Selective disruption of audio-visual interaction studied with transcranial magnetic stimulation

Abstract

Many studies have shown that the brain often combines in a single percept auditory and visual information provided the two sensory inputs are temporally and spatially contiguous, a phenomenon called multi-sensory integration. What is less well understood at present is whether the type of pairing as defined by the stimulus domain and by the type of association between auditory and visual stimuli also plays a role. Evidence from neuropsychology indicates that disruption of audio-visual interactions is often domain?specific in the sense that some audio-visual pairings are disrupted (for example audio-visual speech) while others are preserved (for example ventriloquism or multisensory perception of affect). The present study extends the available methods to understand multisensory processes by the use of Transcranial Magnetic Stimulation (TMS). We compared the impact of TMS on two types of pairs that have extensively been used in the literature (naturalistic voice-face pairs vs. arbitrary tone-shape pairs). Based on earlier findings we selected three sites of stimulation (pre-frontal, left and right posterior parietal sites). Participants were instructed to perform a similar speeded categorisation task in all conditions. TMS applied over the left posterior parietal cortex at 150 ms post-stimulus onset and later disrupted integration as measured by the loss of the latency advantage for categorisation in the audiovisual condition. This effect was limited to the arbitrary pairs indicating a dissociation between Naturalistic and Arbitrary pairs for this stimulation site.