Spatial congruency and the sound-induced flash illusion.
Poster Presentation

David Cottrell
Psychology, James Cook University

John Prescott
Psychology, James Cook University

Collette Purves
Psychology, James Cook University

     Abstract ID Number: 4
     Full text: Not available
     Last modified: May 30, 2007
     Presentation date: 07/06/2007 10:00 AM in Quad Maclauren Hall
     (View Schedule)

Abstract
A single brief visual stimulus when accompanied by multiple beeps is perceived as multiple flashes (Shams et al, 2000). This sound induced flash illusion is thus an interesting example of the modification of the perception of an unambiguous visual stimulus by an auditory stimulus. The temporal properties of the illusion are well documented with the illusion remaining strong as long as all the stimuli occur within a temporal window of approximately 70ms. Other psychophysical limits to the effect are less well known. Based on the assumption that sensory integration is maximised when the stimuli occur together in both time and space, we predicted that the illusion would be sensitive to the special congruency of the stimuli. Results were consistent with this hypothesis in that reports of illusory flashes were more frequent when the auditory stimuli originated from the same spatial location as the visual flash. Unexpectedly, we found that modulation of the illusion by spatial congruency was weaker when the visual stimulus was presented in the right visual field. We speculate that this might be a direct consequence of earlier processing of the illusory stimulus in the right visual pathway.