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This study focuses on inter-individual convergence effects in the perception and categorization of speech sounds. We ask to what extent two listeners can come to establish a shared set of categorization criteria in a phoneme identification task that they accomplish together. Several hypotheses  are  laid  out  in  the  framework  of  a  Bayesian  model  of  speech  perception  that  we  have  developed  to  account  for  how  two  listeners  may  each  infer  the  parameters  that  govern  their partner’s responses. In our experimental paradigm, participants were asked to perform a joint  phoneme  identification  task  with  a  partner  that,  unbeknownst  to  them,  was  an  artificial  agent, whose responses we manipulated along two dimensions, the location of the categorical boundary and the slope of the identification function. Convergence was found to arise for bias but not for slope. Numerical simulations suggested that lack of convergence in slope may stem from the listeners’ prior level of confidence in the variance in VOT for the two phonemic categories. This study sheds new light on perceptual convergence between listeners in the categorization of speech sounds, a phenomenon that has received little attention so far in spite of its central importance for speech communication.

To explain how perception processes are performed, understanding how continuous sensory streams are temporally segmented into discrete units is central. This is particularly the case in speech perception where temporal segmentation is key for identifying linguistic units contained between consecutive events in time. We propose an original probabilistic construct, that we call "Bayesian gates", to segment temporally continuous streams of sensory stimuli into sequences of decoders. We first define Bayesian gates mathematically and describe their properties. We then illustrate their behavior in the context of a model of word recognition in speech perception. We show that, based on an event detection module, they sequentially parse the acoustic stimulus, so that each syllable decoder only processes a segment of the sensory signal.

The influence of motor knowledge on speech perception is well established, but the functional role of the motor system is still poorly understood. The present study explores the hypothesis that speech production abilities may help infants discover phonetic categories in the speech stream, in spite of coarticulation effects. To this aim, we examined the influence of babbling abilities on consonant categorization in 6- and 9-month-old infants. Using an intersensory matching procedure, we investigated the infants' capacity to associate auditory information about a consonant in various vowel contexts with visual information about the same consonant, and to map auditory and visual information onto a common phoneme representation. Moreover, a parental questionnaire evaluated the infants' consonantal repertoire. In a first experiment using /b/-/d/ consonants, we found that infants who displayed babbling abilities and produced the /b/ and/or the /d/ consonants in repetitive sequences were able to correctly perform intersensory matching, while non-babblers were not. In a second experiment using the /v/-/z/ pair, which is as visually contrasted as the /b/-/d/ pair but which is usually not produced at the tested ages, no significant matching was observed, for any group of infants, babbling or not. These results demonstrate, for the first time, that the emergence of babbling could play a role in the extraction of vowel-independent representations for consonant place of articulation. They have important implications for speech perception theories, as they highlight the role of sensorimotor interactions in the development of phoneme representations during the first year of life.

Speech perception in noise remains challenging for Deaf/Hard of Hearing people (D/HH), even fitted with hearing aids or cochlear implants. The perception of sentences in noise by 20 implanted or aided D/HH subjects mastering Cued Speech (CS), a system of hand gestures complementing lip movements, was compared with the perception of 15 typically hearing (TH) controls in three conditions: audio only, audiovisual, and audiovisual + CS. Similar audiovisual scores were obtained for signal-to-noise ratios (SNRs) 11 dB higher in D/HH participants compared with TH ones. Adding CS information enabled D/HH participants to reach a mean score of 83% in the audiovisual + CS condition at a mean SNR of 0 dB, similar to the usual audio score for TH participants at this SNR. This confirms that the combination of lipreading and Cued Speech system remains extremely important for persons with hearing loss, particularly in adverse hearing conditions.

Purpose: Words, syllables, and phonemes have each been regarded as basic encoding units of speech production in various psycholinguistic models. The present article investigates the role of each unit in the interface with speech articulation, using a paradigm from motor control research. Method: Seventy-six native speakers of French were trained to change their production of /be/ in response to an auditory feedback perturbation (auditory-motor learning). We then assessed the magnitude of learning transfer from /be/ to the syllables in 2 pseudowords (/bepe/ and /pebe/) and 1 real word (/bebe/) as well as the aftereffect on the same utterance (/be/) with a between-subjects design. This made it possible to contrast the amplitude of transfer at the levels of the utterance, the syllable, and the phoneme, depending on the position in the word. Linear mixed models allowed us to study the amplitude as well as the dynamics of the transfer and the aftereffect over trials. Results: Transfer from the training utterance /be/ was observed for all vowels of the test utterances but was larger to the syllable /be/ than to the syllable /pe/ at word-initial position and larger to the 1st syllable than to the 2nd syllable in the utterance. Conclusions: Our study suggests that words, syllables, and phonemes may all contribute to the definition of speech motor commands. In addition, the observation of a serial order effect raises new questions related to the connection between psycholinguistic models and speech motor control approaches.

Speech perception involves fusion of multiple sensory inputs, but fusion is not automatic, likely depending on several external and internal factors (e.g., attention, noise, age). In this study, we exploited a specific paradigm in which a short audiovisual context made of coherent or incoherent speech material is displayed before an incongruent audiovisual target likely to provide fusion (McGurk & MacDonald, 1976). We confirmed that incoherent context leads to unbinding, that is, a reduction in the amount of fusion. Importantly, adding acoustic noise in the context though not in the target increases fusion. This suggests that listeners systematically evaluate the reliability of their sensory channels and weight them accordingly in the fusion process. We also showed that older participants display more unbinding than younger participants. We discuss the potential consequences concerning people's ability to understand speech in adverse conditions and relate our findings to a "Binding-and-Fusion" model of audiovisual speech perception.

Purpose: This article investigates jaw-finger coordination in a task involving pointing to a target while naming it with a 'CVCV (e.g., /'papa/) versus CV'CV (e.g., /pa'pa/) word. According to the authors' working hypothesis, the pointing apex (gesture extremum) would be synchronized with the apex of the jaw-opening gesture corresponding to the stressed syllable. Method: Jaw and finger motions were recorded using Optotrak (Northern Digital, Waterloo, Ontario, Canada). The effects of stress position on jaw-finger coordination were tested across different target positions (near vs. far) and different consonants in the target word (/t/ vs. /p/). Twenty native Portuguese Brazilian speakers participated in the experiment (all conditions). Results: Jaw response starts earlier, and finger-target alignment period is longer for CV'CV words than for 'CVCV ones. The apex of the jaw-opening gesture for the stressed syllable appears synchronized with the onset of the finger-target alignment period (corresponding to the pointing apex) for 'CVCV words and with the offset of that period for CV'CV words. Conclusions: For both stress conditions, the stressed syllable occurs within the finger-target alignment period because of tight finger-jaw coordination. This result is interpreted as evidence for an anchoring of the speech deictic site (part of speech that shows) in the pointing gesture.

Purpose: Statistical studies conducted in various languages on both infants and adults have revealed an intersyllabic preference for initiating words with a labial consonant-vowel-coronal consonant sequence. Speech motor constraints have been proposed to explain this so-called "labial-coronal effect." This study was designed to test for a possible perceptual correlate of the labial-coronal effect in French adults. Method: The authors examined the perceptual stabilities of repeatedly presented disyllabic sequences, involving either a labial-vowel-coronal-vowel (LC) or a coronal-vowel-labial-vowel (CL) phonological structure. With this aim, they exploited the "verbal transformation effect," which refers to the perceptual changes experienced while listening to a speech form cycled in rapid and continuous repetition. Two experiments were carried out, involving either voiced or unvoiced plosive consonants. Results: In both experiments, a greater stability and attractiveness was observed for LC stimuli, which suggests that in a (...)LCLC(...) flow, the listener could more naturally provide a segmentation into LC chunks. Conclusion: This study demonstrates that the labial-coronal effect also occurs in the course of online speech processing. This result is interpreted in relation with theories assuming a link between perception and action in the human speech processing system.

The development of speech from infancy to adulthood results from the interaction of neurocognitive factors, by which phonological representations and motor control abilities are gradually acquired, and physical factors, involving the complex changes in the morphology of the articulatory system. In this article, an articulatory-to-acoustic model, integrating nonuniform vocal tract growth, is used to describe the effect of morphology in the acoustic and perceptual domains. While simulating mature control abilities of the articulators (freezing neurocognitive factors), the size and shape of the vocal apparatus are varied, to represent typical values of speakers from birth to adulthood. The results show that anatomy does not prevent even the youngest speaker from producing vowels perceived as the 10 French oral vowels/i y u e [??] o [epsilon] oe [??] a/. However, the specific configuration of the vocal tract for the newborn seems to favor the production of those vowels perceived as low and front. An examination of the acoustic effects of articulatory variation for different growth stages led to the proposed variable sensorimotor maps for newbornlike, childlike, and adultlike vocal tracts. These maps could be used by transcribers of infant speech, to complete existing systems and to provide some hints about underlying articulatory gestures recruited during growth to reach perceptual vowel targets in French.KEY WORDS: speech development, speech perception, physiology, articulatory modeling

Lip reading is the ability to partially understand speech by looking at the speaker's lips. It improves the intelligibility of speech in noise when audio-visual perception is compared with audio-only perception. A recent set of experiments showed that seeing the speaker's lips also enhances "sensitivity" to acoustic information, decreasing the auditory detection threshold of speech embedded in noise [J. Acoust. Soc. Am. 109 (2001) 2272; J. Acoust. Soc. Am. 108 (2000) 1197]. However, detection is different from comprehension, and it remains to be seen whether improved sensitivity also results in an "intelligibility" gain in audio-visual speech perception. In this work, we use an original paradigm to show that seeing the speaker's lips enables the listener to hear better "and hence to understand better." The audio-visual stimuli used here could not be differentiated by lip reading per se since they contained exactly the same lip gesture matched with different compatible speech sounds. Nevertheless, the noise-masked stimuli were more intelligible in the audio-visual condition than in the audio-only condition due to the contribution of visual information to the extraction of acoustic cues. Replacing the lip gesture by a non-speech visual input with exactly the same time course, providing the same temporal cues for extraction, removed the intelligibility benefit. This early contribution to audio-visual speech identification is discussed in relationships with recent neurophysiological data on audio-visual perception.