Evelyne Veuillet

The effect of long-term unilateral deafness on the activation pattern in the auditory cortices of French-native speakers: influence of deafness side.

BackgroundIn normal-hearing subjects, monaural stimulation produces a normal pattern of asynchrony and asymmetry over the auditory cortices in favour of the contralateral temporal lobe. While late onset unilateral deafness has been reported to change this pattern, the exact influence of the side of deafness on central auditory plasticity still remains unclear. The present study aimed at assessing whether left-sided and right-sided deafness had differential effects on the characteristics of neurophysiological responses over auditory areas. Eighteen unilaterally deaf and 16 normal hearing right-handed subjects participated. All unilaterally deaf subjects had post-lingual deafness. Long latency auditory evoked potentials (late-AEPs) were elicited by two types of stimuli, non-speech (1 kHz tone-burst) and speech-sounds (voiceless syllable/pa/) delivered to the intact ear at 50 dB SL. The latencies and amplitudes of the early exogenous components (N100 and P150) were measured using temporal scalp electrodes.ResultsSubjects with left-sided deafness showed major neurophysiological changes, in the form of a more symmetrical activation pattern over auditory areas in response to non-speech sound and even a significant reversal of the activation pattern in favour of the cortex ipsilateral to the stimulation in response to speech sound. This was observed not only for AEP amplitudes but also for AEP time course. In contrast, no significant changes were reported for late-AEP responses in subjects with right-sided deafness.ConclusionThe results show that cortical reorganization induced by unilateral deafness mainly occurs in subjects with left-sided deafness. This suggests that anatomical and functional plastic changes are more likely to occur in the right than in the left auditory cortex. The possible perceptual correlates of such neurophysiological changes are discussed.

Assessment of auditory plasticity using psychoacoustic and electrophysiological measurements

Anatomical and physiological changes may occur under different circumstances, reflecting the plasticity of the human central and peripheral auditory system: deprivation of peripheral auditory input (plasticity induced by hearing deprivation), chronic exposition to sound in deaf subjects (plasticity induced by auditory rehabilitation), or auditory learning (learning-induced plasticity). In this review, we focus on auditory deprivation and rehabilitation-induced plasticity. We first describe some perceptual correlates of cortical plasticity induced by sensory deprivation, and then we present some of our original results showing the influence of hearing aids on perceptual performances of sensorineural hearing impaired listeners. These results are in line with the auditory acclimatization phenomenon (i.e. in monaurally fitted listeners, the aided ear performs better than the unaided ear for fine processing of high-intensity sounds). They also suggest that the auditory acclimatization phenomenon is lateralized with, in right-handed subjects, a more pronounced effect observed on the right side.

Exploration électrophysiologique des voies auditives sous-corticales chez l’humain : du clic au son de parole

There is a growing and unprecedented interest in the objective evaluation of the subcortical processes that are involved in speech perception, with potential clinical applications in speech and language impairments. Here, we review the studies illustrating the development of electrophysiological methods for assessing speech encoding in the human brainstem: from the pioneer recordings of click-evoked auditory brainstem responses (ABR), via studies of frequency-following responses (FFR) to the most recent measurements of speech ABR (SABR) or ABR in response to speech sounds. Recent research on SABR has provided new insights in the understanding of subcortical auditory processing mechanisms. The SABR test is an objective and non-invasive tool for assessing individual capacity of speech encoding in the brainstem. SABR characteristics are potentially useful both as a diagnosis tool of speech encoding deficits and as an assessment tool of the efficacy of rehabilitation programs in patients with learning and/or auditory processing disorders.

Objective measures in cochlear implanted patients: A computational framework to evaluate artifact rejection methodologies

Auditory steady-state responses (ASSRs) constitute a reliable measure of auditory perception in normal hearing subjects. The use of these measures in cochlear implanted patients is hindered by the vast diffusion of the electrical cochlear stimulation artifact that highly contaminates EEG scalp recordings. Therefore, attenuating or moreover suppressing this artifact ahead of response detection is crucial. Yet, the currently used denoising algorithms may have unpredictable effects on these responses (ASSRs). In this paper, we propose a computational framework that allows the simulation of the mixture of the stimulation artifact and its corresponding evoked ASSRs on EEG scalp electrodes. The utility of this relatively basic model resides in its usefulness in quantifying the effects of any applied denoising method on the information contained in the signal of interest (responses known a priori). Here, an application to two independent component analysis algorithms (infomax and infomax extended) is presented. The model predicts a better performance for infomax compared to infomax extended.

Temporal, Intensity and Pitch Relationship on Speech Auditory Brainstem Response to Phonemes /ba/ in Normal Hearing Adults.

The temporal acoustic pattern of a short speech signal is encoded very accurately in the brainstem. This compound remote response can be recorded on the scalp under the form of speech elicited Auditory Brainstem Response (Speech ABR). Speech ABR is described as the succession of a transient Onset Response (OR) and a sustained Frequency Following Response (FFR). It has been shown that the FFR is the compound phase-locking activity of brainstem cells, and that FFR mimics the periodicity of phonemes (Russo et al., 2004). In Experiment 1 reported here, we confirmed this observation (23 subjects). Experiment 2 showed that Speech ABR to /ba/ components, had different latency-intensity functions (around 15ms for FFR and 7 ms for OR), assuming that these two responses were the result of separate processing streams (11 subjects). In Experiment 3, three stimuli with steady fundamental frequencies (F0) at 133, 375 and 575 Hz vowel were used (12 subjects). Speech ABR showed a reproducible onset response (OR) around 6...