Acquisition Of Phonetic Categories Research Articles

Infant Phonetic Learning as Perceptual Space Learning: A Crosslinguistic Evaluation of Computational Models.

In the first year of life, infants' speech perception becomes attuned to the sounds of their native language. This process of early phonetic learning has traditionally been framed as phonetic category acquisition. However, recent studies have hypothesized that the attunement may instead reflect a perceptual space learning process that does not involve categories. In this article, we explore the idea of perceptual space learning by implementing five different perceptual space learning models and testing them on three phonetic contrasts that have been tested in the infant speech perception literature. We reproduce and extend previous results showing that a perceptual space learning model that uses only distributional information about the acoustics of short time slices of speech can account for at least some crosslinguistic differences in infant perception. Moreover, we find that a second perceptual space learning model, which benefits from word-level guidance. performs equally well in capturing crosslinguistic differences in infant speech perception. These results provide support for the general idea of perceptual space learning as a theory of early phonetic learning but suggest that more fine-grained data are needed to distinguish between different formal accounts. Finally, we provide testable empirical predictions of the two most promising models and show that these are not identical, making it possible to independently evaluate each model in experiments with infants in future research.

Impaired and Spared Auditory Category Learning in Developmental Dyslexia

Categorization has a deep impact on behavior, but whether category learning is served by a single system or multiple systems remains debated. Here, we designed two well-equated nonspeech auditory category learning challenges to draw on putative procedural (information-integration) versus declarative (rule-based) learning systems among adult Hebrew-speaking control participants and individuals with dyslexia, a language disorder that has been linked to a selective disruption in the procedural memory system and in which phonological deficits are ubiquitous. We observed impaired information-integration category learning and spared rule-based category learning in the dyslexia group compared with the neurotypical group. Quantitative model-based analyses revealed reduced use of, and slower shifting to, optimal procedural-based strategies in dyslexia with hypothesis-testing strategy use on par with control participants. The dissociation is consistent with multiple category learning systems and points to the possibility that procedural learning inefficiencies across categories defined by complex, multidimensional exemplars may result in difficulty in phonetic category acquisition in dyslexia.

The four-way voicing distinction in Bengali infant directed speech

Although vowels in infant-directed Speech (IDS) are thought to be hyper-articulated, findings from consonants are more mixed. Stops in languages with three- and four-way voicing distinctions, in particular, havebeen found to be hypo-articulated in IDS (Narayan and Yoon, 2011—Korean; Benders et al., 2019—Nepali) compared to adult-directed speech (ADS). We investigated the production of stops and affricates in Bengali which has a four-way voicing and aspiration distinction. IDS and ADS samples of connected speech produced by 10 native speakers (5 male and 5 female) of Bangladeshi Bengali (Yu et al., 2014) were compared. Stops and affricates were analyzed for voice onset time, onset f0 and lenition of the closure. Analyses controlled for prosodic position, lexical stress, and speaker sex—variables that are known to influence hypo-articulation. To compare the overlap between categories, acoustic measures were combined to obtain Pillai scores (Hay et al., 2006). Categories with low Pillai scores have more overlap and are thus, less distinct. The implications of the results for acquisition of phonetic categories will be discussed.

Distributional learning is error-driven: the role of surprise in the acquisition of phonetic categories

Abstract Much previous research on distributional learning and phonetic categorization assumes that categories are either faithful reproductions or parametric summaries of experienced frequency distributions, acquired through a Hebbian learning process in which every experience contributes equally to the category representation. We suggest that category representations may instead be formed via error-driven predictive learning. Rather than passively storing tagged category exemplars or updating parametric summaries of token counts, learners actively anticipate upcoming events and update their beliefs in proportion to how surprising/unexpected these events turn out to be. As a result, rare category members exert a disproportionate influence on the category representation. We present evidence for this hypothesis from a distributional learning experiment on acquiring a novel phonetic category, and show that the results are well described by a classic error-driven learning model (Rescorla, R. A. & A. R. Wagner. 1972. A theory of Pavlovian conditioning: Variations in the effectiveness of reinforcement and nonreinforcement. In A. H. Black & W. F. Prokasy (eds.), Classical conditioning II: Current research and theory, 64–99. New York, NY: Appleton-Century-Crofts).

Developmental change in tone perception in Mandarin monolingual, English monolingual, and Mandarin–English bilingual infants: Divergences between monolingual and bilingual learners

Most languages use lexical tone to discriminate the meanings of words. There has been recent interest in tracking the development of tone categories during infancy. These studies have focused largely on monolingual infants learning either a tone language or a non-tone language. It remains to be seen how bilingual infants learning one tone language (e.g., Mandarin) and one non-tone language (e.g., English) discriminate tones. Here, we examined infants’ discrimination of two Mandarin tones pairs: one salient and one subtle. Discrimination was investigated in three groups: Mandarin–English bilinguals, English monolinguals, and Mandarin monolinguals at 6 months and 9 months of age in a cross-sectional design. Results demonstrated relatively strong Mandarin tone discrimination in Mandarin monolinguals, with salient tone discrimination at 6 months and both salient and subtle tone discrimination at 9 months. English monolinguals discriminated neither contrast at 6 months but discriminated the salient contrast at 9 months. Surprisingly, there was no evidence for tone discrimination in Mandarin–English bilingual infants. In a second experiment, 12- and 13-month-old Mandarin–English bilingual and English monolingual infants were tested to determine whether bilinguals would demonstrate tone sensitivity at a later age. Results revealed a lack of tone sensitivity at 12 or 13 months in bilingual infants, yet English monolingual infants were sensitive to both salient and subtle Mandarin tone contrasts at 12 or 13 months. Our findings provide evidence for age-related convergence in Mandarin tone discrimination in English and Mandarin monolingual infants and for a distinct pattern of tone discrimination in bilingual infants. Theoretical implications for phonetic category acquisition are discussed.

Experimental support for a one-step model of phoneme acquisition

Phonetic category acquisition involves a distributional learning mechanism (Maye, Werker, and Gerken 2002). Some researchers suggest that phonetic category acquisition is only the first step in a two-step model of phonological acquisition by modelling these two steps separately (Guenther and Gjaja, 1996; Boersma, Escudero, and Hayes, 2003; Peperkamp, Pettinato, and Dupoux 2003; Peperkamp, Calvez, Nadal, and Dupoux 2006), while others have argued for a one-step model (Dillon, Dunbar, and Idsardi 2013). This experimental study maps the learning trajectory of three groups of adult learners: (1) a group exposed to a bimodal frequency distribution where both halves of the bimodal distribution occur in complementary environments (Bimodal-Comp group), (2) a group exposed to a bimodal frequency distribution where both halves of the bimodal distribution occur in non-complementary environments (Bimodal-NonComp group), and (3) a group exposed to a monomodal frequency distribution (Monomodal group). This study finds support for a one-step model of phoneme acquisition, with the Bimodal-Comp group having lower sensitivities to critical stimuli than even the Monomodal group at all three exposure times tested.

Word-level information influences phonetic learning in adults and infants

Infants begin to segment words from fluent speech during the same time period that they learn phonetic categories. Segmented words can provide a potentially useful cue for phonetic learning, yet accounts of phonetic category acquisition typically ignore the contexts in which sounds appear. We present two experiments to show that, contrary to the assumption that phonetic learning occurs in isolation, learners are sensitive to the words in which sounds appear and can use this information to constrain their interpretation of phonetic variability. Experiment 1 shows that adults use word-level information in a phonetic category learning task, assigning acoustically similar vowels to different categories more often when those sounds consistently appear in different words. Experiment 2 demonstrates that 8-month-old infants similarly pay attention to word-level information and that this information affects how they treat phonetic contrasts. These findings suggest that phonetic category learning is a rich, interactive process that takes advantage of many different types of cues that are present in the input.

A role for the developing lexicon in phonetic category acquisition.

Infants segment words from fluent speech during the same period when they are learning phonetic categories, yet accounts of phonetic category acquisition typically ignore information about the words in which sounds appear. We use a Bayesian model to illustrate how feedback from segmented words might constrain phonetic category learning by providing information about which sounds occur together in words. Simulations demonstrate that word-level information can successfully disambiguate overlapping English vowel categories. Learning patterns in the model are shown to parallel human behavior from artificial language learning tasks. These findings point to a central role for the developing lexicon in phonetic category acquisition and provide a framework for incorporating top-down constraints into models of category learning.

Supplemental Material for A Role for the Developing Lexicon in Phonetic Category Acquisition

Supplemental Material for A Role for the Developing Lexicon in Phonetic Category Acquisition

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.

Statistical learning of phonetic categories: insights from a computational approach.

Recent evidence (Maye, Werker & Gerken, 2002) suggests that statistical learning may be an important mechanism for the acquisition of phonetic categories in the infant's native language. We examined the sufficiency of this hypothesis and its implications for development by implementing a statistical learning mechanism in a computational model based on a mixture of Gaussians (MOG) architecture. Statistical learning alone was found to be insufficient for phonetic category learning--an additional competition mechanism was required in order for the categories in the input to be successfully learnt. When competition was added to the MOG architecture, this class of models successfully accounted for developmental enhancement and loss of sensitivity to phonetic contrasts. Moreover, the MOG with competition model was used to explore a potentially important distributional property of early speech categories--sparseness--in which portions of the space between phonetic categories are unmapped. Sparseness was found in all successful models and quickly emerged during development even when the initial parameters favoured continuous representations with no gaps. The implications of these models for phonetic category learning in infants are discussed.

Statistical properties of infant-directed versus adult-directed speech: Insights from speech recognition

Previous studies have shown that infant-directed speech ('motherese') exhibits overemphasized acoustic properties which may facilitate the acquisition of phonetic categories by infant learners. It has been suggested that the use of infant-directed data for training automatic speech recognition systems might also enhance the automatic learning and discrimination of phonetic categories. This study investigates the properties of infant-directed vs. adult-directed speech from the point of view of the statistical pattern recognition paradigm underlying automatic speech recognition. Isolated-word speech recognizers were trained on adult-directed vs. infant-directed data sets and were tested on both matched and mismatched data. Results show that recognizers trained on infant-directed speech did not always exhibit better recognition performance; however, their relative loss in performance on mismatched data was significantly less severe than that of recognizers trained on adult-directed speech and presented with infant-directed test data. An analysis of the statistical distributions of a subset of phonetic classes in both data sets showed that this pattern is caused by larger class overlaps in infant-directed speech. This finding has implications for both automatic speech recognition and theories of infant speech perception.

On the flexibility of phonetic categories

Research on phonetic category acquisition suggests that over the course of development children shift the relative weight given to various acoustic cues to particular phonetic categories [S. Nittrouer, J. Phon. 20, 1–32 (1992)]. Adults also show flexibility in acquiring second language categories and learning to recognize synthetic speech. In both cases listeners must shift attention among some acoustic cues and change the weighting and mapping of others. Recent research demonstrated that category-level feedback can induce adult listeners to shift attention between conflicting cues to native stop-consonant categories. Subsequent research showed that adult listeners also reorganize the distribution of their attention to acoustic cues in learning to better understand synthetic speech. Moreover, research on learning foreign phonetic contrasts suggests that listeners can learn to direct attention to unfamiliar acoustic cues. These results suggest that phonetic categories are flexible in terms of the nature and quality of the acoustic cues that define them. We argue that this flexibility is a consequence of the basic nature of the general mechanism that mediates speech perception: In order to resolve the problem of context-conditioned variability, listeners must dynamically modify attention to the acoustic signal in a context-dependent manner.

L’apprentissage du langage : une capacité inné ?

Language acquisition : an innate ability ? This paper presents the arguments that suggest that the capacity to acquire a human language is innate (poverty of the stimulus, specificity to human beings, dissociation with other capacities, creoles). Then it illustrates experimental research on language acquisition in three domains : cerebral representation of language, acquisition of phonetic categories, and syntax acquisition.

Perceptual-magnet effect as categorical perception

The perceptual-magnet effect has received a great deal of attention in recent years as a possible foundation for phonetic category acquisition. This effect is based upon studies showing that category goodness affects intracategory discriminability. Unfortunately, there is a possible confound in many of these demonstrations. Whereas category identity and goodness ratings are collected for stimuli presented in isolation, discrimination scores are obtained for stimulus pairs. In the present study, vowel identification and goodness ratings were obtained from the same stimulus pairs that would later be presented in an AX discrimination task. Stimuli were identical to the vowel vector used by Iverson and Kuhl [J. Acoust. Soc. Am. 97, 553–561 (1995)]. Identification functions varied substantially as a function of the pairings in a manner that may be described as contrastive. Vowels labeled as /e/ when presented with a good /i/ exemplar were labeled as /i/ when presented with a good /e/. These identification functions were used to predict discrimination scores based solely on perceived phonemic identity. Predictions accounted for all of the difference in discriminability between prototypical and nonprototypical exemplars. Perceptual-magnet effects appear to be little more than classic categorical perception. [Work supported by NSF.]