Asymmetric discrimination of non-speech tonal analogues of vowels

Published in final edited form as: J Exp Psychol Hum Percept Perform. 2019 February ; 45(2): 285–300. doi:10.1037/xhp0000603.Directional asymmetries reveal a universal bias in vowel perception favoring extreme vocalic articulations, which lead to acoustic vowel signals with dynamic formant trajectories and well-defined spectral prominences due to the convergence of adjacent formants. The present experiments investigated whether this bias reflects speech-specific processes or general properties of spectral processing in the auditory system. Toward this end, we examined whether analogous asymmetries in perception arise with non-speech tonal analogues that approximate some of the dynamic and static spectral characteristics of naturally-produced /u/ vowels executed with more versus less extreme lip gestures. We found a qualitatively similar but weaker directional effect with two-component tones varying in both the dynamic changes and proximity of their spectral energies. In subsequent experiments, we pinned down the phenomenon using tones that varied in one or both of these two acoustic characteristics. We found comparable asymmetries with tones that differed exclusively in their spectral dynamics, and no asymmetries with tones that differed exclusively in their spectral proximity or both spectral features. We interpret these findings as evidence that dynamic spectral changes are a critical cue for eliciting asymmetries in non-speech tone perception, but that the potential contribution of general auditory processes to asymmetries in vowel perception is limited.Accepted manuscrip

Engaging the articulators enhances perception of concordant visible speech movements

PURPOSE This study aimed to test whether (and how) somatosensory feedback signals from the vocal tract affect concurrent unimodal visual speech perception. METHOD Participants discriminated pairs of silent visual utterances of vowels under 3 experimental conditions: (a) normal (baseline) and while holding either (b) a bite block or (c) a lip tube in their mouths. To test the specificity of somatosensory-visual interactions during perception, we assessed discrimination of vowel contrasts optically distinguished based on their mandibular (English /ɛ/-/æ/) or labial (English /u/-French /u/) postures. In addition, we assessed perception of each contrast using dynamically articulating videos and static (single-frame) images of each gesture (at vowel midpoint). RESULTS Engaging the jaw selectively facilitated perception of the dynamic gestures optically distinct in terms of jaw height, whereas engaging the lips selectively facilitated perception of the dynamic gestures optically distinct in terms of their degree of lip compression and protrusion. Thus, participants perceived visible speech movements in relation to the configuration and shape of their own vocal tract (and possibly their ability to produce covert vowel production-like movements). In contrast, engaging the articulators had no effect when the speaking faces did not move, suggesting that the somatosensory inputs affected perception of time-varying kinematic information rather than changes in target (movement end point) mouth shapes. CONCLUSIONS These findings suggest that orofacial somatosensory inputs associated with speech production prime premotor and somatosensory brain regions involved in the sensorimotor control of speech, thereby facilitating perception of concordant visible speech movements. SUPPLEMENTAL MATERIAL https://doi.org/10.23641/asha.9911846R01 DC002852 - NIDCD NIH HHSAccepted manuscrip

Dissociation between phonological working memory structures and motor programming units during speech motor sequence learning

Accepted manuscrip

Directional asymmetries reveal a universal bias in adult vowel perception

published online 21 April 2017Research on cross-language vowel perception in both infants and adults has shown that for many vowel contrasts, discrimination is easier when the same pair of vowels is presented in one direction compared to the reverse direction. According to one account, these directional asymmetries reflect a universal bias favoring “focal” vowels (i.e., vowels whose adjacent formants are close in frequency, which concentrates acoustic energy into a narrower spectral region). An alternative, but not mutually exclusive, account is that such effects reflect an experience-dependent bias favoring prototypical instances of native-language vowel categories. To disentangle the effects of focalization and prototypicality, the authors first identified a certain location in phonetic space where vowels were consistently categorized as /u/ by both Canadian-English and Canadian-French listeners, but that nevertheless varied in their stimulus goodness (i.e., the best Canadian-French /u/ exemplars were more focal compared to the best Canadian-English /u/ exemplars). In subsequent AX discrimination tests, both Canadian-English and Canadian-French listeners performed better at discriminating changes from less to more focal /u/’s compared to the reverse, regardless of variation in prototypicality. These findings demonstrate a universal bias favoring vowels with greater formant convergence that operates independently of biases related to language-specific prototype categorization.This research was supported by NSERC Discovery Grant No. 105397 to L.P. and NSERC Discovery Grant No. 312395 to L.M

Chunking of phonological units in speech sequencing

Efficient speech communication requires rapid, fluent production of phoneme sequences. To achieve this, our brains store frequently occurring subsequences as cohesive "chunks" that reduce phonological working memory load and improve motor performance. The current study used a motor-sequence learning paradigm in which the generalization of two performance gains (utterance duration and errors) from practicing novel phoneme sequences was used to infer the nature of these speech chunks. We found that performance improvements in duration from practicing syllables with non-native consonant clusters largely generalized to new syllables that contained those clusters. Practicing the whole syllable, however, resulted in larger performance gains in error rates compared to practicing just the consonant clusters. Collectively, these findings are consistent with theories of speech production that posit the consonant cluster as a fundamental unit of phonological working memory and speech sequencing as well as those positing the syllable as a fundamental unit of motor programming.R01 DC007683 - NIDCD NIH HHSAccepted manuscrip

Behavioral and neural correlates of speech motor sequence learning in stuttering and neurotypical speakers: an fMRI investigation

Stuttering is a neurodevelopmental disorder characterized by impaired production of coordinated articulatory movements needed for fluent speech. It is currently unknown whether these abnormal production characteristics reflect disruptions to brain mechanisms underlying the acquisition and/or execution of speech motor sequences. To dissociate learning and control processes, we used a motor sequence learning paradigm to examine the behavioral and neural correlates of learning to produce novel phoneme sequences in adults who stutter (AWS) and neurotypical controls. Participants intensively practiced producing pseudowords containing non-native consonant clusters (e.g., “GVAZF”) over two days. The behavioral results indicated that although the two experimental groups showed comparable learning trajectories, AWS performed significantly worse on the task prior to and after speech motor practice. Using functional magnetic resonance imaging (fMRI), the authors compared brain activity during articulation of the practiced words and a set of novel pseudowords (matched in phonetic complexity). FMRI analyses revealed no differences between AWS and controls in cortical or subcortical regions; both groups showed comparable increases in activation in left-lateralized brain areas implicated in phonological working memory and speech motor planning during production of the novel sequences compared to the practiced sequences. Moreover, activation in left-lateralized basal ganglia sites was negatively correlated with in-scanner mean disfluency in AWS. Collectively, these findings demonstrate that AWS exhibit no deficit in constructing new speech motor sequences but do show impaired execution of these sequences before and after they have been acquired and consolidated.Published versio

A Sound Approach to Language Matters: In Honor of Ocke-Schwen Bohn

The contributions in this Festschrift were written by Ocke’s current and former PhD-students, colleagues and research collaborators. The Festschrift is divided into six sections, moving from the smallest building blocks of language, through gradually expanding objects of linguistic inquiry to the highest levels of description - all of which have formed a part of Ocke’s career, in connection with his teaching and/or his academic productions: “Segments”, “Perception of Accent”, “Between Sounds and Graphemes”, “Prosody”, “Morphology and Syntax” and “Second Language Acquisition”. Each one of these illustrates a sound approach to language matters

On the nature of the natural referent vowel bias

There is considerable debate in the phonetic sciences concerning the nature of the information that is critical for speech perception, and the nature of the processing mechanisms that map the relevant signal properties onto phonetic categories. In the domain of vowel perception, research has shown that the mapping between the speech signal and phonetic structure is non-uniform, in that perceivers (both adult and infant) are universally biased toward the extremes of articulatory/acoustic space (peripheral in F1/F2 space; Polka & Bohn, 2003, 2011). Much of the evidence for this bias comes from studies showing that perceivers consistently discriminate vowels in an asymmetric manner. More precisely, perceivers perform better at detecting a change from a relatively less (e.g., /e/) to a relatively more peripheral vowel (e.g., /i/), compared to the same change presented in the reverse direction. Although the existence of this perceptual phenomenon (i.e., the natural referent vowel [NRV] bias) is well established, the mechanisms and processes that underlie it are poorly understood. One account of the NRV bias, which derives from the Dispersion–Focalization Theory (Schwartz, Abry, Boë, Ménard, & Vallée, 2005), is that extreme vocalic articulations give rise to speech signals that exhibit increased spectral salience due to formant frequency convergence, or "focalization." This dissertation presents a series of experiments aimed at assessing whether adult perceivers are indeed sensitive to differences in formant proximity while discriminating vowel stimuli that fall within a given category, and, if so, whether that sensitivity is attributable to general properties of auditory processing, or to phonetic processes that extract articulatory information available across sensory modalities. In Experiment 1, English- and French-speaking perceivers showed directional asymmetries consistent with the focalization account as they attempted to discriminate synthetic /u/ variants that systematically differed in their peripherality and hence degree of formant proximity (between F1 and F2). In Experiment 2, similar directional effects were found when English perceivers attempted to discriminate natural /u/ productions that differed in their peripherality when only acoustic-phonetic or only visual-phonetic information was present. Experiment 3 investigated whether and how the integration of acoustic and visual speech cues influences the effects documented in Experiment 2. When acoustic and visual cues were phonetically-congruent, an NRV bias was observed. In contrast, when acoustic and visual cues were phonetically-incongruent, this bias was disrupted, confirming that both sensory channels shape this bias in bimodal auditory-visual vowel perception. Collectively, these findings advance our understanding of the sensory and cognitive processes that are fundamental to the mapping between the speech signal and vowel categories. In particular, they suggest that perceivers are universally biased to attend to extreme vocalic gestures specified optically, in terms of articulatory kinematic patterns, as well as acoustically, in terms of formant convergence patterns. A complete understanding of this bias is not only important to speech perception theories, but provides a critical basis for the study of phonetic development as well as the perceptual factors that may constrain vowel inventories across languages.Un débat considérable dans le domaine des sciences phonétiques entoure la nature de l'information pertinente à la perception de la parole et la nature des mécanismes de processus transformant les propriétés des signaux en catégories phonétiques. Dans le domaine de la perception des voyelles, les recherches démontrent que la relation entre le signal de parole et la structure phonétique est déformée, en ce sens que les auditeurs (les adultes comme les nourrissons) sont universellement biaisés à porter attention aux voyelles dotées de propriétés articulatoires / acoustiques extrêmes (en périphérie de l'espace F1/F2; Polka & Bohn, 2003, 2011). Une preuve importante de ce biais provient d'études qui démontrent que les auditeurs discriminent les voyelles de manière asymétrique. Plus précisément, les auditeurs réussissent mieux à détecter un changement d'une voyelle relativement moins périphérique (par exemple, /e/) à une voyelle relativement plus périphérique (par exemple, /i/), comparativement à la même variation dans le sens inverse. Bien que l'existence de ce phénomène perceptif (c.-à-d. le biais de la voyelle référent naturel [VNR]) soit bien établie, les mécanismes et les processus qui le régissent sont mal compris. Une explication du VNR, qui découle de la théorie de la dispersion-focalisation (Schwartz et al., 1997, 2005), est que les articulations vocaliques extrêmes - comme /i/, /a/ et /u/ - donnent naissance à des signaux de parole particulièrement saillant spectralement en raison de la fréquence de convergence des formants, ou «focalisation». Cette thèse présente une série d'études visant à évaluer si les auditeurs sont sensibles aux différences de proximité des formants tout en discriminant le stimulus vocalique qui relève de la même catégorie phonétique, et dans ce cas, si cette sensibilité est attribuable aux propriétés générales de traitement auditif, ou à des processus phonétiques qui opèrent en termes de propriétés articulatoires. Dans l'étude 1, les auditeurs anglophones et francophones ont démontré des asymétries directionnelles en accord avec les prédictions de la focalisation lorsqu'ils tentaient de discriminer des variantes synthétiques de /u/ qui étaient systématiquement différentes dans leur périphérie et, par conséquent, dans le degré de proximité des formants (entre F1 et F2). Dans l'étude 2, des effets directionnels similaires ont été observés lorsque les auditeurs ont tenté de discriminer les réalisations naturelles de /u/ qui diffèrent dans leur périphérie seulement lors que l'information acoustique ou visuelle de parole était présente. L'étude 3 a étudié comment l'intégration des indices acoustiques vocaux et visuels influencent les effets documentés dans l'étude 2. Lorsque des signaux acoustiques et visuels étaient phonétiquement conformes, un biais de VNR a été observé. En revanche, lorsque les repères visuels et acoustiques étaient phonétiquement incongrus, ce biais était perturbé, ce qui confirme que les deux voies sensorielles créent ce biais dans la perception audiovisuelle. De façon globale, ces résultats améliorent notre compréhension des processus sensoriels et cognitifs qui sont essentiels au lien entre les propriétés des signaux et les catégories phonétiques. En particulier, ils suggèrent que les auditeurs sont prédisposés à détecter des signes vocaliques extrêmes visuellement spécifiés, en termes de modèles articulatoires cinématiques, ainsi qu'acoustiques, en termes de convergence de formants. Une compréhension complète de ce biais est non seulement importante pour les théories de la perception de la parole, mais elle fournit également une base crucial pour l'étude du développement phonétique ainsi que pour les éléments perceptuels qui pourraient restreindre les inventaires de voyelles à travers les langues

The Development of articles in children's early Spanish : prosodic interactions between lexical and grammatical form

Studies of English and French show that children’s first articles are more likely to appear when they can be prosodified as part of a disyllabic foot (cf. Gerken, 1996; Demuth & Tremblay, 2008). However, preliminary studies of Spanish suggest that children’s first articles appear in larger prosodic structures, possibly due to the higher frequency of longer words. To assess this issue, this study examined longitudinal data from two Spanish 1- to 2-year-olds. As expected, both produced their early articles with monosyllabic and disyllabic nouns, rapidly expanding article use to trisyllabic nouns as well. The results suggest that the prosodic complexity of the lexicon plays an important role in the development of prosodic structure, providing the context for early prosodic licensing of grammatical morphemes.21 page(s