Janet F. Werker

Cross-language speech perception: Evidence for perceptual reorganization during the first year of life

Previous work in which we compared English infants, English adults, and Hindi adults on their ability to discriminate two pairs of Hindi (non-English) speech contrasts has indicated that infants discriminate speech sounds according to phonetic category without prior specific language experience (Werker, Gilbert, Humphrey, & Tees, 1981), whereas adults and children as young as age 4 (Werker & Tees, in press), may lose this ability as a function of age and or linguistic experience. The present work was designed to (a) determine the generalizability of such a decline by comparing adult English, adult Salish, and English infant subjects on their perception of a new non-English (Salish) speech contrast, and (b) delineate the time course of the developmental decline in this ability. The results of these experiments replicate our original findings by showing that infants can discriminate non-native speech contrasts without relevant experience, and that there is a decline in this ability during ontogeny. Furthermore, data from both cross-sectional and longitudinal studies shows that this decline occurs within the first year of life, and that it is a function of specific language experience.

Infants listen for more phonetic detail in speech perception than in word-learning tasks.

Infants aged 4–6 months discriminate the fine phonetic differences that distinguish syllables in both their native and unfamiliar languages, but by 10–12 months their perceptual sensitivities are reorganized so that they discriminate only the phonetic variations that are used to distinguish meaning in their native language. It would seem, then, that infants apply their well honed phonetic sensitivities as they advance and begin to associate words with objects, but the question of how speech perception sensitivities are used in early word learning has not yet been answered. Here we use a recently developed technique to show that when they are required to pair words with objects, infants of 14 months fail to use the fine phonetic detail they detect in syllable discrimination tasks. In contrast, infants of 8 months—who are not yet readily learning words—successfully discriminate phonetic detail in the same task in which infants aged 14 months fail. Taken together, these results suggest a second reorganization in infantss use of phonetic detail as they move from listening to syllables to learning words.

Developmental changes in perception of nonnative vowel contrasts

Discrimination of 2 German vowel contrasts was examined in English-learning infants of 6-8 and 10-12 months of age using a head turn procedure. The younger infants were better able than the older infants to discriminate the nonnative contrasts, but performance at 6-8 months was below levels that have been reported for nonnative consonant contrasts. A 2nd experiment using a habituation looking procedure showed that 4-month-old infants discriminated both German vowel contrasts, but the 6-month-olds could not. The findings are consistent with previous consonant work, revealing a shift from a language-general toward a language-specific pattern during the 1st year of life. However, that shift begins earlier in development for vowels than for consonants.

Phonemic and phonetic factors in adult cross‐language speech perception

Previous research has indicated that young infants can discriminate speech sounds across phonetic boundaries regardless of specific relevant experience, and that there is a modification in this ability during ontogeny such that adults often have difficulty discriminating phonetic contrasts which are not used contrastively in their native language. This pattern of findings has often been interpreted as suggesting that humans are endowed with innate auditory sensitivities which enable them to discriminate speech sounds according to universal phonetic boundaries and that there is a decline or loss in this ability after being exposed to a language which contrasts only a subset of those distinctions. The present experiments were designed to determine whether this modification represents a loss of sensorineural response capabilities or whether it shows a shift in attentional focus and/or processing strategies. In experiment 1, adult English-speaking subjects were tested on their ability to discriminate two non-English speech contrasts in a category-change discrimination task after first being predisposed to adopt one of four perceptual sets. In experiments 2, 3, and 4 subjects were tested in an AX (same/different) procedure, and the effects of both limited training and duration of the interstimulus interval were assessed. Results suggest that the previously observed ontogenetic modification in the perception of non-native phonetic contrasts involves a change in processing strategies rather than a sensorineural loss. Adult listeners can discriminate sounds across non-native phonetic categories in some testing conditions, but are not able to use that ability in testing conditions which have demands similar to those required in natural language processing.

PRIMIR: A Developmental Framework of Infant Speech Processing

Over the past few years, there has been an increasing emphasis on studying the link between infant speech perception and later language acquisition. This research has yielded some seemingly contradictory findings: In some studies infants appear to use phonetic and indexical detail that they fail to use in other studies. In this article we present a new, unified framework for accounting for these divergent findings. PRIMIR (a developmental framework for Processing Rich Information from Multidimensional Interactive Representations) assumes there is rich information available in the speech input and that the child picks up and organizes this information along a number of multidimensional interactive planes. Use of this rich information depends on the joint activity of 3 dynamic filters. These filters-the initial biases, the developmental level of the child, and requirements of the specific language task the child is facing-work together to differentially direct attention to 1 (or more) plane. In this article we outline the contradictory data that need to be explained, elucidate PRIMIR, including its underlying assumptions and overall architecture, and compare it to existing frameworks. We conclude by presenting core predictions of PRIMIR.

Cross-language evidence for three factors in speech perception

A continuing controversy concerns whether speech perception can be best explained by single-factor psychoacoustic models, single-factor specialized linguistic models, or dual-factor models including both phonetic and psychoacoustic processes. However, our recent cross-language speech perception research has provided data suggesting that a three-factor model, including auditory, phonetic, and phonemic processing, may be necessary to accommodate existing findings. In the present article, we report the findings from three experiments designed to determine whether three separate processing factors are used in speech perception. In these experiments, English and Hindi subjects were tested in a same-different (AX) discrimination procedure. The duration of the interstimulus interval, the number of trials, and the experimental context were manipulated when testing the English-speaking subjects. The combined results from the three experiments provide support for the existence of three distinct speech-perception factors.

Newborn infants’ sensitivity to perceptual cues to lexical and grammatical words

In our study newborn infants were presented with lists of lexical and grammatical words prepared from natural maternal speech. The results show that newborns are able to categorically discriminate these sets of words based on a constellation of perceptual cues that distinguish them. This general ability to detect and categorically discriminate sets of words on the basis of multiple acoustic and phonological cues may provide a perceptual base that can help older infants bootstrap into the acquisition of grammatical categories and syntactic structure.

Two-month-old infants match phonetic information in lips and voice

Infants aged 4.5 months are able to match phonetic information in the face and voice (Kuhl & Meltzoff, 1982; Patterson & Werker, 1999); however, the ontogeny of this remarkable ability is not understood. In the present study, we address this question by testing substantially younger infants at 2 months of age. Like the 4.5-month-olds in past studies, the 2-month-old infants tested in the current study showed evidence of matching vowel information in face and voice. The effect was observed in overall looking time, number of infants who looked longer at the match, and longest look to the match versus mismatch. Furthermore, there were no differences based on male or female stimuli and no preferences for the match when it was on the right or left side. These results show that there is robust evidence for phonetic matching at a much younger age than previously known and support arguments for either some kind of privileged processing or particularly rapid learning of phonetic information.

Detection of Sounds in the Auditory Stream: Event-Related fMRI Evidence for Differential Activation to Speech and Nonspeech

The detection of speech in an auditory stream is a requisite first step in processing spoken language. In this study, we used event-related fMRI to investigate the neural substrates mediating detection of speech compared with that of nonspeech auditory stimuli. Unlike previous studies addressing this issue, we contrasted speech with nonspeech analogues that were matched along key temporal and spectral dimensions. In an oddball detection task, listeners heard nonsense speech sounds, matched sine wave analogues (complex nonspeech), or single tones (simple nonspeech). Speech stimuli elicited significantly greater activation than both complex and simple nonspeech stimuli in classic receptive language areas, namely the middle temporal gyri bilaterally and in a locus lateralized to the left posterior superior temporal gyrus. In addition, speech activated a small cluster of the right inferior frontal gyrus. The activation of these areas in a simple detection task, which requires neither identification nor linguistic analysis, suggests they play a fundamental role in speech processing.

The Roots of Bilingualism in Newborns

The first steps toward bilingual language acquisition have already begun at birth. When tested on their preference for English versus Tagalog, newborns whose mothers spoke only English during pregnancy showed a robust preference for English. In contrast, newborns whose mothers spoke both English and Tagalog regularly during pregnancy showed equal preference for both languages. A group of newborns whose mothers had spoken both Chinese and English showed an intermediate pattern of preference for Tagalog over English. Preference for two languages does not suggest confusion between them, however. Study 2 showed that both English monolingual newborns and Tagalog-English bilingual newborns could discriminate English from Tagalog. The same perceptual and learning mechanisms that support acquisition in a monolingual environment thus also naturally support bilingual acquisition.