Cortical Processes Underlying the Sound Induced Visual Illusion
Poster Presentation

Jyoti Mishra
Dept. of Computational Neurobiology, UCSD

Antigona Martinez
Department of Neurosciences, UCSD; Nathan Kline Institute

Wolfgang Teder-Sälejärvi
Dept. of Psychology, North Dakota State University

Terrence Sejnowski
Computational Neurobio. Lab, Salk Institute, La Jolla

Steven Hillyard
Dept. of Neurosciences, UCSD

     Abstract ID Number: 197
     Full text: Not available
     Last modified: March 20, 2006
     Presentation date: 06/21/2006 8:30 AM in Hamilton Building, McNeil Theatre
     (View Schedule)

Abstract
When a single flash of light is presented interposed between two brief auditory stimuli separated by 70-100 msec, subjects typically report perceiving two flashes (Shams et al 2000, 2002). The neural mechanisms underlying this striking illusory flash phenomenon remain unknown. Preliminary electrophysiological and neuromagnetic evidence from Shams and colleagues (2001, 2005) suggested a visual cortex modulation produced by the paired sounds that qualitatively resembles activity elicited by a real visual stimulus. Using 64 channel ERP recordings, we found that neural activity associated with the illusory flash has significantly different spatio-temporal characteristics from activity evoked by a real visual stimulus. Difference ERPs calculated to reflect the auditory-visual interaction producing the illusory flash included an early positivite difference over bilateral occipital areas at 120 ms after the first sound (pd120), a centrally distributed positivity at 180 ms (pd180) and a centro-parietally distributed negativity at 270 ms (nd270). The difference ERP for the real visual flash on the other hand contained typical occipitally distributed P1 and N1 components over the contralateral hemisphere. Possible mechanisms for the illusory flash effect will be discussed.