 1979). E i l e r s and colleagues i n t e r p r e t t h e s e data.to support the n o t i o n t h a t l i n g u i s t i c experience f u n c t i o n s to f a c i l i t a t e d i s c r i m i n a t i o n performance. In a d d i t i o n to i t s being i n c o n s i s t e n t w i t h other cross-language f i n d i n g s , t h i s c o n c l u s i o n has been questioned f o r both methodological and s t a t i s -t i c a l reasons ( A s l i n £ P i s o n i , 1980a). A s l i n and P i s o n i argue that s t a t e v a r i a b i l i t y makes the requirement of reaching a 5 out of 6 c r i t e r i o n w i t h i n 6 t r i a l s unreasonable f o r i n f a n t s . In a d d i t i o n , they point out that the d i f f e r e n c e between 5 out of 6 c o r r e c t t r i a l s of the Spanish i n f a n t s and the 3 out of 6 c o r r e c t t r i a l s of the E n g l i s h i n f a n t s i s not s t a t i s t i c a l l y s i g n i f i c a n t . A s l i n and h i s co-workers attempted to r e p l i c a t e the r e s u l t s obtained by E i l e r s and colleagues by examining d i s c r i m i n a t i o n performance of E n g l i s h i n f a n t s at s e v e r a l p o i n t s along the VOT continuum ( A s l i n , e t . a l . , 1981). They used a step-wise procedure i n which i n f a n t s were t e s t e d on consecutive p a i r s of sounds f o r a set number of t r i a l s . T heir data, i n c ontrast t o E i l e r s , e t . a l . (1979), showed that E n g l i s h i n f a n t s can d i s -c r i m i n a t e VOT d i f f e r e n c e s at both the E n g l i s h ( l a g ) and the Spanish (lead) boundary although performance i s b e t t e r around the l a g boundary. In a d d i -t i o n , the i n f a n t s d i s c r i m i n a t e d s e v e r a l w i t h i n category d i f f e r e n c e s along with the VOT continuum. I t could be t h a t the step-wise procedure used by Aslin':s research team may have served as a more s e n s i t i v e , psychophysical procedure measuring a c o u s t i c r a t h e r than phonetic d i s -c r i m i n a t i o n a b i l i t i e s . This p o s s i b i l i t y , together with the ambiguous r e s u l t s reported above ( E i l e r s , e t . a l . , 1979; Eimas, 1975a) 39 make i t unclear whether i n f a n t perception of t h i s . l e a d boundary i s p h o n e t i c a l l y s i g n i f i c a n t . • Evidence showing that a d u l t s and c h i l d r e n exposed t o a p a r t i c u l a r language throughout l i f e may have d i f f i c u l t y l a b e l l i n g and/or d i s c r i m i n a t -ing non-native phonemic c o n t r a s t s i s provided by a d d i t i o n a l research (Cochrane, 1977; Goto, 1971; L i s k e r £ Abramson, 1970; McKain, Best S Strange, 19 80; Miyawaki, Strange, Verbrugge, Liberman, J e n k i n s , £ Fujimura, 1975; Singh £ Bl a c k , 1966; Snow £ Hoefnagel-Hohle, 1978; Trehub, 1976; Werker, e t . a l . , 1981). Only two r e p o r t s have compared the r e l a t i v e d i s c r i m i n a t i o n a b i l i t i e s o f i n f a n t s and a d u l t s . Trehub (1976) compared i n f a n t s and a d u l t s on t h e i r a b i l i t y t o d i s c r i m i n a t e non-native c o n t r a s t s . Although her r e s u l t s suggest that i n f a n t s could d i s c r i m i n a t e the sounds with greater ease than the a d u l t s , no d i r e c t comparison could be made as d i f f e r e n t paradigms and d i f f e r e n t analyses were employed w i t h the two age.groups. The i n f a n t data were c o l l e c t e d w i t h a HAS paradigm and analysed w i t h an a n a l y s i s of variance whereas the a d u l t data were c o l l e c t e d with a "change - no change" paradigm (hears two sounds and i n d i c a t e s whether there was a change or not) and analysed w i t h a D' s t a t i s t i c . Our recent report (Werker, e t . a l . , 1981). compared the r e l a t i v e d i s c r i m i n a t i o n a b i l i t i e s of E n g l i s h speaking a d u l t s , H i n d i speaking a d u l t s , and i n f a n t s o n . t h e i r d i s c r i m i n a t i o n of two H i n d i speech c o n t r a s t s . By using the HT procedure we were able t o provide support f o r the no t i o n of a d e c l i n e i n non-native speech d i s -c r i m i n a t o r y a b i l i t i e s as a f u n c t i o n of e i t h e r age and/or language experience. That i s , i n f a n t s and H i n d i a d u l t s could d i s c r i m i n a t e both H i n d i speech c o n t r a s t s , whereas the E n g l i s h a d u l t s had d i f f i c u l t y , e s p e c i a l l y w i t h the 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 . 40 To date, there has been l i t t l e systematic research comparing changes, i n speech perception performance across childhood. The i n v e s t i -gations of speech perception i n young c h i l d r e n have o f t e n been conducted without reference t o i n f a n t work, and have been motivated by the work of Jakobson (1968). Jakobson advocates a theory of p h o n o l o g i c a l development i n which sounds t h a t are common across n a t u r a l languages are acquired e a r l i e r than sounds which have a more l i m i t e d d i s t r i b u t i o n . In support of t h i s , speech pe r c e p t i o n work with young c h i l d r e n has y i e l d e d data suggesting a developmental increase between the ages of 2 t o 7 years i n the accuracy of d i s c r i m i n a t i o n of n a t i v e speech sounds that have a r e s t r i c t e d r e p r e s e n t a t i o n both w i t h i n and across n a t u r a l languages (G a r n i c a , 1973, Shvachkin, 1973). In c o n t r a s t , Barton (.1976; 1978) has r e c e n t l y shown., th a t c h i l d r e n between the ages of 2 and 7 are a l l e q u a l l y able t o d i s c r i m i n a t e phonemic c o n t r a s t s i f they are t e s t e d on words with which they are f a m i l i a r . He f e e l s t h i s does not negate the f i n d i n g s t h a t accuracy of d i s c r i m i n a t i o n of phonetic c o n t r a s t s ( i . e . from nonsense words) improves with age ( G i l b e r t , 1975; Templin, 1957) but i t does undermine the theory proposed by Jakobson. The methodbJogical s o p h i s t i c a t i o n of Barton's work makes i t most comparable to i n f a n t data, and indeed, h i s f i n d i n g s ( i n c o n t r a s t t o those of others) are c o n s i s t e n t w i t h i n f a n t work by showing that even very young c h i l d r e n can perceive a l l the d i s t i n c t i o n s which' are phonemic i n t h e i r own language. 41 R e l a t i n g Language and C o g n i t i v e Development to Speech Perception Babbling Development Since the present work attempts to r e l a t e changes i n speech perception performance t o l i n g u i s t i c and c o g n i t i v e development, a short d i s c u s s i o n of the i s s u e s i n each of these areas w i l l be presented. T h e o r e t i c a l conceptions r e l a t i n g language production t o language per-c e p t i o n i n e a r l y p h o n o l o g i c a l development have taken four d i f f e r e n t forms, (.1) The c h i l d ' s p e r c e p t i o n precedes production (Smith, 1973). (2) Perception and production develop i n tandem as the l i n g u i s t i c apparatus i s tuned through experience' ( K o r n f e l d , 1974). (3) P e r c e p t i o n and production both develop over the f i r s t few years of l i f e , but t h i s development i s independent. Perception w i l l most of t e n precede, though not guide, production ( Z l a t i n £ Koenigsknecht, 1976). (4) Production precedes per c e p t i o n . (A l o g i c a l p o s s i b i l i t y which i s not advocated.) Current research i n e a r l y productive language behaviour examines the kinds of sounds and the combinations of sounds produced by the p r e l i n g u i s t i c i n f a n t . In t h i s , work, i t has been suggested that a l l the d i s t i n c t i v e f e a t u r e s are present i n the v o c a l output of very young i n f a n t s ( F r y , 1975). This v o c a l output i n c l u d e s f e a t u r e s such as i n g r e s s i v e breath d i r e c t i o n , e t c . , that are used d i s t i n c t i v e l y i n very few n a t u r a l languages (Buhr 6 Keating, 1977). Complex f e a t u r e combinations are observed i n e a r l y v o c a l productions, but the combina-t i o n s do not r e f l e c t adult phonetic forms. For example, f e a t u r e s may be combined i n unacceptable sequences, or c r i e s and other vegetative sounds may be i n t e r s p e r s e d w i t h phonetic features ( S t a r k , 42 1980). This shows that the e a r l y v o c a l output of the i n f a n t may be constrained both by the immaturity of the a r t i c u l a t o r s (Lieberman, C r e l i n , £ K l a t t , 1972) and by knowledge of the r u l e s of combining phonetic f e a t u r e s (.Strange £ Broen, 1980). I t has been remarked that babbling becomes r e s t r i c t e d around 10 months of age to r e f l e c t the phonemes of the language to which, the c h i l d i s being exposed (Lenneberg, 1966). Such a comment i s premature, however, as there i s no co n c l u s i v e data t o support i t (.Oiler, 19 80; St a r k , 1980). Rather, i n f a n t v o c a l i z a t i o n s around t h i s age tend to in c l u d e phonetic segments th a t are common across most languages ( O i l e r , Wieman, Doyle, £ Ross, 1975) and such language s p e c i f i c adjustments as s y l l a b l e durations (.Oiler £ Smith, 1977) and VOT (Port £ Preston, 1974) are not apparent i n e a r l y v o c a l output. Thus any r e s t r i c t i o n of babbling sounds reported at around 10 months of age may r e f l e c t a tuning of v o c a l production as a r e s u l t of l i n g u i s t i c i n p u t , or i t could merely r e f l e c t increased a c t i v e c o n t r o l over the a r t i c u l a t o r s . In a recent study, O i l e r and E i l e r s (1982) recorded the v o c a l output of 8 E n g l i s h - and 8 Spanish-learning c h i l d r e n at r e g u l a r i n t e r -v a l s from b i r t h t o age 3. T r a n s c r i p t i o n s of babbling produced when the i n f a n t s were between 11 and 14 months of age showed that the m a j o r i t y of the v o c a l output of i n f a n t s from both language l e a r n i n g groups c o n s i s t e d of v o i c e l e s s , u naspirated, CV s y l l a b l e s . The vowels u t t e r e d by the 2 groups were a l s o very s i m i l a r . However, i n f a n t s from each language l e a r n i n g group produced vowels that were p a r t i c u l a r t o t h e i r language more- f r e q u e n t l y than d i d the i n f a n t s from the other language l e a r n i n g group. This study produces the f i r s t t e n t a t i v e support f o r the n o t i o n that v o c a l output may become modified around 43 the end of the f i r s t year of l i f e as a r e s u l t of a p a r t i c u l a r language experience. The development of v o c a l output during the f i r s t year has a l s o been conceived i n terms of stages, w i t h steps being i d e n t i f i e d as progressions toward the production of the f i r s t word (.Oiler, 1980; S t a r k , 1980). B r i e f l y , these stages can be c h a r a c t e r i z e d as progress-i n g from (.1) r e f l e c t i v e v o c a l i z a t i o n s t o (2) cooing and l a u g h t e r , t o (3) v o c a l p l a y , t o (.4) r e d u p l i c a t e d . b a b b l i n g , (5) non-reduplicated b a b b l i n g , and f i n a l l y t o the (6) production of the f i r s t word ( S t a r k , 1980). Although the stages are conceived as overlapping and somewhat continuous, an Infant's v o c a l output can be c h a r a c t e r i z e d as f a l l i n g predominantly i n t o one or another stage. Two processes are seen as c o n t r i b u t i n g to t h i s development; maturation of a r t i c u l a t o r y c o n t r o l , and emergence of v o l i t i o n a l c o n t r o l over the v o c a l output. Although the second process can be e a s i l y r e l a t e d t o c o g n i t i v e development, i t i s d i f f i c u l t t o know what the i n f a n t can do, and what the i n f a n t would do i f he or she c o u l d , when two such mechanisms are i n v o l v e d . Language and c o g n i t i v e development Although attempts t o r e l a t e language development t o c o g n i t i v e development have been f a i r l y u nsuccessful ( c f . Moorehead £ Moorehead, 1974), some i n t r i g u i n g r e s u l t s have emerged (Bates, 1979; Cromer, 1981). Most of t h i s work has been aimed at t r y i n g to c o r r e l a t e developmental milestones i n the c o g n i t i v e domain with emergent language f u n c t i o n s and c o m p l e x i t i e s i n productive speech. For example, there have been attempts t o compare a c q u i s i t i o n of the f i r s t word to the onset of r e p r e s e n t a t i o n a l (as conceived by P i a g e t , 1962) a b i l i t i e s (Ingram, 1978); 44 the achievement of object permanence t o r a p i d vocabulary growth (Bloom, 1973); and the understanding of means-ends r e l a t i o n s h i p s t o the advent of pragmatic language f u n c t i o n s (Bates, B e n i g n i , B r e t h e r t o n , Camainoin, £ V o l t e r r a , 1975). Although some trends have emerged, no strong r e l a t i o n -ships have been found.• Considerable research has been d i r e c t e d at t r y i n g t o understand the developing c o g n i t i v e a b i l i t i e s o f the i n f a n t during the f i r s t year of l i f e . Perhaps Piaget's work d e s c r i b i n g l e v e l s of sensorimotor development i s the most w e l l known ( P i a g e t , 1954). In t h i s and other work, Piaget c h a r a c t e r i z e s c o g n i t i v e development during the f i r s t 18 months as progression toward the achievement of r e p r e s e n t a t i o n a l thought. He argues t h a t during the sensorimotor p e r i o d the c h i l d comes t o know and a n t i c i p a t e r e g u l a r i t i e s i n the environment through a c t i n g on t h a t environment. The kinds of schemes the c h i l d forms during t h i s p e r i o d are thought t o be a c t i o n based and f l e e t i n g such that they f u n c t i o n as " p r e s e n t a t i o n s " r a t h e r than r e p r e s e n t a t i o n s . He claims t h a t the a b i l i t y to r e p r e s e n t , or to remember and search f o r an object without an en-a c t i v e t r i g g e r i s not achieved u n t i l around 18 months of age, when i t i s achieved across domains as a s i g n of the onset of p r e o p e r a t i o n a l t h i n k i n g . (See a l s o d i s c u s s i o n of r e p r e s e n t a t i o n . ) Recently, other researchers studying c o g n i t i v e growth during infancy suggest t h a t there are demonstrable improvements i n the a b i l i t y to remember events during the f i r s t year of l i f e which l e a d t o q u a l i -t a t i v e changes i n the i n f a n t ' s a b i l i t y t o understand and p r e d i c t events (Fox, Kagan £ Weiskoff, 1979; Grath, Appel £ Evans, 1974; Kagan, 1979). For example, by around 8-12 months of age, i n f a n t s can not only remember events f o r a short p e r i o d of time, but can use that memory to p r e d i c t 45 new events i n memory tasks (Kaga, Kearsley, and Zelazo, 1978; Kagan and Hamburg,: 19 81) and i n c a t e g o r i z a t i o n procedures (Horton £ Markman, 19 81; S t r a u s s , 1979). This k i n d of memory makes much more complex behaviour p o s s i b l e than the k i n d of sensorimotor r e c o g n i t i o n memory which has been demonstrated i n e a r l i e r infancy ( c f . R o v e e - C o l l i e r £ S u l l i v a n , 1980). In attempting t o understand the r e l a t i o n between memory and r e p r e s e n t a t i o n , r e p r e s e n t a t i o n has r e c e n t l y been conceived as an e f f e r e n t , i n t e r n a l l y c o n t r o l l e d achievement ( C o l l i n s £ Hagen, 1979). A k i n d of " e n a c t i v e " r e p r e s e n t a t i o n a l format (where format r e f e r s t o the process of b u i l d i n g the r e p r e s e n t a t i o n , c f . Bruner, 1957; Koslyn, 1978) i s i m p l i e d i n which the c h i l d b u i l d s a f u n c t i o n a l and s t a b l e schema from a c t i n g on stimulus events. To the extent that t h i s schema i s f u n c t i o n a l i n p r e d i c t i n g new events, i t i s s a i d t o have many of t h e . p r o p e r t i e s of P i a g e t i a n r e p r e s e n t a t i o n a l thought. Thus an enactive schema could serve to compare new events to o l d events. Perception of the new events could then be modified on the b a s i s of e x i s t i n g r e p r e s e n t a t i o n s . O u t l i n e of experiments The present research Is designed t o t e s t the i n f l u e n c e of e x p e r i -ence and development on the o r g a n i z a t i o n of speech perception. The focus of the f o l l o w i n g experiments i s t o explore the extent t o which speech perception a b i l i t i e s i n e a r l y infancy r e f l e c t b i o l o g i c a l l y based (phonetic-a l l y r e l e v a n t ) c o n s t r a i n t s which become modified as a r e s u l t of p a r t i c u l a r l i n g u i s t i c experience. I t i s hypothesized that s p e c i f i c experience e a r l y i n l i f e serves t o maintain i n f a n t phonetic c a p a b i l i t i e s which would other-wise disappear ( A s l i n £ P i s o n i ' s u n i v e r s a l t h e o r y ) . A d d i t i o n a l l y , i t i s pro-posed that changes i n speech perception are c o g n i t i v e l y based, and i n v o l v e the 46 s t r u c t u r i n g of phonemic c a t e g o r i e s . In support of t h i s , s p e c i f i c pre-d i c t i o n s are made r e l a t i n g developmental changes i n c o g n i t i v e and l i n g u i s t i c performance to speech perception performance, and p r e d i c t i n g c o n d i t i o n s under which adult speech perception may vary. These e x p e r i -ments stem from e a r l i e r work (see Werker, e t . a l . , 1981) i n which i t was shown that E n g l i s h i n f a n t s and Hindi-speaking a d u l t s could d i s c r i m i n a t e H i n d i (non-English) speech sounds according t o phonetic category, whereas E n g l i s h a d u l t s could not. 47 Table 4 Outl i n e of Experiments Experiment I: Experiment I I : Experiment I I I A : Experiment I I I B : Experiment I I I C : Experiment IV: Experiment V: Cross-language speech sound c a t e g o r i z a t i o n Childhood; E n g l i s h c h i l d r e n ages 4, 8, and 12 years 2 H i n d i c o n t r a s t s , / t a / / t a / and t n / / d h / R e p l i c a t i o n of previous work using a new contrast E n g l i s h i n f a n t s , E n g l i s h a d u l t s , Thompson a d u l t s 1 Thompson c o n t r a s t , / k i / / q i / Cross-language speech sound c a t e g o r i z a t i o n C r o s s - s e c t i o n a l i n f a n t study; Ages 6-8, 8-10, and 10-12 months 1 H i n d i , / t a / / t a / , and 1 Thompson, / k i / / q i / , c ontrast Cross-language speech sound c a t e g o r i z a t i o n L o n g i t u d i n a l i n f a n t study; Ages 6-8, 8-10, and 10-12 months 1 H i n d i , / t a / / t a / , and 1 Thompson, / k i / / q i / , c o n t r a s t C o g n i t i v e and l i n g u i s t i c c o r r e l a t e s of speech perc e p t i o n Ages 8-10 months 1 c o g n i t i v e measure (concept of the object) T r a n s c r i p t i o n s of babbling data 1 H i n d i , / t a / / t a / , and 1 Thompson, / k i / / q i / , c o n t r a s t Cross-language speech sound d i s c r i m i n a t i o n Same-Different (AX.) procedure Adult E n g l i s h speakers 1 H i n d i , / t a / / t a / , and 1 Thompson, / k i / / q i / , c o n t r a s t Influence o f perceptual set c o n d i t i o n s on Cross-language speech sound c a t e g o r i z a t i o n Adult E n g l i s h speakers 4 pe r c e p t u a l s e t s ; phonemic, a c o u s t i c , phonetic, and w i t h i n category v o c a l i c 1 H i n d i , / t a / / t a / , and 1 Thompson, / k i / / q i / , c o n t r a s t 48 EXPERIMENTS Experiment I This experiment was undertaken to examine developmental d i f f e r -ences i n non-native speech d i s c r i m i n a t i o n a b i l i t i e s across childhood and t o c l a r i f y the discrepancy found between the a b i l i t i e s of i n f a n t s and older c h i l d r e n . I t has been hypothesized (see Lenneberg, 1967) th a t considerable per c e p t u a l f l e x i b i l i t y e x i s t s u n t i l puberty; thus i n d i v i d u a l s a c q u i r i n g a second language p r i o r t o the end of t h i s " c r i t i c a l p e r i o d " should be ac c e n t - f r e e , whereas those l e a r n i n g a new language afterwards w i l l not. Although considerable research has y i e l d e d support f o r Lenneberg's hypothesis (Fatham, 1975; S e l i g e r , Krashen £ Ladefoged, 1975), some recent work a c t u a l l y suggests that o l d e r c h i l d r e n and a d u l t s may l e a r n proper p r o n u n c i a t i o n and p o s s i b l y d i s c r i m i n a t i o n f a s t e r than younger c h i l d r e n when a c q u i r i n g a second language (Snow £ Hoefnagel-Hohle, 1977; 1978). The f o l l o w i n g experiment t e s t s non-native speech perception across childhood to t r y t o determine i f the d e c l i n e between infancy and adulthood i n non-native perceptual a b i l i t i e s occurs around puberty, or i f i t occurs much e a r l i e r i n childhood as . suggested by some other s t u d i e s . In a d d i t i o n , i t addresses the g e n e r a l i t y of such a d e c l i n e by examining perception of two very d i f f e r e n t non-English speech c o n t r a s t s . I t i s conceivable t h a t some cross language boundaries may be p e r c e p t u a l l y weaker than others (e.g. i t has been suggested t h a t the l e a d boundary may be weaker than the l a g boundary i n VOT, see 49 I n t r o d u c t i o n ) . "Weaker" boundaries might disappear e a r l i e r i n develop-ment without s p e c i f i c experience than might more robust boundaries, l e a d i n g t o the formation of a broader perceptual category. METHOD Subjects There were 12 subjects t e s t e d at each of three ages; 4 y e a r s , 8 years and 12 years. Subjects were r e c r u i t e d l o c a l l y i n the author's neighbourhood. A l l subjects were u n i l i n g u a l E n g l i s h speakers w i t h , at most, l i m i t e d second language t r a i n i n g . C h i l d r e n aged 8 and 12 were p a i d $5.00 f o r t h e i r p a r t i c i p a t i o n , whereas younger c h i l d r e n (aged 4) were given a g i f t c e r t i f i c a t e t o MacDonald's. S t i m u l i The E n g l i s h contrast used was the 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 , /ba//da/, i n which b i l a b i a l and a l v e o l a r stop consonants are d i f f e r e n t i a t e d . The chosen H i n d i c o n t r a s t s sample two degrees of p e r c e p t u a l d i f f i c u l t y , the f i r s t c o n t r a s t being more d i f f i c u l t than the second. H i n d i i s the o f f i c i a l language spoken i n I n d i a . In a d d i t i o n , H i n d i i s spoken by a l a r g e p o p u l a t i o n i n the Vancouver area. The H i n d i language has 4 places of a r t i c u l a t i o n ( i n comparison to the 3 i n E n g l i s h ) and 4 c a t e g o r i e s of v o i c i n g ( i n comparison to the 2 i n E n g l i s h ) as shown i n Table 5. The f i r s t H i n d i c o n t r a s t , i n p a r t i c u l a -t i o n , i s a very r a r e phonemic d i s t i n c t i o n (a l i n g u i s t i c a l l y "marked" d i s t i n c t i o n ) across languages. As such, i t i s h i g h l y u n l i k e l y t h a t n a t i v e E n g l i s h speakers would have experienced t h i s sound d i f f e r e n t i a -t i o n without s p e c i f i c t r a i n i n g . 50 Table 5 ' H i n d i Stop Consonants • V o i c e l e s s unaspirated V o i c e l e s s a s p i r a t e d Voiced Breathy voiced b i l a b i a l p a l (take care of) p a l (edge of k n i f e ) b a l ( h a i r ) b a l (forehead) d e n t a l t a n " (mode of si n g i n g ) than:'r-V ( r o l l of c l o t h ) dan ( c h a r i t y ) ,h d an"" (paddy) r e t r o f l e x t a l " (postpone) A i (place f o r buying wood) d a l (branch) d a l ( s h i e l d ) p o s t - a l v e o l a r a f f r i c a t e t / a l (go) t / h a l ( d e c e i t ) d 3 a l (water) S3 a-'-(glimmer) v e l a r kan (ear) k an (mine) gan (song) h g an ( k i n d of bundle) *= comparison R e t r o f l e x / D e n t a l ""= comparison V o i c e l e s s Asp/Breathy Voiced (From Ladefoged, 1975) 51 The f i r s t (non-English) H i n d i contrast was the unvoiced unaspirated r e t r o f l e x vs. d e n t a l stop, / t a / / t a / , 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 d i s t i n c t i o n . Although, the a c o u s t i c c h a r a c t e r i s t i c s of r e t r o f l e x i o n are not very w e l l understood, i t appears that the burst and at l e a s t the f i r s t three formant t r a n s i -t i o n s are necessary t o achieve r e l i a b l e i d e n t i f i c a t i o n among n a t i v e speakers (Stevens £ Blumstein, 1975). Because I was i n t e r e s t e d i n " c a t e g o r i z i n g " d i s c r i m i n a t i o n and not j u s t a c o u s t i c r e s o l u t i o n c a p a c i t i e s , a m u l t i p l e n a t u r a l tokens (4 exemplars of each sound) paradigm was used (see Appendix A f o r f u r t h e r r a t i o n a l e ) . The s e v e r a l exemplars of each sound were chosen so that v a r i a t i o n s i n d u r a t i o n , fundamental frequency, and i n t o n a t i o n contour were randomized both w i t h i n and between phonemes. The average d u r a t i o n of a stimulus token was 400 msec, with a 1600 msec i n t e r t r i a l i n t e r v a l . A c o u s t i c analyses (see Figure 5) showed the main cues d i f f e r -e n t i a t i n g these n a t u r a l tokens to be i n the b u r s t , and i n the slope of the t h i r d formant t r a n s i t i o n . The second H i n d i c o n t r a s t used was the unvoiced, a s p i r a t e d d e n t a l stop vs. the breathy voiced d e n t a l stop, /t*V / d n / , i n which a d i f f e r e n c e i n v o i c e onset time i s assumed t o be the c r i t i c a l dimen-s i o n . The VOT f o r an average /t*V token was 131.3 msec compared with -121.5 msec f o r an average / d n / token i n t h i s study. As evident i n the spectograms (see Figure 6 ) , p e r i o d i c i t y precedes the r e l e a s e burst at the l e v e l of Formant 1 f o r the breathy sound. CM FIGURE 5 SPECTOGRAMS OF THE FIRST HINDI CONTRAST RETROFLEX vs D E N T A L , ta/ta Time (msec) C O in FIGURE 6 SPECTOGRAMS OF THE SECOND HINDI CONTRAST UNVOICED ASPIRATED vs. VOICED ASPIRATED DENTAL, f h / d h Time (msec) 54 A l l s t i m u l i were recorded from a n a t i v e speaker i n the phonetics l a b o r a t o r y at UBC. F i n a l tapes were prepared at Haskins Lab o r a t o r i e s i n New Haven, Connecticut. Four tokens of each n a t u r a l l y produced sound were d i g i t i z e d and re-recorded at a 10 khz sampling r a t e on the Haskins PDP-224.computer. In a d d i t i o n t o the manipulations already d i s c u s s e d , s t i m u l i were equated f o r amplitude ( f o r i n t e n s i t y ) and f o r d u r a t i o n both w i t h i n and across sound c a t e g o r i e s . Procedure A l l subjects were t e s t e d i n a simple d i s c r i m i n a t i o n paradigm which had minimal memory requirements ( c f . Carney, Widin, S V i e m e i s t e r , 1977) and was s i m i l a r t o the i n f a n t Head Turn (HT) paradigm (a complete d e s c r i p t i o n o f t h i s paradigm i s o u t l i n e d i n Experiment I I ) . In t h i s a d u l t and c h i l d v e r s i o n of the HT paradigm, the subject was i n s t r u c t e d t o press a button when there was a change i n the speech s t i m u l i . Feed-back was provided f o r c o r r e c t button r e l e a s e s o n l y , w i t h the i l l u m i n a -t i o n of l i g h t s i n s i d e a smoked p l e x i g l a s s box. In t h i s study, the tapes were set up d i c h o t i c a l l y , and l i n e d up f o r onset on each of the t r a c k s . That i s , s t i m u l i from one phoneme category i . e . /ba/ were on Track 1, and s t i m u l i from the other c a t e -gory i . e . /da/ were on Track 2. Change t r i a l s were i n i t i a t e d by changing t r a c k s . Appropriate c o n t r o l s i n p r e s e n t a t i o n i n the equip-ment and m o d i f i c a t i o n s were made t o ensure t h a t i r r e l e v a n t cues could not a i d i n the d i s c r i m i n a t i o n . A l l s t i m u l i were played on a Revox A-77 tape r e c o r d e r , and p r o j e c t e d over a s i n g l e - d r i v e r speaker at ap p r o x i -mately 65 dB SPL i n a T r a c o u s t i c s double-walled sound attenuated booth. 55 The t i m i n g f o r p r e s e n t a t i o n of c o n t r o l (no change) and e x p e r i -mental (change) t r i a l s , and f o r a c t i v a t i o n of the l i g h t s was c o n t r o l l e d by a l o g i c system. Experimental t r i a l s occurred at i r r e g u l a r i n t e r v a l s (every 4 to 15 tokens). Responses were recorded on a Grason S t a d l e r event r e c o r d e r . E i g h t out of 10 c o r r e c t response to change t r i a l s w i t h a maximum of e i t h e r 2 misses or 2. f a l s e p o s i t i v e was considered c r i t e r i o n f o r evidence of d i s c r i m i n a t i o n . Because o f the number of f a l s e p o s i t i v e p o s s i b i l i t i e s , the p r o b a b i l i t y of ac h i e v i n g t h i s c r i t e r i o n by chance alone i s extremely low (p<.001). The--criterion f o r - d e c i d i n g a- subject could not reach c r i t e r i o n was set at 25 change t r i a l s . That i s , i f w i t h i n 25 change t r i a l s a subject showed no evidence of approaching c r i t e r i o n , t e s t i n g was stopped. RESULTS The number o f subjects who reached and d i d not reach c r i t e r i o n on each of the two H i n d i sound c o n t r a s t s i s reported i n Table 5, along w i t h r e l e v a n t data from our previous research. An a n a l y s i s of propor-t i o n s based on the Scheffe theorem ( M a r a s c u i l o , 1966) was a p p l i e d t o the"se new-data, together with the data from three groups t e s t e d under i d e n t i c a l c o n d i t i o n s e a r l i e r . This a n a l y s i s was designed to compare the p r o p o r t i o n of i n d i v i d u a l s e i t h e r reaching or not reaching c r i t e r i o n on . a .-giv en m easure. In the case of the H i n d i R e t r o f l e x / D e n t a l c o n t r a s t , the o v e r a l l Chi-square obtained from the a n a l y s i s of proportions had a p r o b a b i l i t y of p<.05 (x2 = 42.693) suggesting s i g n i f i c a n t d i f f e r e n c e s between the s i x groups of subjects t e s t e d (see Table 6 f o r group numbers). To determine which groups v a r i e d s i g n i f i c a n t l y , a s e r i e s of palrr-.wise 56 Table 6 D i s c r i m i n a t i o n Performance on Two H i n d i Speech Contrasts Group . (1) E n g l i s h ' Infants (2) (3) (4) 4 years 8 years 12 years (5) E n g l i s h Adults (6) H i n d i Adults Reached C r i t e r o n The r e t r o f l e x / d e n t a l contrast / t a / / t a / YES 11 0 0 1 1 5 NO 1 12 12 11 The v o i c i n g c o n t r a s t / t n / / d h / 9 0 YES 10 0 4 4 4 5 NO 2 12 8 8 6 0 57 Table 7 Pa i r - w i s e M u l t i p l e Comparisons on the H i n d i R e t r o f l e x / D e n t a l Contrast Comparison Confidence I n t e r v a l P r o b a b i l i t y S i g n i f i c a n t 2-1 -1.200 t o -0.634 . .000 Yes 3-1 -1.234 t o -0.433 .000 Yes. 3-2 -0.200 t o 0.366 .955 No 4-1 -1.225 t o -0.275 .000 Yes 4-2 -0.215 to 0.548 .791 No 4-3 -0.392 t o 0.559 .996 No 5-1 -1.257 to -0.377 .000 Yes 5-2 -0.237 t o 0.437 .953 No 5-3 -0.423 t o 0.457 1.000 No -5-4 -0.576 to 0.442 .999 No 6-1 -0.200 t o 0.366 .955 No 6-2 0.634 t o 1.200 • 0 0 0 Yes 6-3 0.634 to 1.200 .000 Yes 6-4 0.452 t o 1.215 .000 Yes 6-5 0.563 to 1.237 .000 Yes Groups are defined i n Table 6 58 comparisons based on Marascuilo (.1966), between 2 groups was performed. The r e s u l t s from the m u l t i p l e comparisons are presented i n Table 6. Comparisons between Group 1 w i t h Groups 2, 3, and 4-, and between Group 6 w i t h Groups 2, 3, and 4, were a l l s i g n i f i c a n t , but none of the comparisons between Groups 2, 3, 4 and 5 or between Groups 1 and 6 were s i g n i f i c a n t . In summary the H i n d i a d u l t s (.Group 6) and E n g l i s h i n f a n t s (Group 1) d i s c r i m i n a t e d these c o n t r a s t s s i g n i f i c a n t l y b e t t e r than the other groups. Furthermore, there were no changes or d i f f e r e n c e s across childhood (ages 4, 8 and 12) i n the a b i l i t y to d i s c r i m i n a t e t h i s con-t r a s t according t o phonemic category, i . e . subjects at a l l three ages were poor and not s i g n i f i c a n t l y d i f f e r e n t from one another. In the case of the H i n d i unvoiced, a s p i r a t e d d e n t a l vs. unvoiced, unaspirated d e n t a l c o n t r a s t , the o v e r a l l Chi-square obtained was s i g n i f i c a n t (p < .05; x 2 = 24.617). A s e r i e s o f m u l t i p l e comparisons was again performed to determine which groups v a r i e d and the r e s u l t s are summarized i n Table 8. The f o l l o w i n g comparisons between two groups reached s i g n i f -icance: these were Group 1 vs. 2 and Group 6 vs. 2, 3, 4, and 5. The E n g l i s h i n f a n t s (Group 1) performed b e t t e r than the 4 year olds (Group 2) and the H i n d i a d u l t s performed b e t t e r than a l l groups except the E n g l i s h i n f a n t s . Although the d e c l i n e i n the a b i l i t y to d i s c r i m i n a t e t h i s con-t r a s t according to phonemic category i s not as pronounced as i t i s f o r the f i r s t c o n t r a s t ( p o s s i b l y because i t i s a p e r c e p t u a l l y e a s i e r d i f f e r -ence), i t can be seen t h a t the d e c l i n e i s evident by age 4. To under-stand these data f u r t h e r , a s e r i e s of Chi squares was run comparing two groups. This a n a l y s i s showed the comparisons between c h i l d r e n aged 8- and 12- w i t h the 4-year-old c h i l d r e n to be s i g n i f i c a n t l y d i f f e r e n t (p_ < .05; 59 Table g Pair - w i s e M u l t i p l e Comparisons on the H i n d i V o i c i n g Contrast Comparison Confidence I n t e r v a l P r o b a b i l i t y S i g n i f i c a n t 2-1 -1.215 t o -0.452 .000 Yes 3-1 -1.116 t o 0.116 .140 No 3-2 -0.150 to 0.816 .306 No 4-1 -1.116 to 0.116 .140 No 4-2 -0.150 to 0.816 .306 No 4-3 -0.683 t o 0.683 1.000 No 5-1 -1.103 t o 0.346 .383 No 5T2 -0.150 t o 0.9.50 .247 No 5-3 -0.665 t o 0.798 1.000 No 5-4 -0.665 to 0.798 1.000 No 6-1 -0.215 to 0.548 .791 No 6-2 .184 t o 1.150 .000 Yes 6-3 0.184 to 1.150 .000 Yes 6-4 0.184 t o 1.150 .000 Yes 6-5 0.050 t o 1.150 .010 Yes Groups are defined In Table 6. 60 X 2 = 7.5). This suggested t h a t the 4-year olds performed more poor l y on t h i s c o n t r a s t than the o l d e r c h i l d r e n . A summary of the r e s u l t s from t h i s experiment together w i t h those from Werker, e t . a l . , 1981, i s shown i n Figure 7. DISCUSSION These f i n d i n g s support the n o t i o n that cross-language speech per-ception does not d e c l i n e i n a gr a d u a l , l i n e a r f a s h i o n across development. Most i m p o r t a n t l y , the e f f e c t s of s p e c i f i c l i n g u i s t i c experience seem t o be evident by age 4. Such, a f i n d i n g i s not s u r p r i s i n g given t h a t 4-year-o l d c h i l d r e n are already r e l a t i v e l y accomplished speakers. However, t h i s f i n d i n g i s i n c o n s i s t e n t w i t h the r e l a t i v e l y l a t e adolescent d e c l i n e suggested by Lennebegg(0-967). Rather, these r e s u l t s provide support f o r the a l t e r n a t i v e n o t i o n and the subsequent work supporting i t (Fatham, 1975; S e l i g e r , e t . a l . , 1975) that second language l e a r n i n g may not neces-s a r i l y be e a s i e r i n e a r l y childhood. Furthermore, the r e l a t i v e recovery of d i s c r i m i n a t i o n by age 8 f o r the VOT contrast suggests t h a t simple m a t u r a t i o n a l explanations may not s u f f i c e , and that a more complex explanation may be r e q u i r e d t a k i n g both the r e l a t i v e d i f f i c u l t y or a c o u s t i c parameters of the speech sounds, and or the l e v e l of c o g n i t i v e development o f c h i l d r e n i n t o account. Moreover, i n the paradigm which we used, i n v o l v i n g m u l t i p l e exemplars of each sound, subjects may have been predisposed t o adopt a native-language phonemic perceptual s t r a t e g y . That i s , they may have used the phonemic ca t e g o r i e s of t h e i r n a t i v e .. language to guide t h e i r performance. I t may be th a t 4-year-olds are simply r i g i d r u l e f o l l o w e r s (.as has been shown i n other c o g n i t i v e t a s k s ) 61 FIGURE 7 SUBJECTS REACHING CRITERION ON HINDI STOP CONSONANTS 62 and cannot e a s i l y drop t h a t phonemic s t r a t e g y i n order t o attend t o the phonetic or a c o u s t i c features d i f f e r e n t i a t i n g the sounds, whereas the 8- and 12-year-olds can adopt such a t a s k - s p e c i f i c perceptual s t r a t e g y i n the case of a somewhat l e s s d i f f i c u l t c o n t r a s t . Experiment I I The f i r s t experiment, together with our e a r l i e r work (Werker, e t . a l . , 1981) showed th a t i n f a n t s could d i s c r i m i n a t e two (non-English) H i n d i speech c o n t r a s t s as w e l l as H i n d i a d u l t s , and t h a t there was a d e c l i n e i n t h i s a b i l i t y , by age 4. These r e s u l t s were i n t e r p r e t e d as showing t h a t i n f a n t s d i s c r i m i n a t e the u n i v e r s a l set of n a t u r a l l y produced phonetic c o n t r a s t s without s p e c i f i c language experience, and t h a t there i s a d e c l i n e i n t h i s a b i l i t y as a f u n c t i o n of age and/or l i n g u i s t i c experience. To examine the g e n e r a l i t y of t h i s i n f a n t a b i l i t y and subsequent d e c l i n e , a f u r t h e r t e s t using a new non-English speech co n t r a s t was undertaken. In Experiment I I , i n f a n t s 6-8 months of age from E n g l i s h -only f a m i l i e s were compared to mono-lingual E n g l i s h a d u l t s and Thompson speaking a d u l t s on t h e i r a b i l i t y t o d i s c r i m i n a t e a (non-English) Thompson co n t r a s t . The Thompson language i s an I n t e r i o r S a l i s h (Native Indian) language spoken i n south c e n t r a l B r i t i s h Columbia. The consonantal system of t h i s language (see Table 9') has two c o n s t r a s t i n g s e r i e s of back stops i n c l u d i n g p l a i n and g l o t t a l i z e d v e r s i o n s of rounded and un-rounded sounds. These are v a r i o u s l y c a l l e d v e l a r s (k's) and uvulars ( q ' s ) , or pre- and p o s t - v e l a r sounds (Mayes, 1979; Thompson £ Thompson, i n p r e s s ) . In E n g l i s h , there i s no d i s t i n c t i o n between back consonants, i n t h a t only v e l a r stops are phonemic. The Thompson p a i r chosen c o n t r a s t s g l o t t a l i z e d v e l a r and g l o t t a l i z e d uvular sounds, / & i / / q i / . METHOD Subj ects Ten i n f a n t s (7 g i r l s , 3 boys) ranging i n age from 6 months, 4 days to 7 months, 29 days, w i t h an average age of 6 months, 29 days were r e c r u i t e d by a d v e r t i s i n g i n newspapers s e r v i n g the UBC area. An a d d i -t i o n a l two i n f a n t s had t o be discarded because they d i d not reach c r i t e r i o n on the E n g l i s h /ba//da/ c o n t r a s t . Infants were requested t o p a r t i c i p a t e 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 t h a t each i n f a n t was comfortable i n the experimental room before t e s t i n g began. Ten E n g l i s h speaking a d u l t s (6 males, 4 females) aged 22 - 35 were r e c r u i t e d from the UBC campus. As i t i s d i f f i c u l t t o .find a d u l t s w i t h no second language t r a i n i n g , notes were made on formal and i n f o r m a l t r a i n i n g . No E n g l i s h a d u l t s had exposure to a second language con-t a i n i n g the contrast being s t u d i e d . T e s t i n g of E n g l i s h i n f a n t s and a d u l t s took place i n the speech perception l a b at UBC. F i v e native-Thompson speaking a d u l t s (3 females, 2 males) ranging i n age from 30 t o 65 (very few young people speak the language any more; making; i t necessary to work w i t h the e l d e r s ) were t e s t e d on t h e i r d i s c r i m i n a t i o n (and/or i d e n t i f i c a t i o n ) of the Thompson tokens. Subjects were r e c r u i t e d w i t h the help of a l i n g u i s t , Yvonne Hebart, who has s t u d i e d I n t e r i o r Salis.h languages. With Yvonne's i n t r o d u c t i o n , I was able t o present my p r o j e c t to the Band C o u n c i l and r e c e i v e formal approval from the N i c o l a V a l l e y C h i e f , Robert S t e r l i n g . Because the subjects l i v e i n the N i c o l a V a l l e y around M e r r i t t , B.C., adult S a l i s h subjects were t e s t e d i n t h e i r community, r a t h e r than i n the speech perception l a b . Testing took place i n a quiet basement 64 Table 9 THOMPSON CONSONANTAL SYSTEM P h 1 b a a a i 1 1 p r r 1 d a V a u y y a e t e 1 V V n n b n e o a e u g g i t r 1 t 1 1 e e a a a a a a a a a 1 1 1 r 1 r r 1 1 obstruent P t c c k kw q q w <; ' P' t ' k' c' k' k'W q t q'w •i'w h 1 s s .. x * x w X x w sonorant m n 1 z y Y w m1 n' 1» z' y' Y' w1 C = g l o t t a l i z e d k' = ( t ' l ) or ( t ' l ) c C w = l a b i a l i z e d c' = Ct's) c (From Mayes, 1979, p. 12) room i n a p r i v a t e house. The tape recorder and experimenter were i n a separate room around the corner from the l i s t e n e r . S t i m u l i The Thompson (nonEnglish) contrast / k i / / q i / was used t o compare E n g l i s h i n f a n t s , E n g l i s h a d u l t s , and Thompson a d u l t s 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 a non-English c o n t r a s t . This c o n t r a s t s two g l o t t a l i z e d v o i c e l e s s stop consonants where the uvular vs. v e l a r 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 i s the c r i t i c a l d i f f e r e n c e . These sounds are produced by o b s t r u c t i n g the a i r flow by r a i s i n g the back of the tongue e i t h e r against the velum ( v e l a r ) or behind the velum ( u v u l a r ) . Back conson-ants, although r a r e across n a t u r a l languages, are c h a r a c t e r i s t i c of North American Indian languages. In r e c o r d i n g n a t i v e Indians who are not accustomed t o reading t h e i r language, i t was necessary t o record whole words, and then ask the speaker t o repeat the f i r s t consonant-vowel (CV) sound. I t was then p o s s i b l e t o perform a c o u s t i c analyses of words and CV r e p e t i t i o n s to ensure t h a t the CV s y l l a b l e s contained the same consonant sounds as the words (they d i d not, i n a l l cases). O r i g i n a l l y , we wanted t o contrast u n g l o t t a l i z e d back stops w i t h the vowel /a/ t o compare a back (Thompson) with a f r o n t ( H i n d i ) non-English place d i s t i n c t i o n . However the vowels i n I n t e r i o r S a l i s h languages vary (somewhat i n f r e e v a r i a -t i o n and i n a somewhat systematic fashion) between speakers and between consonants (Thompson Kinkade;, i n p r e s s ) . In our many n a t u r a l recordings of k and q words and sounds from three d i f f e r e n t speakers, we were unable t o f i n d tokens wherein a s i m i l a r enough vowel f o l l o w e d m u l t i p l e CV only r e p e t i t i o n s of k and q. 66 In the CV r e p e t i t i o n s from the words £ixm ( t o f r y an egg) and qixm ( t o make one s e e ) , however, there was one token of / R i / and one token of / q i / i n one speaker's r e c o r d i n g where the vowels sounded n e a r l y i d e n t i c a l and where they appeared s i m i l a r i n a wave form. Since there i s a d i s c o n t i n u i t y i n the wave form of g l o t t a l i z e d s t o p s , (as opposed t o u n g l o t t a l i z e d ) i t was easy t o use the / i / p e r i o d i c segment from a s i n g l e / k i / and the / i / p e r i o d i c p o r t i o n from a s i n g l e / q i / to s p l i c e on to a d d i t i o n a l exemplars of the b u r s t / t r a n s i t i o n p o r t i o n of other £ and of q r e p e t i t i o n s . This was done t o y i e l d three tokens of / k i / (with a s i n g l e / i / segment) and three tokens of / q i / ( w i t h a s i n g l e / i / segment). I d i d not wish to use a s i n g l e p e r i o d i c / i / p o r t i o n across both k~ and q as important consonantal i n f o r m a t i o n i s i n c l u d e d i n the p e r i o d i c segment i n n a t u r a l speech. F i n a l s t i m u l i were recorded by Jim Toodlican, (although a d d i t i o n a l h e l p f u l recordings • were su p p l i e d by Mary Coutlee and Mabel Joe.) Since c l a s s i c a l specto graphic a n a l y s i s has been shown t o pro-vide l i t t l e i n f o r m a t i o n as t o the a c o u s t i c d i f f e r e n c e s between v e l a r and uvular sounds (see Mayes, 1979; Bengeureal,^.) •. ; a waveform a n a l y s i s was done. This showed the amplitude and d u r a t i o n of the /q/ burst to be greater than that of the /k/ b u r s t . The p e r i o d of c l o s u r e preceding the r e l e a s e of the burst was longer f o r the /k/ than f o r the /q/. This can be seen i n Figure 8. The average duration f o r each token was fOO msec with a 1700 msec s i l e n t i n t e r v a l between tokens. Tapes were d i g i t i z e d and set up as i n Experiment I . This i n f o r m a t i o n i s from a personal communication with A.P. Bergeureal, May, 1982 based on both h i s own work and some recent work of Ladefoged's on u v u l a r / v e l a r sounds. FIGURE 8 WAVEFORM OF THE THOMPSON GLOTTALIZED VELAR/UVULAR CONTRAST *i/qi 68 Procedure Infants were t e s t e d i n a "head t u r n " (ET) sometimes r e f e r r e d to as " 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 i n which the i n f a n t i s conditioned t o t u r n i t s head away from an experimental a s s i s t a n t and toward a loud speaker w i t h i n a s p e c i f i e d time i n t e r v a l (M% sec) when there i s a change i n the a u d i t o r y s t i m u l u s . Correct head turns are r e i n f o r c e d w i t h the p r e s e n t a t i o n and i l l u m i n a -t i o n of an e l e c t r i c a l l y a c t i v a t e d toy animal i n s i d e a smoked p l e x i g l a s s box (see Figures 9 and 10) and w i t h s o c i a l reinforcement ( i . e . , good boy, c l a p hands) while f a l s e p o s i t i v e s are not r e i n f o r c e d . The i n c l u -s i o n of s o c i a l reinforcement has been shown to g r e a t l y f a c i l i t a t e c o n d i t i o n i n g i n t h i s paradigm (Moore, Wilson, £ Thompson, 1976, Wilson, Moore, S Thompson, 1976). This paradigm was f i r s t developed as a v a r i a t e of the c l a s s i c play audiometric procedure used by Dix and H a l l p i k e (1947). In the 1970s., t h i s procedure was f u r t h e r modified f o r use as an audiometric technique w i t h i n f a n t s as young as 5% months of age (Wilson, e t . a l . , 1976). V a r i a t i o n s i n the procedure (e.g., bar press i n s t e a d of head turn) make t h i s procedure u s e f u l w i t h o l d e r i n f a n t s (12-24 months), young c h i l d r e n and a d u l t s . . . E i l e r s , Wilson,arid Moore,(.1977) f i r s t m odified the procedure t o measure d i s c r i m i n a t i o n of speech sounds. Since then, i t has been used (with v a r i a t i o n s ) by s e v e r a l speech per-ception researchers ( H i l l e n b r a n d , M i n i f i e , S Edwards, 1979; K uhl, 1977; Werker, e t . a l . , 1981). In the experimental set-up, the i n f a n t s i t s on i t s parent's lap f a c i n g a t a b l e i n the sound attentuated chamber. Parent and 69 FIGURE 9 ARRANGEMENT OF EXPERIMENTAL SITE Parent C Qi E a • mm* D cr IY""" Infant Speaker^ VR Visual / Reinforcer Signal Experimenter 2 Window Experimenter 1 o FIGURE 10A Infant O r i e n t a t i o n During C o n t r o l T r i a l FIGURE 10B Infant O r i e n t a t i o n During Experimental T r i a l 72 i n f a n t face toward an experimental a s s i s t a n t (E2) who s i t s f a c i n g a t a b l e d i r e c t l y i n f r o n t of them. The loud speaker and the v i s u a l r e i n f o r c e r are l o c a t e d at a 110-degree angle three fee t t o the l e f t of the p a r e n t / i n f a n t (see Figure 9). Both the parent and E2 wear head-phones through which music i s played so they w i l l not be able t o i n f l u e n c e the i n f a n t ' s behaviour. The E2 keeps the i n f a n t l o o k i n g i n h i s / h e r d i r e c t i o n by manipulating toys. Another experimenter ( E l ) s i t s outside the booth, observing the i n f a n t and monitoring the l o g i c system. In the c o n d i t i o n i n g phase, r e p e t i t i o n s of a s i n g l e sound, e.g. ba, are played over the speaker. When the i n f a n t appears to be i n a s t a t e of re a d i n e s s , i . e . l o o k i n g toward the E2, but not too a c t i v e l y i n v o l v e d i n the t o y s , E l changes the stimulus to a new sound by changing t r a c k s on the tape recorder ( i . e . , . da). Immediately f o l l o w -ing the changed sound, the v i s u a l r e i n f o r c e r i s a c t i v a t e d f o r the durat i o n of the "da" sounds, approximately 4% sec. The i n f a n t t urns h i s / h e r head toward the v i s u a l r e i n f o r c e r t o see i t . The sound change and r e i n f o r c e r a c t i v a t i o n are pa i r e d f o r three p r e s e n t a t i o n s , a f t e r which the experimenter begins g i v i n g the i n f a n t longer and longer i n t e r v a l s i n which t o t u r n h i s / h e r head before a c t i v a t i n g the r e i n f o r c e r . The i n f a n t thus l e a r n s t o a s s o c i a t e sound change with the a c t i v a t i o n of the r e i n f o r c e r . Once t h i s a s s o c i a t i o n i s formed, ( u s u a l l y w i t h i n 2 t o 10 t r i a l s ) the i n f a n t , upon hearing the sound change, turns i t s head toward the r e i n f o r c e r . When c o n d i t i o n i n g i s s u c c e s s f u l ( i . e . , three c o r r e c t a n t i c i -patory head turns i n a row) a c t i v a t i o n of the v i s u a l r e i n f o r c e r becomes c o n t r o l l e d by a l o g i c system. Every time the i n f a n t turns i t s head, E2 presses a button on the f l o o r . A l l button presses were 73 recorded on a Grason-Stadler event recorder. I f the button press occurred w i t h i n M-Jg sec of the s t i m u l i changing from one phoneme (.i.e. ba) t o another ( i . e . da), the v i s u a l r e i n f o r c e r was a c t i v a t e d by the l o g i c system. C r i t e r i o n f o r d i s c r i m i n a t i o n was set at 8 out of 10 c o r r e c t responses t o change t r i a l s . C r i t e r i o n f o r d e c i d i n g an i n f a n t could not d i s c r i m i n a t e a c o n t r a s t had two requirements. F i r s t , the i n f a n t had t o s u c c e s s f u l l y d i s c r i m i n a t e /ba/ vs. /da/ d i r e c t l y before and a f t e r f a i l -i ng a non-native contrast to ensure t h a t the f a i l u r e of the i n f a n t was not due to n o n - s p e c i f i c f a c t o r s such as boredom, d i r t y d i a p e r s , e t c . Second, the i n f a n t was given at l e a s t 25. change t r i a l s on the non-n a t i v e c o n t r a s t i n an attempt t o reach c r i t e r i o n . (For f u r t h e r elabora-t i o n of t h i s paradigm as used i n various-labs; see Appendix B). A v a r i a t e of t h i s paradigm (as described i n the procedure sec-t i o n of Experiment I) was used with a d u l t E n g l i s h s u b j e c t s . Since the adul t Thompson speakers were t e s t e d i n t h e i r community r a t h e r than i n the speech perception l a b , the button press and the v i s u a l r e i n f o r c e r s were not used. Rather, subjects were asked to c a l l out "change" when they thought the sound had changed. Responses were scored by hand. Two of the " e l d e r s " simply refused t o p a r t i c i p a t e i n such a s i l l y task. A f t e r c o n s u l t a t i o n , they agreed t o i d e n t i f y the tokens i f I would not rush them. Having a n t i c i p a t e d t h i s problem, I had prepared an i d e n t i -f i c a t i o n tape with the same tokens separated by 10 sec of s i l e n c e . This allowed me t o t u r n the tape recorder o f f between pre s e n t a t i o n s and wait f o r the answer. (Since the t e s t l i s t e n i n g c o n d i t i o n s were worse than those present i n the sound attenuated chamber, and sin c e i d e n t i f i c a t i o n i s a more d i f f i c u l t task than d i s c r i m i n a t i o n , any b i a s i n the t e s t i n g c o n d i t i o n s would have worked against the hypothesis.) 74 The c r i t e r i o n f o r d i s c r i m i n a t i o n was set at 8 out of 10 c o r r e c t r e -sponses to change t r i a l s (.i.e., no more than 2 misses or 2 f a l s e p o s i t i v e s ) . Because observation i n t e r v a l s were demarcated i n the i d e n t i f i c a t i o n t a s k , c r i t e r i o n f o r i d e n t i f i c a t i o n was set at 9 out of 10 c o r r e c t responses. The c r i t e r i o n f o r d e c i d i n g an adult subject could not reach c r i t e r i o n f o r d i s c r i m i n a t i o n performance was set at 25 change t r i a l s . RESULTS AND DISCUSSION The number of subjects that e i t h e r reached or d i d not reach c r i t e r i o n on the Thompson con t r a s t are reported i n Table 10. As i n Experiment I , an a n a l y s i s of proportions was a p p l i e d t o these data. This y i e l d e d a s i g n i f i c a n t o v e r a l l Chi-square (p < .05; X 2 = 8.94). M u l t i p l e comparisons between the d i f f e r e n t groups were performed t o determine which groups d i f f e r e d . The r e s u l t s showed the Adult E n g l i s h speakers d i d s i g n i f i c a n t l y worse than e i t h e r the Adult Thompson or the Infant E n g l i s h groups. The d i f f e r e n c e between the E n g l i s h i n f a n t s and the Thompson a d u l t s was not s i g n i f i c a n t . These r e s u l t s are s i m i l a r to those obtained i n our e a r l i e r work. They show th a t a d e c l i n e i n cross language speech perception i s evident between infancy and adulthood. That i s , young i n f a n t s seem to be able t o d i s c r i m i n a t e the u n i v e r s a l set of phonetic con-t r a s t s according to l i n g u i s t i c category, whereas adu l t speech percep-t i o n i s more l i m i t e d , r e f l e c t i n g c a t e g o r i z i n g d i s c r i m i n a t i o n of only those c o n t r a s t s which are phonemic i n t h e i r n a t i v e language. 75 Table 10 D i s c r i m i n a t i o n Performance on the Thompson Contrast Group (1) (2) (3) Adult Thompson Adult E n g l i s h Infant E n g l i s h Reached C r i t e r i o n YES 5 3 8 NO 0 7 2 76 Experiment'II IA This next experiment was designed t o t r y to determine when the d e c l i n e i n non-native speech perception c a t e g o r i z i n g occurs. I f speech perception performance i s r e l a t e d t o , or mediated by more general cog-n i t i v e s t r u c t u r e s , the d e c l i n e i n non-native d i s c r i m i n a t i o n should c o i n c i d e w i t h the a b i l i t y t o hold (or represent) events^suggesting that t h i s d e c l i n e should occur i n very e a r l y childhood. However, since we had no data examining cross-language perception between 7 months and 4 years of age, c h i l d r e n of English-speaking parents were t e s t e d at a l l these ages. P r e l i m i n a r y c r o s s - s e c t i o n a l i n v e s t i g a t i o n revealed that important d i f f e r e n c e s were emerging i n the f i r s t year of l i f e . At that point the i n v e s t i g a t i o n was narrowed t o studying i n f a n t s at three d i f f e r e n t ages; 6-8 months, 8-10 months, and 10-12 months. Infa n t s i n these three age ^groups were compared on t h e i r a b i l i t y t o d i s c r i m i n a t e both the Thompson con t r a s t C/ki/ vs. / q i / ) and the H i n d i contrast ( / t a / / t a / ) . Although evidence from our e a r l i e r work (Werker, et. a l . , 1981) and Experiment I I on the a b i l i t y of H i n d i and Thompson a d u l t s to d i s c r i m i n a t e provides a t e s t of the hypothesis t h a t s p e c i f i c l i n g u i s t i c experience serves t o at l e a s t maintain phonetic d i s c r i m i - . n a t i o n , t h i s i n t e r p r e t a t i o n would be strengthened i f r e l e v a n t d i s -c r i m i n a t i o n s performance could be assessed i n appropriate aged i n f a n t s from H i n d i and S a l i s h speaking homes. There was a l s o an attempt t o t e s t i n f a n t s from H i n d i or Thompson speaking homes 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 the r e l e v a n t speech c o n t r a s t s . 77 METHODS Subjects In t h i s study, data were c o l l e c t e d i n a c r o s s - s e c t i o n a l design from i n f a n t s aged 8-10 and 10-12 months of age, and were compared t o the e a r l i e r data we had c o l l e c t e d from i n f a n t s aged 6-8 months under i d e n t i c a l t e s t i n g c o n d i t i o n s . In the 8-10 month group, 7 females and 5 males, ranging i n age from 8 months 3 days to 9 months 10 days, with an average age of 8 months, 20 days were t e s t e d on the H i n d i c o n t r a s t . Nine females and 5 males, ranging i n age from 8 months t o 9 months 12 days, w i t h an average age of 8 months 18 days were t e s t e d on the S a l i s h c o n t r a s t . An a d d i t i o n a l 3 i n f a n t s were dropped from the study f o r f a i l i n g to reach c r i t e r i o n on /ba//da/. In the 10-12 month group, 5 females and 5 males, ranging i n age from 10 months 2 days to 11 months 15 days with an average age of 10 months 20 days were t e s t e d on the H i n d i c o n t r a s t . F i v e males and 5 females ranging i n age from 10 months 2 days to 12 months 4- days, with an average of 10 months 29 days were t e s t e d on the S a l i s h c o n t r a s t . Twelve i n f a n t s aged 10-12 months had to be discarded from the study because they f a i l e d to reach c r i t e r i o n on the /ba//da/ co n t r a s t the r e q u i r e d number of times. A l l subjects were r e c r u i t e d from advertisements i n the l o c a l newspapers. Parents were paid $5.00 f o r each v i s i t t o the l a b . S t i m u l i and Procedures The H i n d i r e t r o f l e x / d e n t a l contrast / t a / / t a / (as described i n Experiment I) and the Thompson g l o t t a l i z e d v e l a r / u v u l a r contrast / k i / / q i / (as described i n Experiment I I ) were used i n t h i s study. 78 Infants were t e s t e d i n the H.T procedure, as described i n Experiment I I . RESULTS AND DISCUSSION The number of subjects that e i t h e r reached or d i d not reach c r i t e r i o n on the two c o n t r a s t s i s shown i n Table 11. Most of the i n f a n t s aged 6-8 months reached c r i t e r i o n on both c o n t r a s t s , whereas by 10-12 months of age, few i n f a n t s reached c r i t e r i o n on e i t h e r . An a n a l y s i s of p r o p o r t i o n s was performed on these data f o r each of the two c o n t r a s t s . The o v e r a l l x 2 w a s s i g n i f i c a n t (,p_ < .05) f o r both c o n t r a s t s (x 2 = 21.67 f o r / k i / / q i / ; x2'= 24.59 f o r / t a / / t a / ) . Planned m u l t i p l e comparisons showed the s i g n i f i c a n t d i f f e r e n c e s t o be between the 6-8 month and the 10-12 month groups (p_ < .001), and be-tween the 8-10 and the 10-12 month groups (p_ < .05). This suggests t h a t the 10 month olds performed s i g n i f i c a n t l y l e s s w e l l than the younger i n f a n t s on both c o n t r a s t s . The number of t r i a l s t o c r i t e r i o n was compared across c o n t r a s t s and across ages f o r those i n f a n t s who could d i s c r i m i n a t e the sounds. A 3 x 2 repeated measures a n a l y s i s of variance showed there were no s i g n i f i c a n t d i f f e r e n c e s e i t h e r between age groups (.F = 1.577; p > .05) or between sound c o n t r a s t s (F_ = 2.779; p_ > .05). Thus i t would be d i f f i c u l t t o argue that there was a gradual increase across age i n the number of t r i a l s r e q u i r e d to reach c r i t e r i o n . To date, 4 i n f a n t s (2 H i n d i and 2 Thompson) 11-12 months of age who are experiencing r e g u l a r and extensive r e l e v a n t l i n g u i s t i c input have been t e s t e d . Of the 3 out of 4 babies who would c o n d i t i o n i n the paradigm, a l l 3 could d i s c r i m i n a t e t h e i r n a t i v e (non-English) c o n t r a s t . 79 -Table 11 Infant D i s c r i m i n a t i o n Performance on Two Non-English Speech Contrasts 'Reached C r i t e r i o n (1) (2) 6-8 months 8-10 months 10-(3) -12 months Th e R e t r o f l e x / D e n t a l Contrast / t a / / t a / YES 11 8 2 NO 1 4 8 The Velar/Uvular Contrast / k i / / q i / YES 8 8 1 NO 2 6 9 80 A l l s u bjects reached c r i t e r i o n w i t h i n 10 t r i a l s , whereas E n g l i s h i n f a n t s aged 10-12 months who could d i s c r i m i n a t e these c o n t r a s t s r e q u i r e d an average of 13 t r i a l s i n the case of the H i n d i c o n t r a s t and 16 t r i a l s i n the case of the Thompson c o n t r a s t . The number of subjects was too sma l l t o compare these means f o r s i g n i f i c a n t d i f f e r e n c e s , but there do not appear to be d i f f e r e n c e s . These f i n d i n g s show the d e c l i n e In the a b i l i t y t o c a t e g o r i z e phonetic c o n t r a s t s t o occur w i t h i n the f i r s t year of l i f e . That i s , most of the i n f a n t s t e s t e d could d i s c r i m i n a t e both c o n t r a s t s a t 6-8 months of age. By 8-10 months a smaller percentage could d i s c r i m i n a t e the c o n t r a s t s , and by 10-12 months the i n f a n t s were performing as poorly as the young c h i l d r e n and a d u l t s i n Experiments I and I I . However, i n f a n t s being exposed r e g u l a r l y t o H i n d i and Thompson sounds could s t i l l d i s c r i m i n a t e the co n t r a s t s at 11-12 months of age. These r e s u l t s c l e a r l y support the s u p p o s i t i o n t h a t s p e c i f i c l i n g u i s t i c experience, and not :just maturation, f u n c t i o n s t o maintain phonetic d i s c r i m i n a t i o n a b i l i t y . Without such experience, there i s a l o s s i n t h i s a b i l i t y by 10-12 months of age. Experiment I I I B Experiment I I I B r e p l i c a t e d and extended Experiment I I I A by examining the extent to which the age changes i n non-native speech d i s c r i m i n a t i o n performance uncovered i n c r o s s - s e c t i o n a l research would a l s o be apparent i n a w i t h i n - s u b j e c t s l o n g i t u d i n a l design. In p a r t i c u l a r , there was concern about the high d i s c a r d r a t e f o r the 10-12 month group. Infants f a i l e d to provide c l e a r data because by 81 10-12 months, they were c l e a r l y not as impressed with the HT procedure, and p r e f e r r e d to t r y to get to the v i s u a l r e i n f o r c e r . As such, i t was not c l e a r t h a t the i n f a n t s f i n a l l y t e s t e d were a r e p r e s e n t a t i v e sample, or that they were performing o p t i m a l l y . An attempt was made t o c o n t r o l f o r these problems by c o l l e c t i n g l o n g i t u d i n a l data from a small sample of cooperative i n f a n t s at three times corresponding t o the ages used i n Experiment IV. To t e s t t h i s , s i x i n f a n t s were followed l o n g i t u d -i n a l l y s t a r t i n g at age 6-8 months and t e s t e d at approximately two month i n t e r v a l s on t h e i r a b i l i t y t o d i s c r i m i n a t e both the H i n d i and Thompson c o n t r a s t s . METHOD Subj ects S i x s u b j e c t s , 3 males and 3 females, were t e s t e d at three p o i n t s i n time. • During Time 1, (6-8 months), i n f a n t s ranged i n age from 6 months 22 days t o 7 months 29 days, with an average age of 7 months 15 days. . At Time 2, (8-10 months), the i n f a n t s ranged i n age from 8 months 22 days.to 9 months 25 days, w i t h an average of 9 months 2 days. At Time 3, (10-12 months), the i n f a n t s ranged i n age from 10 months 2 days t o 11 months 11 days, with an average of 10 months 22 days. / S t i m u l i The H i n d i c o n t r a s t / t a / / t a / (as des c r i b e d i n Experiment I) and the S a l i s h contrast / k i / / q i / (as described i n Experiment I I ) were 82 used i n t h i s study. The ET procedure (as described i n Experiment I I ) was used f o r a l l i n f a n t s . RESULTS AND DISCUSSION The r e s u l t s from t h i s l o n g i t u d i n a l study r e p l i c a t e those from the c r o s s - s e c t i o n a l i n f a n t study. In t h i s experiment, a l l 6 s ubjects reached c r i t e r i o n on both non-English c o n t r a s t s when they were 6-8 months of age. When the subjects reached 8-10 months, a l l 6 reached c r i t e r i o n on the H i n d i c o n t r a s t , and only 3 reached c r i t e r i o n on the Thompson c o n t r a s t . By 10-12 months of age, 0 of the 6 i n f a n t s reached c r i t e r i o n on e i t h e r c o n t r a s t even though they could reach i t on the E n g l i s h /ba//da/ both before and a f t e r f a i l i n g the non-native sounds. Since repeated observations on the same i n d i v i d u a l s were used i n t h i s study, i t was not p o s s i b l e t o use an A n a l y s i s of P r o p o r t i o n s . Because such a small sample s i z e was t e s t e d , any r e s u l t s from a repeated measures Chi-square t e s t would be d i f f i c u l t t o i n t e r p r e t . However, i n examining the data, i t can be seen t h a t the r e s u l t s from the l o n g i t u d -i n a l study c l o s e l y match those from the c r o s s - s e c t i o n a l study. The p a t t e r n of change across infancy i s p r e c i s e l y mirrored f o r the Thompson contrast w i t h a gradual d e c l i n e across age i n the f i r s t year of l i f e . The time course of the change was somewhat d i f f e r e n t i n the case of the H i n d i c o n t r a s t , w i t h an apparent abrupt d e c l i n e i n d i s c r i m i n -a b i l i t y o c c u r r i n g when subjects reached 10-12 months of age. A graphic summary of the r e s u l t s from Experiments IIA and IIB i s presented i n Figure 11. 83 Figure 11 Proportion of Infant Subjects Reaching Criterion on Hindi and Salish Contrasts 100 r-80 6-8 months Cross-Sectional Data 8-10 months Jlilftt 10-12 months 100 r-80 h •£ 60 <u u <u °- 40 20 0 Longitudinal Data L l J Hindi / t a / vs. / t a / C] Salish / £ i / vs. / q i / 84 Experiment I I I C Experiment II I C was designed t o determine why the d e c l i n e i n phonetic d i s c r i m i n a t i o n performance occurs at one r a t h e r than another po i n t i n development. I f t h i s d e c l i n e i s mediated by developing cog-n i t i v e a b i l i t i e s , i t might be expected t o occur around the onset of r e p r e s e n t a t i o n a l a b i l i t i e s . That i s , the development of n a t i v e -language, phonemic-based speech per c e p t i o n could be seen as an instance of category f o r m u l a t i o n . In order t o form such c a t e g o r i e s , however, i t may be necessary to have the a b i l i t y t o represent or h o l d stimulus information i n memory. Although e a r l y P i a g e t i a n research showed the achievement of f u l l r e p r e s e n t a t i o n a l p o t e n t i a l t o occur around 18 months of age, r e -cent work has suggested t h a t an e a r l i e r , somewhat d i f f e r e n t k ind of a b i l i t y t o hold events i n memory seems to develop between 8-12 months of age (Kagan, 1979). The p o s s i b i l i t y that t h i s more f r a g i l e r epre-s e n t a t i o n a l a b i l i t y may be a necessary achievement before speech d i s c r i m i n a t i o n performance can become phonemic was i n v e s t i g a t e d i n t h i s study. C o g n i t i v e development was measured by each c h i l d ' s progression along the Uzgiris-Hunt (1975) " V i s u a l Pursuit-and Permanence of Object" s c a l e . The Uzgiris-Hunt s c a l e s were developed over s e v e r a l years as a means f o r assessing p s y c h o l o g i c a l development during the f i r s t two years of l i f e . The o r i g i n a l m o t i v a t i o n and s t r u c t u r i n g of the s c a l e s stemmed from Piaget's (1954) observations of h i s own three c h i l d r e n . In the process of d e v i s i n g and v a l i d a t i n g the i n f a n t s c a l e s , U z g i r i s and Hunt came to question the v a l i d i t y of a stage-concept f o r d e s c r i b i n g the 85 l e v e l s of sensorimotor i n t e l l i g e n c e as they observed v a r y i n g r a t e s of development i n the d i f f e r e n t domains of c o g n i t i v e f u n c t i o n i n g through-out the sensorimotor p e r i o d . Their research d i d provide support f o r a h i e r a r c h i c a l l y i n t e g r a t e d .and l o g i c a l l y i n v a r i a n t sequence of develop-ment w i t h i n each of the separate domains of p s y c h o l o g i c a l development, however. Thus the f i n a l t e s t instruments assess i n f a n t development w i t h i n each of s i x independent p s y c h o l o g i c a l areas according t o the i n f a n t ' s progress along s p e c i f i e d o r d i n a l s c a l e s . These s c a l e s are not t i e d d i r e c t l y t o l e v e l of sensorimotor i n t e l l i g e n c e ; however, l e v e l of development w i t h i n any one s c a l e can be seen as progress toward the>: achievement of f u l l P i a g e t i a n sensorimotor r e p r e s e n t a t i o n , ( U z g i r i s - H u n t , 1975). The s c a l e e n t i t l e d " V i s u a l p u r s u i t and permanence of o b j e c t s " was chosen because i t can be argued that such a s c a l e not only measures progress towards P i a g e t i a n r e p r e s e n t a t i o n , but that i t a l s o measures memory development-(Collins 6 Hagan, 1979; Gratch, e t . a l . , 1974). That i s , i t has been argued that searching f o r an object r e q u i r e s the a b i l i t y t o remember that such an object e x i s t s . Such an a b i l i t y can be conceived as an enactive form of r e p r e s e n t a t i o n . (.See I n t r o d u c t i o n ) In a d d i t i o n , a p r e l i m i n a r y attempt was made to explore the e l u s i v e perception/production l i n k . I t was hypothesized that such developing r e p r e s e n t a t i o n a l a b i l i t i e s might a l s o be r e f l e c t e d i n the s t r u c t u r i n g of language s p e c i f i c babbling sounds, and that as the c h i l d developed appropriate l i n g u i s t i c p erceptual c a t e g o r i e s , he/she would begin t o experiment with these l i n g u i s t i c c a t e g o r i e s . Even though a c h i l d could w e l l have such l i n g u i s t i c competence and s t i l l e i t h e r not choose t o use i t or not be able t o c o n t r o l the a r t i c u l a t o r y movements, 86 babbling was c o l l e c t e d from c h i l d r e n at t h i s age i n order t o compare i t to speech perception performance. Since r e p r e s e n t a t i o n a l a b i l i t i e s and babbling performance should both improve as a f u n c t i o n o f age, i t would not be very u s e f u l t o study i n f a n t s at widely v a r y i n g ages. I t would be more.use t o compare i n f a n t s i n the 8-10 month range who could and could not d i s c r i m i n a t e the non-native c o n t r a s t . Thus, t h i s experiment compared 8-10 month-olds on speech per-cep t i o n performance, c o g n i t i v e (memory) performance and v o c a l output. METHOD Subj ects F i f t e e n i n f a n t s , 7 males and 8 females, ranging i n age from 8 months 3 days to 9 months 25 days, w i t h an average age of 8 months 24 days were included i n t h i s study. Of the 15 i n f a n t s , 9 were t e s t e d i n I I I A and 6 were t e s t e d i n I I I B on speech perception performance. Procedure Subjects were t e s t e d on the " v i s u a l p u r s u i t and permanence of o b j e c t s " s c a l e i n a s i n g l e 20-minute session i n the speech perception l a b o r a t o r y . Babies were seated on a rug i n f r o n t of t h e i r mothers, f a c i n g an experimenter who was a l s o seated on the rug. Objects were presented and hidden according t o the s p e c i f i c a t i o n s i n the U z g i r i s -Hunt s c a l e (see Appendix 3A). Testing ceased when the baby f a i l e d t o pass three consecutive l e v e l s on the s c a l e . Subjects were scored according t o the highest l e v e l at which they s u c c e s s f u l l y (and c o r r e c t l y ) r e t r i e v e d the object at l e a s t 2 out of 3 of the presentations (.see s c o r i n g sheet i n Appendix C3). 87 Babbling was recorded, both during and a f t e r the i n f a n t was being t e s t e d on c o g n i t i v e tasks i n the l a b . The experimenter c o n t i n u a l l y t r i e d to e l i c i t b abbling from the c h i l d during the experimental s e s s i o n . Thus there was the opportunity f o r approximately 30 min of laboratory-based babbling r e c o r d i n g s . This method of gathering babbling data has been c r i t i c i z e d ( c f . Stark, 1980) as not being r e p r e s e n t a t i v e of the reper-t o i r e and frequency of sounds the i n f a n t may use outside the l a b . The experimenter was aware of t h i s l i m i t a t i o n . Babbling sounds were t r a n s c r i b e d by a person t r a i n e d i n phonetics who was unaware of the hypotheses of the study. T r a n s c r i p t i o n s were then set up according to Ingram's (1981) Phonetic Inventory Scale wherein r e p e r t o i r e of sounds, number of r e p e t i t i o n s , p o s i t i o n of sound i n u t t e r -ance, and complexity of utterance are s y s t e m a t i c a l l y recorded. (See Appendix 4). Ingram's s c a l e r e q u i r e s t h a t a baby produce a sound at l e a s t 6 times before i t can be s a f e l y i n cluded as being i n that c h i l d ' s phonetic inventory. Because only one of the babies babbled enough.to have the v o c a l output q u a l i f y f o r i n c l u s i o n , b a b bling was f i n a l l y only scored as t o whether / t / and /k/ sounds were produced. RESULTS AND DISCUSSION I f speech pe r c e p t i o n and babbling performance were both medi-ated by developing c o g n i t i v e s t r u c t u r e s , i t would be p r e d i c t e d that performance on the c o g n i t i v e t e s t would be a b e t t e r p r e d i c t o r of per-c e p t i o n and production than age. The r e s u l t s , however, from t h i s p r e l i m i n a r y study are not c o n c l u s i v e . Data were considered according 88 to speech perception performance, c o g n i t i v e score, number of r e l e v a n t ( t ' s and k's) babbling sounds, and age. Speech perception performance was c o l l a p s e d i n t o 4 groups: Group (.1) , could s t i l l d i s c r i m i n a t e both non-English c o n t r a s t s ; Group (2) could only d i s c r i m i n a t e the H i n d i con-t r a s t ; Group (3) could only d i s c r i m i n a t e the Thompson c o n t r a s t ; and Group (.4) could d i s c r i m i n a t e n e i t h e r c o n t r a s t . The average age of i n d i v i d u a l s i n the 4 groups was.8 months 26 days, 9 months 2 days, 8 months 9 days, and 8 months 24 days r e s p e c t i v e l y . Two of the subjects i n Groups (.1) and (2) were producing both t ' s and k's whereas only 1 was i n Group (.4) and none i n Group (.3). Thus i t can be seen t h a t the scores obtained on these measures do not r e l a t e to the speech per c e p t i o n performance. However, i n the case of the c o g n i t i v e (memory) score, subjects i n Group (1) achieved an average l e v e l of 5.0, whereas the average was 7.2, 7.5, and 8.3 r e s p e c t i v e l y f o r the other 3 groups. A t - t e s t was done, comparing c o g n i t i v e scores obtained by subjects i n Group (1) to those i n Group ( 4 ) , but the r e s u l t a n t t_ was not s i g n i f i c a n t (t_ = 2. 558, p_ > .05). Since the number of subjects i n each group i s q u i t e s m a l l , and since the v a r i a b i l i t y i n scores on a s i n g l e c o g n i t i v e measure i s l i m i t e d , i t i s not s u r p r i s i n g t h a t s i g n i f i c a n t r e s u l t s were not obtained. However, the l a r g e d i f f e r e n c e between the means f o r these two groups provides t e n t a t i v e encouragement f o r the hypothesis that a c e r t a i n l e v e l of "remembering events over time" may be necessary f o r the s t r u c t u r i n g of l a n g u a g e - s p e c i f i c phonemic c a t e g o r i e s . Since the data ace not con-c l u s i v e , i t i s e q u a l l y p o s s i b l e t h a t cumulative experience can account f o r the age s p e c i f i c d e c l i n e . Furthermore, i t i s p o s s i b l e t h a t both speech perception performance and c o g n i t i v e a b i l i t y were changing as 89 a r e s u l t of maturation, and cannot be c a u s a l l y l i n k e d . This experiment needs t o be repeated w i t h a l a r g e r sample, and w i t h a d d i t i o n a l measures of memory development (such as i n Kagan £ Hamburg, 1981) and c a t e g o r i z a -t i o n (such as i n Sherman, 1981; S t r a u s s , 1979). I t would be u s e f u l t o i n c l u d e c o g n i t i v e tasks that should a l s o be improving as a f u n c t i o n of maturation, but which should not n e c e s s a r i l y be r e l a t e d t o speech per-c e p t i o n . Causal r e l a t i o n s h i p s can only be supported by showing that some c a p a c i t i e s p r e d i c t performance and others do not. Since the babbling recorded i n the l a b o r a t o r y was not a s u f f i c i e n t sample, i t might be i n f o r m a t i v e to c o l l e c t b e t t e r samples of v o c a l output ( i n -home r e c o r d i n g s ) , and again compare the data t o speech pe r c e p t i o n performance. Experiment IV Experiments I - I I I , together w i t h e a r l i e r work (Werker et. a l . , 1981) suggest t h a t i n f a n t s can d i s c r i m i n a t e sounds according t o phonetic category without s p e c i f i c l i n g u i s t i c or " t u n i n g " experience, and t h a t there i s a d e c l i n e i n t h i s a b i l i t y across age t h a t i s evident by the end of the f i r s t year of l i f e . However, the a v a i l a b l e data do not shed any l i g h t on why such tuning occurred, nor can they account f o r the .curious f i n d i n g i n Experiment I showing the very poor performance of the 4- years olds on the H i n d i v o i c i n g c o n t r a s t r e l a t i v e t o the 8 and 12 year o l d s . The next three experiments were designed to explore whether the observed d e c l i n e i s a f u n c t i o n of s p e c i f i c sensory l o s s or the r e s u l t of a more g e n e r a l , c o g n i t i v e / p e r c e p t u a l r e o r g a n i z a t i o n . The f i r s t of these was designed to explore whether the d e c l i n e 90 i n non-native phonemic c a t e g o r i z i n g i s based on a f u n c t i o n a l l o s s of auditory d i s c r i m i n a t i o n , or whether the observed d e c l i n e depends more on the relevance of the t e s t i n g c o n d i t i o n . That i s , are non-native speakers q u i t e incapable of d i s c r i m i n a t i n g these c o n t r a s t s , or do they simply f a i l t o d i s c r i m i n a t e them i n a c a t e g o r i z i n g format? To explore t h i s question, a d u l t s were given 34 t r a i n i n g t r i a l s and then t e s t e d i n a same-different (AX) d i s c r i m i n a t i o n task with only 500 msec between sounds. The t r a i n i n g and shortened i n t e r v a l between sounds were introduced t o optimize t e s t i n g c o n d i t i o n s i n order t o determine i f the subjects s t i l l had the sensory c a p a b i l i t i e s to d i s t i n g u i s h the sounds,in both the H i n d i and Thompson place of a r t i c u l a t i o n c o n t r a s t s . METHOD Ten E n g l i s h a d u l t s u b j e c t s , 5 males and 5 females, were t e s t e d . They were r e c r u i t e d from the students and f a c u l t y i n the Psychology Department at UBC. Both the H i n d i (/ta//ta/) and the Thompson ( / k i / / q i / ) . (as described i n Experiments I and I I ) c o n t r a s t s were set up on tapes f o r : use i n the AX task.. Within t r i a l s , the sounds were separated by 500 msec of s i l e n c e . There were 2500 msec of s i l e n c e between t r i a l s . Subjects were t e s t e d i n an AX paradigm to determine i f , i n comparing only two sounds, they could d i s c r i m i n a t e the non-native sounds according to phonetic category b e t t e r than chance. The AX paradigm i s considered t o be one of the most s e n s i t i v e proceudres f o r y i e l d i n g d i f f i c u l t ( i . e . , w i t h i n category) speech d i s c r i m i n a t i o n s (Carney, et. a l . , 1977; P i s o n i , A s l i n , Perey, £ Hennessy, 19 79; P i s o n i £ Tash, 1974; Repp, i n press) because i t makes very low demands on memory and because i t f o r c e s the subject to make a choice each t r i a l . Four exemplars of each H i n d i sound and 3 of each Thompson sound were used. The d i f f e r e n t p o s s i b l e p a i r i n g s of sounds were presented to the subjects i n v a r y i n g order. For each c o n t r a s t , subjects were i n s t r u c t e d to l i s t e n t o the sounds f o r 4 blocks of 34 t r i a l s . In the f i r s t block of 34 t r i a l s , s ubjects were given a score sheet which showed whether each t r i a l contained 2 exemplars from the same phonetic category (S) or ex-emplars from 2 d i f f e r e n t phonetic c a t e g o r i e s (D). Subjects then l i s t e n e d to the p a i r s of sounds and noted whether each p a i r contained 2 sounds that were from the same or from a d i f f e r e n t phonetic category. Follow-ing t h i s , s u bjects heard 3 blocks of 34 t r i a l s each, and were i n s t r u c t e d to mark an "S" or a "D" a f t e r each t r i a l on the score sheet t h a t was provided (as i n Repp, 1981b). A l l 10 subjects were t e s t e d on both con-t r a s t s w i t h order of t e s t i n g counterbalanced across s u b j e c t s . Subjects were given a 10 minute break half-way through the t e s t s e s s i o n . In t o t a l , the 3 blocks of 34 t r i a l s of the H i n d i c o n t r a s t had 53% Same t r i a l s and 47% D i f f e r e n t t r i a l s . The 3 blocks of Thompson t r i a l s had 46% Same t r i a l s and 54% D i f f e r e n t . RESULTS AND DISCUSSION An A' score was computed from the p r o p o r t i o n of c o r r e c t (D) r e -sponses and the p r o p o r t i o n of i n c o r r e c t (D) responses f o r each subject on both c o n t r a s t s . The A' procedure i s a non-parametric analogue of D', and i s used to approximate the area under a curve when informat i o n necessary t o d e r i v e an ROC ( r e c e i v e r operating curve) i s not a v a i l a b l e . A' y i e l d s a value, between .5 and 1, where .5 represents chance performance and 1 repre-sents p e r f e c t performance, ( f o r a f u r t h e r d i s c u s s i o n of A' see Gescheider, 1976 and G r i e r , 1971). The average A' score f o r the 10 subjects on the H i n d i contrast was .867, and .8774: on the Thompson c o n t r a s t . A f t e r computing the A' v a l u e s , a s e r i e s of u n i v a r i a t e T-tests was done comparing the mean A' t o a h y p o t h e t i c a l mean of .5 (Glass £ Stanley, 1970) t o determine i f subjects performed b e t t e r than would be p r e d i c t e d by chance. The o v e r a l l T-score obtained was s i g n i f i c a n t f o r both non-English c o n t r a s t s . In the case of the H i n d i c o n t r a s t , t_ = 3.37, p_ < .01; and i n the case of the Thompson--contrast t =12.001 p < .001. A T-test comparing the A' means between the two.non-native c o n t r a s t s d i d not y i e l d a s i g n i f i c a n t r e s u l t Ct_ = .039; p_ > .05), suggesting that performance of the subjects was comparable on the two c o n t r a s t s . Data were then analyzed i n terms of p a i r - w i s e comparisons t o determine i f c o r r e c t responses t o same t r i a l s c o n t a i n i n g 2 i d e n t i c a l (as opposed t o 2 d i f f e r e n t ) exemplars o f the same sound were elevated r e l a -t i v e to other responses (see Figure 12). Wi t h i n category comparisons are broken down i n t o I d e n t i c a l ( i . e . comparing a token w i t h i t s e l f ) and Same (comparing token with another token of the same phoneme) f o r each of the sounds. A l l the d i f f e r e n t between-category ( D i f f e r e n t ) p a i r i n g s are presented. A l l p o s s i b l e combinations were t e s t e d on the / k i / / q i / c o n t r a s t , but only 13 of the. 16 p o s s i b l e p a i r i n g s were t e s t e d on the / t a / / t a / c o n t r a s t . As can be seen i n Figure 12, performance on only one p a i r i n g ( R e t r o f l e x 2 vs. Dental 3) was d i f f e r e n t than the others. In a l l other eases, performance across the p o s s i b l e combinations was com-parable. This shows th a t the r e s u l t s i n the a n a l y s i s were not the f u n c t i o n of su p e r i o r performance on a few s e l e c t p a i r i n g s . That i s , performance.on almost a l l p a i r i n g s was e q u a l l y good. Although the r e s u l t s from the T-tests performed on the A' scores c l e a r l y suggest that subjects can d i s c r i m i n a t e these c o n t r a s t s b e t t e r than chance, i t could be argued t h a t these r e s u l t s are not d i r e c t l y com-parable to those obtained i n our previous experiments. To render the a n a l y s i s more comparable, an 8 out of 10 c o r r e c t response to change (D) 93 FIGURE 12 PROPORTION OF SUBJECTS RESPONDING CORRECTLY IN THE SAME/DIFFERENT (AX) PROCEDURE 100 90 80 70 60 50 40 30 20 10 -GLOTTALLIZED VELAR/UVULAR CONTRAST C/Si//qi/) SAME PHONEME r DIFFERENT PHONEME A J L J 1 I L J L ki = K q.i = Q NON-IDENTICAL IDENTICAL TOKENS TOKENS NONIDENTICAL TOKENS Q Q O Q KI Q l KI KI Q2 Q3 K2 Q i K2 K2 K3 Q2 Q3 Q l PAIRWISE COMPARISONS K3 K3 Q2 Q3 100 90 80 70 60 50 40 30 20 10 RETROFLEX/DENTAL CONTRAST ( / t o / A , / ) SAME PHONEME r _ l _ J i_ DIFFERENT PHONEME NON-IDENTICAL IDENTICAL TOKENS TOKENS R D R D RI R D R D DI NONIDENTICAL TOKENS RI D2 RI D3 R2 DI R2 D3 R2 D4 R3 DI R3 D2 R3 D3 R3 D4 R4 DI R4 D2 R4 D3 PAIRWISE COMPARISONS 94 t r i a l s was a p p l i e d t o these data. That i s , i f subjects c o r r e c t l y responded "D" t o at l e a s t 8 out of 10 "D" t r i a l s In a row with no more than e i t h e r 2 f a l s e p o s i t i v e s or misses, they were scored as having reached c r i t e r i o n . Even with t h i s c o r r e c t i o n , however, the frequency of change t r i a l s was not comparable between the two procedures. Change t r i a l s occurred on approximately 50% of the t r i a l s i n the AX procedure, and only every 6-20 tokens i n the button-press procedure. In t h i s a n a l y s i s , 6 out of 10 subjects reached c r i t e r i o n on the H i n d i c o n t r a s t , while 9 out of 10 d i d so on the Thompson c o n t r a s t . The performance i n the AX procedure was s i g n i f i c a n t l y d i f f e r e n t from the performance i n the button-press v e r s i o n of the HT procedure i n the case of both c o n t r a s t s (x2 = 3.956; p_ < .05 f o r the H i n d i c o n t r a s t and x2 = 7.407; p_ < .01 f o r the Thompson c o n t r a s t ) . The mean number of t r i a l s t o c r i t e r i o n f o r those 6 subjects who passed the H i n d i c o n t r a s t was 8.2, while i t was 19.1 f o r the 9 subjects who passed the Thompson c o n t r a s t . Both these means were lower than the 25 t r i a l s allowed f o r adult subjects i n Werker et a l . , 1981 and i n Experiment I I . Thus i t cannot be argued t h a t subjects were given more t r i a l s t o reach c r i t e r i o n i n t h i s study. These r e s u l t s s t r o n g l y suggest that the d e c l i n e i n the a b i l i t y to d i s c r i m i n a t e non-native c o n t r a s t s that was evident i n the e a r l i e r experiments was not due t o a f u n c t i o n a l l o s s i n d i s c r i m i n a t o r y a b i l i t i e s . Subjects performed s i g n i f i c a n t l y b e t t e r than p r e d i c t e d by chance i n the AX procedure, and s i g n i f i c a n t l y b e t t e r than they d i d i n the adult v e r s i o n of the HT procedure. Nevertheless, although the two s t u d i e s are not d i r e c l y comparable, t h i s experiment shows that adult subjects can d i s c r i m i n a t e the phonetic d i f f e r e n c e between the non-English c o n t r a s t s under optimal t e s t i n g c o n d i t i o n s . 95 Experiment V The r e s u l t s of previous experiments suggest t h a t the d e c l i n e i n cross-language speech per c e p t i o n may not i n v o l v e a f u n c t i o n a l sensory l o s s s i n c e subjects can d i s c r i m i n a t e those sounds i n the same/different (AX) procedure t h a t was employed. However, the a b i l i t y t o d i s c r i m i n a t e p a i r s of sounds does not a i d i n the processing of n a t u r a l language. One unique aspect of speech processing i s that a l i s t e n e r recognizes and c a t e g o r i z e s d i f f e r e n t r e p e t i t i o n s of a. sound as the same phoneme rega r d l e s s of speaker v a r i a t i o n , i n t o n a t i o n contour, p o s i t i o n i n the u t t e r a n c e , e t c . Thus to be able to use speech d i s c r i m i n a t o r y a b i l i t i e s f o r understanding language, subjects have to be able t o show at l e a s t a rudimentary a b i l i t y to c a t e g o r i z e the sounds. Although subjects d i d not e x h i b i t t h i s a b i l i t y i n Werker e t . a l . (1981) and i n Experiments I - I I I , i t could be argued that they may have shown such an a b i l i t y i f t e s t i n g c o n d i t i o n s had been somewhat d i f f e r e n t . For i n s t a n c e , i n the modified HT procedure not only were m u l t i p l e n a t u r a l tokens used, but i n a d d i t i o n , the subjects were f a m i l i a r i z e d t o the paradigm by being r e q u i r e d to d i s t i n g u i s h ari E n g l i s h c o n t r a s t , /ba//da/ according to phonemic category. Such a task may have r e s u l t e d i n subjects l i s t e n i n g f o r d i f f e r e n c e s they were f a m i l i a r w i t h i n t h e i r own langu-age, and ignoring d i f f e r e n c e s they would otherwise be able t o d i s c r i m -i n a t e . Thus l i s t e n i n g to /ba//da/ f i r s t may have predisposed, or "primed" subjects t o adopt a native-language phonemic perc e p t u a l s t r a t e g y . Extensive research has been done on the e f f e c t of p e r c e p t u a l set manipulations ( o f t e n r e f e r r e d t o as "priming", " i n s t r u c t i o n a l s e t " , 96 and sometimes discussed w i t h regard t o " s e l e c t i v e a t t e n t i o n " ) over the l a s t 65 years. In g e n e r a l , t h i s research has supported the n o t i o n that i f s p e c i f i c i n s t r u c t i o n s or even s u b t l e d i s t r a c t o r s are used t o predispose subjects t o attend to p a r t i c u l a r dimensions of a complex mult i d i m e n s i o n a l s t i m u l u s , awareness o f the unemphasized dimensions w i l l d e c l i n e r e l a t i v e t o t h a t of the emphasized c h a r a c t e r i s t i c s ( c f . Bruner, 1957; Haber, 1966; N e i s s e r , 1967, 1976; Rosenthal, 1966; Toche 6, Shulte, 1961). Of p a r t i c u l a r s i g n i f i c a n c e i s recent work examining the e f f e c t of p e r c e p t u a l set on d i s c r i m i n a t i o n of ambiguous sounds which has y i e l d e d data showing that such manipulations can a l t e r performance i n speech perception t a s k s . When l i s t e n e r s hear sounds that are ambigu-ous, i . e . not c l e a r l y speech or non-speech, they have been shown to d i s c r i m i n a t e those sounds according t o phonetic category i f they hear them as speech. However, i f the l i s t e n e r s t h i n k those same ambiguous sounds are not speech, the phoneme boundary e f f e c t i s not evident ( B a i l e y , Summerfield, Dorman, 1977; Best, et. a l . , 1981; Liberman, et. a l . , 1981; Repp, 1981b). Hearing the sounds as speech y i e l d s a "phonetic" type of p e r c e p t i o n , and hearing them as non-speech y i e l d s an " a c o u s t i c " type of perception. I t could be argued t h a t i n our previous experiments per c e p t u a l set may have predisposed E n g l i s h subjects t o c a t e g o r i z e according to known phonemic boundaries causing them t o f a i l t o attend t o d i s t i n g u i s h a b l e a c o u s t i c or phonetic i n f o r m a t i o n . To examine t h i s p o s s i b i l i t y , a d u l t s were t e s t e d 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 the H i n d i and Thompson place of a r t i c u l a t i o n c o n t r a s t s a f t e r being predisposed to s e v e r a l d i f f e r e n t perceptual set c o n d i t i o n s . In t h i s endeavour, a d u l t s were f i r s t r e q u i r e d to perform d i s c r i m i n a t i o n tasks which required,.-ej=ther a c o u s t i c and/or -phonetic perceptual s t r a t e g i e s . 97 Following t h i s "priming" they were then r e q u i r e d to d i s c r i m i n a t e the Thompson and H i n d i c o n t r a s t s according t o phonemic category. METHOD Subj ects Seventy ad u l t s u b j e c t s , a l l students and f a c u l t y i n the Depart-ment of Psychology at UBC, were t e s t e d i n t h i s study. Care was taken t o ensure that no subject' spoke a language d i f f e r e n t i a t i n g one of the c o n t r a s t s i n question, and that they were naive as t o the hypotheses. Procedure and S t i m u l i In t h i s experiment, subjects were t e s t e d 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 m u l t i p l e n a t u r a l tokens of the non-native sound c o n t r a s t s according t o phonemic category under d i f f e r e n t p e r c e p t u a l set condi-t i o n s . The four experimental c o n d i t i o n s were chosen to predispose subjects to employ e i t h e r a (1) native-language phonemic,an (2) a c o u s t i c c a t e g o r i z i n g , a (3) s i n g l e - t o k e n phonetic, or a (4) w i t h i n category v o c a l i c perceptual s t r a t e g y . These experimental "priming" c o n d i t i o n s corresponded t o the f i r s t s e v e r a l minutes of d i s c r i m i n a t i o n t e s t i n g . In p e r c e p t u a l set c o n d i t i o n ( 1 ) , 20 subjects were t o l d they would be p a r t i c i p a t i n g i n a speech perception experiment. They were 3 The use of the l a b e l s a c o u s t i c and phonetic i s somewhat mis-l e a d i n g s i n c e the a c o u s t i c tokens c o n t a i n phonetic i n f o r m a t i o n since they are taken from the f i r s t 40 msec of speech sounds. In a d d i t i o n , the phonetic tokens could be d i f f e r e n t i a t e d by the use of an a c o u s t i c s t r a t e g y since only s i n g l e tokens are used. However, si n c e subjects reported the " a c o u s t i c " tokens to be non-speech and the "phonetic" tokens to be very short speech sounds, the l a b e l s w i l l be kept. 98 given i n s t r u c t i o n s to l i s t e n c a r e f u l l y t o two speech sounds taken from English,./ba/ and /da/, and t o push the button whenever the sound changed from one category ( i . e . , ba) to the other ( i . e . , da). -Subjects were t o l d t h a t a f t e r d i s c r i m i n a t i n g the E n g l i s h sounds, they would be asked to d i s c r i m i n a t e sounds from a f o r e i g n language t h a t are not used i n E n g l i s h . Ten subjects were t e s t e d on /ba//da/ and then t e s t e d on the H i n d i c o n t r a s t / t a / / t a / . Ten d i f f e r e n t subjects were t e s t e d on the Thompson con t r a s t / k i / / q i / a f t e r f i r s t being t e s t e d on /ba//da/. They were I n s t r u c t e d t o push the button when the sound changed from one category to another. In the a c o u s t i c c a t e g o r i z i n g set c o n d i t i o n ( 2 ) , 20 subjects were f i r s t r e q u i r e d to d i s c r i m i n a t e m u l t i p l e n a t u r a l exemplars of the e j e c t i v e p o r t i o n (the burst and a s p i r a t i o n ) , of g l o t t a l i z e d v e l a r ( K i ) , and g l o t t a l i z e d u v u l a r ( q i ) stop consonants. Since these sounds are g l o t t t a l i z e d , there i s a n a t u r a l d i s c o n t i n u i t y i n the wave form which makes i t p o s s i b l e to separate and r e - r e c o r d the e j e c t i v e segment alone. As such, the e j e c t i v e p o r t i o n of these sounds does not resemble speech at a l l ; r a t h e r , i t resembles c l i c k s or drops of water. Although some v o c a l i c i n f o r m a t i o n must have been, provided i n the a n t i c i p a t o r y g l o t t a l a r t i c u l a t i o n s because of c o a r t i c u l a t i o n e f f e c t s , no vowel can be heard In these sounds. The i n s t r u c t i o n s f o r set 2 were somewhat d i f f e r e n t than set 1. In set 2, subjects were asked to p a r t i c i p a t e i n a sound d i s c r i m i n a t i o n study. They were t o l d they would hear drops of water f a l l i n g i n t o buckets of two d i f f e r e n t s i z e s and were i n s t r u c t e d t o press the button when the drops f e l l i n t o a d i f f e r e n t bucket. Subjects were t o l d t h a t a f t e r hearing the drops, they would hear longer sounds and were asked 99 to press the button when these longer sounds changed as they had with the drops of water. Ten subjects were t e s t e d on the "drops of water" f o l l o w e d by the H i n d i c o n t r a s t , and 10 d i f f e r e n t s ubjects were t e s t e d on the Thompson co n t r a s t a f t e r being "primed" with the "drops of water". The wave form of a c h a r a c t e r i s t i c exemplar of each of these sounds i s shown i n Figure 1!3. As can be seen, these sounds are very short i n d u r a t i o n , w i t h both the amplitude and the d u r a t i o n of the burst being greater f o r /q/ than f o r /k/. The p e r i o d i c i t y preceding the burst i s longer f o r /k/. In the phonetic set c o n d i t i o n ( 3 ) , subjects were r e q u i r e d t o d i s c r i m i n a t e a s i n g l e truncated v e r s i o n of a n a t u r a l l y produced H i n d i r e t r o f l e x sound / t a / from a s i n g l e truncated H i n d i d e n t a l sound./ta/. The r a t i o n a l e f o r only "using Jthe B u r s t / T r a n s i t i o n i s not immediately apparent. Although c o n t e x t u a l i n f o r m a t i o n ( v o c a l i c segment) aids i n 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 f o r n a t i v e speakers, i t may mask p o t e n t i a l l y important cues f o r non-native speakers. Since research has shown that t r a i n e d subjects can d i s c r i m i n a t e and i d e n t i f y not only the consonant, but a l s o the f o l l o w i n g vowel from only 10-20 msec of sound (Blumstein £ Stevens, 1980) i t was f e l t t hat t h i s k i nd of phonetic priming could help subjects attend t o the r e l e v a n t cues i n the d i s c r i m i n a t i o n task. The sounds we used corresponded t o the f i r s t - 4-0 msec of the / t a / / t a / tokens. (See Figure -5) In t h i s p e r c e p t u a l set c o n d i t i o n , subjects were i n s t r u c t e d t o l i s t e n very c a r e f u l l y t o a s e r i e s of very short sounds, and to press a button whenever the sound changed. They were t o l d t h a t , f o l l o w i n g t h i s , they would hear longer sounds and should again press the button when the sounds changed. Ten subjects were t e s t e d on the truncated FIGURE 13 Waveform o f the e j e c t i v e po r t i on of the Thompson g l o t t a l i z e d velar/uvular c o n t r a s t Time i n msec • , , . . , '..,.. 0 10 20 30 40T 50 60 70 80 90 g l o t t a l i z e d uvu la r / q i / 101 / t a / / t a / and then on the m u l t i p l e n a t u r a l exemplars of the f u l l s y l l a b l e s / t a / / t a / . Ten d i f f e r e n t subjects were f i r s t t e s t e d on the truncated / t a / / t a / f o i l e d by /£i//qi/. In the w i t h i n category v o c a l i c p e r c e p t u a l set 04), subjects were r e q u i r e d t o d i s c r i m i n a t e a s i n g l e p e r i o d i c p o r t i o n from / k i / (the / i / p o r t i o n ) from a s i n g l e p e r i o d i c p o r t i o n from / q i / (.the / i / p o r t i o n ) . The waveform f o r the / i / p o r t i o n s i s shown i n the l a s t 260 msec of Figure 8. (Because of c o a r t i c u l a t i o n e f f e c t s , some subjects thought they heard an "h" consonant at the beginning of these sounds.) I n s t r u c -t i o n s were s i m i l a r t o perceptual set Co n d i t i o n ( 3 ) . Subjects were only t e s t e d on / k i / and / q i / f o l l o w i n g t h i s priming c o n d i t i o n . A l l subjects were t e s t e d i n the adult (button-press) v a r i a t e of the HT procedure. C r i t e r i o n f o r reaching or not reaching c r i t e r i o n was the same as described i n Experiment I I . RESULTS AND DISCUSSION The number of subjects reaching c r i t e r i o n (YES) or not reaching c r i t e r i o n (NO) i n the priming and i n the t e s t i n g phases i s presented i n Table 11 f o r the 4 perc e p t u a l set c o n d i t i o n s . To t e s t f o r the. e f f e c t of priming, an a n a l y s i s o f proport i o n s was a p p l i e d to the data c o l l e c t e d under each perceptual set c o n d i t i o n f o r each c o n t r a s t . The a n a l y s i s was not s i g n i f i c a n t i n the case of e i t h e r the H i n d i (/ta//ta/) contrast (p_ = .999) or the Thompson con-t r a s t (p_ = .910), showing t h a t priming c o n d i t i o n s d i d riot a f f e c t performance. Subjects performed po o r l y on the d i s c r i m i n a t i o n task r e g a r d l e s s of perceptual set manipulations. 102 Table 12 Performance on Priming and Tes t i n g Phases•in Perceptual Set Conditions - .Condition 1(A) Reached C r i t e r i o n /Ba/ /Da/ YES NO 10 0 / t a / / t a / 1 9 Condition 1('.B) /Ba/ /Da/ / k i / / q i / 10 0 YES NO Condi t i o n 2(A) B / k i / / q i / / t a / / t a / Condi t i o n 2(B) B / k i / / q i / / k i / / q i / 10 0 YES NO Condition 3(A) BT/ta/ta/ / t a / / t a / Condition 3(B) JT/ta/ / t a / / k i / / q i / YES NO Condition 4 P e r i o d i c / i / / i / / k i / / q i / 9 2 1 8 103 In the priming c o n d i t i o n s (2) and (4), subjects were r e q u i r e d to d i s c r i m i n a t e the two p o r t i o n s of the t o t a l / l e i / / q i / s y l l a b l e s . In order to determine the r e l a t i v e d i s c r i m i n a b i l i t y of the p o r t i o n s as compared t o the e n t i r e s y l l a b l e , r e s u l t s from the 40 subjects who were t e s t e d on / k i / / q i / were pooled, and compared t o the 20 subjects t e s t e d on the B p o r t i o n of / R i / / q i / ( C o n d i t i o n 2) and t o the 10 sub-j e c t s t e s t e d on the p e r i o d i c / i / p o r t i o n of /J c i / / q i / ( C o n d i t i o n 4). An a n a l y s i s of proportions showed there t o be s i g n i f i c a n t d i f f e r e n c e s between those groups (x2 = 54.9 59; p < .001:).., To determine which groups d i f f e r e d , a s e r i e s of m u l t i p l e comparisons was done. Perform-ance on the whole s y l l a b l e was s i g n i f i c a n t l y poorer than performance on e i t h e r of the p o r t i o n s o f the s y l l a b l e . That i s , subjects could d i s c r i m i n a t e both p o r t i o n s of the Thompson contrast when presented i n i s o l a t i o n , however, they could not d i s c r i m i n a t e the contrast when the two p a r t s were presented together as a complete s y l l a b l e . The r e s u l t s support our e a r l i e r f i n d i n g s i n both the adult v a r i a t e of the HT procedure (Werker, e t . a l . , 1981 and Experiments I and I I ) and the same/different (Experiment IV) procedures. That i s , subjects have the sensory a b i l i t y t o d i s c r i m i n a t e the phonetic con-t r a s t s , but they cannot use th a t a b i l i t y when r e q u i r e d to perform i n a l i n g u i s t i c a l l y r e l e v a n t c a t e g o r i z i n g procedure. These r e s u l t s negate the p o s s i b i l i t y t h a t our e a r l i e r r e s u l t s evidencing a d e c l i n e were the outcome of confusing demand c h a r a c t e r i s t i c s . Rather, i t seems t h a t subjects maintain the a b i l i t y (which i s evident i n e a r l y infancy) t o d i s c r i m i n a t e the u n i v e r s a l set of phonetic c o n t r a s t s . However, i n the course of l e a r n i n g and speaking a p a r t i c u l a r language, l i s t e n e r s c o n s t r u c t r a t h e r r i g i d phonemic categ o r i e s which a i d them i n 104 segmenting and understanding the sp;eech stream of t h e i r n a t i v e language. These phonological categories t h a t organize and -const-rain speech percep-t i o n are evident i n t e s t i n g procedures which m i r r o r n a t u r a l language ( c o n t i n u i n g v a r i a t i o n s i n r e p e t i t i o n s of a s i n g l e u t t e r a n c e ) . However, when t e s t i n g procedures are used t h a t are l e s s s i m i l a r t o n a t u r a l language p r o c e s s i n g , the sensory-based phonetic d i s c r i m i n a t i o n a b i l i t i e s are evident. SUMMARY OF RESULTS The r e s u l t s from these experiments and t h e i r r e l a t i o n s h i p t o e x i s t i n g models of perc e p t u a l development and speech perception t h e o r i e s w i l l be considered i n the Dis c u s s i o n . The major conclusions from these data t h a t w i l l have t o be considered are: (1) There are p h o n e t i c a l l y r e l e v a n t perceptual p r e d i s p o s i t i o n s i n the i n f a n t . (Experiments I I and I I ) (2) There i s a d e c l i n e across age, which i s evident by age 4 i n the a b i l i t y t o d i s c r i m i n a t e the u n i v e r s a l set of phonetic c o n t r a s t s . (Experiment I) (3) This d e c l i n e appears to occur during the f i r s t year of l i f e . (Experiment I I I ) (4) Phonemically r e l e v a n t phonetic perception can be d i f f e r -e n t i a t e d from u n i v e r s a l phonetic p e r c e p t i o n . (Experiments IV and V) (5) C o g n i t i v e processes may be r e l a t e d t o speech perception performance. (Experiment V and.possibly I I I C ) 105 DISCUSSION In the f o l l o w i n g general d i s c u s s i o n , the main f i n d i n g s from the f i v e experiments w i l l be discussed i n r e l a t i o n t o previous r e s e a r c h and to t h e o r e t i c a l i s s u e s . I t seems evident from our r e s u l t s that young i n f a n t s are able to d i s c r i m i n a t e most speech c o n t r a s t s according to phonetic category without s p e c i f i c experience. This i s c o n s i s t e n t w i t h a wide body of data which has been c o l l e c t e d over the l a s t decade (see Table 3 ). Several researchers i n the area o f i n f a n t speech perception have suggested that the i n f a n t data may be explained by an e v o l u t i o n a r y match between the production ( a r t i c u l a t o r y ) domain and the perc e p t u a l ( a u d i t o r y ) domain ( c f . , Kuhl, 1979; P i s o n i , 1979), and th a t human languages have evolved i n p a r a l l e l with the a r t i c u l a t o r y and perc e p t u a l systems (Jusczyk, P i s o n i , Walley, £ Murray, 1980; Stevens, 1975). The above researchers suggest that the r e s u l t a n t p e r c e p t u a l c o n s t r a i n t s predispose the human i n f a n t t o respond d i f f e r e n t i a l l y t o c e r t a i n a c o u s t i c combinations. Because of the p a r a l l e l e v o l u t i o n of language and s t r u c -t u r e , i t i s suggested that the most s e n s i t i v e regions of a u d i t o r y d i s -c r i m i n a b i l i t y should correspond to (among others) t r a n s i t i o n p o i n t s that have been used to convey meaning d i f f e r e n c e s i n n a t u r a l languages (Jusczyk, i n press; P i s o n i , 1979). Several arguments regarding e v o l u t i o n a r y theory can be brought to bear on t h i s i s s u e . According t o the models o u t l i n e d above, an ev o l u t i o n a r y model i s assumed i n which changes i n one system (a u d i t o r y ) would have e f f e c t s i n other ( a r t i c u l a t o r y ) systems. According t o Rozin (1976), however, a s p e c i f i c model of e v o l u t i o n a r y change wherein 106 changes th a t occur i n one system do not n e c e s s a r i l y occur i n other systems i s proposed as being both more economical and e f f i c i e n t than a g e n e r a l i z e d model. Rozin argues that s p e c i f i c s u r v i v a l needs (e.g. the need t o communi-cate) f u n c t i o n t o pressure changes th a t have r a m i f i c a t i o n s at a l l l e v e l s w i t h i n a p a r t i c u l a r subsystem, (e.g. the language system) but do not neces-s a r i l y have e f f e c t s on other systems. Many speech researchers (Studdert-Kennedy, e t . a l . , 1970) apply such an argument t o human speech, and suggest that i n f a n t speech per c e p t i o n shows s p e c i a l i z e d language processing. Although there i s e m p i r i c a l evidence t o support a s p e c i f i c l i n g u i s t i c subsystem i n a d u l t s , such evidence has not been provided i n the case of i n f a n t s . Without such evidence, i t i s not p o s s i b l e t o con-clude whether i n f a n t perception i s s p e c i f i c a l l y , l i n g u i s t i c . Rather i t i s l o g i c a l l y p o s s i b l e t h a t a l i n g u i s t i c subsystem (1) be i n n a t e l y provided, (2) be i n n a t e l y g i v e n , but r e q u i r e s p e c i f i c experience to become func-t i o n a l , (3) could develop as a r e s u l t of l i n g u i s t i c experience and p e r c e p t u a l / c o g n i t i v e development. Further research i s needed t o determine which of these p o s s i b i l i t i e s i s most l i k e l y . The second c o n c l u s i o n that can be drawn from these f i v e e x p e r i -ments i s t h a t there i s a d e c l i n e i n the a b i l i t y t o d i s c r i m i n a t e non-n a t i v e p l a c e - o f - a r t i c u l a t i o n c o n t r a s t s by the end of the f i r s t year of l i f e . This i s c o n s i s t e n t w i t h the p r e d i c t i o n s made by A s l i n £. P i s o n i ' s u n i v e r s a l theory (1980a), and those made by both Morse (1978) and Werker and c o l -leagues, (1981). However, i t i s I n c o n s i s t e n t w i t h the p r e d i c t i o n s proposed by E i l e r s , e t . a l . , 1979. In support of t h e i r viewpoint., 1 E i l e r s and c o l -leagues have provided evidence that s p e c i f i c l i n g u i s t i c experience i s r e q u i r f o r i n f a n t s aged 6-8 months to be able t o d i s c r i m i n a t e v o i c i n g c o n t r a s t s i n the l e a d r e g i o n of the VOT continuum ( E i l e r s , e t . a l . , 1977; E i l e r s , e t . a l . , 1979). There are three p o s s i b l e explanations f o r t h i s i n c o n s i s t e n c y which 107 w i l l be discussed: Cl) D i f f e r e n c e s i n the use of the HT procedure, . . (2) formal d i f f e r e n c e s between v o i c i n g and p l a c e - o f - a r t i c u l a t i o n d i s t i n c -t i o n s , (3) a gradual d e c l i n e i n the a b i l i t y to d i s c r i m i n a t e non-native co n t r a s t s over the f i r s t year of l i f e . The key d i f f e r e n c e i n the use of the HT procedure i n the two l a b o r a t o r i e s was the number of t r i a l s t o c r i t e r i o n . In E i l e r s ' work, i n f a n t s were r e q u i r e d to reach c r i t e r i o n w i t h i n 6 t r i a l s , whereas In our work, i n f a n t s were allowed up to 25 change t r i a l s (see Appendix B f o r f u r t h e r c l a r i f i c a t i o n ) . I t i s p o s s i b l e that the E n g l i s h i n f a n t s t e s t e d i n the E i l e r s e t . a l . (.1970) study could have reached c r i t e r i o n i f they had been given an adequate number of t r i a l s . The p o s s i b i l i t y that there may be formal d i f f e r e n c e s between v o i c i n g and place of a r t i c u l a t i o n d i f f e r e n c e s i s supported by other research i n i n f a n t speech perception, (see I n t r o d u c t i o n and Table 3). I t has been shown t h a t i n f a n t s c o n s i s t e n t l y c a t e g o r i z e place c o n t r a s t s but not v o i c i n g c o n t r a s t s . This could be due t o the almost e x c l u s i v e use of VOT as a measure of v o i c i n g d i f f e r e n c e s ; i t could be caused by the increased d i f f i c u l t y of the (lead) VOT boundary ( B u t t e r f i e l d 6 C a i r n s , 1974); or i t could be due t o the l e s s d i s c r e t e nature of the boundaries of v o i c i n g c o n t r a s t s ( W i l l i a m s , 1980) as compared to place c o n t r a s t s . More research i s needed to r e s o l v e t h i s i s s u e . One u s e f u l focus of t h i s proposed research would be t o examine the p e r c e p t i o n of n a t u r a l r a t h e r than s y n t h e t i c tokens. This could c l a r i f y whether the d i f f i c u l t y i n v o i c i n g d i s c r i m i n a t i o n r e s u l t s from using exemplars i n which only VOT v a r i e s ; whether the l e a d v o i c i n g boundary i s a c t u a l l y l e s s p e r c e p t u a l l y s a l i e n t ; or whether d i s c r i m i n a t i o n f u n c t i o n s are a c t u a l l y l e s s d i s c r e t e f o r v o i c i n g d i f f e r e n c e s . 108 D i f f e r e n c e s between the r e s u l t s from these experiments and from E i l e r s ' work w i t h v o i c i n g c o n t r a s t s might be explained by a gradual de-c l i n e i n u n i v e r s a l phonetic perception over the f i r s t year of l i f e . That i s , as a r e s u l t of l i n g u i s t i c experience, i n i t i a l s e n s i t i v i t i e s may become g r a d u a l l y reduced, and i t may take more t r i a l s t o reach c r i t e r i o n on non-native c o n t r a s t s across i n c r e a s i n g age. However, our a n a l y s i s (see Experiment I I I A ) showed no s i g n i f i c a n t d i f f e r e n c e i n number of t r i a l s t o c r i t e r i o n e i t h e r across age or across speech con-t r a s t s , and hence these data do not support the notion of a gradual d e c l i n e . The f i n d i n g that 4-year olds were i n f e r i o r t o o l d e r c h i l d r e n on t h e i r a b i l i t y t o d i s c r i m i n a t e the p e r c e p t u a l l y e a s i e r v o i c i n g c o n t r a s t i s c o n s i s t e n t with the e m p i r i c a l work by Snow £ Hoefnagel-Ho.hle (1977; 1978) but not w i t h t h a t of Cochrane (1977; Cochrane £ Sachs, 1979). Because such d i f f e r e n t procedures and d i f f e r e n t speech c o n t r a s t s were used i n these s t u d i e s , i t i s impossible t o compare r e s u l t s . However, the data reported here are a l s o c o n s i s t e n t with a body of data c o l l e c t e d r e c e n t l y showing that i t may be e a s i e r t o l e a r n a l l aspects of a second language i n l a t e r than i n e a r l i e r childhood (McLaughlin, 1977). The f o u r t h c o n c l u s i o n t h a t can be drawn from the present research i s t h a t speech perception i s organized according t o u n i v e r s a l phonetic c a t e g o r i e s i n i n f a n t s and according t o phonemic categ o r i e s i n adult l i s t e n e r s . Furthermore, t h i s phonemic o r g a n i z a t i o n i s such that the a d u l t l i s t e n e r can only r e l i n q u i s h i t t o employ other p e r c e p t u a l s t r a t e g i e s i n c e r t a i n task c o n d i t i o n s . This work, s i m i l a r to other recent work (Liberman, e t . a l . , 1981; Repp, 1981) suggests t h a t more than one way of processing language sounds i s p o s s i b l e . Although a c o u s t i c and phonetic modes of processing have been proposed p r e v i o u s l y 109 (Wood, 1975; Repp, i n press) t h i s work provides evidence t h a t a f u r t h e r d i f f e r e n t i a t i o n between phonetic and phonemic processing may be r e q u i r e d . The evidence suggests that a d u l t s , when l i s t e n i n g t o speech as speech, d i s c r i m i n a t e the sounds-according to the subset of phonetic d i s -t i n c t i o n s which f u n c t i o n as phonemes i n t h e i r language. That i s , although a d u l t s cannot r e l i a b l y l a b e l non-native v o i c i n g c o n t r a s t s ( L i s k e r £ Abramson, 1970; Singh £ B l a c k , 1966), they can l e a r n t o d i s c r i m i n a t e them according t o category with a minimum (only 25 t r i a l s ) of t r a i n i n g (Werker e t . a l . , 1981). Furthermore, even though a d u l t s could not l e a r n t o c a t e g o r i z e non-native place d i s t i n c t i o n s as e a s i l y as they could the v o i c i n g d i s t i n c t i o n s i n e i t h e r l a b o r a t o r y t r a i n i n g (Werker, e t . a l . , 1981) or n a t u r a l (second language l e a r n i n g ) procedures (Tees £ Werker, 1982), they can d i s c r i m i n a t e the phonetic d i f f e r e n c e i f t e s t e d i n a non-categor-i z i n g procedure with minimal memory demands (Experiment I V ) . I t may be e a s i e r t o r e l e a r n v o i c i n g than place o f a r t i c u l a t i o n , phonetic d i s t i n c t i o n s . F i n a l l y , there i s evidence that, a d u l t s can d i s c r i m i n a t e w i t h i n category a c o u s t i c v o i c i n g d i f f e r e n c e s i f t e s t e d i n s e n s i t i v e psychophysical t a s k s i n which considerable t r a i n i n g i s provided (Samuel, 1977; Shouten, 1980). I t becomes apparent from t h i s quick review that a d u l t s d i s c r i m -i n a t e according t o phonemic, u n i v e r s a l phonetic, or a c o u s t i c parameters depending on the t e s t i n g c o n d i t i o n s . Phonemic c a t e g o r i z a t i o n appears to be the e a s i e s t and the most robust. The t e s t i n g of phonetic d i s -c r i m i n a t i o n which has been so e x t e n s i v e l y r e p o r t e d , has a c t u a l l y i n v o l v e d t e s t i n g p e r c e p t i o n o f phonetic c o n t r a s t s which are phonemic t o the l i s t e n e r s . Thus although i t i s o f t e n claimed that f i n d i n g s from adult speech research support the existence of a s p e c i f i c phonetic processor, we should consider whether i t i s a s p e c i f i c 110 phonetic or a phonemic processor which i s being supported. I t could be argued t h a t the only way to t e s t p u r e l y phonetic (non-phonemic) perception i s through cross-language work, examining perception of phonetic c o n t r a s t s which are not phonemic i n th a t p a r t i c u l a r language. To the extent that a contrast i s phonemic, i t i s p o s s i b l e t h a t consider-able l e a r n i n g has occurred w i t h regard to t h a t c o n t r a s t , r a t h e r than t h a t p e r c e p t i o n r e f l e c t s some s p e c i f i c a l l y l i n g u i s t i c inborn competence. A p o t e n t i a l confound.in any cross-language.research-I s t h a t some phonetic c o n t r a s t s are more widely d i s t r i b u t e d across n a t u r a l languages than others. I t may be th a t those widely d i s t r i b u t e d c o n t r a s t s are e i t h e r "unmarked" fea t u r e s i n the underlying U n i v e r s a l Grammar, or a l t e r n a t i v e l y , t h a t they represent a c o u s t i c combinations which take advantage of p a r t i c u l a r l y s a l i e n t s e n s i t i v i t i e s i n the perce p t u a l system. E i t h e r way, one could argue that such c o n t r a s t s would be e a s i e r f o r a l i s t e n e r t o d i s c r i m i n a t e than l e s s common con-t r a s t s r e g a r d l e s s of s p e c i f i c experience. I f cross-language work i s undertaken i n an attempt to d i f f e r e n t i a t e phonetic from phonemic per-c e p t i o n , i t w i l l be necessary t o examine perception of both widespread and r e s t r i c t e d c o n t r a s t i v e sounds. C e r t a i n l y the two non-English place c o n t r a s t s used i n t h i s research are ra r e across n a t u r a l langu-ages, whereas the v o i c i n g d i s t i n c t i o n i s l e s s r e s t r i c t e d i n i t s d i s t r i b u t i o n (see Ruhlen, 1976). The r e s u l t s from the experiments reported here suggest that phonetic perception i s not as robust as phonemically r e l e v a n t percep-t i o n , but th a t i t can be demonstrated i f proper experimental c o n d i t i o n s are used. Although ad u l t E n g l i s h speakers performed l e s s a c c u r a t e l y than n a t i v e speakers f o r a l l three non-native c o n t r a s t s i n Experiment I I I l l and i n previous research (Werker e t . a l . , 1981), very l i m i t e d t r a i n i n g d i d improve performance In the case o f the H i n d i v o i c i n g c o n t r a s t s , but not i n the case of the place contrast (Werker et. a l . , 1981). How-ever, a l t e r n a t i v e d i s c r i m i n a t i o n tasks (Experiment IV) showed evidence th a t p h o n e t i c a l l y (non-phonemic) based perception was p o s s i b l e . Further-more, i n the priming p o r t i o n of Experiment V, subjects d i s c r i m i n a t e d the truncated p o r t i o n s of the sounds according t o parameters which could c o n t r i b u t e s p e c i f i c a l l y phonetic i n f o r m a t i o n . That i s , although per-c e p t u a l set priming d i d not i n f l u e n c e phonemic c a t e g o r i z a t i o n of f u l l s y l l a b l e s , c a t e g o r i z a t i o n of the Burst p o r t i o n of the Thompson sounds was s u c c e s s f u l l y performed according t o phonetic boundaries, and d i s -c r i m i n a t i o n of s i n g l e tokens of the B u r s t - T r a n s i t i o n p o r t i o n s of the H i n d i place c o n t r a s t was a l s o p h o n e t i c a l l y r e l e v a n t . I t i s c o n s i s t e n t w i t h the above t o note t h a t i n Experiment I , c h i l d r e n aged 8 and 12 years were able t o use non-phonemic, phonetic perc e p t u a l s t r a t e g i e s f o r d i s c r i m i n a t i n g the H i n d i v o i c i n g c o n t r a s t . However, the 4-year-old subjects could only use the phonemic s t r a t e g y . This provides support f o r the ease o f u t i l i z a t i o n h i e r a r c h y p o s i t e d above regarding phonemic, phonetic, and a c o u s t i c d i s c r i m i n a t i o n . The most parsimonious explanation f o r a l l these data would be that cumulative experience f u n c t i o n s to g r a d u a l l y d i m i n i s h d i s c r i m i n -a b i l i t y of non-native c o n t r a s t s , and makes phonemic perception the most a v a i l a b l e . However, s e v e r a l i n c o n s i s t e n c i e s e x i s t which make such an explanation untenable and suggest a c o g n i t i v e explanation. F i r s t , i t i s u s e f u l t o note that many non-phonemic sounds are s t i l l used " a l l o p h o n i c a l l y " i n a language. That i s , although r e t r o f l e x i o n cannot be used to d i f f e r e n t i a t e meaning i n E n g l i s h , E n g l i s h speakers do produce 112 r e t r o f l e x t : , s and d's i n some sound combinations (Ladefoged, 1975). Thus we do continue t o "experience" these sounds, but th a t experience i s not r e l e v a n t t o meaning. Second, a cumulative experience model would p r e d i c t that the d e c l i n e i n the a b i l i t y to d i s c r i m i n a t e non-n a t i v e c o n t r a s t s would occur g r a d u a l l y , but t h i s i s not supported by the a n a l y s i s of t r i a l s t o c r i t e r i o n i n Experiment I I I A . Rather, i t seems t o occur r a t h e r a b r u p t l y i n each i n f a n t between 8 and 12 months of l i f e . T h i r d , adult subjects showed evidence of being able t o use a phonemic or a phonetic k i n d of perception depending upon task c o n d i t i o n s . Results from Experiments IV and V suggested that one ki n d of perception was p a r t i c u l a r t o processing language and the other t o pro c e s s i n g non-language sounds. Some explanation as to why one or the other type of perce p t i o n i s used i n a p a r t i c u l a r context needs to be provided. F i n a l l y , the r e s u l t s from Experiment I showing that 4-year old s cannot use phonetic perception ( e s p e c i a l l y i n the case of the H i n d i v o i c i n g c o n t r a s t ) , even though evidence from ad u l t s t u d i e s shows there has been no l o s s i n sensory d i s c r i m i n a t i o n a b i l i t i e s , i s very hard t o understand using a cumulative experience model. One explanation i s that the c h i l d may have t o a t t a i n a c e r t a i n degree of c o g n i t i v e f l e x i b i l i t y before being able t o switch from one t o the other perceptual mode i n accordance w i t h c o n t e x t u a l s p e c i f i c a t i o n . Futher e l a b o r a t i o n of t h i s w i l l be pro-vided i n the proposed model. Since most e x i s t i n g models o f speech per c e p t i o n are non-developmental, i t i s hard t o r e l a t e the r e s u l t s from these experiments to them. However, an attempt w i l l be made t o r e l a t e the major r e s u l t s to current Issues i n t h e o r i z i n g about perceptual development. Where 113 i t i s r e l e v a n t , the f i n d i n g s w i l l be discussed i n r e l a t i o n to speech perc e p t i o n models. According t o d i f f e r e n t i a t i o n t h e o r i e s of perceptual development, humans are described as becoming i n c r e a s i n g l y able t o d i f f e r e n t i a t e d i s c r e t e p r o p e r t i e s i n the stimulus a r r a y as a r e s u l t of experience with that array i n a v a r i e t y of transformations and contexts (E. Gibson, 1969). Furthermore, i n recent work, (E. Gibson, 1982) developmental explanations of "event" perception (.or "affordance" as described i n the I n t r o d u c t i o n ) are conceived w i t h i n a d i f f e r e n t i a t i o n model of p e r c e p t u a l development. The p r o p o s i t i o n t h a t p e r c e p t i o n , i n g e n e r a l , and speech, i n p a r t i c u l a r , i s organized i n terms of an "event p e r c e p t i o n " model leaves s e v e r a l questions unanswered. Although such a model can ade-quately deal w i t h data from i n f a n t s t u d i e s where i n f a n t s are shown t o d i s c r i m i n a t e v i r t u a l l y a l l phonetic c o n t r a s t s according t o category boundaries without s p e c i f i c experience by c l a i m i n g that the young i n f a n t responds t o the i n v a r i a n t s " a f f o r d e d " by the environment i n a f u n c t i o n a l l y s i g n i f i c a n t (phonetic) manner, such a model cannot account f o r ontogenetic d e c l i n e s . As shown i n the present experiments, i n f a n t s became l e s s able to d i f f e r e n t i a t e some of the d i s c r e t e p r o p e r t i e s i n the perceptual a r r a y as a r e s u l t of experience. In a d d i t i o n , the adult subjects d i f f e r e n t i a t e d more or l e s s of the stimulus array depending on task c o n d i t i o n s ( i . e . , phonemic vs. phonetic p e r c e p t i o n ) . I t i s hard t o appreciate how a d i f f e r e n t i a t i o n model can account f o r the d i f f e r e n t types of speech perception i n adult s u b j e c t s . Although i t could be argued t h a t experience could a i d i n l e a r n i n g t o d i s c r i m i n a t e i n i t i a l l y n o n -discriminable a c o u s t i c changes, i t i s d i f f i c u l t t o understand how 114 i t could f u n c t i o n to render a c o u s t i c , phonetic, or phonemic perception depending on con t e x t u a l s p e c i f i c a t i o n without some form of r e p r e s e n t a t i o n . The data presented i n t h i s t h e s i s may be b e t t e r accounted f o r by a refinement model of perc e p t u a l development wherein i t i s hypothesized that the p e r c e i v e r forms "schemas", and that these schemas guide per-c e p t i o n . Perception then can become l e s s dependent upon the p a r t i c u l a r c h a r a c t e r i s t i c s pf the stimulus array and more dependent upon the expec-t a t i o n s of the p e r c e i v e r . Much of the work showing that l i s t e n e r s respond d i f f e r e n t i a l l y to sounds when they hear them as speech r a t h e r than as non-speech (Best, e t . a l . , 1980; Liberman, e t . a l . , 1981) suggests schema, guided p e r c e p t i o n . The f i n d i n g s presented i n Experiments.IV and V d i f -f e r e n t i a t i n g phonemic from phonetic perception a l s o support such a no t i o n . That i s , given that one r a t h e r than another l e v e l of percep-t i o n f u n c t i o n s i n any s p e c i f i e d c o ntext, i t i s necessary (as argued above) to p o s i t some k i n d of r e p r e s e n t a t i o n . Event perception models cannot account f o r the va r y i n g perceptual o r g a n i z a t i o n of i d e n t i c a l stimulus input under d i f f e r e n t circumstances. Neisser (1976) has attempted t o i n t e g r a t e the c o n t r i b u t i o n s of Gibs'onian and schema-based t h e o r i e s with a h y p o t h e t i c a l "perceptual c y c l e " . In t h i s model, p e r c e p t i o n i s not a l l i n the stimulus a r r a y , nor i s i t a l l i n the expectations of the p e r c e i v e r . Rather, i n t e r n a l schemas f u n c t i o n as a n t i c i p a t o r y s t r u c t u r e s that prepare the p e r c e i v e r t o respond to one k i n d of s t i m u l a t i o n r a t h e r than another (see Figure 14). In Neisser's model the p e r c e i v e r samples the a v a i l a b l e i n f o r m a t i o n s e l e c t i v e l y and perceives information from the stimulus array at the l e v e l and of the kind which he/she a n t i c i p a t e s . The advantage o f such a c o n c e p t u a l i z a t i o n i s t h a t , i n t h i s way, a s i n g l e model can account FIGURE 14 NEISSER'S PERCEPTUAL CYCLE ; This f i gure i l l u s t r a t e s how a schema can function to sample information in the environment s e l e c t i v e l y . In th i s way the perce iver can attend to information of a cer-t a i n kind at a Se lect level (From N e i s s e r , 1976). 116 f o r more than one type o f perc e p t i o n . That i s , i n some cases, percep-t u a l l e a r n i n g may l e a d t o f i n e r d i s c r i m i n a t i v e a b i l i t i e s (Gibson, 1953) whereas i n other cases (e.g. phonemic p e r c e p t i o n ) , p e r c e p t u a l l e a r n i n g may lead t o category formation r e s u l t i n g i n a decreased a b i l i t y t o d i s -c r i m i n a t e w i t h i n category features (Donderi, e t . a l . , 1973). E l l i s and Muhler, (1964) showed th a t perceptual l e a r n i n g can l e a d t o both o f these e f f e c t s i n the same subject depending on whether a "broad" or a "narrow" l a b e l l i n g system i s used i n the t r a i n i n g procedure. Although Neisser's model improves on e x i s t i n g t h e o r i e s , i t does not answer a l l the requirements of a develop-mental model. According t o a developmental model, i t i s necessary t o e x p l a i n how the present schema came t o be mo d i f i e d , and what processes l e d to the tuning. In a d d i t i o n , i t i s necessary t o s p e c i f y not only what i s "given" ( i . e . the c o n s t r a i n t s ) i n the i n f a n t organism and apparent i n the a d u l t , but a l s o the c o n s t r a i n t s i n the environment, and the process by .which these c o n s t r a i n t s i n t e r a c t through the course of development. Furthermore, accepting t h a t refinement t h e o r i e s best account f o r the development of speech p e r c e p t i o n , i t i s necessary to o u t l i n e the form of the proposed r e p r e s e n t a t i o n . F i n a l l y , s p e c u l a t i o n as t o how the c h i l d c o n s t r u c t s t h a t r e p r e s e n t a t i o n would be u s e f u l t o increase both the p r e d i c t i v e power and the t e s t a b i l i t y of any proposed developmental model. In review, i n order t o develop a complete developmental model t o account f o r speech p e r c e p t i o n , we need t o understand the f o l l o w i n g : (1) i s speech p e r c e p t i o n handled by a s p e c i f i c l i n g u i s t i c processor ? (2) what are the perceptual c o n s t r a i n t s i n the i n f a n t ? 117 (3) what are the constraints, i n the environment (speech sounds)? (4) what i s the i n t e r a c t i o n between these c o n s t r a i n t s ? (.5) when and how does l i n g u i s t i c experience a f f e c t i n i t i a l c o n s t r a i n t s ? (6) what i s the: form of i n i t i a l and modified schema? (7) how can we account f o r phonetic and phonemic (.and p o s s i b l y a c o u s t i c ) perception of the same stimulus input under d i f f e r e n t c o n t e x t u a l c o n d i t i o n s ? (8) are there q u a l i t a t i v e changes i n r e p r e s e n t a t i o n across ontogeny? These eight p o i n t s w i l l be discussed and i n t e g r a t e d i n t o a proposed model f o r understanding developmental aspects of speech pe r c e p t i o n . In a recent paper, Liberman (.1982) argues that c o g n i t i v e f u n c t i o n s and speech i n p a r t i c u l a r , are organized i n a " v e r t i c a l " r a t h e r than a " h o r i z o n t a l " f a s h i o n . By v e r t i c a l , he i s r e f e r r i n g t o a processing n o t i o n p a r a l l e l to Rozin's e v o l u t i o n a r y notion wherein c o n s t r a i n t s , r u l e s , and changes occur w i t h i n s p e c i f i c subsystems (or modules) r a t h e r than across and between modules. Although there i s reason t o argue that speech per c e p t i o n may be v e r t i c a l l y organized a f t e r the f i r s t year of l i f e ( i . e . may be handled by a l i n g u i s t i c processor) data from the p r e l i m i n a r y work presented i n Experiment I I I C r e q u i r e s a more h o r i z o n t a l type of explanation. Since c o g n i t i v e f u n c t i o n i n g , at l e a s t i n the task measured, was a s s o c i a t e d w i t h speech perception data b e t t e r than age i n the 8-10 month range, i t i s conceiv-able t h a t c e r t a i n general developmental a b i l i t i e s may be necessary before s p e c i f i c t u n i n g of i n i t i a l schemas can occur In any p a r t i c u l a r sub-system. That i s , the idea of v e r t i c a l o r g a n i z a t i o n can account f o r most of the data, but i t cannot e x p l a i n why developmental changes 118 i n cross-language speech perception occur at one, r a t h e r than another, point i n development. I t i s at t h i s l e v e l , and p o s s i b l y only at t h i s l e v e l , that general c o g n i t i v e processes may be r e l a t e d t o speech perception performance. Consideration of the nature, use, and m o d i f i c a t i o n o f i n i t i a l i n f a n t a b i l i t i e s has already been discu s s e d , however, d i s c u s s i o n of the c o n s t r a i n t s i n the environment has not yet been provided. An accumulation of research has shown that there may be a s p e c i f i a b l e o r g a n i z a t i o n i n speech sounds which i s based on the l i m i t a t i o n s of the human a r t i c u l a t o r y apparatus. These l i m i t a t i o n s should r e s u l t i n h i g h l y p r e d i c t a b l e ( a l b e i t complex) a c o u s t i c s t r u c t u r e s . That i s , speech sounds should have a p r e d i c t a b l e s t r u c t u r e based on the r e g u l a r -i t i e s of p o s i t i o n i n g the v o c a l organs i n the a r t i c u l a t i o n of s p e c i f i e d phones (see P i c k e t t , 1980). So f a r , most attempts t o i d e n t i f y i n v a r i a n t a c o u s t i c features t h a t could match l i n g u i s t i c f e a t u r e s have been un-s u c c e s s f u l (as reviewed i n the I n t r o d u c t i o n ) . Since research i n speech perception stemmed from l i n g u i s t i c a n a l y s i s of the d i s t i n c t i v e f e a t u r e s used t o produce speech segments, a naive f e a t u r a l approach has been taken i n the search f o r a c o u s t i c i n v a r i a n t s . This search has concentrated on i s o l a t e d a c o u s t i c cues. Given t h a t speech i s dynamic, and t h a t the speech stream i s c o n s t a n t l y changing as the a r t i c u l a t o r s move from one p o s i t i o n to another, i t i s easy t o appreciate that s t a t i c f e a t u r a l models might be unsuccessful i n i d e n t i f y i n g a c o u s t i c i n v a r i -ants. More recent attempts at s p e c i f y i n g the a c o u s t i c cues have examined the patterns or r e l a t i o n s between a c o u s t i c cues r a t h e r than measuring s i n g l e cues i n i s o l a t i o n (.Stevens £ Blumstein, 1975; Blumstein £ Stevens, 1980). Thus i t i s s t i l l p o s s i b l e that there may 119 be r e g u l a r i t i e s i n the environment which, although based on the con-s t r a i n t s of a dynamic a r t i c u l a t o r y apparatus, may be s p e c i f i a b l e i n terms o f s t r u c t u r a l a c o u s t i c i n f o r m a t i o n . Some researchers have r e c e n t l y conceived of speech perception w i t h i n a c a t e g o r i z i n g framework ( B o r n s t e i n , 1981; Jusczyk, i n press; Kuhl, 1979; Mehler £ B e r t o n c i n i , 1979). This approach i s c o n s i s t e n t with t h a t of Rosch (Rosch, 1977; Rosch, Mervis, Gray, Johnson, £ Boyes-Braem, 1976) who argues that c a t e g o r i z a t i o n i s an ubiquitous c o g n i t i v e process which serves to help the p e r c e i v e r reduce chaos and increase p r e d i c t a b i l i t y by d i s t i n g u i s h i n g only those s t i m u l i that belong t o d i f f e r e n t c a t e g o r i e s ( a l s o see Bruner, 1957). A c a t e g o r i z a t i o n model would suggest t h a t the match between i n i t i a l i n f a n t a b i l i t i e s (con-s t r a i n t s i n perception) and the s t r u c t u r e d r e g u l a r i t i e s i n stimulus i n f o r m a t i o n (environmental c o n s t r a i n t ) should serve t o organize i n i t i a l category boundaries. This match between c o n s t r a i n t s i n the i n f a n t and i n the environment favours a phonetic c a t e g o r i z a t i o n of speech sounds. In the above experiments, l i n g u i s t i c experience appears t o modify the i n i t i a l boundaries by the end of the f i r s t year of l i f e so t h a t they r e f l e c t the phoneme categ o r i e s the c h i l d hears i n h i s / h e r n a t i v e language. Although t r a d i t i o n a l models of c l a s s i f i c a t i o n d e f ine c a t e g o r i e s i n terms of conjunctive features (Bruner, 1957), recent work i n cate-g o r i z a t i o n favours a prototype form of r e p r e s e n t a t i o n . A prototype model i s conceived as a set of f e a t u r e s , none of which are necessary, but each of which i s present i n some instances of a p a r t i c u l a r category. In t h i s sense, cate g o r i e s are l i k e "fuzzy s e t s " . B o r n s t e i n (1981) used t h i s idea t o e x p l a i n i n f a n t v i s u a l and speech per c e p t i o n . When one considers the recent work i n t r a d i n g r e l a t i o n s showing that 120 two very d i f f e r e n t a c o u s t i c cues can lead t o the same percept, and the work by L i s k e r (1978) showing t h a t up t o 16 p o s s i b l e a c o u s t i c cues (none being necessary) can c o n t r i b u t e to the perception of the E n g l i s h v o i c i n g d i s t i n c t i o n , i t becomes reasonable to consider phonetic, or at l e a s t phonemic, perception i n terms of a prototype r e p r e s e n t a t i o n . Prototypes are defined as i d e a l i z e d "best exemplars" of a category, and new input i s c l a s s i f i e d as belonging t o a category i f i t f i t s more c l o s e l y t o one r a t h e r than another prototype. Studies show-ing t h a t subjects c l a s s i f y more p r o t o t y p i c a l exemplars of a phoneme category more q u i c k l y than they do l e s s t y p i c a l exemplars (Eimas S C o r b i t , 1973; Samuel, 1982) provides a d d i t i o n a l support f o r a prototype model. Furthermore, research i n d i c a t e s t h a t a d d i t i o n a l information ( i . e . burst plus formant t r a n s i t i o n ; d u r a t i o n of s i l e n c e i n a d d i t i o n to formant t r a n s i t i o n s ; i n c l u s i o n of unchanging f i r s t formant) i s not necessary f o r but improves the accuracy and ease o f c a t e g o r i z i n g d i s -c r i m i n a t i o n i n a d u l t s ( F i t c h , e t . a l . . 1980) and may be necessary f o r ac h i e v i n g the phoneme boundary e f f e c t i n i n f a n t s (Eimas, 1974; 1975). F i n a l l y , recent research studing the e f f e c t of s e l e c t i v e adapatation on phonetic boundaries supports a prototype model (Samuel, 1982). A prototype model of r e p r e s e n t a t i o n can serve t o c l a r i f y the p o t e n t i a l d i f f e r e n c e s between our f i n d i n g s and those o f E i l e r s , e t . a l . (1970) on the e f f e c t of experience on speech d i s c r i m i n a -t i o n performance. Results from Experiments I I I and IV could provide support f o r the idea t h a t i n the t r a n s i t i o n from phonetic t o phonemic c a t e g o r i z a t i o n , e a r l y experience f u n c t i o n s t o maintain e x i s t i n g capa-b i l i t i e s i n regard to the place of a r t i c u l a t i o n continuum. However, i t i s d i f f i c u l t to understand at f i r s t glance how s p e c i f i c experience 121 should then f a c i l i t a t e p erceptual development (.Gottlieb, 1976; Tees, 1976) w i t h regard t o the v o i c i n g continuum as evidenced i n E i l e r ' s work. By viewing speech perception w i t h i n a c a t e g o r i z i n g framework, and by proposing a prototype model of r e p r e s e n t a t i o n , i t i s p o s s i b l e t o argue t h a t evidence of u n i v e r s a l phonetic d i s c r i m i n a t i o n of place d i s t i n c t i o n s i l l u s t r a t e s a more d i s c r e t e , and non-overlapping s e r i e s of c a t e g o r i e s , i . e . a c l o s e and non-overlapping match between the p e r c e p t u a l and environmental s t r u c t u r e s . Infant v o i c i n g perception could be seen as a more approximate match between these two s e r i e s of c o n s t r a i n t s . As such, perceptual c a t e g o r i e s f o r v o i c i n g would be organized on the b a s i s of more overlapping i n f o r m a t i o n , and i n i t i a l p e r ception would thus be l e s s d i s c r e t e . I f the i n i t i a l p e r c e p t u a l c a t e g o r i e s f o r v o i c i n g c o n t r a s t s are l e s s d i s t i n c t than those f o r place c o n t r a s t s , i t would be u s e f u l to compare d i s c r i m i n a t i o n of v o i c i n g c o n t r a s t s i n young i n f a n t s using both n a t u r a l and s y n t h e t i c tokens. Recent data show th a t the i n -t e r n a l s t r u c t u r e , (the h o l i s t i c set of r e l a t i o n s between f e a t u r e s ) r a t h e r than d i s c r e t e f e a t u r a l i n f o r m a t i o n , i s used by pre-school aged c h i l d r e n i n forming some kinds of c a t e g o r i e s (Horton £ Markman, 1980). In c o n t r a s t t o e a r l i e r work suggesting a developmental s h i f t from p e r c e p t u a l l y based t o f u n c t i o n a l l y based c l a s s i f i c a t i o n (Bruner, 1957), t h i s recent work suggests t h a t very young c h i l d r e n c a t e g o r i z e on the b a s i s of o v e r a l l s i m i l a r i t y (Sherman, 1981) and i n t e r n a l s t r u c t u r e , and only l a t e r are they able t o break events down i n t o t h e i r component feat u r e s (Rosch, et. a l . , 1976; Smith, 1979). I f t h i s f i n d i n g were to be a p p l i e d to speech c a t e g o r i e s , i t would be d i f f i c u l t t o imagine how young i n f a n t s could c l a s s i f y synthesized v o i c i n g tokens wherein 122 r e l e v a n t i n f o r m a t i o n i s only provided on a s e l e c t number of fe a t u r e s ( i . e . only two or three formants; e i t h e r v o i c i n g or a s p i r a t i o n or f i r s t formant cutback, but not a l l t h r e e ) . To the degree t h a t v o i c i n g cate-g o r i e s could be i n i t i a l l y o v e r l a p p i n g , and t o the degree t h a t the i n f a n t cannot s e l e c t i v e l y attend to one r a t h e r than another f e a t u r e , f u l l y s p e c i f i e d , complex n a t u r a l tokens may be r e q u i r e d to a t t a i n the re q u i r e d match between the organism and the environment making phonetic percep-t i o n p o s s i b l e i n young i n f a n t s . I t i s i n t e r e s t i n g t o speculate why the same phonetic d i s t i n c -t i o n s t h a t are i n i t i a l l y d i s c r e t e f o r i n f a n t s (non-native place o f a r t i c u l a t i o n ) are the hardest f o r a d u l t s t o r e l e a r n . Most models o f perceptual development would p r e d i c t t h a t these d i s t i n c t i o n s should be e a s i e s t f o r an a d u l t to r e l e a r n . However, i f speech perception i s viewed w i t h i n a prototype framework, i t could be argued that the i n i t i a l l y d i s c r e t e d i s t i n c t i o n s are represented i n non-overlapping c a t e g o r i e s . These ca t e g o r i e s could be made up of instances which are a l l r e l a t i v e l y s i m i l a r to the i d e a l i z e d prototype. That i s , a l l exemplars of the category would share many a c o u s t i c f e a t u r e s , and those fe a t u r e s would be uncommon i n instances of other phonetic c a t e g o r i e s . I t would then be u n l i k e l y that a l i s t e n e r would have heard the various a c o u s t i c d i s -t i n c t i o n s which d i f f e r e n t i a t e two phonetic c a t e g o r i e s i f a p a r t i c u l a r c o n t r a s t Is not used phonemically i n th a t l i s t e n e r ' s n a t i v e language. This l a c k of experience would make i t d i f f i c u l t f o r an adul t to r e -acquire the a b i l i t y t o d i s c r i m i n a t e a non-native d i s t i n c t i o n . S i m i l a r l y , the f i n d i n g that a d u l t s can more e a s i l y r e l e a r n the same phonetic c o n t r a s t s that are i n i t i a l l y more d i f f i c u l t f o r i n f a n t s (the non-native v o i c i n g d i s t i n c t i o n s ) could be explained by a prototype model. For example, i t i s p o s s i b l e that the many dependencies that e x i s t between the dimensions of v o i c i n g sounds (e.g. the dependency between v o i c i n g and a s p i r a t i o n i n E n g l i s h ) could c o n t r i b u t e to l e s s d i s c r e t e category boundaries i n which instances of one phonetic cate-gory would be l i k e l y to share a c o u s t i c cues with instances of another category. This would r e q u i r e t h a t a l i s t e n e r i n i t i a l l y have more f e a t u r a l i n f o r m a t i o n i n order to match a sound t o a p a r t i c u l a r phonetic category. N a t u r a l speech sounds would be more l i k e l y t o supply t h a t a d d i t i o n a l i n f o r m a t i o n than synthesized sounds d i f f e r i n g i n only a . . l i m i t e d number of fea t u r e s (e.g. only VOT). I t would thus be pre-d i c t e d t h a t i n f a n t s would more l i k e l y show d i s c r i m i n a t i o n at the phonetic boundary f o r n a t u r a l than f o r s y n t h e t i c v o i c i n g c o n t r a s t s . In the case of the non-native ad u l t l i s t e n e r , overlapping c a t e g o r i e s could make i t e a s i e r f o r a s o p h i s t i c a t e d p e r c e i v e r to acquire a re l e v a n t "phonetic" d i s t i n c t i o n . Perceptual s e n s i t i v i t i e s could have been maintained through experiencing some of the many a c o u s t i c cues th a t c o n t r i b u t e to a phonetic category i n instances (speech sounds) from other c a t e g o r i e s . C e r t a i n l y there are d i f f e r e n c e s i n VOT i n the H i n d i v o i c i n g c o n t r a s t s used i n Experiment I , which span the E n g l i s h VOT boundary. E n g l i s h l i s t e n e r s could e i t h e r d i s c r i m i n a t e these tokens on the b a s i s of that d i f f e r e n c e alone, or they could match the two H i n d i sounds t o prototype r e p r e s e n t a t i o n s of the English, v o i c i n g c o n t r a s t s . Although the match would not be p e r f e c t , i t could be accommodated by a "fuzzy s e t " o r g a n i z a t i o n . Given t h a t E n g l i s h l i s t e n e r s r e q u i r e d at l e a s t some l e a r n i n g t o be able to d i s c r i m i n a t e t h i s c o n t r a s t i n Experiment I , the notio n of a f l e x i b l e prototype matching i s supported. 124 Consideration of the nature of the c o n s t r a i n t s . i n the i n f a n t and i n speech sounds has been discussed i n the l a s t s e v e r a l paragraphs, however, no mechanism f o r e x p l a i n i n g how i n i t i a l i n f a n t s e n s i t i v i t y -changes and how i t can f u n c t i o n to c l a s s i f y new stimulus events has been provided. That i s , phonetic c a t e g o r i e s have no l i n g u i s t i c f u n c t i o n f o r the i n f a n t unless they can be a c t i v e l y employed t o d i f f e r e n t i a t e meaning-f u l segments i n h i s / h e r language; that i s , u n t i l they become phonemic. Data from Experiment I I I C provides a p o s s i b l e but s p e c u l a t i v e explanation as to how the system might become phonemic. I t i s suggested th a t once the i n f a n t has the memory c a p a c i t i e s to compare speech sounds to i n t e r n a l schemas which are organized according t o phonetic boundaries, these schemas can be modified to r e f l e c t boundaries t h a t are phonemic i n the language he or she i s hearing. When modified schemas can be s t a b l y represented, at l e a s t f o r a short p e r i o d of time, they can serve as a l t e r n a t i v e guides t o c l a s s i f y i n g new stimulus input according to r e l e v a n t c u l t u r a l boundaries. Since i t has been argued that these derived phonemic schemas are i n i t i a l l y formed v i a an "e n a c t i v e " or "sensorimotor type" r e p r e s e n t a t i o n a l format, i t i s reasonable t o assume th a t such schemas would-be i n f l e x i b l e and ung e n e r a l i z a b l e . I t i s only a f t e r the c h i l d achieves more advanced means of r e p r e s e n t i n g i n f o r m a t i o n , and only when t h a t r e p r e -s e n t a t i o n i s derived by a more "symbolic" process which i s not dependent upon a c t i o n s or immediate perceptual s i g n i f i e r s , that the schemas can be more f l e x i b l y a p p l i e d to. d i f f e r e n t kinds of stimulus i n f o r m a t i o n . In t h i s regard, the derived schemas evident i n the young i n f a n t and the 4-year-old c h i l d (Experiments I and I I I ) would only l e a d t o phonemic processing. However, the symoblic schemas of the o l d e r c h i l d (that i s 125 an untested assumption which i s c o n s i s t e n t w i t h the data i n Experiment I f o r the 8- and 12-year o l d s , and with both previous research and Experiment V) could make e i t h e r phonemic or phonetic processing p o s s i b l e depending on co n t e x t u a l s p e c i f i c a t i o n . O u t l i n e of Proposed Model The present experiments lend support to a modified refinement theory of perceptual development, wherein changes i n the d i s c r i m i n a t i o n of phonemically r e l e v a n t phonetic segments are understood w i t h i n a c a t e g o r i z i n g framework. Furthermore, i t i s suggested that the i n i t i a l ( p h o n e t i c a l l y r e l e v a n t ) prototype o r g a n i z a t i o n i s i n n a t e l y determined and non-meaningful, and that i t serves t o c o n s t r a i n speech perception such t h a t only those s t r u c t u r e d , complex s t i m u l i which correspond c l o s e l y to one r a t h e r than another perceptual prototype w i l l be d i f f e r -e n t i a t e d . Through development, the c h i l d modifies these i n i t i a l schemas to r e f l e c t more p r e c i s e l y s t r u c t u r e d input he or she i s experiencing i n l i s t e n i n g t o , and t r y i n g to produce, speech sounds. Toward the end of the f i r s t : year of l i f e when the c h i l d has developed the memory c a p a c i t i e s f o r comparing past events to new events, these p r o t o t y p i c a l l y organized response p r o c l i v i t i e s become f u n c t i o n a l l y represented as e n a c t i v e l y derived schemas, and begin t o r e f l e c t the phonemic boundaries t h a t are s i g n i f i c a n t i n the c h i l d ' s p a r t i c u l a r l i n g u i s t i c environment. These i n i t i a l d e r ived schemas w i l l be r i g i d l y a p p l i e d , but as the c h i l d progresses i n c o g n i t i v e development so th a t symbolic schemas can be formed, the r e s u l t i n g schemas w i l l become more f l e x i b l y r epre-sented and thus useable f o r d i f f e r e n t i a t i n g i n f o r m a t i o n at d i f f e r e n t l e v e l s as s p e c i f i e d by the context. At t h i s j u n c t u r e , a per c e p t u a l 126 c y c l e s i m i l a r to Neisser's (.1976) can e x p l a i n why the same stimulus i n -put i s processed d i f f e r e n t l y i n d i f f e r e n t contexts. The i n i t i a l i n f a n t response p r o c l i v i t i e s (unmodified p r o t o t y p i c a l l y organized schemas) may or may not provide support f o r a s e l e c t i v e phonetic processor. However, evidence i s provided suggesting t h a t speech perception becomes s p e c i f i c a l l y l i n g u i s t i c by the end of the f i r s t year of l i f e . A graphic o u t l i n e of t h i s model i s presented i n Figure 15. As can be'seen, there i s a match between the i n i t i a l c o n s t r a i n t s i n the i n f a n t and those i n the environment. The i n i t i a l c o n s t r a i n t s i n the i n f a n t are modified as a r e s u l t of s p e c i f i c experience when the i n f a n t has a t t a i n e d the c o g n i t i v e a b i l i t y to hold events i n memory f o r a p e r i o d of time. The r e s u l t i n g ( e n a c t i v e l y derived) schemas are hypothe-s i z e d to be i n f l e x i b l y a p p l i e d to a l l speech input rendering only phonemic c a t e g o r i z a t i o n . Through development, the c h i l d d e r i v e s symbolic schemas which can be f l e x i b l y a p p l i e d at e i t h e r phonemic, phonetic, or a c o u s t i c l e v e l s depending on environmental s p e c i f i c a t i o n . I t i s argued t h a t i n i t i a l c o n s t r a i n t s and derived schemas are organized according to a prototype o r g a n i z a t i o n . This o r g a n i z a t i o n i s i n n a t e l y given (and p h o n e t i c a l l y r e l e v a n t , although not n e c e s s a r i l y l i n g u i s t i c -a l l y s p e c i f i c ) i n the i n f a n t , and. i s constructed i n the o l d e r i n f a n t , c h i l d and a d u l t . Once a derived schema i s formed (be i t enactive or symbolic) the speech categories are s a i d t o be "represented" i n the c h i l d ' s mind. This r e p r e s e n t a t i o n can then guide f u r t h e r p e r c e p t i o n . The r e p r e s e n t a t i o n i n the o l d e r i n f a n t , c h i l d , and adult i s s a i d t o be language s p e c i f i c . 127 FIGURE 15 SCHEMATIC ILLUSTRATION OF PROPOSED SPEECH PERCEPTION MODEL 128 By understanding speech, perception w i t h i n a c a t e g o r i z i n g framework, i t i s easy to account f o r perception at the phonemic, u n i v e r s a l phonetic, and a c o u s t i c l e v e l s . That i s , j u s t because we more e a s i l y c l a s s i f y two sounds as the E n g l i s h phoneme /b/, does not mean that there i s not an a l t e r n a t i v e , perceptual c a p a c i t y f o r d i f f e r e n t i a t i n g two (non-phonemic) French /b's/. A d d i t i o n a l l y , i t does not negate the p o s s i b i l i t y t h a t the perceptual system can s t i l l d i f f e r e n t i a t e each of the a c o u s t i c f e a t u r e s which c o n t r i b u t e s t o t h a t prototype representa-t i o n . A c a t e g o r i z i n g , prototype model simply p r e d i c t s t h a t i n process-ing and t r y i n g to understand language, a device which can serve t o group meaningful sounds together as s i m i l a r , and other sounds as n o n - s i m i l a r , w i l l be u s e f u l i n segmenting the speech stream. As does Neisser's model, t h i s model p r e d i c t s that c o n t e x t u a l i n f o r m a t i o n w i l l guide the p e r c e i v e r t o respond t o environmental i n -put according t o one or another l e v e l of (schematic) prototype o r g a n i z a t i o n . Years of responding t o language according t o phonemic ca t e g o r i e s w i l l render prototype r e p r e s e n t a t i o n s at the phonemic l e v e l the most robust; however, the p o t e n t i a l f o r responding at other l e v e l s w i l l s t i l l remain. As i n other refinement t h e o r i e s , i t i s then pre-d i c t e d t h a t l e s s i n f o r m a t i o n w i l l be r e q u i r e d through the course of development t o match incoming input t o one or another category. T h i s , i n combination with the f i n d i n g that young c h i l d r e n may f i r s t respond to i n t e g r a t e d s t r u c t u r e s (Sherman, 1981), and only l a t e r be able to s e l e c t i v e l y d i f f e r e n t i a t e component parts (Rosch, e t . a l . , 1976; Smith, 1979), could account f o r the d i f f e r e n c e i n r e s u l t s between the 4—year olds and the o l d e r c h i l d r e n i n Experiment I , and could e x p l a i n why a d u l t s could d i s c r i m i n a t e the very truncated tokens used i n Experiments 129 IV and V. In a d d i t i o n , i t would p r e d i c t that f u l l i n f o r m a t i o n ( n a t u r a l l y not synthesized tokens) would be r e q u i r e d f o r young i n f a n t s t o c o n s i s t e n t l y show the a b i l i t y t o d i s c r i m i n a t e the u n i v e r s a l set of v o i c i n g c o n t r a s t s . The proposed model is'.speculative and l i g h t l y sketched at t h i s time, but i t can serve as a framework w i t h i n which t o examine develop-mental issues i n speech p e r c e p t i o n . Although i t i s not yet f u l l y e l aborated, i t can help guide f u t u r e research e f f o r t s which, w i l l , i n t u r n , . l e a d t o m o d i f i c a t i o n s i n the model. In i t s present form, t h i s model would p r e d i c t s e v e r a l s p e c i f i c research outcomes. F i r s t , t h i s model would p r e d i c t that subjects at a l l ages should be able t o d i s c r i m i n a t e w i t h i n phonetic category a c o u s t i c changes i f t e s t e d i n an appropriate procedure. A s l i n and h i s co-workers ( A s l i n , et. a l . , 1981) have provided t e n t a t i v e support for. ' t h i s by showing th a t i n f a n t s aged 6-8 months can d i s c r i m i n a t e w i t h i n category d i f f e r -ences i n VOT i f t e s t e d i n step-wise comparisons. This model would p r e d i c t that those w i t h i n category d i s c r i m i n a t i o n s would not be as robust as would be between phonetic category d i s c r i m i n a t i o n s . I plan to t e s t t h i s p r e d i c t i o n by comparing g e n e r a l i z a t i o n f u n c t i o n s w i t h i n and between phonetic c a t e g o r i e s . I t i s p r e d i c t e d that i n f a n t s w i l l be able t o d i s c r i m i n a t e both kinds of changes, but w i l l a l s o be able to Ignore w i t h i n category changes t o form a broader ..(generalized) category corresponding t o phonetic boundaries but w i l l be unable t o ignore e q u a l l y d i f f e r e n t between category changes to form a category which spans a phonetic boundary. Secondly, the proposed model would p r e d i c t that i n f a n t s would have t o show enactive representation before they would evidence a d e c l i n e i n non-native phonetic d i s c r i m i n a t i o n performance. Although 130 i t i s p o s s i b l e that development i n both the above domains could progress g r a d u a l l y across the second h a l f of.the f i r s t year of l i f e , i f the c o r r e l a t i o n between these two a b i l i t i e s i s higher than that between speech p e r c e p t i o n and other measures of maturation (e.g. age, l a r g e motor development, e t c . ) , t h i s p r e d i c t i o n would be supported. T h i r d , t h i s model would p r e d i c t that c h i l d r e n i n l a t e infancy and e a r l y childhood would be i n f e r i o r t o both young i n f a n t s and o l d e r c h i l d r e n (and a d u l t s ) 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 p e r c e p t u a l l y easy non-native phonetic c o n t r a s t s . This could be t e s t e d by comparing d i s c r i m i n a t i o n performance of young i n f a n t s , young c h i l d r e n , and o l d e r c h i l d r e n on the non-English l e a d boundary i n VOT.. (At the same time, performance on both n a t u r a l and synthesized tokens could be compared to t e s t the p r e d i c t i o n that young i n f a n t s w i l l be able to d i s c r i m i n a t e t h i s d i s t i n c t i o n more e a s i l y i f t e s t e d w i t h n a t u r a l tokens). I t would be p r e d i c t e d that young c h i l d r e n would perform more po o r l y on t h i s task than e i t h e r i n f a n t s or older c h i l d r e n . Furthermore, t h i s model would p r e d i c t that l i m i t e d t r a i n i n g would be more l i k e l y t o f a c i l i t a t e performance i n o l d e r c h i l d r e n than i t would i n younger c h i l d r e n . In c o n t r a s t , most e x i s t i n g models would p r e d i c t t h a t younger c h i l d r e n would r e q u i r e l e s s t r a i n i n g . Since we have only gathered l i m i t e d data across childhood (Experiment I ) , the p r e d i c t i o n s r e s u l t i n g from the middle p o r t i o n of the model are the most tenuous. However, i t would be expected that c h i l d r e n must develop the c a p a c i t y to represent events s y m b o l i c a l l y before they w i l l be able t o apply schemas f l e x i b l y to perceive speech at e i t h e r a phonemic, phonetic, or a c o u s t i c l e v e l as s p e c i f i e d by the context. To t e s t t h i s p r e d i c t i o n , young c h i l d r e n could be t e s t e d i n c o n d i t i o n s s i m i l a r t o those, i n Experiments IV and V. Since i t i s unknown how young c h i l d r e n w i l l perform i n these c o n d i t i o n s , f u r t h e r s p e c i f i c a t i o n of the model could be provided by the r e s u l t s obtained from such research. 132 References Asher, J . J . , £ G a r c i a , R. The optimal age t o l e a r n a f o r e i g n language. 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New York: Academic Pr e s s , 1980. W i l l i a m s , L., £ Bush, M. The d i s c r i m i n a t i o n by young i n f a n t s of voiced stop consonants with and without r e l e a s e b u r s t s . J o u r n a l  of the A c o u s t i c a l S o c i e t y of America, 1978, 63_, 1223-1225. Wilson, W.R., Moore, J.M., £ Thompson, G. Sound f i e l d a u d i t o r y thresholds of i n f a n t s u t i l i z i n g v i s u a l reinforcement audiometry (VRA). Paper presented at The American Speech and Hearing A s s o c i a t i o n , Houston, 1976. Wood, C.C. D i s c r i m i n a b i l i t y , response b i a s , and phonemic categ o r i e s i n d i s c r i m i n a t i o n of voice onset time. J o u r n a l of the A c o u s t i c a l  S o c i e t y of America, 1976, 60, 1381-1389. Z l a t i n , M.A., £ Koenigsknecht, R.A. Development of the v o i c i n g c o n t r a s t : A comparison of voice onset time i n stop perception and production. J o u r n a l of Speech and Hearing Research, 1976, 19, 93-11. 15.1 APPENDIX A:. The. r a t i o n a l e behind the use of m u l t i p l e - n a t u r a l tokens M u l t i p l e n a t u r a l tokens as s t i m u l i were used i n t h i s work to make the d i s c r i m i n a t i o n task " e c o l o g i c a l l y v a l i d " . That i s , when we l i s t e n t o speech, we perc e i v e and ca t e g o r i z e a l l the d i f f e r e n t repe-t i t i o n s of a phoneme as the same sound, r e g a r d l e s s of v a r i a t i o n s i n i n t e n s i t y , d u r a t i o n , fundamental frequency, e t c . Since there are p e r c e p t u a l l y d i s t i n g u i s h a b l e d i f f e r e n c e s between any two r e p e t i t i o n s of the same sound, speech perception experiments which t e s t d i s -c r i m i n a t i o n of a s i n g l e exemplar o f one phoneme category from a s i n g l e exemplar o f another phoneme category may only be assessing a u d i t o r y (not phonetic) d i s c r i m i n a t i o n a b i l i t i e s . In h i s examination of colour perception i n i n f a n c y , B o r n s t e i n (19 81) has shown th a t although i n f a n t s can d i s c r i m i n a t e two d i f f e r e n t wavelengths from e i t h e r w i t h i n a hue category or across a hue boundary, they can only g e n e r a l i z e ( c a t e g o r i z e ) wavelengths from w i t h i n a hue category. S i m i l a r l y , speech research has shown that subjects can d i s c r i m i n a t e two speech sounds from w i t h i n or between two phonetic c a t e g o r i e s , but have only been shown to c a t e g o r i z e sound from w i t h i n a phonetic category. As reviewed i n the I n t r o d u c t i o n , there i s strong support f o r the n o t i o n t h a t two very d i f f e r e n t types of processing ( a u d i t o r y and phonetic) may be used by subjects i n experiments i n v o l v i n g speech sounds. To the extent that p s y c h o l i n g u i s t i c research examines the perception o f meaningful speech, procedures should be used that allow the subject t o g e n e r a l i z e across tokens w i t h i n a phonetic category. 152 By r e c o r d i n g m u l t i p l e r e p e t i t i o n s of each sound from a s i n g l e speaker, we can be sure t h a t there w i l l be (non-phonetic) a c o u s t i c d i f f e r e n c e s i n the n a t u r a l tokens i n such parameters as d u r a t i o n , i n t e n s i t y , e t c . w i t h i n each phonetic category. As such, subjects w i l l have t o ignore those w i t h i n category d i f f e r e n c e s and d i s t i n g u i s h the s e v e r a l tokens on the b a s i s of phonetic boundaries. Although .this procedure does not measure c a t e g o r i c a l perception i n the c l a s s i c a l sense ( i t does not p r e d i c t d i s c r i m i n a t i o n from i d e n t i f i c a t i o n f u n c t i o n s ) , i t does lead to c a t e g o r i z i n g d i s c r i m i n a t i o n and, as such, i s s i m i l a r t o the way i n which we respond t o n a t u r a l language. 153 APPENDIX iB.: , d e t a i l s of the • HT procedure as implemented i"n -'^airious l a b o r a t o r i e s The HT procedure i s employed somewhat d i f f e r e n t l y i n every l a b o r a t o r y i n which i t i s used. In our l a b o r a t o r y , i n f a n t s are r e -quired to reach an 8 out of 10 c o r r e c t response c r i t e r i o n t o change t r i a l s . Although some labs (see Kuhl, 1980) r e q u i r e a 9 out of 10 c r i t e r i o n , responses to both change and non-change t r i a l s are counted. In Kuhl's use of the procedure, E2 i n d i c a t e s when the i n f a n t i s i n a s t a t e of r e a d i n e s s , and t h i s i n d i c a t i o n i n i t i a t e s a demarcated observa-t i o n i n t e r v a l . As such, the random head turns when the i n f a n t i s f u s s y , e t c . (not i n a s t a t e of readiness) are not counted. Other labs (see E i l e r s , Gavin, £ Wilson, 1979) a l s o use demarcated observation i n t e r -v a l s , but r e q u i r e only a 5 out of 6 c o r r e c t response c r i t e r i o n . In these l a b s , approximately one-half of the demarcated observation i n t e r v a l s c o n t a i n a "change" (changes t o a new sound) t r i a l , and approximately one-half a " c o n t r o l " (continues p l a y i n g same sound) t r i a l . Because of equipment l i m i t a t i o n s and experimenter preference, there i s no demarcated observation i n t e r v a l i n our l a b o r a t o r y . Since E2 does not know when t r i a l s may begin or end, he/she must i n d i c a t e (by p r e s s i n g a button on the f l o o r ) every i n f a n t head t u r n . Since every head t u r n i s counted, the r o l e of E2 i s extremely important. He/she must keep the i n f a n t gazing i n h i s / h e r d i r e c t i o n by manipulating the toys to reduce the number of f a l s e p o s i t i v e head t u r n s , but E2 must be c a r e f u l not to make the toy manipulation so i n t e r e s t i n g that the i n f a n t w i l l not t u r n i t s head when the "background" stimulus changes. A s u c c e s s f u l E2.keeps the i n f a n t i n a s t a t e of a l e r t readiness during most of the t e s t i n g . 154 By counting a l l head turns r a t h e r than j u s t observing head turns during a demarcated observation interval,we ended up wi t h a task t h a t was more d i f f i c u l t than t h a t used by Kuhl. Kuhl r e p o r t s an approxi-mately 90% success r a t e f o r c o n d i t i o n i n g i n f a n t s . The r a t e i n our l a b runs between 85% ( f o r i n f a n t s aged 6-8 months) t o 60% ( f o r i n f a n t s aged 10-12 months). In E i l e r s ' l a b , i n f a n t s are r e q u i r e d t o reach the 5 out of 6 c r i t e r i o n w i t h i n the f i r s t 6 t r i a l s . This requirement has been c r i t i c i z e d s i n c e i t can be argued t h a t s t a t e v a r i a t i o n s i n i n f a n c y ( c r y i n g , f u s s i n g , etc.) r e q u i r e that the i n f a n t be given more t r i a l s i n order t o determine how.well he/she can perform i n the task. In Kuhl's l a b , i n f a n t s are t e s t e d u n t i l they reach c r i t e r i o n and the number of t r i a l s t o c r i t e r i o n i s scored. A s i m i l a r procedure i s used by A s l i n , e t . a l . (1979; 1981). In our l a b , i n f a n t s are given 25 "change" t r i a l s to reach c r i t e r i o n . Although i t could be argued that i n f a n t s might reach c r i t e r i o n on a d d i t i o n a l c o n t r a s t s i f given more t r i a l s , we were concerned t h a t . p e r c e p t u a l l e a r n i n g could occur i f too many t r i a l s were allowed. Thus 25 t r i a l s was chosen as a f i g u r e t h a t would a l l o w us to determine how w e l l the i n f a n t could perform without the chance t o l e a r n about the sounds. vH Uzgiris, I.C., and Hunt, J. Mc V. : Assessment ... in Infancy. Urbana: University of Illinois Press, 1975. Copyright University of Illinois Press. A p p e n d i x ci The Development of Visual Pursuit and the Permanence of Objects A. V I S U A L P U R S U I T O F S L O W L Y M O V I N G O B J E C T S 1. F O L L O W I N G A S L O W L Y MOVING O B J E C T T H R O U G H A 1 8 0 0 ARC Location: Object: Directions: Repeat: The infant may be supine on a flat surface, in an in-fant seat, or sitting up by himself. Any bright object that attracts the infant's attention, but does not make a sound when moved, e.g., the multicolored ring. Hold the object about 1 0 inches in front of the in-fant's eyes, until he focuses on it. With a young in-fant it may be necessary to shake the object lightly in order to attract attention or to vary its distance from the infant's eyes, to find the optimal focal distance. If an older infant tends to focus on the examiner rather than on the object, stand behind the infant. Once the infant has focused on the ob-ject, move it slowly through a lateral arc of 180 0. 3-4 times. Assessment in Infancy Infant Actions: a. Docs not follow object. o b. Follows object through part of arc with jerky accommodations, c. Follows object through part of arc, with smooth accommodations. *d. Follows object through the complete arc smoothly.1 2 . NOTICING THE DISAPPEARANCE OF A SLOWLY MOVING OBJECT Location: Object: Directions: Repeat: Infant Actions: Same as in situation i, but not on the floor. Same as in situation i. Once the infant has focused on the object, move it slowly to one side and away from the infant, making it disappear below the edge of the infant's seat or the surface on which he is placed. After a few moments, bring the object back in front and slightly above the infant's eyes from the opposite side (i.e., move the object behind the infant). Always move the object in the same direction and have it disappear at the same point. 3-4 times. a. Does not fellow object to point of disappearance. b. Loses interest as soon as object disappears (eyes begin to wander and then focus on any interest-ing object within view). *c. Lingers with glance at the point where the ob-ject has disappeared. *d. After several presentations, returns glance to the starting point or the point of reappearance (slightly above normal eye level) before the object has reappeared. e. Searches with eyes around the point where the object has disappeared.2 1 As noted on p. 146, an italic letter before the description of an infant action indicates that the action is considered cri t ical for achievement of a step in the scale. A n asterisk i n -dicates an action which has been used to judge the level of an infant's development for the •eating analyses of this investigation. * Th i s action appeared too seldom to be included in the scaling analysis so the asterisk Scale I Note: If a tendency of the infant to move the head to one side and to keep it there is suspected in,the course of the presentation, repeat the whole procedure at a later time, making the object disappear on the opposite side. B. S E A R C H F O R S I M P L Y H I D D E N O B J E C T S 3. FINDING AN OBJECT WHICH IS PARTIALLY COVERED Location: The infant must be in a sitting position with both hands free to manipulate objects. A young infant may be propped up in an infant seat or on a sofa using pillows. A n older infant may be seated in a high chair or on a rug on the floor. A working sur-face must be available in front of and to the side of the infant; it may be provided by placing a board across the infant seat, by pushing the high chair against a table, or by using the rug-covered space around the infant, if he is sitting on the floor. A n infant feeding-table is also suitable. Object: Any object which the infant demonstrates interest in by reaching for it; and, for a cover or screen, a white nontransparent scarf. It is important that the object be unitary, and that no portion of the object should look equivalent to the whole. A plastic doll or animal may be used, but an object such as a necklace would be unsuitable. Use of a white non-transparent scarf for the screen helps to minimize the interest of infants in the screen. Directions: To ascertain that an infant desires the object, place it on the surface and observe that the infant reaches for it. Take the object, while making sure the infant is focusing on it, place it on the surface within his is omitted even though "searching with the eyes around the point where the object dis-appeared" may appear to be equivalent to a " l ingering of the glance" i n implying the beginnings of object permanence. The term "searching" is an interpretation. It implies movement of the eyes, and the meaning of such motion in this situation is sti l l empir ical ly unclear. Assessment in Infancy Repeat: Infant Actions: reach, and cover it with the screen in such a way that a small poriion of the object remains visible (the feet of the doll, the tail of the animal, etc.). If, in his attempts to obtain the object, the infant covers it up completely, start a new presentation. If the infant's interest in the object becomes doubtful, interpose a presentation in which the object is left uncovered on the surface to determine if he will still reach for it. 3 times. a. Loses interest in the object once it is partially covered. b. Reacts to the loss of the object, but docs not reach for it and does not obtain it once it is partially covered. *c. Obtains the object by pulling it out from under the screen or by removing the screen and pick-ing up the object. 4. FINDING AN OBJECT WHICH is COMPLETELY COVERED Location: Same as in situation 3. Object: Any object in which the infant shows a strong in-terest and which is small enough to be completely covered by each of the screens without bulging too conspicuously may be used. A necklace has been • very popular, but a small doll, car, and plastic flower have also been used. Use the same white, nontrans-parent scarf used in situation 3 as the screen. Directions: Ascertain that the infant desires the object by hold-ing it out to him and observing whether he reaches for it. If the infant starts to reach for the object, place it on the surface within his reach and cover it completely with a screen, before the infant grasps the object. Do not stretch the scarf Hat, but bunch it up so that the contours of the object do not show through the screen. If the infant succeeds in obtain-ing the object on the first presentation, shift the work Scale I area to one side of the infant (left or right) and make all subsequent presentations on the same side. It is important here to differentiate the search for the hidden object from pulling at the screen out of a desire to play with the screen itself. In general, if the infant has demonstrated a desire for the object be-fore it was hidden and reaches for it either while lifting the screen or immediately afterwards, one may assume that the infant is searching for the hid-den object. On the other hand, if the infant lifts the screen and holds it for a considerable length of time before reaching for the now exposed object, possibly even looking at and handling the screen, one may assume that the infant has lifted the screen for its own sake. Repeat: 3 times. Infant Actions: a. Loses interest in the object once it is completely covered. b. Reacts to the loss of the object, but does not search or obtain it from under the screen. c. Pulls the screen, but not enough to uncover the object, and does not obtain the object. *d. Pulls the screen off and obtains the object. 5. FINDING AN OBJECT WHICH IS COMPLETELY COVERED WITH A SINGLE SCREEN IN TWO PLACES Location: Same as in situation 3. It is important to work on a sound-absorbing surface or to use a soft toy so that the noise created in putting the object down does not serve as an additional clue to the object's location. Object: Same as in situation 3. Use as the second screen a piece of nontransparent cloth of a dull color dif-ferent from that of the scarf. Directions: If the infant obtains the object covered by a single screen on two successive presentations, place the second screen on the opposite side of the infant during the last covering of the object with the first Assessment in Infancy screen, making sure both screens are within the in-fant's reach. Then, hide the object in the same man-ner under the second screen. Make sure that both co screens are bundled rather than flat. To repeat the ^ presentation, hide the object under the second screen two more times, and then switch to hiding the object under the first screen, counting the last hiding as the second presentation of this situation. Repeat: 2 times. Infant Actions: a. Loses interest in the object once it is hidden under the second screen. b. Searches for the object where it was previously found, i.e., under the first screen on the first presentation. c. Searches for the object where it disappeared, i.e., under the second screen, on the first pre-sentation.3 6. FINDING AN OBJECT WHICH IS COMPLETELY COVERED WITH A SINGLE SCREEN IN TWO PLACES ALTERNATELY Same as in situation 5. Same as in situation 5. Hide the object under each of the two screens al-ternately, covering the object completely with the screen each time. 3-5 times. a. Becomes perplexed and loses interest in the ob-ject. b. Searches haphazardly under one or both screens. *c. Searches correctly under each of the screens. * Action c carries no asterisk here because the actions in this situation were not included in the scaling analysis. They arc included here intuitively. Even though this situation may elicit actions which duplicate those in Situation 6 , this situation would appear to put some-what lesser demands on flexibility in dissociating objects from actions previously directed at them. Location: Object: Directions: Repeat: Infant Actions: Scale I 7. FINDING AN OBJECT WHICH IS COMPLETELY COVERED WITH A SINGLE SCREEN IN THREE PLACES Location: Same as in situation 5. Object: Same as in situation 5. Use the pillow or a third non-transparent cloth, discriminable from the other two, as the third screen and place it directly in front of the infant, within his reach. Directions: Hide the object under each of the three screens, selecting the screen to be used on each presentation at random. (Sample order: 2d, 1st, 3d, 1st, 1st, 3d, 2d) Repeat: 5-7 times. Infant Actions: a. Loses interest in the object. b. Searches haphazardly under some or all screens. *c. Searches directly under the screen where the object disappeared. Note: In most cases, it is best to present situations 3-7 in succession. It is extremely important that the infant have a strong interest in the object chosen for these situations. It is permissible to change objects at any point, but it should be recognized that loss of interest may also signify that the task is becoming too difficult. If the examiner suspects that the infant is losing interest due to the difficulty of the task, the same object should be hidden in a simpler way (i.e., a way that the infant was previously able to handle) to see whether the infant will then search for the object. If the infant is still interested in the object, he will usually search for it in the easier situa-tion. The constant disappearance of a desired object often proves frus-trating to young infants. When it seems that the loss of interest in the situation may be due to frustration, the infant may be permitted to play with the object for a short while without interference in an at-tempt to restore his cooperation and his interest in it. On the other hand, if the need to relinquish the object after each trial appears to be causing frustration, it is best to pick up the object as soon as the infant removes the screen and is reaching for it, without permitting the infant actually to hold the object each time. Assessment in Infancy Since these situations are presented to infants varying considerably i n age, certain adjustments in procedure are helpful with younger and older infants. The younger infants tend to become frustrated, and it is necessary to check their interest in the object being used as well as their attention to the task. Conversely, older infants tend to become bored with the simple hidings, and, if this basis for their behavior is clear, it is often desirable to cut the number of presentations of the simple hidings to a minimum required for assurance of competence in order to prolong their cooperation. The cooperation of older infants may also be secured by helping them sec the situations as a game and by permitting them a turn at hiding the object, if they so desire. C. S E A R C H F O L L O W I N G M O R E C O M P L E X H I D I N G 8. FINDING AN OBJECT AFTER SUCCESSIVE VISIBLE DISPLACEMENTS Location: Object: Directions: Repeat: Infant Actions: Same as in situation 5. Same as in situation 7. Flide the object successively under each of the three screens located around the infant by moving the hand holding the toy in a path from left to right or from right to left so that the object becomes hidden under one of the screens, then reappears in the space between the screens, and again becomes hid-den as the hand passes under another screen. Make sure the infant attends to the complete hiding pro-cedure, the complete series of object appearances and disappearances. Check for position preference by reversing the direction of hiding after a few presentations. Check for screen preference by chang-ing positions of particular screens after a few pre-sentations. 3-5 times. a. Does not follow the successive hidings. b. Searches only under the first screen under which the object disappeared. c. Searches under the'screen where the object was found on the previous presentation. Scale I d. Searches under all screens haphazardly. c. Searches under all screens in the order of hiding. f. Searches directly under the last screen in the path (the one under which the object disap-peared last).'1 Note: If the infant fails to attend to the whole series of successive hid-ings, he may have to be moved back from the screens during the hiding and then moved closer again to within reach of the screens once the hiding is completed. 9. FINDING AN OBJECT UNDER THREE SUPERIMPOSED SCREENS Location: Same as in situation 5. Object: Same as in situation 7. Directions: Ascertain that the infant is interested in the object and place it in front of him within his reach. Cover the object with one screen, then take a second screen and cover the first screen with the second, and so on. Arrange the screens in such a way that the infant cannot remove all of them with one swipe (e.g., use the pillow as the middle screen). Repeat: 2-3 times. Infant Actions: a. Loses interest in the object. b. Lifts one or two screens, but gives up before finding the object. *c. Removes all screens and finds the hidden object. Note: When multiple screens arc used, an infant sometimes begins to pull all screens in sight without paying much attention to the dis-placements of the object. The examiner may check for this by going through the hiding procedures and retaining the object so that it is clearly visible to the infant, instead of leaving it under a screen. If the infant still persists in searching under screens, his behavior is no longer a valid indication of his construct of the object which is here of interest to the examiner. In such an instance, it is desirable to interrupt the ' Actions (c) and (f) in this situation tarry no asterisks because there were too few to be included in the scaling analysis, these actions may point to more than one step between steps 7 and 9 which may i d l e d increasing flexibility in the spatial localization of the object constructs as well as greater persistence of the centra! processes representing the objects. Assessment in Infancy presentation of this sequence and to intersperse other activities or a period of free play. In general, it may be advisable to introduce a break after each group of situations in order to minimize the occur-rence of indiscriminate removal of all screens. D. S E ARCH F O L L O W I N G A N INVISIBLE D I S P L A C E M E N T io. FINDING AN OBJECT FOLLOWING ONE INVISIBLE DISPLACEMENT WITH A SINGLE SCREEN Location: Object: Directions: Repeat: Infant Actions: Same as in situation 5. Use a small object which would readily fit into the box to be used to hide the object in order to pro-duce the invisible displacement (e.g., miniature doll, small stuffed animal, small car, etc.). Use a card-board box, without a cover, which is deep enough to make the object invisible to the infant once it is lowered into it. Use as a screen a piece of nontrans-parent cloth which is large enough to allow the examiner to invert the box under it withou' ex-posing the object. While the infant watches, lower the object into the box and then hide the box under the screen. Turn the box over under the screen, leaving the object hidden, and remove the empty box. If the infant hesitates, show him that the box is empty. If the in-fant appears to lose interest in the object, check on the difficulty of the task by hiding the same object under the screen directly. 3 times. a. Loses interest in the object. b. Reacts to the loss of the object, but does not search for it. c. Searches only in the box for the hidden object. *d. Checks the box and proceeds to find the object under the screen where the box disappeared. *e. Searches for the object directly under the screen where the box disappeared. 11. FINDING AN OBJECT FOLLOWING ONE INVISIBLE DISPLACEMENT WITH TWO SCREENS Location: Same as in situation 5. Object: Same as in situation 10. Use as the second screen another piece of cloth differing from the first in. either color:or pattern. Directions: Place the second screen to the side of the infant op-posite to that of the first during the last presentation of situation 10. Hide the object in the same manner (using the box to produce the invisible displace-ment) under the second screen. To repeat the presentation, hide the object under the second screen two more times and then switch to hiding the ob-ject under the first screen, counting this last hiding as a second presentation of the situation. Repeat: 2 times. Infant Actions: a. Searches only in the box. b. Searches under the screen where the object was previously found. *c. Searches correctly under the screen where the box disappeared. 12. FINDING AN OBJECT FOLLOWING ONE INVISIBLE DISPLACEMENT WITH TWO SCREENS ALTERNATED Location: Object: Directions: Repeat: Infant Actions: Same as in situation 5. Same as in situation 10. Hide the object, using the box to produce the in-visible displacement, under one of the two screens, alternating on each presentation. Place the empty box in the center between the two screens. 3 times. a. Loses interest in the object. b. Searches haphazardly under the two screens. *c. Searches directly under the screen where the box disappeared. Assessment in Infancy 13. FINDING AN OBJECT FOLLOWING ONE INVISIBLE DISPLACEMENT WITH THREE SCREENS Location: Same as in situation 5. Object: Same as in situation 10. Use as the third screen the pillow or an obviously different piece of cloth. Place it to the other side of the first screen. Directions: Using the box to create the invisible displacement by first lowering the object into it, make the box disappear under one of the three screens at random on each presentation, leaving the object hidden under the screen each time. Repeat: 5-7 times. Infant Actions: a. Loses interest in the object. b. Searches haphazardly under all three screens. *c. Searches directly under the correct screen where the box disappeared. E. S E A R C H F O L L O W I N G SUCCESSIVE IN VISI li L E DIS PL A CEMENTS 14. FINDING AN OBJECT FOLLOWING A SERIES OF INVISIBLE DISPLACE-MENTS Location: Object: Directions: Same as in situation 5. Same as in situation 13. The object should be small enough to fit in the palm of the hand since it is more convenient to produce (he invisible displacements by hiding the object in the palm of the hand. While the infant watches, place the object in the palm of one hand and hide it by closing the hand. Move the hand in a path in one direction (e.g., from left to right), making the hand disappear under the first screen then reappear between the first and second screens, disappear again under the second screen, and so on. Db not open the hand between screens. Leave the object under the last screen in the path and show the infant that the hand is empty Repeat the presentations by following the path ii the same direction each time. Repeat: 4-6 times. Infant Actions: a. Searches only in the examiner's hand or aroun< the room. b. Searches only under the first one or two screen in the path and does not obtain the object. *c. Searches under all screens in the path in th same order as followed by the examiner's ham and finds the object under the last screen. *d. Searches directly under the last screen on a least two successive presentations following sue cess in finding the object there. 15. FINDING AN OBJECT FOLLOWING A SERIES OF INVISIBLE DISPLACI MENTS BY SEARCHING IN REVERSE OF THE ORDER OF HIDING Note: Present this situation only to infants who search directly und( the last screen at least twice in situation 14, and only immediately sul sequent to situation 14. Location: Same as in situation 5. Object: Same as in situation 14. Directions: Immediately following the presentation of situatic 14, having established an expectation that the o l ject is to be found under the last screen, move t) hand in which the object is hidden in the same ma ner and in the same direction as in situation 14, 1 leave the object under the first screen in the p; Continue the movement of the hand to the seceir and third screen, then show the infant that it empty. In order to remember to stop momentari under the last screen, open the now empty hai there also. This situation can be repeated only I repeating situation 14 first, and then presenting t "trick" of situation 15. To check for position pn erence, repeat situation 14 by moving the hand the opposite direction, thus making the screen whi Appendix C2 i[.L'LY. E X A M I N A T I O N R'v .< - A 1 ) IV >?:i CO T H E D E V E L O P M E N T O F V I S U A L P U R S U I T A N D T H E P E R M A V E N G E O F O B J E C T S N~::e: B::.J:datc: B? of Examination: P R E S E N T A T I O N (Suggested number aj presentation /cr .*.:<•<"< illusion is indicated in petenthtcrs) SrruATtos i a 3 4 5 6 7 £. [•'rtfcmng a Sicwly Mimug Object through 'i • &>" Arc (3-.J.) a. Does not fa!low object •• b. Follows j;rkily through patt of arc c. Follows sujoothly^hrough part of ;?rc *'d. Follows object smoothly through complete arc. — — Other: _ 2. M:>Ue:r.r it.t Oiaippfsretntg of a Slowly M-i-::; Object (3-4) a. Bcrs nut follow to M i n t cf disap-pearance b. Loses intercut as soon as object dis-appears V Lmgeis with glance on point of diss ppc.'1. ra rwe V . Returns glance to starting poitit niter ECVC!-ii p t s n a l k m ? c. Searches around point of disap-pearance Other: 3. Fiseuzg en Object Which Is Partially Cov-ered (3) a. Loses interest ., .. . b. Reacts to the loss, but docs not ob-tain object *r. Obtains the object \\ Other: 4. fiWt.-i' an Object Which Is Ccr.p!ete!f, Cprrr.:? (3) a. hurwt _ _ _ (Sagftil-i number cf preset taticms jar teuh si*..~,lwr. is kiitit'd in parent heres) Srn-AnON !' « a 3 4 5 6 7 b. React? to Io;-?, but docs not ob-tain object c. Pulls screen, but not enough to obtain object *d. Pulls screen o:T and obtains object -Other: 5. Finding an Object Completely Cover?,! in T::-o Places {2} a. Loses interest b. Searches for object where it was previously fount! c. Searches for object whirc it is last hidden Other: fi. Finding rrv Object Completely Centred in Two Hares AUemixUly (3-5) a. Becomes perpicved and lore? in-tr.-Mt b. Searches haph..?j.ai-d!y ur.dcT ont or both t-creens V .Search-:? correr.'Jy under each- cf the ser wis Other: 7. finding sn Object Cotr.pleidy €•:•:«> ed in Thee Places (5-7) a. Loses interest b. e]e;i:c'sc; haphazardly under setae, or all screens *c. Searches directly under correct scree:-! Other: 8. Finding an 0'jcc! after Successive Visible Displacements (3-5) a. Does not follow successive hidings b. Searches only under the. first screen c. Search'.-.; under screen where ob-ject was previously found d. Searches haphazardly tinder a l l screens e. Search's i:» order of hiding Appendix DI CHILD SYLLABLE SHEET Child's name and age other segments c 1 u s t e r s Total: Vowel Monosyllables CV CVC CVC? Multi-syllables CVCV Comp. Red Part. Red Non-Red Other Other multi-Red CVCVC syll. CVCV Non Other Other CV CVC CVCJ CSVCS Comp.R Part.R Red: Red CVCVC multi V VC VC5 VCV VCV 165 A p p e n d i x D2 LEXICON SHEET Child's name and age. types types lexical phonetic lexical ^Pes types Phonetic lexical phonetic lexical phonetic 166V Appendix, D3 Child's Phonetic Inventory Word initial segments I n n p ; b . t d t ; k g f V 9 0 / 3 z Vowel w r j h 1 ITEM AND REPLICA SHEET Child's name and age Child's Substitutions Syllable initial consonants Word final consonants I TX n 0 p b t d k g f v e d T 3 z / 3 r i 1 i Syllable final consonants 16% Appendix E l : Infant speech perception task 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 under-stand that the procedures may be terminated at any time at my request. PROCEDURE: The infant w i l l be held on his/her parent's lap i n the testing chanber. He or she w i l l see a serie s of toys, and w i l l hear a series of one s y l l a b l e speech sounds. The infant w i l l be watched by the experimenter i n the adjoining room, and by the assistant i n the t e s t i n g chamber. Whenever the infant turns toward the loud-speaker during a test t r i a l , the experimenter and the assistant w i l l press a button. I f t h i s head turn has occurred when there i s a change i n the speech s t i m u l i , a toy animal i n s i d e the dark pl e x i g l a s s box w i l l begin per-forming. A record of a l l the baby's responses to the speech sounds w i l l be kept. The baby w i l l be held by the parent at a l l times. Whenever the parent desires, there w i l l be a break i n or an end to the t e s t i n g session. i n the following place: and designated i n the following manner Date: Name: Signature: Appendix E2: Infant cognit ive and l i n g u i s t i c tasks THE UNIVERSITY OF BRITISH COLUMBIA 2075 Kesbrook I'al.1 Vancouver, F-.C, Canada V6T 1175 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 c h i l e 1 ' w i l l be engaged i n a serie s of games by the experimenter i n t M s task. The games are designed to give us an i n d i c a t i o n of the c h i l d ' s use of language, and of the way he or she i s coming to understand the world around. A record of your c h i l d ' s responses i n each game si t u a t i o n w i l l be kept, and a tape recording of your c h i l d ' s speech w i l l he made. You w i l l be i n the room with your c h i l d at a l l times. If you f e e l i t i s necessary, there w i l l he a rest period or any early end to the play session. tiy signature below c e r t i f i e s that I consent to the experimental procedure which has been described and which i s to be conducted on the following date: i n the following place: and designated i n the following manner: Date : Name: Signature: Appendix E3 : Adult and ch i l d speech perception task IFF UNIVERSITY OF BRITISH COLUtiSIA 2075 T-'esbrook I**II Vancouver, B.C., Canada V6T 1H5 Hepartnent of Psychology CONSENT FORu This experimental procedure has leen requested by I have been informed of the procedures and understand then. I a l s o understand that the procedures riry be terminated at any time at my request. PROCEDURE: This i s a stu4y i n speech perception. You w i l l be s i t t i n g on a c h a i r f a c i n g a loud speaker i n the t e s t i n g chamber. A s e r i e s of one s y l l a b l e speech sounds " i l l be played over the speaker. Your task w i l l be to press a button whenever you detect a cl'arpo i n the speech sounds. Every c o r r e c t d i s c r i m i n a t i o n response w i l l Le s i g n a l l e d hy f l a s i n g l i g h t s . A record of a l l your responses " i l l be ::ent. I f at any time ycu d e s i r e , there w i l l be a brea^; i n , or t e r m i n a t i o n of, the t e s t i n g s e s s i o n . I'.y signature below c e r t i f i e s that I consent to the experimental procedure which has ! sen described and which i s to he conducted on the follo'wrp: date: i n the f o l l o w i n g place: and de si.Tate'' in the following manner: f a t e : Nans: Signature: Appendix E4: Same/Different speech discr imination task THE UNIVERSITY OF BRITISH C0LUH3IA 2075 I'esbrook H a l l Vancouver, B.C., Canada V6T 11/5 Department of Psychology CONSENT FORM This experimental procedure has been requested by I have been informed of the procedures and understand them. I a l s o understand that the procedures may be terminated at any time at my request. PROCEDURE: This i s a study i n speech perception. You w i l l be s i t t i n g on a c h a i r f a c i n g a loud speaker i n the t e s t i n g chamber. A s e r i e s of one s y l l a b l e sounds w i l l be played over the speaker i n p a i r s . Your task w i l l he to i n d i c a t e whether each p a i r contains two r e p e t i t i o n s of the same speech, sound category, or r e p e t i t i o n s of two d i f f e r e n t sounds. I f you f e e l the p a i r contains two r e p e t i t i o n s of the same speech sound, mark an S on the score sheet. I f you f e e l the p a i r contains two sounds from d i f f e r e n t speech c a t e g o r i e s , mark a D on the score sheet. I f at any time you d e s i r e , there w i l l be a break i n , or t e r m i n a t i o n of, the t e s t i n g s e s s i o n . My signature below c e r t i f i e s that I consent to the experimental procedure which lias been described and which i s to be conducted on the f o l l o w i n g date: i n the f o l l o w i n g place: and designated i n the f o l l o w i n g manner: Rate : Name : Signature: PUBLICATIONS Werker, J.F. £ Tees, R.C. Perceptual r e o r g a n i z a t i o n In the f i r s t year of l i f e . Paper presented at Canadian P s y c h o l o g i c a l A s s o c i a t i o n . Montreal, June, 1982, Tees, R.C. £ Werker, J.F. Perceptual f e l x i b i l i t y : Recovery of the a b i l i t y to d i s c r i m i n a t e non-native speech sounds. Paper presented at Canadian P s y c h o l o g i c a l A s s o c i a t i o n . Montreal, June, 1982. Werker, J.F. £ Tees, R.C. Developmental changes i n cross-language speech sound c a t e g o r i z a t i o n : Ages 4-12. Paper presented, at Canadian P s y c h o l o g i c a l A s s o c i a t i o n . Toronto, June, 1981. Werker, J.F.., G i l b e r t , J.H.V., Humphrey, K. , £ Tees, R.C. Developmental aspects of cross-language speech perception. C h i l d Development, 1981, 52, 349-355. Tees, R.C. 6 Werker, J.F. The development of speech p e r c e p t i o n : Evidence of f u n c t i o n a l d e c l i n e i n neonatal a b i l i t y . Paper presented at Winter Conference on B r a i n Research. Keystone, Colorado, January, 1981. Humphrey, G.K. , Tees, R.C, S Werker, J.F. A u d i t o r y - v u s a l i n t e g r a t i o n of temporal r e l a t i o n s i n i n f a n t s . Canadian J o u r n a l of Psychology, 1979, 33, 347-352. 

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