Masking the sound induced flash illusion

When a single flash of a visual stimulus is accompanied by two auditory beeps, the single flash is perceived as two flashes. This is the sound induced flash illusion. A growing body of evidence suggests that the auditory information influences visual processing very early in the visual processing pathway, perhaps in V1 (e.g. Mishra, Martinez, Terrence, Sejnowski & Hillyard; 2007, Watkins, Shams, Tanaka, Haynes & Rees; 2006). We have recently demonstrated targets that selectively and coherently drive the M-pathway, such as a high contrast flashed disc, result in a strong illusion (van der Zwan, Cottrell, Brooks, & Reid; 2007). In the reported experiment we followed up these findings by testing the hypothesis that the illusion depends, to a large extent, activity in the M-pathway. We presented he illusion inducing stimuli flanked by either a forward or backward visual mask at either short (50ms) or long (200ms) SOA. The illusion remained strong in all but the forward masking condition at the short SOA. We argue that this finding is consistent with the illusion being dependent on activity in the ON and OFF channels of the M-pathway.