Examination of perceptual reorganization for nonnative speech contrasts: Zulu click discrimination by English-speaking adults and infants

The language environment modifies the speech perception abilities found in early development. In particular, adults have difficulty perceiving many nonnative contrasts that young infants discriminate. The underlying perceptual reorganization apparently occurs by 10-12 months. According to one view, it depends on experiential effects on psychoacoustic mechanisms. Alternatively, phonological development has been held responsible, with perception influenced by whether the nonnative sounds occur allophonically in the native language. We hypothesized that a phonemic process appears around 10-12 months that assimilates speech sounds to native categories whenever possible; otherwise, they are perceived in auditory or phonetic (articulatory) terms. We tested this with English-speaking listeners by using Zulu click contrasts. Adults discriminated the click contrasts; performance on the most difficult (80% correct) was not diminished even when the most obvious acoustic difference was eliminated. Infants showed good discrimination of the acoustically modified contrast even by 12-14 months. Together with earlier reports of developmental change in perception of nonnative contrasts, these findings support a phonological explanation of language-specific reorganization in speech perception.     

The interaction between acoustic salience and language experience in developmental speech perception: evidence from nasal place discrimination

Previous research suggests that infant speech perception reorganizes in the first year: young infants discriminate both native and non‐native phonetic contrasts, but by 10–12 months difficult non‐native contrasts are less discriminable whereas performance improves on native contrasts. In the current study, four experiments tested the hypothesis that, in addition to the influence of native language experience, acoustic salience also affects the perceptual reorganization that takes place in infancy. Using a visual habituation paradigm, two nasal place distinctions that differ in relative acoustic salience, acoustically robust labial‐alveolar [ma]–[na] and acoustically less salient alveolar‐velar [na]–[?a], were presented to infants in a cross‐language design. English‐learning infants at 6–8 and 10–12 months showed discrimination of the native and acoustically robust [ma]–[na] (Experiment 1), but not the non‐native (in initial position) and acoustically less salient [na]–[?a] (Experiment 2). Very young (4–5‐month‐old) English‐learning infants tested on the same native and non‐native contrasts also showed discrimination of only the [ma]–[na] distinction (Experiment 3). Filipino‐learning infants, whose ambient language includes the syllable‐initial alveolar (/n/)–velar (/?/) contrast, showed discrimination of native [na]–[?a] at 10–12 months, but not at 6–8 months (Experiment 4). These results support the hypothesis that acoustic salience affects speech perception in infancy, with native language experience facilitating discrimination of an acoustically similar phonetic distinction [na]–[?a]. We discuss the implications of this developmental profile for a comprehensive theory of speech perception in infancy.     

Learning words’ sounds before learning how words sound: 9-Month-olds use distinct objects as cues to categorize speech information

One of the central themes in the study of language acquisition is the gap between the linguistic knowledge that learners demonstrate, and the apparent inadequacy of linguistic input to support induction of this knowledge. One of the first linguistic abilities in the course of development to exemplify this problem is in speech perception: specifically, learning the sound system of one’s native language. Native-language sound systems are defined by meaningful contrasts among words in a language, yet infants learn these sound patterns before any significant numbers of words are acquired. Previous approaches to this learning problem have suggested that infants can learn phonetic categories from statistical analysis of auditory input, without regard to word referents. Experimental evidence presented here suggests instead that young infants can use visual cues present in word-labeling situations to categorize phonetic information. In Experiment 1, 9-month-old English-learning infants failed to discriminate two non-native phonetic categories, establishing baseline performance in a perceptual discrimination task. In Experiment 2, these infants succeeded at discrimination after watching contrasting visual cues (i.e., videos of two novel objects) paired consistently with the two non-native phonetic categories. In Experiment 3, these infants failed at discrimination after watching the same visual cues, but paired inconsistently with the two phonetic categories. At an age before which memory of word labels is demonstrated in the laboratory, 9-month-old infants use contrastive pairings between objects and sounds to influence their phonetic sensitivity. Phonetic learning may have a more functional basis than previous statistical learning mechanisms assume: infants may use cross-modal associations inherent in social contexts to learn native-language phonetic categories.     

Characterizing the influence of native language experience on adult speech perception

Previous cross-language research has indicated that some speech contrasts present greater perceptual difficulty for adult non-native listeners than others do. It has been hypothesized that phonemic, phonetic, and acoustic factors contribute to this variability. Two experiments were conducted to evaluate systematically the role of phonemic status and phonetic familiarity in the perception of non-native speech contrasts and to test predictions derived from a model proposed by Best, McRoberts, and Sithole (1988). Experiment 1 showed that perception of an unfamiliar phonetic contrast was not less difficult for subjects who had experience with an analogous phonemic distinction in their native language than for subjects without such analogous experience. These results suggest that substantive phonetic experience influences the perception of non-native contrasts, and thus should contribute to a conceptualization of native language-processing skills. In Experiment 2, English listeners’ perception of two related nonphonemic place contrasts was not consistently different as had been expected on the basis of phonetic familiarity. A clear order effect in the perceptual data suggests that interactions between different perceptual assimilation patterns or acoustic properties of the two contrasts, or interactions involving both of these factors, underlie the perception of the two contrasts in this experiment. It was concluded that both phonetic familiarity and acoustic factors are potentially important to the explanation of variability in perception of nonphonemic contrasts. The explanation of how linguistic experience shapes speech perception will require characterizing the relative contribution of these factors, as well as other factors, including individual differences and variables that influence a listener’s orientation to speech stimuli.     

Infant sensitivity to distributional information can affect phonetic discrimination.

For nearly two decades it has been known that infants' perception of speech sounds is affected by native language input during the first year of life. However, definitive evidence of a mechanism to explain these developmental changes in speech perception has remained elusive. The present study provides the first evidence for such a mechanism, showing that the statistical distribution of phonetic variation in the speech signal influences whether 6- and 8-month-old infants discriminate a pair of speech sounds. We familiarized infants with speech sounds from a phonetic continuum, exhibiting either a bimodal or unimodal frequency distribution. During the test phase, only infants in the bimodal condition discriminated tokens from the endpoints of the continuum. These results demonstrate that infants are sensitive to the statistical distribution of speech sounds in the input language, and that this sensitivity influences speech perception.     

Characterizing the influence of native language experience on adult speech perception.

Previous cross-language research has indicated that some speech contrasts present greater perceptual difficulty for adult non-native listeners than others do. It has been hypothesized that phonemic, phonetic, and acoustic factors contribute to this variability. Two experiments were conducted to evaluate systematically the role of phonemic status and phonetic familiarity in the perception of non-native speech contrasts and to test predictions derived from a model proposed by Best, McRoberts, and Sithole (1988). Experiment 1 showed that perception of an unfamiliar phonetic contrast was not less difficult for subjects who had experience with an analogous phonemic distinction in their native language than for subjects without such analogous experience. These results suggest that substantive phonetic experience influences the perception of non-native contrasts, and thus should contribute to a conceptualization of native language-processing skills. In Experiment 2, English listeners' perception of two related nonphonemic place contrasts was not consistently different as had been expected on the basis of phonetic familiarity. A clear order effect in the perceptual data suggests that interactions between different perceptual assimilation patterns or acoustic properties of the two contrasts, or interactions involving both of these factors, underlie the perception of the two contrasts in this experiment. It was concluded that both phonetic familiarity and acoustic factors are potentially important to the explanation of variability in perception of nonphonemic contrasts. The explanation of how linguistic experience shapes speech perception will require characterizing the relative contribution of these factors, as well as other factors, including individual differences and variables that influence a listener's orientation to speech stimuli.     

Infant-directed speech supports phonetic category learning in English and Japanese

Across the first year of life, infants show decreased sensitivity to phonetic differences not used in the native language [Werker, J. F., & Tees, R. C. (1984). Cross-language speech perception: evidence for perceptual reorganization during the first year of life. Infant Behaviour and Development, 7, 49-63]. In an artificial language learning manipulation, Maye, Werker, and Gerken [Maye, J., Werker, J. F., & Gerken, L. (2002). Infant sensitivity to distributional information can affect phonetic discrimination. Cognition, 82(3), B101-B111] found that infants change their speech sound categories as a function of the distributional properties of the input. For such a distributional learning mechanism to be functional, however, it is essential that the input speech contain distributional cues to support such perceptual learning. To test this, we recorded Japanese and English mothers teaching words to their infants. Acoustic analyses revealed language-specific differences in the distributions of the cues used by mothers (or cues present in the input) to distinguish the vowels. The robust availability of these cues in maternal speech adds support to the hypothesis that distributional learning is an important mechanism whereby infants establish native language phonetic categories.     

Object labeling influences infant phonetic learning and generalization

Different kinds of speech sounds are used to signify possible word forms in every language. For example, lexical stress is used in Spanish (/‘be.be/, ‘he/she drinks’ versus /be.’be/, ‘baby’), but not in French (/‘be.be/ and /be.’be/ both mean ‘baby’). Infants learn many such native language phonetic contrasts in their first year of life, likely using a number of cues from parental speech input. One such cue could be parents’ object labeling, which can explicitly highlight relevant contrasts. Here we ask whether phonetic learning from object labeling is abstract—that is, if learning can generalize to new phonetic contexts. We investigate this issue in the prosodic domain, as the abstraction of prosodic cues (like lexical stress) has been shown to be particularly difficult. One group of 10-month-old French-learners was given consistent word labels that contrasted on lexical stress (e.g., Object A was labeled /‘ma.bu/, and Object B was labeled /ma.’bu/). Another group of 10-month-olds was given inconsistent word labels (i.e., mixed pairings), and stress discrimination in both groups was measured in a test phase with words made up of new syllables. Infants trained with consistently contrastive labels showed an earlier effect of discrimination compared to infants trained with inconsistent labels. Results indicate that phonetic learning from object labeling can indeed generalize, and suggest one way infants may learn the sound properties of their native language(s).     

Phonetic, phonemic, and phonological factors in cross-language discrimination of phonotactic contrasts

Previous research indicates that multiple levels of linguistic information play a role in the perception and discrimination of non-native phonemes. This study examines the interaction of phonetic, phonemic and phonological factors in the discrimination of non-native phonotactic contrasts. Listeners of Catalan, English, and Russian are presented with an initial #CC-#C?C contrast in a discrimination task. For the Catalan group, the phonemes and their phonetic implementation were native, but the #CC phonotactics were not. For Russian listeners, the phonemes and phonetic implementation were not native but Russian allows a large number of #CC sequences. For English listeners, none of the phonetics, phonemes, nor phonotactics are native. Two task variables, stimuli length and order of presentation, were also manipulated. Results showed that the Russian listeners were most accurate overall, suggesting that the presence of the phonotactic structure in the listeners' native language may be more important than either phonemic or phonetic information. The interaction between the task manipulations and the linguistic variables is also addressed.     

婴儿语音感知发展及其机制

语音感知的发展状况对个体的语言发展有着深远影响。生命的第一年中, 在语言经验的作用下, 婴儿的语音感知从最初的普遍性感知逐渐发展为对母语的特异性感知。研究者们提出统计学习机制对这一过程加以解释, 即婴儿对语言环境中语音的频次分布十分敏感, 可以通过对频次分布的计算, 从语音的连续体中区分出在母语中起区别意义作用的各个语音范畴。同时, 功能性重组机制和一些社会性线索也会对婴儿语音感知的发展产生重要影响。     

The effects of distributional learning on rats' sensitivity to phonetic information

During the first year of life, infants show decreased sensitivity to phonetic differences not used in their native language and increased sensitivity to the differences that are used. It has been shown that this change in speech perception is a function of the distributional properties of the input. The present study explores whether the mechanism responsible for the developmental changes regarding the organization of phonetic categories is a general mechanism shared with other animals. The results demonstrate that the distributional exposure to a phonetic continuum affects the subsequent discrimination of these phonemes in rats, indicating that the ability to use distributional cues to change the phonetic category structure extends beyond humans.     

婴儿期母语音位范畴习得：来自言语知觉的证据

婴儿期言语知觉研究表明婴儿最初（1~4个月）可以分辨几乎所有的语音范畴对比;随母语经验增加,婴儿言语知觉逐渐表现出母语语音特征的影响,辅音知觉表现为对母语语音范畴界限敏感性的提高和对非母语范畴界限敏感性的下降,非母语范畴开始同化到母语音系中去,母语元音知觉表现出知觉磁体效应。这些证据表明婴儿逐渐习得母语音位范畴,音位范畴习得顺序可能依赖范畴例子本身的声学特征、发生频率等因素     

The acquisition of phonetic categories in bilingual infants: new data from an anticipatory eye movement paradigm

Contrasting results have been reported regarding the phonetic acquisition of bilinguals. A lack of discrimination has been observed for certain native contrasts in 8-month-old Catalan-Spanish bilingual infants (Bosch & Sebastián-Gallés, 2003a), though not in French-English bilingual infants (Burns, Yoshida, Hill & Werker, 2007; Sundara, Polka & Molnar, 2008). At present, the data for Catalan-Spanish bilinguals constitute an exception in the early language acquisition literature. This study contributes new findings that show that Catalan-Spanish bilingual infants do not lose the capacity to discriminate native contrasts. We used an adaptation of the anticipatory eye movement paradigm (AEM; McMurray & Aslin, 2004) to explore this question. In two experiments we tested the ability of infants from Catalan and Spanish monolingual families and from Catalan-Spanish bilingual families to discriminate a Spanish-Catalan common and a Catalan-specific vowel contrast. Results from both experiments revealed that Catalan-Spanish bilingual infants showed the same discrimination abilities as those shown by their monolingual peers, even in a phonetic contrast that had not been discriminated in previous studies. Our results demonstrate that discrimination can be observed in 8-month-old bilingual infants when tested with a measure not based on recovery of attention. The high ratio of cognates in Spanish and Catalan may underlie the reason why bilinguals failed to discriminate the native vowels when tested with the familiarization-preference procedure but succeeded with the AEM paradigm.     

Impact of second-language experience in infancy: brain measures of first- and second-language speech perception

Language experience 'narrows' speech perception by the end of infants' first year, reducing discrimination of non-native phoneme contrasts while improving native-contrast discrimination. Previous research showed that declines in non-native discrimination were reversed by second-language experience provided at 9-10 months, but it is not known whether second-language experience affects first-language speech sound processing. Using event-related potentials (ERPs), we examined learning-related changes in brain activity to Spanish and English phoneme contrasts in monolingual English-learning infants pre- and post-exposure to Spanish from 9.5-10.5 months of age. Infants showed a significant discriminatory ERP response to the Spanish contrast at 11 months (post-exposure), but not at 9 months (pre-exposure). The English contrast elicited an earlier discriminatory response at 11 months than at 9 months, suggesting improvement in native-language processing. The results show that infants rapidly encode new phonetic information, and that improvement in native speech processing can occur during second-language learning in infancy.     

Perceptual learning for speech

Adult language users have an enormous amount of experience with speech in their native language. As a result, they have very well-developed processes for categorizing the sounds of speech that they hear. Despite this very high level of experience, recent research has shown that listeners are capable of redeveloping their speech categorization to bring it into alignment with new variation in their speech input. This reorganization of phonetic space is a type of perceptual learning, or recalibration, of speech processes. In this article, we review several recent lines of research on perceptual learning for speech.     

Cognitive influences on cross-language speech perception in infancy

Previous research has shown that young infants can discriminate both native and nonnative phonetic contrasts with ease. By 10 to 12 months of age, however, infants—like adults—typically have difficulty discriminating consonant contrasts that are not used to distinguish meaning in their native language. Although the timing of this change in speech perception has been firmly established, little is currently known about the processes or mechanisms involved in this selective and adaptive reorganization in nonnative phonetic discrimination. This study was designed to determine if there is a relation between age-related changes in speech perception performance and other developing cognitive abilities. A total of 40 8- to 10-month-old infants were tested on a nonnative consonant discrimination task and then on two additional tasks (a visual categorization task and an object search task) in an attempt to determine whether changes in nonnative consonant perception coincide with changes in these other areas of cognitive/perceptual functioning. The results indicate that changes in task performance occur in synchrony across all three tasks, and that this synchrony is not explained by simple age effects. These findings suggest that domain-general cognitive/perceptual competencies may influence developmental changes in speech perception by the end of the 1st year of life.     

Brain potentials to native and non-native speech contrasts in 7- and 11-month-old American infants

Abstract Behavioral data establish a dramatic change in infants' phonetic perception between 6 and 12 months of age. Foreign-language phonetic discrimination significantly declines with increasing age. Using a longitudinal design, we examined the electrophysiological responses of 7- and 11-month-old American infants to native and non-native consonant contrasts. Analyses of the event-related potentials (ERP) of the group data at 7 and at 11 months of age demonstrated that infants' discriminatory ERP responses to the non-native contrast are present at 7 months of age but disappear by 11 months of age, consistent with the behavioral data reported in the literature. However, when the same infants were divided into subgroups based on individual ERP components, we found evidence that the infant brain remains sensitive to the non-native contrast at 11 months of age, showing differences in either the P150-250 or the N250-550 time window, depending upon the subgroup. Moreover, we observed an increase in infants' responsiveness to native language consonant contrasts over time. We describe distinct neural patterns in two groups of infants and suggest that their developmental differences may have an impact on language development.     

Development of coronal stop perception: bilingual infants keep pace with their monolingual peers

Previous studies indicate that the discrimination of native phonetic contrasts in infants exposed to two languages from birth follows a different developmental time course from that observed in monolingual infants. We compared infant discrimination of dental (French) and alveolar (English) place variants of /d/ in three groups differing in language experience. At 6-8 months, infants in all three language groups succeeded; at 10-12 months, monolingual English and bilingual but not monolingual French infants distinguished this contrast. Thus, for highly frequent, similar phones, despite overlap in cross-linguistic distributions, bilingual infants performed on par with their English monolingual peers and better than their French monolingual peers.     

Language-experience facilitates discrimination of /d-th/ in monolingual and bilingual acquisition of English

To trace how age and language experience shape the discrimination of native and non-native phonetic contrasts, we compared 4-year-olds learning either English or French or both and simultaneous bilingual adults on their ability to discriminate the English /d-th/ contrast. Findings show that the ability to discriminate the native English contrast improved with age. However, in the absence of experience with this contrast, discrimination of French children and adults remained unchanged during development. Furthermore, although simultaneous bilingual and monolingual English adults were comparable, children exposed to both English and French were poorer at discriminating this contrast when compared to monolingual English-learning 4-year-olds. Thus, language experience facilitates perception of the English /d-th/ contrast and this facilitation occurs later in development when English and French are acquired simultaneously. The difference between bilingual and monolingual acquisition has implications for language organization in children with simultaneous exposure.     

The effect of listening experience on the discrimination of /ba/ and /pa/ in Hebrew-learning and Arabic-learning infants

Infant speech discrimination can follow multiple trajectories depending on the language and the specific phonemes involved. Two understudied languages in terms of the development of infants’ speech discrimination are Arabic and Hebrew.PurposeThe purpose of the present study was to examine the influence of listening experience with the native language on the discrimination of the voicing contrast /ba-pa/ in Arabic-learning infants whose native language includes only the phoneme /b/ and in Hebrew-learning infants whose native language includes both phonemes.Method128 Arabic-learning infants and Hebrew-learning infants, 4-to-6 and 10-to-12-month-old infants, were tested with the Visual Habituation Procedure.ResultsThe results showed that 4-to-6-month-old infants discriminated between /ba-pa/ regardless of their native language and order of presentation. However, only 10-to-12-month-old infants learning Hebrew retained this ability. 10-to-12-month-old infants learning Arabic did not discriminate the change from /ba/ to /pa/ but showed a tendency for discriminating the change from /pa/ to /ba/.ConclusionsThis is the first study to report on the reduced discrimination of /ba-pa/ in older infants learning Arabic. Our findings are consistent with the notion that experience with the native language changes discrimination abilities and alters sensitivity to non-native contrasts, thus providing evidence for ‘top-down’ processing in young infants. The directional asymmetry in older infants learning Arabic can be explained by assimilation of the non-native consonant /p/ to the native Arabic category /b/ as predicted by current speech perception models.