This chapter discusses the need to develop theories of speech perception that can account for changes across development from infancy to adulthood. While early research found similarities between infants' and adults' abilities to discriminate speech sounds, children must learn to represent linguistic units like phonemes and words. The chapters in this volume detail developmental changes in speech perception and how innate abilities are shaped by experience. A unified theory is needed to explain how perceptual mechanisms and representations develop, integrating findings from infant, child, and adult research. Such a theory would describe how innate capacities support learning of phonetic categories and words, and how this knowledge influences speech perception throughout life.

1. The Development of Speech Perception:
The Transition from Speech Sounds to Spoken Words
Edited by
Judith C. Goodman and
Howard C. Nusbaum
A Bradford Book
The MIT Press
Cambridge, Massachusetts
London, England
title: The Development of Speech Perception : The Transition
From Speech Sounds to Spoken Words
author: Goodman, Judith
publisher: MIT Press
isbn10 | asin: 0262071541
print isbn13: 9780262071543
ebook isbn13: 9780585021256
language: English
subject Language acquisition--Congresses, Speech perception--
Congresses, Perceptual learning--Congresses.
publication date: 1994
lcc: P118.D46 1994eb
ddc: 401/.93
subject: Language acquisition--Congresses, Speech perception--
Congresses, Perceptual learning--Congresses.
cover
© 1994 Massachusetts Institute of Technology
All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means
(including photocopying, recording, or information storage and retrieval) without permission in writing from the

2. publisher.
This book was set in Times Roman by Asco Trade Typesetting Ltd., Hong Kong, and was printed and bound in the
United States of America.
Library of Congress of Cataloging-in-Publication Data
The Development of speech perception: the transition from speech sounds to spoken words/ edited by Judith Goodman
and Howard C. Nusbaum.
p. cm.(Language, speech, and communication)
Papers presented at the Workshop on Recognizing Spoken Language which was held June 1989, University of Chicago.
"A Bradford book."
Includes bibliographical references and index.
ISBN 0-262-07154-1
1. Language acquisitionCongresses. 2. Speech perceptionCongresses. 3. Perceptual learningCongresses. I. Goodman,
Judith, 1958 II. Nusbaum, Howard C. III. Workshop on Recognizing Spoken Language (1989: University of Chicago) IV.
Series.
P118.D46 1994
401'.93dc20 93-11391
CIP
cover-0
Contents
Preface vii
Contributors xi
Introduction 1
Chapter
1 Developing Theories of Speech Perception: Constraints from Developmental Data 3
Judith C. Goodman, Lisa Lee, and Jenny DeGroot
Part I Innate Sensory Mechanisms and Constraints on Learning 35
Chapter
2 Observations on Speech Perception, Its Development, and the Search for a Mechanism 37
Joanne L. Miller and Peter D. Eimas
Chapter
3
The Importance of Childhood to Language Acquisition: Evidence from American Sign
Language 57
Rachel I. Mayberry
Part II Perceptual Learning of Phonological Systems 91
Chapter
4 Cross-Language Speech Perception: Developmental Change Does Not Involve Loss 93
Janet F. Werker

3. cover-1
Page vi
Chapter
5
Perceptual Learning of Nonnative Speech Contrasts: Implications for Theories of Speech
Perception 121
David B. Pisoni, Scott E. Lively, and John S. Logan
Chapter
6
The Emergence of Native-Language Phonological Influences in Infants: A Perceptual
Assimilation Model 167
Catherine T. Best
Part III Interactions of Linguistic Levels: Influences on Perceptual Development 225
Chapter
7 Infant Speech Perception and the Development of the Mental Lexicon 227
Peter W. Jusczyk
Chapter
8
Sentential Processes in Early Child Language: Evidence from the Perception and Production
of Function Morphemes 271
LouAnn Gerken
Chapter
9 Learning to Hear Speech as Spoken Language 299
Howard C. Nusbaum and Judith C. Goodman
Index 339
page_vi
Page vii
Preface
Traditionally, theories of speech perception have sought to explain primarily the way adults recognize spoken language,
seldom considering the problem of the way this ability develops. Of course, any theory of speech perception must
account for performance by mature language users, but our goal in developing this book was to encourage researchers to
consider the proposition that theories must also account for the development of linguistic processing and the changes that
occur with maturation and experience.
Although developmental questions have been addressed in speech research, this work initially focused on the way speech
perception develops in prelinguistic infants. Several researchers have asked how innate abilities interact with perceptual
experience over the course of the first year of life, but it is important to expand this focus to allow an examination of the
role of developing linguistic knowledge and increasing experience using language in understanding the way speech
perception develops. Perceptual processing may be modified when children begin to learn their native phonologies and
lexicons, as well as higher levels of linguistic structure, and research on very young infants alone fails to capture this sort
of development.
Indeed, the chapters in this volume report that changes related to the acquisition of linguistic knowledge do occur. While
the contributors to this volume do not all agree on the specific nature of the processes involved in speech perception or
the way in which these processes develop, together, these chapters document the striking changes that take place, not
only in early childhood but throughout life. In addition, the authors use these findings to make suggestions as to how
theories of speech perception will need to be modified if they are to explain such changes.

4. This volume grew out of the Workshop on Recognizing Spoken Language that was held at the University of Chicago in
June 1989. The goal
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Page viii
of this workshop was to examine transitions in the perceptual processing of speech from infancy to adulthood. The
workshop participants were scientists who have carried out speech research with infants, children, and/or adults. Their
task was to consider in detail the theoretical implications of their research for a well-specified and complete theory of
speech perception that could address issues concerning speech perception in children and adults, as well as the
development of those abilities. In particular, the participants were invited to speculate about how their findings constrain
the nature of the mechanisms and representations that mediate speech perception during infancy, childhood, and
adulthood.
This is a tall order, and these chapters contain a wealth of information on the development of perceptual processing, as
well as constraints and prescriptions for the development of theories of perceptual processing. The findings reported here
cover many critical issues for theory buildingfor example, how maturation and experience modify innate sensory
mechanisms, how structural knowledge is acquired, whether young children represent linguistic information in the same
way as adults, and how segment- and word-recognition processes differ among children and adults. In addition, they
include proposals regarding the nature of the mechanisms behind the perception of linguistic units, the acquisition of
early word patterns, and the development of the mental lexicon.
This book differs from previous books on speech perception in several respects. First, it attempts to integrate research
involving infants, young children, and adults. Although in recent years several books have considered a wide range of
issues in speech perception, these books have not thoroughly addressed developmental issues; at best they have included
only one or two chapters on speech perception in infants. Second, this book tries to explore systematically how adult
perceptual abilities develop from early infant capabilities, focusing in particular on the nature of the transitional stages
and the constraints they place on theories of speech perception. Other recent books on speech perception that have
focused on a single theoretical issue have not addressed the transition from recognition of speech segments to recognition
of spoken words. Finally, unlike other books that have addressed issues in perceptual development, this book also focuses
on speech perception. We hope that researchers and students in the areas of psychology, linguistics, cognitive science,
and speech and hearing will find this approach stimulating.
We are deeply grateful to the authors who contributed to this volume. We appreciate their level of commitment, their
willingness to go beyond their data to make theoretical speculations, and their patience during both
page_viii
Page ix
the workshop and the preparation of the book. We are grateful to Dr. John Tangney and the Air Force Office on Speech
Research (grant no. AFOSR 89-0389) and to the Council on Advanced Studies in the Humanities and Social Sciences at
the University of Chicago for financial support to conduct the Workshop on Recognizing Spoken Language. Several
graduate students made the preparation for the workshop much smoother; they include Kevin Broihier, Anne Farley,
Jenny DeGroot, and Lisa Lee. In addition, several colleagues and students participated in the workshop discussions,
enriching the experience for everybody. We thank Jenny DeGroot, Starkey Duncan, Susan Duncan, Anne Farley, Steve
Goldinger, John Goldsmith, Beth Greene, Janellen Huttenlocher, Karen Landahl, Lisa Lee, Susan Levine, Jerre Levy,
David McNeill, Todd Morin, Nancy Stein, and Michael Studdert-Kennedy for their participation. We wish to express
special thanks to Anne Cutler for her valuable contributions to the workshop. Jennifer Jahn assisted in preparation of the
manuscript. We express gratitude to Teri Mendelsohn, our editor at the MIT Press, for her patience and guidance.
page_ix
Page xi

5. Contributors
Catherine T. Best Department of Psychology, Wesleyan University, Middletown, CT; Haskins Laboratory, New Haven,
CT
Jenny DeGroot Department of Psychology, University of Chicago, Chicago, IL
Peter D. Eimas Department of Cognitive and Linguistic Sciences, Brown University, Providence, RI
LouAnn Gerken Department of Psychology, State University of New York at Buffalo, Buffalo, NY
Judith C. Goodman Department of Psychology, University of California at San Diego, La Jolla, CA
Peter W. Jusczyk Department of Psychology, State University of New York at Buffalo, Buffalo, NY
Lisa Lee Department of Psychology, University of Chicago, Chicago, IL
Scott E. Lively Department of Psychology, Indiana University, Bloomington, IN
John S. Logan Department of Psychology, Carleton University, Ottawa, Ontario, CANADA
Rachel I. Mayberry School of Human Communication Disorders, McGill University, Montreal, Quebec, CANADA
Joanne L. Miller Department of Psychology, Northeastern University, Boston, MA
Howard C. Nusbaum Department of Psychology, University of Chicago, Chicago, IL
page_xi
Page xii
David B. Pisoni Department of Psychology, Indiana University, Bloomington, IN
Janet F. Werker Department of Psychology, University of British Columbia, Vancouver, B.C., CANADA
page_xii
Page 1
Introduction
page_1
Page 3
Chapter 1
Developing Theories of Speech Perception: Constraints from Developmental Data
Judith C. Goodman, Lisa Lee, and Jenny DeGroot
A tremendous proportion of research in speech perception has focused on a listener's ability to identify or discriminate
phonetic contrasts. This focus on lower-level segmental perception until recently dominated research with both adults
and infants (Eimas et al. 1971; Mattingly et al. 1971; Pisoni 1973; see also Aslin, Pisoni, and Jusczyk 1983 for a review
of segmental perception abilities by infants). As a result of this focus and the sorts of data these studies provide,
theoretical questions have addressed whether the mechanisms responsible for speech perception are best described as
innate and speech specific (Liberman et al. 1967; Liberman and Mattingly 1985; Repp 1982) or as properties of the
general auditory system (Lane 1965; Pastore 1981; Pisoni 1977).

6. The chapters in this volume suggest that either characterization alone is too narrow because they have concentrated on
studying perception in stable periods rather than trying to explain developmental change. By focusing on questions
regarding change in the processes of language perception across the lifespan, however, it can be seen that infants have
innate perceptual biases that are shaped by subsequent experience. Further, it appears that many levels of linguistic
structure provide informative constraints on one another (cf. Gerken, this volume; Jusczyk 1985; Katz, Baker, and
MacNamara 1974; Menn 1983 for discussions of the role of word learning in phonological development and semantics
and syntax in word learning) and that young listeners must learn about each level and how they may be related in
language processing. In addition, these developmental lessons appear to be useful in explaining language processing and
perceptual learning in mature listeners as well.
Our goal in this chapter is to abstract from the set of papers in this volume broad themes that must be considered in
explaining the development of speech perception and language understanding. These themes, on
page_3
Page 4
the whole, are concerned with the nature of linguistic experience and its influences on perceptual development.
Historically, research in speech perception dealt with how adults identify and discriminate phonetic information in the
acoustic input. This focus on adults is not surprising because what investigators sought to explain was the end statethat is,
how the mature listener perceived linguistic information. A challenge for these theories was to explain how listeners
handle the lack of invariance in the speech stream: no one-to-one mapping exists between information in the acoustic
waveform and the listener's percept. Many theorists proposed innate, speech-specific mechanisms to account for this fact
(Liberman et al. 1967; Liberman and Mattingly 1985; Repp 1982). In order to evaluate that claim, developmental data
was required, and the discrimination abilities of young infants were assessed. Still, it was not immediately apparent that
any developmental change in speech perception occurs because much of the early work found that very young infants
possess discrimination and identification abilities that are remarkably similar to those of adults (Eimas et al. 1971; Kuhl
1979; see Aslin, Pisoni, and Jusczyk 1983; Jusczyk 1981 for reviews).
This path of research has resulted in a gap between our knowledge of the infant's early sensory abilities and the adult's
processing of speech. We know that prelinguistic infants are sensitive to acoustic information which is linguistically
relevant and that there are striking similarities between their sensitivities and those of adults on tasks that involve the
discrimination of discrete, phonetic segments. But we also know that children come to represent linguistic unitsthat is,
they not only discriminate phonetic contrasts but they develop, for example, phone categories and lexical knowledge as
well. In other words, despite the perceptual parallels that exist between very young infants and adults, speech perception
does undergo development, and a theoretical account of the transition from the infant's sensory capacities to the child's
ability to identify words and perceptual learning by adults must be provided.
The chapters in this volume detail the changes that occur and propose mechanisms by which innate prelinguistic
discriminatory abilities may come to handle the representation and perception of linguistic structures. Further, many of
the changes we see during early childhood appear to have parallels in the processing of speech input by adults. Hence, the
mechanisms responsible for the development of speech perception may play a role in processing throughout the lifespan
and, therefore, may be important factors in explaining speech perception. This is not to claim that no differences exist
between children and adults. They do, and they
page_4
Page 5
must be explained. Nonetheless, the similarities are very suggestive about what sorts of mechanisms affect both
perceptual learning and the identification of linguistic units.
Due to the recent wealth of information concerning the nature of developmental change in language processing, it should
be possible to narrow the gap that exists between our theories of the innate processing mechanisms of infants and of
adults' abilities to recognize discrete linguistic units. The parallels noted above highlight the possibility of developing a
single, coherent theory of speech perception to account for the abilities of children and adults rather than having a
collection of theories each accounting for the perceptual abilities of a single age group.

7. This has not generally been the case. Most theories of adult speech perception do not consider how perceptual
mechanisms and linguistic representations develop (Elman and McClelland 1986; Liberman et al. 1967; Liberman and
Mattingly 1985). However, an understanding of developmental changes in the nature of these mechanisms and
representations could constrain theories of how adults use knowledge about structural properties of phonemes and words
to mediate language recognition. Therefore, in constructing theories of speech perception, it is important to consider how
maturation and experience modify innate sensory mechanisms, how structural knowledge is acquired, and whether young
children represent linguistic information in the same way as adults.
Similarly, studies of infant speech perception have seldom attempted to explain fully how the ability to recognize words
develops from innate perceptual abilities (but see Jusczyk 1985; Studdert-Kennedy 1986). A complete theory of speech
perception must describe how innate perceptual mechanisms come to support recognition of consonants and vowels as
phonetic categories, as well as the role of phonetic categories in the acquisition of early word patterns and the
development of the mental lexicon. Finally, theories of vocabulary acquisition in early childhood (Clark 1983; Markman
1991) and word recognition in middle childhood (Tyler and Marslen-Wilson 1981) are rarely linked to the infant's innate
perceptual abilities or to lower-level segmental processing at any age. In short, there is a need to integrate the findings
and conclusions of speech research from early perceptual encoding in infants to word recognition in adults.
While a great deal of work remains before a theoretical integration of this sort can be accomplished, we hope to further a
consideration of what a coherent theory might include by detailing factors that influence the development of speech
perception. We are not attempting to provide
page_5
Page 6
a theory, but we wish to highlight issues raised by the contributors to this volume that may shed light on the perceptual
processing of speech throughout the lifespan.
Three issues seem particularly important for building a theory of speech perception. The first of these issues concerns the
relationship between levels of linguistic knowledge in processing. A language is a multileveled system for
communication supporting the production and perception of phonemes, words, syntax, and paralinguistic information,
such as prosody. Information at one level may serve to constrain learning and perception at another level. For example,
children's phonological knowledge may emerge from their early lexical development (Menn 1983). Data concerning the
processes involved in understanding linguistic information at one level of representation may constrain the types of
processes that operate at other levels of representation. The chapters in this volume suggest that we should construe our
notion of level of linguistic structure or knowledge quite broadly indeed. Hence we will consider the role of stress and
prosody in the development of speech perception and the relationship between linguistic production and linguistic
perception, as well as processing interactions between levels of linguistic structure, such as the lexical and phoneme
levels. A consideration of data from both children and adults supports the conclusion that a theory of speech perception
should integrate the findings of research concerning language processing across levels of perceptuolinguistic analysis.
The second issue is concerned with the role of early linguistic experience. Early linguistic experience has two sorts of
effects. First, a critical period may exist for language learning (Lenneberg 1967), and, second, knowledge of one
language affects the learning and processing of a second language (Best, this volume; Best, McRoberts, and Sithole
1988; Lively, Pisoni, and Logan 1991; Logan, Lively, and Pisoni 1991; Pisoni, Lively, and Logan, this volume; Werker,
this volume; Werker and Lalonde 1988; Werker and Tees 1983). Something seems to be special about early childhood
with respect to language development. While some amount of perceptual learning is possible throughout the lifespan,
Mayberry's work shows that, if children are not exposed to linguistic input during the early years, subtle deficits exist
even after twenty years of language use (this volume; Mayberry and Eichen 1991; Mayberry and Fischer 1989). We will
consider the nature of this critical period and the sorts of developmental mechanisms that might account for it. One
possibility is that a critical learning period exists during which specialized neurological structures may be established for
perceptual processing of language. A second
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Page 7
possibility is that it is easier to learn some aspects of linguistic structure in the absence of other higher-order knowledge

8. because the latter may focus one's attention at the wrong level of analysis (see Pisoni et al., this volume). Most people do,
of course, learn a first language in early childhood, and the knowledge of that language influences their ability to learn
and to process a second language. The chapters by Pisoni, Lively, and Logan; Werker; and Best show that limitations on
the perceptual learning of a second language exist as a result of phonological knowledge of a first language. In addition,
work by Cutler et al. (1989, 1992) and by Grosjean (1988, 1989) indicates that even bilinguals show limitations in
learning two languages.
The third issue concerns the role of attention in perceptual learning. Experience with language modifies perceptual
processing both for children (Best, McRoberts, and Sithole 1988; Kuhl et al. 1992; Werker and Lalonde 1988; Werker
and Tees 1983) and adults (Lively, Pisoni, and Logan 1991; Logan, Lively, and Pisoni 1991; Pisoni et al. 1982; Samuel
1977). Current theories of speech perception cannot account for the development of perceptual abilities, however,
because they do not include a mechanism of change as part of the perceptual process. Many chapters in this volume
suggest that dynamic mechanisms-that is, processing mechanisms that allow a listener to change what information is
attended to according to input propertiesare critical for theories concerning the recognition and comprehension of spoken
language (Best, this volume; Jusczyk, this volume; Mayberry, this volume; Nusbaum and Goodman; this volume; Pisoni,
Lively, and Logan, this volume; Werker, this volume). Dynamic mechanisms will be an important component of a theory
that accounts both for the way speech perception develops throughout childhood and for the way perceptual processes are
modified by adults. Many authors in this volume argue that perceptual learning involves shifting one's attention to
particularly informative aspects of the acoustic signal. In other words, the effect of experience with one's native language
or, later, with a second language is to learn how to direct attention to the acoustic, segmental, lexical, and sentential
properties of an utterance that work together to specify the linguistic interpretation of the utterance. Below we address the
evidence related to each of these issues.
Relationships between Levels of Linguistic Structure in Speech Perception and Language Understanding
Theories of word recognition have commonly incorporated the use of information from multiple linguistic levels (Elman
and McClelland 1986;
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Page 8
Morton 1969; Marslen-Wilson 1975, 1987; Marslen-Wilson and Tyler 1980; Marlsen-Wilson and Welsh 1978) though
theories of speech perception seldom do (Liberman et al. 1967; Liberman and Mattingly 1985; Stevens and Blumstein
1981; Stevens and Halle 1967). However, several of the contributors to this volume, as well as other researchers, have
demonstrated interactions between levels of linguistic structure during language processing. Below, we look at the
interactions between phonemes, words, syntax, and prosody, as well as between perception and production. A single
coherent theory that explains processing and acquisition at a number of linguistic levels for a wide variety of input
contexts is needed to account for these findings.
Interactions between Different Levels of Linguistic Structure
In her chapter, Gerken notes that a common view about language acquisition is that children start with the smallest units
and gradually learn about larger and larger units as they acquire language. This seems intuitively plausible. After all, if
words are composed of phonemes, one must first learn phonemes, and if sentences are composed of words, then word
learning must precede sentence learning.
However, a great deal of research suggests that different levels of linguistic information are highly interactive both in
language acquisition and in language processing by children. A number of examples illustrate this point. Gerken (this
volume) suggests that syntactic information influences perception and learning at the lexical level in 2-year-olds. Recent
work by McDonough and Goodman (1993) finds that 2-year-olds use semantic information provided by a familiar verb
such as eats to assign meaning to an unfamiliar sound pattern such as rutabaga and that 2-year-olds' identification of an
ambiguous sound pattern in a sentence is influenced by semantic context (Goodman 1993). Lexical knowledge influences
phoneme perception by children: children's perception of ambiguous phonemes is influenced by lexical context (Hurlburt
and Goodman 1992). In addition, changes in phoneme perception occur around 10 months of age (Werker and Lalonde
1988; Werker and Tees 1983), suggesting that interactions may occur between the development of phoneme perception
and the acquisition of a child's earliest-comprehended lexical units. Finally, suprasegmental information influences
perception of other units: HirshPasek et al. (1987; see also Kemler Nelson et al. 1989) have shown that suprasegmental

9. information may direct infants' attention to linguistic units such as clauses and phrases. These findings are not raised to
make claims about temporal properties of interactive processing but to note
page_8
Page 9
that at some stage in processing (perceptual or postperceptual decision) information at one level affects identification and
acquisition at other levels of linguistic structure.
How can these sorts of interactions in acquisition and processing be explained? In his chapter, Jusczyk provides one
suggestion of how various levels of linguistic structure might interact to result in phonological learning. The model of
word recognition and phonetic structure acquisition (WRAPSA) that Jusczyk presents suggests that children do not work
up unidirectionally from smaller to larger units. Jusczyk theorizes that young infants store exemplars of the utterances
they hear, perhaps represented in syllabic or larger units. With linguistic experience, they begin to weigh the properties of
the utterance according to their relative importance in signaling meaningful distinctions. Segmental representations arise
from the discovery of similarities and contrasts among these exemplars. Due to the temporal nature of speech (simply
put, the listener hears the initial portions of an item first), this process may be biased toward segments in initial position.
For example, utterances with initial segments that share acoustic characteristics may be classified together, forming the
basis for distinguishing these segments from other segments.
In her chapter, Best also speculates that infants' phone categories are not necessarily segmental in size but may involve
larger units such as syllables and words. Phonological knowledge may arise from a refinement of these larger units.
Best's view of what information is important in signaling meaningful distinctions between phone categories differs from
that suggested by Jusczyk. In particular, she suggests that infants come to represent phone categories by learning the
articulatory-gestural properties of speech. According to this view, both speech perception and production are guided by
knowledge of articulatory gestures.
Although the details of these models may not all be correct, the models attempt to deal with a void in theories of speech
perception, namely the mechanisms by which infants hone in on the phonology of their native language. Whatever the
nature of phoneme representations, an integration of levels of linguistic structure may be critical in learning the relevant
categories because it provides important constraints on the identity of acoustic information. Thus, the acquisition of a
lexicon might contribute to the categorization of speech because it is informative with respect to the correlations of
distributional properties that signal meaningful distinctions (for example, phonemes distinguish words).
The same kind of interactive constraint process may operate at other levels of linguistic structure. For example,
suprasegmental information in
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English may signal the onset of a word (Cutler et al. 1992). This issue is important in accounting for perception in adults
as well as children. Pisoni, Lively, and Logan (this volume) show that perceptual learning occurs in adults and is affected
by the position in a word where the phoneme occurs. Ganong (1980) found that lexical information affects phoneme
perception in monolingual adults, and Grosjean (1988; Burki-Cohen, Grosjean, and Miller 1989) found that, under certain
conditions, phoneme perception by adult bilinguals is affected by the language of the surrounding words.
To note the role of higher-level information in perceptual learning does not preclude the simultaneous occurrence of
within-level learning. For example, infants may develop vowel categories prior to any knowledge of word level
information. Kuhl et al. (1992) tested infants from the United States and Sweden on their perception of native- and
foreign-language vowel prototypes. Their results showed that by 6 months of agebefore they have acquired wordsinfants
have become sensitive to vowels that are prototypical of their native language. These vowel categories may emerge not
from the acquisition of words but from the way infants are predisposed to store information. Nonetheless, interactions
between different levels of linguistic knowledge play an important role in other sorts of perceptual development, and any
theory of speech perception must provide an account of these interactions.
Stress and Prosody

10. Although language development is most often studied in terms of growing knowledge of segmental units of various
sizes, such as phonemes, morphemes, and words (Bates, Bretherton, and Snyder 1988; Ferguson and Farwell 1975;
Menyuk and Menn 1979; Walley, Smith, and Jusczyk 1986), the suprasegmental level of linguistic information also
contributes to speech perception and its development. Suprasegmental information includes the patterns of stress and
prosody that are characteristic of a language. A growing body of research suggests ways in which stress and prosody are
important for language processing. Listeners use this information to interpret language and to learn more about the
structure of speech.
The prosodic structure of language can guide adult listeners in their perception of speech. Cutler (1976) showed that the
stress contours of an utterance focus a listener's attention on the location in a sentence of important semantic information.
Thus, prosodic information influences word identification by directing a listener's attention to particular items in an
utterance.
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More recently, Cutler and her colleagues (Cutler et al. 1986, 1989, 1992; Cutler and Norris 1988) have shown that
prosody can play a role in lexical segmentation for speakers of languages in which it is a predictable cue to word
boundaries. For example, English is a stress-timed language comprised of sequences of strong and weak syllables. Strong
syllables are more likely to signal the beginning of a content word than are weak syllables. French has a very different
prosodic structure; speech rhythm is syllable based. Cutler and her colleagues have found that English and French
listeners adopt different segmentation strategies that reflect the rhythmic structure of their respective languages. Native
English listeners segment the speech at strong-syllable boundaries, thus increasing the likelihood of finding and accessing
a content word (Cutler and Norris 1988). Native French listeners, however, use a syllable-based strategy (Cutler et al.
1986, 1989). Thus, prosodic features affect perceptual processing. Further, since they affect processing in language-
specific ways, they must be learned.
In addition to highlighting word boundaries and semantic information for adult listeners, prosodic variables may play a
role in the development of language recognition and language production. Many researchers have provided evidence that
stress patterns affect early lexical development (Blasdell and Jensen 1970; du Preez 1974; Gleitman and Wanner 1982;
Slobin 1982): stressed words may stand out in a stream of fluent speech. In other words, they may be easier to segment
from the speech stream. This hypothesis is supported by the fact that content words, such as object names, which tend to
receive primary stress, tend to be learned early (Nelson 1973). Although it is plausible that children fail even to perceive
words in an utterance that do not receive stress, it is more probable that, like adults, stress simply directs them to the
important semantic information. Gerken's work (this volume) demonstrates that children do, in fact, perceive unstressed
items. Although they apparently recognize these items, they often fail to produce them in their own utterances. But, even
their omissions demonstrate their sensitivity to and knowledge of the prosodic patterns of English: when utterance
complexity causes children to omit words from their speech, they follow the metrical pattern of English, producing words
in strong positions and omitting weak syllables that follow them. This suggests that young children know a great deal
about the prosodic patterns of sentences.
In fact, even before children begin to understand spoken language, they are sensitive to the prosodic properties of speech
that facilitate perception. In a series of experiments, Kemler Nelson et al. (1989) suggest how sen-
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Page 12
tence prosody may provide cues to segmentation of linguistic units, such as clauses and phrases. Kemler Nelson et al.
(1989), for example, found that 6-month-old infants are sensitive to the prosody of clausal units. The infants heard
speech samples in which one-second silences were inserted either at clause boundaries or in the middle of clauses. The
investigators hypothesized that the sentences with silence inserted at clause boundaries would sound more natural. The
infants preferred the more natural utterances, suggesting that they are sensitive to the relationship between prosody and
linguistic units.
At nine months, infants preferred speech in which silences were inserted between syntactic phrases than speech in which
silences were inserted within phrases. These findings held even when the phonemic content was filtered out of the

11. speech, leaving the prosodic contours. This suggests that, before they are a year old, infants gain sensitivity to linguistic
units that are marked by prosodic structure. This sensitivity should help them to direct attention to linguistically relevant
information when listening to fluent speech.
These findings demonstrate that a theory of speech perception should incorporate prosodic influences. In development,
prosody may focus infants' attention on relevant linguistic unitssee Fernald (1984) for the role of prosodic information in
attention to language very early in infancy. Prosody could play an important role in semantic development as well. For
example, stress may help to direct children's attention to important semantic information, facilitating processing of those
items relative to unstressed items (Cutler and Swinney 1987). Furthermore, the segmentation work of Cutler (1976) and
her colleagues (Cutler et al. 1989, 1992) demonstrates that prosodic factors affect processing throughout the lifespan and
must be incorporated into theories of language understanding. Regularities in prosodic structure facilitate lexical
segmentation and focus listeners' attention on important semantic information.
The process by which the prosodic structure is learned has not been specified. One great mystery is the extent to which
prosodic information of a second language can be learned. Some evidence suggests that, with brief exposure to an
unfamiliar language, listeners can learn to use prosodic information to determine the constituents of an utterance
(Wakefield, Doughtie, and Yom 1974). Other work has suggested that this ability exists independently of specific training
in the foreign language (Pilon 1981). Cutler et al.'s (1992) work demonstrates that even bilinguals seem unable to
maintain two prosodic structures, one for each of their lan-
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guages. Clearly, the acquisition of a prosodic structure, as well as its role in language learning and speech perception,
must be further explored.
The Relation between Language Production and Language Perception
The notion that speech production plays a role in speech perception is not new. The motor theory of speech perception
proposes that listeners perceive speech by recognizing the articulatory gestures that produced the signal and that this is
carried out by language-specific specialized mechanisms (Liberman et al. 1967; Liberman and Mattingly 1985). Early
accounts of motor theory focused on adult perception and did not address the development of speech perception abilities.
However, speech production may play a role in the development of speech perception. Indeed, some discussion as to how
a specialized, motor-based speech perception system might develop has been presented recently. Studdert-Kennedy
(1986) suggests that language evolved in the left hemisphere of the brain to take advantage of the neural organization for
manual coordination already centered in that hemisphere. For each child, the development of speech or sign language
requires the development of a perceptuomotor link in the left hemisphere; experience in a language environment enables
this neural development to occur.
Another look at the relation between production and perception has been offered by Miller and Eimas (this volume). In
their chapter in this volume, Miller and Eimas discuss how listeners might normalize changes in speaking rate. They
examine infants' and adults' discrimination of phonemes that occur in syllables of various durations (a correlate of
speaking rate). The authors suggest that a specialized mechanism for speech perception might explain the striking
similarities in rate normalization in infants and adults. They note that other relationships between perception and
production are possible but that there is not sufficient human neurophysiological data to evaluate the various possibilities.
However, neurophysiological data from other species (namely, barn owls and bats) indicate that a specialized perceptual
process may in fact be an emergent property of underlying neuronal behavior patterns. A similar sort of processing
system could be true of human speech perception as well.
The motor theory assumes that articulation-based mechanisms of perception are specialized for speech. Best (this
volume) also argues that perception is intrinsically linked to knowledge of how speech is produced. Her view of
acquisition and perception, however, is closely tied to Gibson's ecological theory of perception (1966, 1979; see also
Fowler 1986,
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12. 1989, 1991), and she argues that children learn these relations as they learn about other nonlinguistic stimuli. Thus, like
other types of perception, speech perception is said to involve the perception of distal objects or events. In the case of
speech, the relevant distal events are the articulations that produced the speech signal. Language-specific speech
perception develops as the child detects systematicity (sound-meaning correspondences) in the articulatory gesture
patterns produced by mature speakers. The development of the child's production is guided by these perceived gestural
patterns.
Other work demonstrates that infants are sensitive to production factors of speech. Infants as young as 5 months of age
can match a face producing a vowel with the appropriate auditory input (Kuhl and Meltzoff 1984). Thus, infants appear
to be quite good at making intermodal connections between sources of perceptual information. A consequence of this
ability could be that visual information (lip movement) constrains the interpretation of speech input (Massaro 1987;
Massaro and Cohen 1983; McGurk and MacDonald 1976). If infants make a connection between their kinesthetic
sensations in production and what they see during perception, this might facilitate their categorization of sounds. In other
words, knowledge about articulatory gestures and their correspondence to auditory patterns provides another sort of
constraint that may be important in perceptual learning and processing.
The Role of Linguistic Experience
Although perceptual learning occurs throughout the lifespan, something seems to be special about childhood. Adults can
learn nonnative contrasts, but limitations on this learning appear to exist. For example, in their chapter Pisoni, Lively,
and Logan report that Japanese listeners' ability to identify /r/ and /1/ differed according to word position, suggesting that
nonnative listeners did not really learn a context-independent phoneme category. Although the structure of phoneme
categories for native speakers of a language is not clear, such speakers do not show similar word-position effects in
discrimination. These findings suggest that perhaps one cannot learn a second language to native proficiency if learning
begins after some critical period. If there is a critical period during which language must be learned, what is it that is
critical to language learning?
In her contribution to this volume, Mayberry suggests that, if one is not exposed to linguistic input in the first few years
of life, subtle but identifiable differences will exist in the way language is processed. She presents
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evidence from deaf people who use American Sign Language (ASL). In one study, congenitally deaf ASL signers, who
varied in age of acquisition from birth to 18 years, performed shadowing and recall tasks. Mayberry found significant
differences that depended on the age of acquisition even when she controlled for the number of years of use.
Analyses of errors in which signers substituted one word for another revealed interesting patterns that differentiated early
and late learners. Early learners are more likely to make errors in which they substitute words with similar meaning in
the shadowing and recall tasks. In contrast, late learners have a greater tendency to produce phonological errors, in which
the intended sign is structurally but not semantically similar to the incorrect sign. Mayberry's interpretation is that late
learners fail to learn an automatic encoding of phonological forms. Hence, they devote too much attention to deciphering
low-level information in the sign at the expense of subsequent semantic analysis. Newport (1984, 1988) similarly argues
that late ASL learners learn a frozen form and have difficulty decomposing the input into its components for both lexical
and syntactic levels of analysis.
Importantly, Mayberry shows that early experience with any language will facilitate language processing later in life.
Mayberry's evidence shows that late learners of ASL who became deaf after acquiring spoken English or who had
residual hearing that may have allowed them to perceive some speech during early childhood perform better and more
like native signers than late learners who had little or no early linguistic experience. Her argument is that the group that
had some linguistic experience early in life may still have subtle deficits in analyzing the phonological information of
sign language but are better able to use higher-level constraints to fill in than are signers who had no systematic language
input in early development. Thus, Mayberry's work shows the importance of early linguistic experience to normal
language development.
As noted earlier, Pisoni, Lively, and Logan found that one's native language exerts a lifelong effect that limits perceptual
learning in adults. Further evidence of the role of early linguistic experience in later language processing is Cutler et al.

13. (1986) and Cutler and Norris's (1988) findings that the segmentation strategies adult listeners use in understanding speech
are determined by their native language. These experiments, mentioned in the stress and prosody section above, provide
evidence that monolingual English listeners use a stress-based segmentation strategy and monolingual French listeners
use a syllable-based strategy to segment linguistic units in speech. Further, when presented with stimuli in their
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nonnative language (French for English speakers and English for French speakers), they do not switch segmentation
strategies (Cutler et al. 1989). The strategies listeners use appear to depend on the characteristics of their native language.
The findings of Pisoni, Lively, and Logan (this volume) and Cutler et al. from work with monolinguals listening to
nonnative languages (see also Best, this volume) could theoretically result from a critical period (e.g., second-language
learning or processing took place after the critical period), but Cutler and her colleagues (1989, 1992) found that even
bilinguals show limitations based on experience with one of their languages. Since bilinguals are natively fluent in both
their languages, it is reasonable to expect that they may switch processing strategies depending on the language being
perceived. But surprisingly, these listeners did not show such flexibility. These results suggest that there is a limit to the
perceptual flexibility listeners have. Even listeners who learn two languages in childhood and seem natively fluent in both
show the influence of their dominant language. This suggests that experience with one language exerts subtle limitations
on the processing of another language independent of limitations set by a critical period. Further work is necessary to
establish how findings relevant to critical periods and bilinguals are related, how they can be explained, and how each
constrains theories of speech perception.
How might one language limit learning and processing of a second language? This is, of course, a complex question for
which there may not be any single answer. In her chapter, Best (see also Best, McRoberts, and Sithole 1988) offers one
explanation for the difficulty in perceiving nonnative phonetic contrasts: her perceptual assimilation model captures the
patterns of influence that a native language has on learning and on perception of another language. According to her
model, difficulty in discriminating a nonnative contrast can be predicted according to the relationship between the native
and the nonnative phonologies. For example, if each member of a nonnative contrast is similar to a different native
phoneme, discrimination of the nonnative contrast should be very good. If instead both members of the nonnative
contrast are similar to a single native phoneme, then discrimination abilities depend on the degree of similarity of each
member of the nonnative contrast and the native phoneme. If members of the nonnative contrast are equally similar to
the native phoneme, discrimination is hypothesized to be poor. However, if they differ in how similar they are, they
should be relatively more diseriminable. Finally, if the characteristics of the nonnative contrast are
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quite different from any native contrast, the nonnative items may be easily discriminated as nonspeech sounds. Best
presents evidence for the perceptual assimilation model by examining the performance of native English speakers on the
discrimination of different Zulu contrasts.
Further evidence that perception of nonnative contrasts is guided by the listener's native language comes from learning
studies. Werker (this volume; Werker and Tees 1983; Tees and Werker 1984) has found that native English listeners are
quite good at learning to discriminate a Hindi voicing contrast but are poor at discriminating a retroflex-dental place
contrast. This finding is easily accounted for by Best's framework (this volume; Best, McRoberts, and Sithole 1988). The
voicing contrast is distinctive in English, and the Hindi contrast spans two different categories in English and is easily
discriminated. In contrast, the retroflex-dental place contrast is not distinctive in English. According to the perceptual
assimilation model, this contrast is very difficult for native English listeners to learn to perceive because they assimilate
both of the nonnative tokens into a single native category.
Thus, it is clear that one's early linguistic experiences have a lasting effect on speech perception and perceptual learning
throughout life. Best's model explains what listeners do when they hear a nonnative contrastthey interpret it in terms of
the phonological categories of their native language. But why can't second-language learners simply learn not to do this;
why are they limited in learning to attend to the features that are phonemic in another language? One possibility is that,
like the ASL learners studied by Mayberry (this volume; see also Newport 1984, 1988), they find it difficult to attend to

14. phonological distinctions in the input. They focus on the larger unit instead (e.g., a lexical item). When an older learner
tries to parse the speech stream, he or she brings along cognitive abilities and world knowledge that are not available to
the infant hearing speech in the first year of life. The older learner may attend more to semantic aspects of the input to
get the gist of what a speaker is saying.
Early phonological and lexical learning might also result in structural changes, that is, the way the brain responds may
change as a function of learning. Thus, when learning later in life, brain structures and responses are different than when
learning during the first year. In fact, Mills, Coffey, and Neville (1991) using ERP data find changes in brain responses
as a consequence of learning words in late infancy. Children at 13-17 and 20 months of age heard words that were
generally learned very early by children (among the ten first words) or learned relatively late. ERPs indicated differences
in responses to comprehended and unknown words.
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In addition, specialization begins to occur at this early age. At 13-17 months, the response differences are bilateral and
widely distributed over areas of the brain anterior to the occipital regions. By 20 months, these differences are confined
to the left hemisphere and to the temporal and parietal regions.
At both age groups, language ability affects the extent and nature of the reported differences, suggesting that the changes
in brain response and language processing are closely linked. Furthermore differences occur between possible English
words and backwards English words at around 10 months (Mills, personal communication)an age that closely
corresponds to Werker's and Best's findings of perceptual losssuggesting structural changes appear as children learn the
phonotactics of their language. Thus, changes in neural representation of language emerge as a function of age and of
linguistic ability. These structural changes during early childhood may contribute to the limitations that are evident in
perceptual learning later in life.
In sum, critical periods may emerge as a consequence of learning and structural changes associated with learning. One
could speculate that, if areas of the brain that normally become specialized for language are not used early in life, those
areas may be allocated to some other function. Just as one cannot unlearn native contrasts because structural changes in
the brain have occurred, one cannot easily unlearn the other functions that have taken over those regions either. A second
reason behind this need to learn early that phonological forms map to word meanings may be that it becomes more
difficult to shift attention to lower-level linguistic input in a signal as the age of the language learner increases, focusing
instead on frozen forms (cf. Newport 1990). People seem unable to parse wholes into their component parts unless they
learn those parts early in life.
Despite an adult's limitations in perceptual learning, these findings also demonstrate remarkable flexibility in learning a
second language long past the onset of any purported critical period. The chapters in this volume by Pisoni, Lively, and
Logan and Werker show that adults can, with training, learn to discriminate nonnative contrasts with a surprising rate of
success. Just as the limitations described above are in need of a principled theoretical account, the flexibility that allows
perceptual learning throughout the lifespan is critical to any complete theory of speech perception. How can we account
for this learning? Many of the contributors to this volume note that attentional mechanisms may be crucial in explaining
perceptual learning. These mechanisms may be important both
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for infants learning their first language and for adults learning a second language as well.
The Role of Attention in Speech Perception
Attention as a Developmental Mechanism
Listeners must learn just what acoustic input is relevant to meaningful distinctions in their native language and come to
attend to those language-specific characteristics of the input during speech perception while ignoring other information.
Thus, one could think of the development of speech perception as involving attentional shifts. In addition, adult
perceptual processing may involve attentional shifts depending on contextual factors. As listeners gain experience with a

15. language, they learn which dimensions of the input are relevant to deciphering a message. The chapters by Pisoni, Lively,
and Logan and Jusczyk turn to a metaphor provided by Nosofsky (1986, 1987) to capture this shift. With experience, one
stretches out important dimensions and shrinks unimportant dimensions. Consequently, small differences along important
dimensions are now magnified and easy to discriminate. Differences along unimportant dimensions, on the other hand,
are made smaller and are unlikely to be detected. In other words, experience tells one what information is important and
draws one's attention to those aspects of the input. What is important may vary depending on the available context and on
the listener's knowledge about various linguistic levels.
The result of learning what information is important is a means of identifying linguistic units by weighting the input
components according to how reliable and valid they have been in a listener's past experience (cf. Bates and
MacWhinney 1989 for a syntax-processing model that makes use of these constructs). As listeners analyze a sound
pattern, they interpret the acoustic input with respect to these learned weights. Consequently, they attend differentially to
various aspects of the input in order to arrive at a meaningful percept. This allows listeners to impose a linguistic
structure on a speech signal that lacks acoustic-phonetic invariance. Different languages employ different information in
making meaningful distinctions, so various aspects of the input will be weighted differently across languages. Hence,
experienced users of different languages may interpret the same acoustic input differently. As one gains more experience
with a languagethat is, as one has many experiences with information that is reliable and valid in signaling meaningful
distinctions in one's languagethe weights used during analysis of the input should become
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more entrenched and difficult to change (Bates and Elman 1992). Thus, it becomes increasingly difficult to learn a
second language. Nonetheless, with effort, even entrenched weight systems can be altered: adult listeners can learn to
attend to previously ignored phonetic information in the signal and use it to determine that two inputs differ.
This approach suggests why what had looked like perceptual loss of sensory discrimination abilities (Eimas 1975;
Strange and Jenkins 1978) is really perceptual reorganization of perceptual biases. Werker (this volume) and Pisoni,
Lively, and Logan (this volume) note that the early training studies failed to find perceptual learning in adults who tried
to categorize nonnative contrasts. According to the view presented above, their weight systems for attending to and
identifying acoustic-phonetic input were entrenched. Pisoni, Lively, and Logan point out in their chapter that the training
paradigms in those early studies often used synthetic input even though the discrimination tests involved natural input.
Further, the training sets generally used word-initial contrasts, while the test sets used contrasts in several word positions.
If subjects learned new weighting systems based on the training input, the new system should not strongly influence their
perception of the test set because the characteristics of the test set differed substantially from the training input. As a
result, training would not affect perceptual learning of nonnative contrasts. The failure of early training studies had been
attributed to a loss of sensory mechanisms.
Pisoni, Lively, and Logan provided listeners with large amounts of experience across the broad range of situations in
which they would actually hear nonnative contrasts (many speakers and many contexts using natural speech) and found
that listeners' abilities to perceive nonnative contrasts improved. Listeners may have learned to shift weights in relevant
ways. In this sense, listeners reorganized their perceptual processing such that they now could stretch previously
irrelevant dimensions of the input (see Pisoni, Lively, and Logan, this volume; Werker, this volume).
One consequence of this approach is that similar cognitive mechanisms can be used to describe perceptual change in both
children and adults (see also Pisoni, Lively, and Logan, this volume), thus bringing coherence to a theory of speech
perception. Adults learn to focus attention on specific properties of the speech signal to make linguistic judgments as do
children. This attentional shift occurs because the listener's language-specific knowledge changes. Thus, the processes by
which a listener perceives speech might not differ greatly with age; rather, the knowledge a listener has to impose
linguistic structure on the acoustic input changes (see also
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Goodman 1993; Nusbaum and Goodman, this volume). Of course, this leaves open how one comes to learn which
dimensions are important in a given language, that is, how a listener comes to set the weights. Answering this question is

16. a critical challenge for the coming years.
A second consequence of this approach is that similar cognitive mechanisms can be used to describe processing across
linguistic levels. In their chapter, Nusbaum and Goodman point out that, rather than positing one sort of mechanism to
explain speech perception and different sorts of mechanisms to explain other kinds of language processing, such as
grammatical acquisition or word recognition, an investigation of attentional mechanisms may highlight commonalities in
processing across these domains. Listeners may attend to information across levels of linguistic processing in establishing
the weighting system. As a result, they will draw on information from a variety of sources (acoustic-phonetic, semantic,
syntactic, and talker) to identify a segment or a word, and information from one level of linguistic analysis may constrain
identification of units at another level. In essence, the weighting representation builds in variations due to context and
level of analysis. Similar claims of a process of constraint satisfaction have been made with respect to learning a
grammar (Bates and MacWhinney 1989), to machine learning (Bates and Elman 1992), and to development of
identification of complex visual forms (Aks and Enns 1992). In order to provide an account of perceptual processing,
future research will have to explain how a listener learns to which cues to attend across linguistic levels and how
listeners represent interlevel constraints.
In short, work presented in this volume suggests that future research should explore the role that shifts in attention may
play in perceptual learning in children and adults and in relating processing across linguistic levels. Based on linguistic
experience, listeners appear to develop a weighting scheme that directs their attention differentially to various aspects of
the acoustic input. The acoustic input, of course, includes information from many linguistic levels simultaneously, so that
listeners distribute their attention to capture regularities across linguistic levels and thus develop a multilevel weighting
scheme or distributed representation, as a consequence. Through experience with a language, this will result in increased
knowledge about the structural properties of spoken language and how they interact (Nusbaum and Goodman, this
volume): listeners assign weights to multiple sources of information to form a sort of contextual map. During speech
perception, the focus and distribution of attention at any one point in time will depend on this knowledge or weight
scheme.
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Problems with Attentional Explanations
There are two important problems with this speculation on the role of attention in the development of speech perception.
First, perceptual learning is limited in ways that cannot be accounted for only in terms of influences by one's native
language. For example, bilingual learners might have a dominant language. No mechanism is inherent in this attentional
explanation to address those limitations. Second, and related to the first problem, the above account unfortunately does
not make clear how one comes to learn which dimensions are reliable and valid in signaling meaningful distinctions, that
is, the attentional explanation does not show how people learn what is important for perception or along what dimensions
perceptual reorganization takes place when learning a second language. Addressing these issues, upon which we expand
below, will be critical in accounting for the development of speech perception.
The fact that perceptual learning later in life is less effective than early learning could be due in part to one's first
language interfering with setting weights for a second language (hence the less-than-perfect discrimination performance
on nonnative contrasts despite training (Pisoni, Lively, and Logan, this volume)). However, the problem is not solely due
to the established weight system for a first language because late learning of a first language also seems to take a
different path than early learning (Mayberry, this volume; Newport 1984, 1988, 1990). This suggests that, when an adult
learns a second language, two factors may influence perceptual learning, structural knowledge of a native language and
attention to a structural level different from that to which a child learner attends.
The issue here is that, while attention to important information may enable the listener to structure the input in a way that
facilitates recognition, we still need to explain why this apparent critical period exists and how it constrains later
learning. One possibility is that neural maturation affects language learning later in life. The second possibility is that as
other learning occurs, one's perception of the world changes, and consequently, language learning takes place in different
machinery in an older learner than language learning in an infant. Newport (1990) has suggested that late learners are less
able to analyze forms into morphological components. In her chapter, Mayberry (this volume) makes a similar claim with
respect to phonology. These findings imply that late learners have difficulty in determining what information is important
in language processing, that is, what information should be heavily weighted.

17. It is still more difficult to account for Cutler et al.'s (1989, 1992) findings concerning segmentation strategies of
bilinguals. Those findings suggest
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that the capacity to represent two languages is limited even when both languages are learned early. Unfortunately, we
lack detailed information of learning in bilinguals, such as those in Cutler et al.'s study, so we cannot make strong
inferences on why the weights of one language dominate the other. Clearly, this is a problem that awaits future empirical
findings.
This leads to our second problem. We need some theory to explain how listeners at any point along the developmental
span learn which information is reliable and valid. Jusczyk (this volume) suggests that listeners store very specific
representations and over time abstract out regularities and central tendencies. Indeed, Kuhl et al. (1992) find that infants
appear to attend to central tendencies very earlythey recognize the prototypical vowels for their language at around 6
months of age. These vowel prototypes presumably emerge as a result of infants storing many exemplars of a vowel and
learning the central tendencies of their language's vowel space from the acoustic information. Listeners do retain very
specific information about acoustic input they hear, suggesting that they may indeed store exemplars. For example,
Nygaard, Sommers, and Pisoni (1992) demonstrate that adults retain information concerning the speaker of spoken
words. In other words, listeners may store not only particular words they hear on a list but the speaker characteristics as
well.
Kuhl's account also suggests that vowel categories are constructed from the bottom up, that is, infants' vowel categories
may be independent of accompanying phonetic or semantic information. It is not clear that prototypes for consonant
categories could develop this way. For example, Best and Jusczyk both propose in their chapters that children begin to
develop a phonological system by first responding to the more global characteristics of the structure of speech that they
hear in their environments and that they only gradually come to break down the speech signal into phonemelike
segments. In other words, rather than a bottom-up building of phonetic features to words, the child (and adult learner)
may move progressively from relatively large undifferentiated units to smaller, context-dependent units and, then, to
phonological categories (Best, this volume; Jusczyk, this volume; see also Walley, Smith, and Jusczyk 1986).
One implication of this is that higher-level context may provide important constraints in learning what is reliable and
valid information in phoneme identification. It is interesting that late learners appear to store the larger units or the
context-dependent units but seem to have difficulty in abstracting out the regularities and central tendencies necessary for
learning abstract phoneme categories (Mayberry, this volume; Pisoni, Lively,
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and Logan, this volume). Perhaps the difference between early and late learners is that children are able to abstract out
regularities from these more global, contextbound chunks, while adults, who perhaps focus more on meaning, are unable
to unpack this information.
If children learn abstract phoneme categories, then the question remains as to how that learning takes place. Two
possibilities bear future exploration. Kuhl et al.'s (1992) work suggests that prelinguistic infants form vowel prototypes
and, thus, supports the possibility that listeners construct prototypes from the most frequent or central exemplars
encountered in the acoustic input. However, vowels differ from consonants in duration and complexity, so consonant
prototypes, if they do exist, might be based on more information than the bottom-up segmental input alone. Important
constraining information might include not only acoustic qualities, but also information regarding the context of
occurrence (that is, surrounding phonemes), the lexical context, and other characteristics of the input information.
Jusczyk (this volume) has proposed that initial prototypes might be syllables. Further, when children learn words, they
might represent lexical items holistically. These representations could ultimately support phoneme prototype
representations as listeners reorganize sound patterns to facilitate discrimination between words. This system requires
storage of a very large number of exemplars. Jusczyk shows that even infants can remember a phonetic category for two
minutes and that this memory improves between 4 days and 2 months of age. While this period is very brief, perhaps by

18. later infancy they retain information about various linguistic units for much longer. These exemplars could be used to
construct prototypical representations of linguistic entities.
The second way a prototype could be established is that the listener updates his or her representation with each input. An
initial prototype could be formed on the basis of a single instance. If subsequent input is identified as similar to some
developing prototype on the basis of any acoustic or contextual information, that input will be used to update the stored
category representation. Those features that are valid and reliable in identifying inputs for a particular language will be
used to identify the speech and, therefore, to update the stored representation. In this way, the most constraining
information across linguistic levels will be assigned the greatest weight over time.
The strength of positing prototype representations of phoneme categories is that they readily explain why it is difficult to
perceive nonnative contrasts. If listeners represent prototypes and consequently differentially
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weight various acoustic dimensions, they will try to interpret it within the phonological system of their native language
when they hear a speech sound from another language. Acoustic information that is similar to a native weighting scheme
will be pulled into that prototype, a phenomenon labeled the perceptual magnet effect by Kuhl (1991). Hence, the
nonnative sound will be identified as a native phoneme. However, with a great deal of experience listening to nonnative
contrasts, particularly with training, new prototypes for the second language might be formed.
The weakness of positing prototype representations of phoneme categories is that it is difficult to account for interlevel
contextual effects. Consider, for example, Ganong's (1980) finding that lexical context influences phoneme perception.
The same acoustic information is interpreted as different phonemes depending on context (e.g., a /d/ in the context of -
ash, but a /t/ in the context of-ask). Recent work (Hurlburt and Goodman 1992) finds that children may shift their
responses to make them compatible with words even when the initial phoneme is clear natural speech.
If listeners represent a fixed phoneme prototype, why does the context spur two different interpretations of the same
acoustic information? Nusbaum and Goodman (see also Nusbaum and DeGroot 1990; Nusbaum and Henly 1992, in
press) suggest in their chapter that, if the features that are important for identifying speech change with context, then
perhaps listeners do not represent context-independent prototypes. Rather than learning a prototype representation, in
distributing attention across the acoustic input and the language situation, one might develop a theory based upon a wide
variety of context-dependent input (see also Medin 1989; Murphy and Medin 1985). The theories of phoneme categories
may consist of propositions concerning information about the function of the category, an abstract specification of its
form and how context operates on it, and its relationship to other linguistic knowledge. Indeed, listeners do represent
context-dependent phonetic categories (Miller and Volaitis 1989; Volaitis and Miller 1992). They may develop context-
dependent phoneme recognition processes based on multiple linguistic levels as well. Development of speech perception
would require attention to constraining information across contexts to learn about the structure, nature, or function of
linguistic categories.
Conclusion
The goal of this book is to examine how children develop the ability to perceive their native language. In so doing,
perhaps light will be shed
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on perceptual processing in mature listeners as well. The mechanisms by which we learn to interpret acoustic input are
unclear. In fact, not much research has directly addressed the question of how perceptual categories are learned. In the
past, perceptual processing in infants generally has been treated as independent from speech perception in adults. The
dynamic mechanisms important in the transition from the infant's early sensory abilities to perception of linguistic
categories were not of central interest. A second aspect of earlier research which may have obscured the nature of
dynamic mechanisms is that much of the exploration of speech perception has examined processing within a single
linguistic level. The constraints of the acoustic signal provided by interactions from other levels have not been as

19. thoroughly investigated.
Considering these issues may seem to add noise and complexity to a question that has already proved difficult to answer.
However, we hope that turning to these areas may add clarity by providing an account of how listeners interpret the
language they hear regardless of the context in which it occurs. The chapters in this volume describe the nature of
learning throughout the lifespanboth our flexibility and limitations and speculate about the mechanisms by which that
learning occurs. The focus on learning has highlighted the need to incorporate dynamic mechanisms in processing, both
to explain development and to explain processing across the wide array of contexts mature listeners regularly encounter.
These chapters suggest that speech perception does indeed develop. Further, it develops in a bidirectional interplay with
higher level lexical and phrasal structures. These findings reported in this volume suggest that it is a mistake to view
speech perception as an isolated domain, running on its own autonomous principles and, thus, independent from other
properties of language. Clearly, theories of the development of speech perception must incorporate these findings in order
to account for how the infant's impressive innate perceptual abilities are modified by experience. What is more, a
consideration of the theoretical mechanisms that account for these developmental findings invites speculation that similar
mechanisms may also account for the flexibility demonstrated by adults identifying speech in its endlessly varying
contexts.
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PART I
Innate Sensory Mechanisms and Constraints on Learning
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Chapter 2
Observations on Speech Perception, Its Development, and the Search for Mechanism
Joanne L. Miller and Peter D. Eimas
A fundamental issue in the field of speech perception is how the listener derives a phonetic representation from the
acoustic signal of speech. This is not a simple matter. Considerable research over the past few decades has established
rather convincingly that the mapping between the acoustic signal and the sequence of consonants and vowelsthe phonetic
segmentsthat define the lexical items of the language is far from straightforward (e.g., Liberman et al. 1967; Liberman
and Mattingly 1985; but see also Stevens and Blumstein 1981). The acoustic form of any given word typically varies
substantially when spoken by different speakers, at different rates of speech, or with different emotional force, and the
acoustic form of any given phonetic segment can vary dramatically as a function of the surrounding segments. A theory
of speech perception must explicate the precise nature of the complex, yet systematic mapping between acoustic signal
and phonetic structure, and it must describe the perceptual mechanisms that allow the listener to recover the phonetic
structure of utterances during language processing. Furthermore, to be complete, the theory must give an account of the
developmental course of the ability to perceive speech.
Over the years, considerable progress has been made in describing both the mapping between acoustic and phonetic
structure for adult listeners and the precursors of this mapping during early infancy. It is now clear that young infants
come to the task of language acquisition with highly sophisticated abilities to process speech and that critical aspects of
the mapping between acoustic and phonetic structures in adults find their roots in the mapping between acoustic and
prelinguistic structures in infants. Progress on the issue of mechanism has been much slower in coming. Indeed, very

25. little is known about the nature of the perceptual mechanisms that allow the listener, whether adult or infant, to perceive
speech. This is not due to the lack of attention to this problem since considerable
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research over the past decades has been directed precisely to the issue of underlying mechanism. However, little real
progress has been made, and the issue remains highly controversial.
In this chapter, we illustrate this state of affairsthe overall success in describing the nature of the mapping between
acoustic and phonetic structure in adults and the origins for this mapping in infancy, coupled with the relative lack of
progress in discovering the nature of the perceptual mechanisms that underlie speech perception. We have organized our
discussion in terms of three sections. First, we depict the context-dependent nature of the mapping between acoustic
signal and phonetic structure in adult and infant listeners, using as a case study contextual variation due to a change in
speaking rate. It is such context-dependency (i.e., lack of invariance between acoustic property and phonetic unit) that
has fueled much of the debate surrounding underlying mechanism. Second, we consider two highly controversial and
alternative theoretical accounts of the mechanism underlying the listener's ability to recover phonetic structure despite
context-dependency, again using rate-dependent processing as a case study. Finally, we offer some observations on why
the issue of mechanism has proved to be so intractable, and we speculate on the kinds of data that might lead to progress
on this issue.
The Phenomenon: Context-Dependent Speech Processing in Adults and Infants
It is well established that listeners do not process speech in a strictly linear manner, acoustic segment by acoustic
segment, with each acoustic segment associated in a one-to-one fashion with a given phonetic segment. Rather, a single
segment of the acoustic signal typically contains information in parallel for more than one phonetic segment, and
conversely, the information for a given phonetic segment is often distributed across more than one acoustic segment
(Liberman et al. 1967). A consequence of this complex mapping is that speech perception is largely context-dependent.
One form of this context-dependency is that later-occurring information in the speech signal often contributes to the
processing of an earlier-occurring acoustic property.
A case in point, and the example considered in this chapter, concerns the distinction in manner of articulation between
syllable-initial /b/ and /w/, as in the syllables /ba/ and /wa/. A major distinguishing characteristic of /b/ and /w/ is the
abruptness of the consonantal onset, with the onset of/b/ being considerably more abrupt than that of /w/. One parameter
of
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the consonantal onset is the duration of the initial formant transitions into the following vowel: /b/ is typically produced
with short transitions and /w/ with long transitions. Moreover, it has been known for some time that listeners use
transition duration to distinguish the two consonants (Liberman et al. 1956). With all other parameters set appropriately
and held constant, listeners hear syllables with short transitions as beginning with /b/ and those with long transitions as
beginning with /w/. Thus, listeners divide a continuum of syllables varying in transition duration into two categories, /b/
and /w/. Furthermore, as has been shown for other consonantal contrasts, discrimination of two stimuli drawn from the
continuum is considerably better if the two stimuli belong to different categories (i.e., one is labeled /b/ and the other
/w/), than if they belong to a single category (i.e., both are labeled /b/ or both /w/) (Miller 1980). Therefore, ample
evidence exists that transition duration maps onto the phonetic categories /b/ and /w/.
This mapping, however, is not invariant. Miller and Liberman (1979) showed that precisely which transition durations are
mapped onto /b/ and which onto /w/ depends on the duration of the syllable, a property known to vary with changes in
speaking rate. They created a set of /ba/-/wa/ speech series such that, within each series, the syllable varied in transition
duration from short (16 msec) to long (64 msec), so as to range perceptually from /ba/ to /wa/.1Across series, the
syllables differed in overall duration, which ranged from 80 to 296 msec. The change in syllable duration was
accomplished by extending the steady-state vowel portion of the syllables. Subjects were presented stimuli in random
order and were asked to categorize each as /ba/ or /wa/.