Sound alters activity in human V1 in association with illusory visual perception
Poster Presentation

susanne watkins
UCL

Ladan Shams

Shigeki Tanaka

John -Dylan Haynes

Geraint Rees

     Abstract ID Number: 27
     Full text: Not available
     Last modified: March 8, 2005

Abstract
The auditory induced double flash illusion shows that conscious visual perception can be dramatically altered by irrelevant auditory stimulation. When a single brief visual flash is accompanied by two auditory bleeps, the single flash is frequently perceived incorrectly as two flashes. Here, we used event-related functional MRI in conjunction with retinotopic mapping of early visual cortex to examine the neural basis of this illusory phenomenon. On each trial, participants were presented with either one or two successively flashed high contrast annuli around fixation, either alone or in association with one or two binaurally presented bleeps. Participants indicated on each trial whether they perceived either one or two flashes. Behaviorally, on a significant proportion of single flash trials that were accompanied by two bleeps, participants reported the perceptual experience of two flashes i.e. the illusion. We then compared brain activity evoked by physically identical but perceptually dissimilar (illusion versus no illusion) one-flash-two-bleep trials. In V1, there was significantly greater activation for illusion versus no illusion trials. Such activation cannot reflect a general auditory alerting effect as the trials in such a comparison are physically identical. Our findings indicate that multisensory interactions can occur at the very earliest stages of cortical processing in humans.