When subjects were shown a single flash of light interposed between two brief sounds, many subjects reported seeing two distinct flashes of light. Investigating the timing and location of the brain processes that underlie this illusory effect ?the illusion of seeing two flashes in the presence of two auditory signals, when only one flash actually occurs ?can reveal how information from different senses are integrated in the brain.
The study of 34 subjects was carried out in the laboratory of Steven A. Hillyard, Ph.D., UCSD professor of neurosciences. "This type of perceptual illusion has been described before," said first author Jyoti Mishra, graduate student in the Hillyard lab. "The surprising finding we made is that the illusion depends on a rapidly timed sequence of interactions between the auditory and visual cortical areas."
"This is part of a set of new findings by scientists in the field that show how integration of multiple sensations can happen much more rapidly than we thought before," said Mishra. "We show physiological evidence that visual and auditory stimulation might not be processed separately, then merged together, as previously assumed, but that an almost-simultaneous integration of the sensations may actually take place in the brain."
The UCSD scientists measured event-related potentials (ERPs), brain responses that are directly related to the perceptual experiences induced by sensory stimuli, using an electrophysiological or EEG recording procedure that measures
Source:University of California - San Diego