Sound-induced illusory £ash perception: role of gamma band responses

In the recently discovered sound-induced illusory £ash phenomen-on, a single £ash accompaniedwith two auditorybeeps isperceived as two£ashes in amajorityof trials.Herewe askedwhat theneural substrates distinguishing illusion and no-illusion (i.e. perception of single £ash) percepts are under identical stimulus con¢guration. Wavelet based method was used to analyze g band (4 30Hz) re-sponses in the event-related potential (ERP) signals recorded over visual cortical regions.We found: (i) signi¢cantly higher oscillatory and induced g band responses in illusion than in no-illusion trials, and (ii) signi¢cant supra-additive audio-visual interactions only in illusion trials.These results provide a clear neurophysiological cor-relate to the perception of illusion. Furthermore, the results sug-gest that auditory stimuli modulate cortical processing of visual stimuli, and the £ash illusion (qualitative alteration of visual per-cept) only takes place when this modulation exceeds some critical threshold for the registration of conscious awareness.NeuroRepor