Bimodal speech: early suppressive visual effects in human auditory cortex

• Published in: The European journal of neuroscience Vol. 20; no. 8; pp. 2225 - 2234
• Main Authors: Besle, Julien, Fort, Alexandra, Delpuech, Claude, Giard, Marie-Hélène
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.10.2004; Wiley; Blackwell Science
• Subjects: Acoustic Stimulation; Acoustic Stimulation - methods; Adult; audiovisual; Auditory Cortex; Auditory Cortex - physiology; Comparative Study; electrophysiology; Evoked Potentials; Evoked Potentials - physiology; Female; Humans; Least-Squares Analysis; Life Sciences; Male; multisensory integration; Neurons and Cognition; Photic Stimulation; Photic Stimulation - methods; Reaction Time; Reaction Time - physiology; Research Support, Non-U.S. Gov't; Speech; Speech - physiology; speech perception; Visual Perception; Perception visuelle; Multisensory Intregration; Intégration Multisensorielle
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/j.1460-9568.2004.03670.x

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.