Abstract
Previous studies show that visual stimuli can influence auditory localization. The present study investigates the role of primary visual cortex (V1) on multisensory-mediated auditory localization, using rTMS (inhibitory theta-burst stimulation, iTBS). Subjects were asked to localize an auditory stimulus alone or with a concurrent near-threshold visual stimulus presented at the same spatial position or at spatial disparity, in two counterbalanced sessions performed outside (baseline) or within the inhibitory effects created by iTBS of V1. Compared to baseline, after iTBS, visual capture (i.e. perceptual translocation of the auditory stimulus toward the visual one, when audio-visual stimuli are spatially disparate) disappeared into the visual field contralateral to the stimulated site, whereas no effect was found into the ipsilateral visual field. However, when audio-visual stimuli were spatially coincident, an acoustical localization enhancement of the same magnitude in the contralateral and in the ipsilateral field was found in both sessions, suggesting an audio-visual integration effect. These results suggest that visual capture and multisensory integration for spatially coincident audio-visual stimuli are functionally independent and mediated by different neural circuits: V1 activity is necessary in mediating visual capture, whereas audio-visual integration is unaffected by V1 inhibition and may be mediated by subcortical structures such as Superior Colliculus.
