Etude de la perception de la voix chez le patient sourd post lingual implanté cochléaire unilatéral et le sujet normo-entendant en condition de simulation d'implant : psychophysique et imagerie

Ce travail de thèse a consisté à étudier les mécanismes perceptif set neurofonctionnels impliqués lors de la perception de la voix chez des patients sourds postlinguaux implantés cochléaires unilatéralement, et chez des sujets normo-entendants en simulation d'implant. Pour répondre à cet objectif, nous avons testé les performances comportementales des patients implantés dans des tâches de détection de la voix ainsi que dans des tâches de perception de l'information paralinguistique de la voix, comme le genre. Les patients ont été testés au cours d'un suivi ainsi qu'en mesures transversales. Nous avons comparé leurs performances à celles de sujets normo-entendants en condition de simulation d'implant cochléaire (vocoder). Nous avons également testé les sujets normo-entendants dans un protocole IRMf consistant à mesurer l'activité spécifique à la voix lors de la simulation d'implant. Dans l'ensemble, ces travaux montrent qu'après implantation cochléaire, les patients sourds sont déficitaires en matière de perception de la voix, contrairement à la compréhension du langage. Ce déficit n'est pas uniquement lié à la dégradation du signal par le processeur de l'implant cochléaire, mais aussi certainement à des réorganisations corticales subséquentes à la surdité.This work consisted in studying perceptual and the underlying neuronal mechanisms involved during voice perception in postlingually deaf cochlear-implanted patients and normal-hearing controls stimulated through cochlear implant simulation. We have analyzed behavioral performance of implanted patients during a voice detection task and other protocols perception tasks of paralinguistic information, such as gender. Two groups of patients were tested using either a longitudinal follow-ups or a transversal approach. We compared their performances to those of control normal-hearing subjects tested in cochlear implant simulation (vocoder). In addition, we have performed in normal-hearing subjects, a fMRI study, to reveal the effect of a cochlear implant simulation in the cortical activity of areas sensitive to human voice. Results agree to point out, following cochlear implantation, a deficit in voice perception, unlike speech comprehension. This deficit is not only due to the degradation of the signal by the vocoder, but probably results from cortical reorganization induced by deafness

Voice discrimination in cochlear-implanted deaf subjects.

International audienceThe human voice is important for social communication because voices carry speech and other information such as a person's physical characteristics and affective state. Further restricted temporal cortical regions are specifically involved in voice processing. In cochlear-implanted deaf patients, the processor alters the spectral cues which are crucial for the perception of the paralinguistic information of human voices. The aim of this study was to assess the abilities of voice discrimination in cochlear-implant (CI) users and in normal-hearing subjects (NHS) using a CI simulation (vocoder). In NHS the performance in voice discrimination decreased when reducing the spectral information by decreasing the number of channels of the vocoder. In CI patients with different delays after implantation we observed a strong impairment in voice discrimination at time of activation of the neuroprosthesis. No significant improvement can be detected in patients after two years of experience of the implant while they have reached a higher level of recovery of speech perception, suggesting a dissociation in the dynamic of functional recuperation of speech and voice processing. In addition to the lack of spectral cues due to the implant processor, we hypothesized that the origin of such deficit could derive from a crossmodal reorganization of the temporal voice areas in CI patients

Effects of vocoding and intelligibility on the cerebral response to speech

<p><b>Background:</b> Degrading speech through an electronic synthesis technique called vocoding has been shown to affect cerebral processing of speech in several cortical areas. However, it is not clear whether the effects of speech degradation by vocoding are related to acoustical degradation or by the associated loss in intelligibility. Using vocoding and a parametric variation of the number of frequency bands used for the encoding, we investigated the effects of the degradation of auditory spectral content on cerebral processing of intelligible speech (words), unintelligible speech (words in a foreign language), and complex environmental sounds.</p> <p><b>Results:</b> Vocoding was found to decrease activity to a comparable degree for intelligible and unintelligible speech in most of the temporal lobe. Only the bilateral posterior temporal areas showed a significant interaction between vocoding and intelligibility, with a stronger vocoding-induced decrease in activity for intelligible speech. Comparisons to responses elicited by environmental sounds showed that portions of the temporal voice areas (TVA) retained their greater responses to voice even under adverse listening conditions. The recruitment of specific networks in temporal regions during exposure to degraded speech follows a radial and anterior-posterior topography compared to the networks recruited by exposure to speech that is not degraded.</p> <p><b>Conclusions:</b> Different brain networks are involved in vocoded sound processing of intelligible speech, unintelligible speech, and non-vocal sounds. The greatest differences are between speech and environmental sounds, which could be related to the distinctive temporal structure of speech sounds.</p&gt

Gender categorization in cochlear implant users.

International audiencePURPOSE: In this study, the authors examined the ability of subjects with cochlear implants (CIs) to discriminate voice gender and how this ability evolved as a function of CI experience. METHOD: The authors presented a continuum of voice samples created by voice morphing, with 9 intermediate acoustic parameter steps between a typical male and a typical female. This method allowed for the evaluation of gender categorization not only when acoustical features were specific to gender but also for more ambiguous cases, when fundamental frequency or formant distribution were located between typical values. RESULTS: Results showed a global, though variable, deficit for voice gender categorization in CI recipients compared with subjects with normal hearing. This deficit was stronger for ambiguous stimuli in the voice continuum: Average performance scores for CI users were 58% lower than average scores for subjects with normal hearing in cases of ambiguous stimuli and 19% lower for typical male and female voices. The authors found no significant improvement in voice gender categorization with CI experience. CONCLUSIONS: These results emphasize the dissociation between recovery of speech recognition and voice feature perception after cochlear implantation. This large and durable deficit may be related to spectral and temporal degradation induced by CI sound coding, or it may be related to central voice processing deficits