Linda Polka

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.

A cross-language comparison of /d /–/ð / perception: Evidence for a new developmental pattern

Previous studies have shown that infants perceptually differentiate certain non-native contrasts at 6-8 months but not at 10-12 months of age, whereas differentiation is evident at both ages in infants for whom the test contrasts are native. These findings reveal a language-specific bias to be emerging during the first year of life. A developmental decline is not observed for all non-native contrasts, but it has been consistently reported for every contrast in which language effects are observed in adults, In the present study differentiation of English /d-th/ by English- and French-speaking adults and English- and French-learning infants at two ages (6-8 and 10-12 months) was compared using the conditioned headturn procedure. Two findings emerged. First, perceptual differentiation was unaffected by language experience in the first year of life, despite robust evidence of language effects in adulthood. Second, language experience had a facilitative effect on performance after 12 months, whereas performance remained unchanged in the absence of specific language experience. These data are clearly inconsistent with previous studies as well as predictions based on a conceptual framework proposed by Burnham [Appl. Psycholing. 7, 201-240 (1986)]. Factors contributing to these developmental patterns include the acoustic properties of /d-th/, the phonotactic uniqueness of English /th/, and the influence of lexical knowledge on phonetic processing.

Asymmetries in vowel perception

Asymmetries in vowel perception occur such that discrimination of a vowel change presented in one direction is easier compared to the same change presented in the reverse direction. Although such effects have been repeatedly reported in the literature there has been little effort to explain when or why they occur. We review studies that report asymmetries in vowel perception in infants and propose that these data indicate that babies are predisposed to respond differently to vowels that occupy different positions in the articulatory/acoustic vowel space (defined by F1-F2) such that the more peripheral vowel within a contrast serves as a reference or perceptual anchor. As such, these asymmetries reveal a language-universal perceptual bias that infants bring to the task of vowel discrimination. We present some new data that support our peripherality hypothesis and then compare the data on asymmetries in human infants with findings obtained with birds and cats. This comparison suggests that asymmetries evident in humans are unlikely to reflect general auditory mechanisms. Several important directions for further research are outlined and some potential implications of these asymmetries for understanding speech development are discussed.

Language-experience facilitates discrimination of /d- / 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.

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.

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.

Production of Coronal Stops by Simultaneous Bilingual Adults.

This study investigated acoustic-phonetics of coronal stop production by adult simultaneous bilingual and monolingual speakers of Canadian English (CE) and Canadian French (CF). Differences in the phonetics of CF and CE include voicing and place of articulation distinctions. CE has a two-way voicing distinction (in syllable initial position) contrasting short-and long-lag VOT; coronal stops in CE are described as alveolar. CF also has a two-way voicing distinction, but contrasting lead and short-lag VOT; coronal stops in CF are described as dental. Acoustic analyses of stop consonants for both VOT and dental/alveolar place of articulation are reported. Results indicate that simultaneous bilingual as well as monolingual adults produce language-specific differences, albeit not in the same way, across CF and CE for voicing and place. Similarities and differences between simultaneous bilingual and monolingual adults are discussed to address phonological organization in simultaneous bilingual adults.

Natural Referent Vowel (NRV) framework: An emerging view of early phonetic development

The aim of this paper is to provide an overview of an emerging new framework for understanding early phonetic development—the Natural Referent Vowel (NRV) framework. The initial support for this framework was the finding that directional asymmetries occur often in infant vowel discrimination. The asymmetries point to an underlying perceptual bias favoring vowels that fall closer to the periphery of the F1/F2 vowel space. In Polka and Bohn (2003) we reviewed the data on asymmetries in infant vowel perception and proposed that certain vowels act as natural referent vowels and play an important role in shaping vowel perception. In this paper we review findings from studies of infant and adult vowel perception that emerged since Polka and Bohn (2003), from other labs and from our own work, and we formally introduce the NRV framework. We outline how this framework connects with linguistic typology and other models of speech perception and discuss the challenges and promise of NRV as a conceptual tool for advancing our understanding of phonetic development.

A developmental study of audiovisual speech perception using the McGurk paradigm

The development of audiovisual speech perception was examined in this experiment using the McGurk paradigm (McGurk and MacDonald, 1976), in which a visual recording of a person saying a particular syllable is synchronized with the auditory presentation of another syllable. Previous audiovisual speech studies have shown that adult perception is strongly influenced by the visual speech information whereas the perception of young children (5–8 years) shows a very weak influence of visual speech patterns and a strong bias favoring the auditory speech information. In this investigation 46 children in four age groups (5, 7, 9, and 11 year olds) and 15 adults were presented with conflicting audiovisual syllables in which an auditory /ba/ sequence was combined with visual /va/, /θa/, /da/, and /ga/ sequences, respectively. The results indicated that the influence of auditory information decreased with increasing age, while the influence of visual information and the integration of auditory and visual information ...

The Conditioned Head Turn Procedure as a Method for Testing Infant Speech Perception

B.C. Research Institute for Child and Family Health, Vancouver, CanadaThe purpose of this paper is to present and describe theConditioned Head Turn procedure, with primary focus on itsuse as a method for testing infant speech perception. The paperbegins with a brief history of the Conditioned Head TurnProcedure followed by a fairly detailed description of howthe procedure is currently implemented. We then briefly outlinethe methods of analysis that are best suited for data obtained withthe Conditioned Head Turn procedure. Next discussed arevariations in the Conditioned Head Turn procedure when it isused with subjects of different ages. Then, some of the kinds offindings that have been revealed in the area of infant speechperception are presented to give the reader a sense of the range ofquestions that can be answered using this procedure. Followingthis, the strengths and limitations of the procedure are discussedfrankly. We end with a presentation of new variations to theprocedure that have been developed in recent years, and note howthese new variations are expanding the range of questions theprocedure can address. ’1997 John Wiley & Sons, Ltd.