Sound alters visual evoked potentials in humans

When a single flash is accompanied by two auditory beeps, the single flash is perceived as two flashes. We investigated whether this crossmodal influe nce on visual perception occurs at the level of the modality-specific visua l pathway or later. We compared the visual evoked potentials (VEPs) in the presence and absence of sound. Activity was modulated extensively and with short latency in trials in which an illusory flash was perceived. In additi on, the brain potentials for the illusory flash were qualitatively very sim ilar to those for a physical flash, suggesting that the same mechanism unde rlies the percept of both illusory and physical flashes. These results sugg est that the activity in the visual cortex can be modulated by sound. This implication challenges the general belief that the visual cortical processi ng is independent of other modalities. NeuroReport 12:3849-3852 (C) 2001 Li ppincott Williams & Wilkins.