Biomedical subjects

Claude Delpuech

Publications and source records attributed to Claude Delpuech.

4 recordsLinked to original sources

PubMed2006

Brain responses to a subject's own name uttered by a familiar voice.

Hearing one's own first name automatically elicits a robust electrophysiological response, even in conditions of reduced consciousness like sleep. In a search for objective clues to superior cognitive functions in comatose patients, we looked for an optimal auditory stimulation paradigm mobilizing a large population of neurons. Our hypothesis was that wider ERPs would be obtained in response to the subject's own name (SON) when a familiar person uttered it. In 15 healthy awake volunteers, we tested a passive oddball paradigm with three different novels presented with the same probability (P = 0.02): SON uttered by a familiar voice (FV) or by an unknown voice (NFV) and a non-vocal stimulus (NV) which preserved most of the physical characteristics of SON FV. ERP (32 electrodes) and scalp current density (SCD) maps were analyzed. SON appeared to generate more robust responses related to involuntary attention switching (MMN/N2b, novelty P3) than NV. When uttered by a familiar person, the SON elicited larger response amplitudes in the late phase of novelty P3 (after 300 ms). Most important differences were found in the late slow waves where two components could be temporally and spatially dissociated. A larger parietal component for FV than for NFV suggested deeper high-level processing, even if the subjects were not required to explicitly differentiate or recognize the voices. This passive protocol could therefore provide a valuable tool for clinicians to test residual superior cognitive functions in uncooperative patients.

Acoustic Stimulation↗

PubMed2004

Bimodal speech: early suppressive visual effects in human auditory cortex.

While everyone has experienced that seeing lip movements may improve speech perception, little is known about the neural mechanisms by which audiovisual speech information is combined. Event-related potentials (ERPs) were recorded while subjects performed an auditory recognition task among four different natural syllables randomly presented in the auditory (A), visual (V) or congruent bimodal (AV) condition. We found that: (i) bimodal syllables were identified more rapidly than auditory alone stimuli; (ii) this behavioural facilitation was associated with cross-modal [AV-(A+V)] ERP effects around 120-190 ms latency, expressed mainly as a decrease of unimodal N1 generator activities in the auditory cortex. This finding provides evidence for suppressive, speech-specific audiovisual integration mechanisms, which are likely to be related to the dominance of the auditory modality for speech perception. Furthermore, the latency of the effect indicates that integration operates at pre-representational stages of stimulus analysis, probably via feedback projections from visual and/or polymodal areas.

Acoustic Stimulation↗

PubMed2002

Early auditory-visual interactions in human cortex during nonredundant target identification.

A common finding of behavioral studies is that objects characterized by redundant multisensory cues are identified more rapidly than the same objects presented in either unimodal condition. In a previous electrophysiological study in humans, we have described a network of crossmodal interactions that could be associated with this facilitation effect [M.H. Giard, F. Peronnet, J. Cogn. Neurosci. 11(5) (1999) 473-490]. Here, we sought to determine whether the recognition of objects characterized by nonredundant bimodal components may still induce crossmodal neural interactions. Subjects had to identify three objects defined either by auditory or visual features alone, or by the combination of nonredundant auditory and visual features. As expected, behavioral measures showed no sign of facilitation in bimodal processing. Yet, event-related potential analysis revealed the existence of early (<200 ms latency) crossmodal activities in sensory-specific and nonspecific cortical areas, that were partly dependent on the sensory dominance of the subjects to perform the task. Comparative analysis of the interaction patterns involved in redundant and nonredundant cue processing provides evidence for the robustness of the principle of crossmodal neural synergy that applies whatever the stimulus content (redundant or nonredundant information), and for the high flexibility of the neural networks of integration that are sensitive both to the nature of the perceptual task and to the sensory skill of the individual in that particular task.

Adult↗

PubMed2002

Dynamics of cortico-subcortical cross-modal operations involved in audio-visual object detection in humans.

Very recently, a number of neuroimaging studies in humans have begun to investigate the question of how the brain integrates information from different sensory modalities to form unified percepts. Already, intermodal neural processing appears to depend on the modalities of inputs or the nature (speech/non-speech) of information to be combined. Yet, the variety of paradigms, stimuli and technics used make it difficult to understand the relationships between the factors operating at the perceptual level and the underlying physiological processes. In a previous experiment, we used event-related potentials to describe the spatio-temporal organization of audio-visual interactions during a bimodal object recognition task. Here we examined the network of cross-modal interactions involved in simple detection of the same objects. The objects were defined either by unimodal auditory or visual features alone, or by the combination of the two features. As expected, subjects detected bimodal stimuli more rapidly than either unimodal stimuli. Combined analysis of potentials, scalp current densities and dipole modeling revealed several interaction patterns within the first 200 micro s post-stimulus: in occipito-parietal visual areas (45-85 micro s), in deep brain structures, possibly the superior colliculus (105-140 micro s), and in right temporo-frontal regions (170-185 micro s). These interactions differed from those found during object identification in sensory-specific areas and possibly in the superior colliculus, indicating that the neural operations governing multisensory integration depend crucially on the nature of the perceptual processes involved.

Acoustic Stimulation↗