Articulating What Infants Attune to in Native Speech.

To become language users, infants must embrace the integrality of speech perception and production. That they do so, and quite rapidly, is implied by the native-language attunement they achieve in each domain by 6-12 months. Yet research has most often addressed one or the other domain, rarely how they interrelate. Moreover, mainstream assumptions that perception relies on acoustic patterns whereas production involves motor patterns entail that the infant would have to translate incommensurable information to grasp the perception-production relationship. We posit the more parsimonious view that both domains depend on commensurate articulatory information. Our proposed framework combines principles of the Perceptual Assimilation Model (PAM) and Articulatory Phonology (AP). According to PAM, infants attune to articulatory information in native speech and detect similarities of nonnative phones to native articulatory patterns. The AP premise that gestures of the speech organs are the basic elements of phonology offers articulatory similarity metrics while satisfying the requirement that phonological information be discrete and contrastive: (a) distinct articulatory organs produce vocal tract constrictions and (b) phonological contrasts recruit different articulators and/or constrictions of a given articulator that differ in degree or location. Various lines of research suggest young children perceive articulatory information, which guides their productions: discrimination of between- versus within-organ contrasts, simulations of attunement to language-specific articulatory distributions, multimodal speech perception, oral/vocal imitation, and perceptual effects of articulator activation or suppression. We conclude that articulatory gesture information serves as the foundation for developmental integrality of speech perception and production.

Investigating the role of articulatory organs and perceptual assimilation of native and non-native fricative place contrasts.

The perceptual assimilation model (PAM; Best, C. T. [1995]. A direct realist view of cross-language speech perception. In W. Strange (Ed.), Speech perception and linguistic experience: Issues in cross-language research (pp. 171-204). Baltimore, MD: York Press.) accounts for developmental patterns of speech contrast discrimination by proposing that infants shift from untuned phonetic perception at 6 months to natively tuned perceptual assimilation at 11-12 months, but the model does not predict initial discrimination differences among contrasts. To address that issue, we evaluated the Articulatory Organ Hypothesis, which posits that consonants produced using different articulatory organs are initially easier to discriminate than those produced with the same articulatory organ. We tested English-learning 6- and 11-month-olds' discrimination of voiceless fricative place contrasts from Nuu-Chah-Nulth (non-native) and English (native), with one within-organ and one between-organ contrast from each language. Both native and non-native contrasts were discriminated across age, suggesting that articulatory-organ differences do not influence perception of speech contrasts by young infants. The results highlight the fact that a decline in discrimination for non-native contrasts does not always occur over age.

Computational simulation of CV combination preferences in babbling.

There is a tendency for spoken consonant-vowel (CV) syllables, in babbling in particular, to show preferred combinations: labial consonants with central vowels, alveolars with front, and velars with back. This pattern was first described by MacNeilage and Davis, who found the evidence compatible with their "frame-then-content" (F/C) model. F/C postulates that CV syllables in babbling are produced with no control of the tongue (and therefore effectively random tongue positions) but systematic oscillation of the jaw. Articulatory Phonology (AP; Browman & Goldstein) predicts that CV preferences will depend on the degree of synergy of tongue movements for the C and V. We present computational modeling of both accounts using articulatory synthesis. Simulations found better correlations between patterns in babbling and the AP account than with the F/C model. These results indicate that the underlying assumptions of the F/C model are not supported and that the AP account provides a better and account with broader coverage by showing that articulatory synergies influence all CV syllables, not just the most common ones.

Biomechanically preferred consonant-vowel combinations fail to appear in adult spoken corpora.

Certain consonant/vowel (CV) combinations are more frequent than would be expected from the individual C and V frequencies alone, both in babbling and, to a lesser extent, in adult language, based on dictionary counts: Labial consonants co-occur with central vowels more often than chance would dictate; coronals co-occur with front vowels, and velars with back vowels (Davis & MacNeilage, 1994). Plausible biomechanical explanations have been proposed, but it is also possible that infants are mirroring the frequency of the CVs that they hear. As noted, previous assessments of adult language were based on dictionaries; these "type" counts are incommensurate with the babbling measures, which are necessarily "token" counts. We analyzed the tokens in two spoken corpora for English, two for French and one for Mandarin. We found that the adult spoken CV preferences correlated with the type counts for Mandarin and French, not for English. Correlations between the adult spoken corpora and the babbling results had all three possible outcomes: significantly positive (French), uncorrelated (Mandarin), and significantly negative (English). There were no correlations of the dictionary data with the babbling results when we consider all nine combinations of consonants and vowels. The results indicate that spoken frequencies of CV combinations can differ from dictionary (type) counts and that the CV preferences apparent in babbling are biomechanically driven and can ignore the frequencies of CVs in the ambient spoken language.

Processing speech signal using auditory-like filterbank provides least uncertainty about articulatory gestures.

Understanding how the human speech production system is related to the human auditory system has been a perennial subject of inquiry. To investigate the production-perception link, in this paper, a computational analysis has been performed using the articulatory movement data obtained during speech production with concurrently recorded acoustic speech signals from multiple subjects in three different languages: English, Cantonese, and Georgian. The form of articulatory gestures during speech production varies across languages, and this variation is considered to be reflected in the articulatory position and kinematics. The auditory processing of the acoustic speech signal is modeled by a parametric representation of the cochlear filterbank which allows for realizing various candidate filterbank structures by changing the parameter value. Using mathematical communication theory, it is found that the uncertainty about the articulatory gestures in each language is maximally reduced when the acoustic speech signal is represented using the output of a filterbank similar to the empirically established cochlear filterbank in the human auditory system. Possible interpretations of this finding are discussed.

Response to MacNeilage and Davis and to Oller.

The article by MacNeilage and Davis in this issue, entitled "In Defense of the 'Frames, then Content' (FC) Perspective on Speech Acquisition: A Response to Two Critiques" appears to assume that the only alternative to segment-level control is oscillation specifically of the jaw; however, other articulators could be oscillated by infants as well. This allows the preferred CV combinations to emerge without positing a level of segmental control in babbling. Their response does not address our modeling work, which, rather similarly to Davis's own modeling (Serkhane, Schwartz, Boë, Davis, & Matyear, 2007), shows little support for the Frame-then-Content (F/C) account. Our results show substantial support for the Articulatory Phonology (AP) one. A closer look at feeding in infants shows substantial control of the tongue and lips, casting further doubt on the foundation of the F/C account.

An Articulatory Phonology Account of Preferred Consonant-Vowel Combinations.

Certain consonant/vowel combinations (labial/central, coronal/front, velar/back) are more frequent in babbling as well as, to a lesser extent, in adult language, than chance would dictate. The "Frame then Content" (F/C) hypothesis (Davis & MacNeilage, 1994) attributes this pattern to biomechanical vocal-tract biases that change as infants mature. Articulatory Phonology (AP; Browman and Goldstein 1989) attributes preferences to demands placed on shared articulators. F/C implies that preferences will diminish as articulatory control increases, while AP does not. Here, babbling from children at 6, 9 and 12 months in English, French and Mandarin environments was examined. There was no developmental trend in CV preferences, although older ages exhibited greater articulatory control. A perception test showed no evidence of bias toward hearing the preferred combinations. Modeling using articulatory synthesis found limited support for F/C but more for AP, including data not originally encompassed in F/C. AP thus provides an alternative biomechanical explanation.

VOT in the babbling of French- and English-learning infants.

Different languages use voice onset time (VOT) in different ways to signal the voicing contrast, for example, short lag/long lag (English) vs. prevoiced/short lag (French). Also, VOT depends on place of articulation, with labial VOTs being shorter than velar and alveolar and, sometimes, alveolar being shorter than velar. Here we examine the VOT in babbled utterances of five French-learning and five English-learning infants at ages 9 and 12 months. There was little or no difference between the languages for duration of positive VOTs, which were usually in the "short lag" range. The duration of prevoicing also did not differ between languages, but the proportion of prevoiced utterances did (French-learning infants: 44.2% prevoicing; English-learning: 14.3%). Labial, alveolar and velar stops differed in VOT, with alveolar longer than labial and velar longer than alveolar, suggesting a mechanical cause. The lack of long-lag VOT indicates that the English-learning infants have not mastered aspiration by 12 months. The different proportions of prevoicing, however, suggest that the French-learning infants attempt to imitate the prevoicing that is used frequently (and contrastively) in their native language environment. The results suggest that infants are sensitive to the voicing categories of the ambient language but that they may be able to control prevoicing more successfully than aspiration.