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12/13/2000 08:00:00

New research shows that the ears can sometimes trick the eyes

Though it seems to follow common sense that vision is the most dominant of the human senses, a new study by California Institute of Technology researchers shows that auditory signals can sometimes trick test subjects into misinterpreting what they have seen.

In a new study appearing in the Dec. 14 issue of the journal Nature, Caltech psychophysicists Ladan Shams, Yukiyasu Kamitani, and Shinsuke Shimojo report that auditory information can alter the perception of accompanying visual information, even when the visual input is otherwise unambiguous.

"We have discovered a visual illusion that is induced by sound," the authors write in the paper. Using a computer program that runs very short blips of light accompanied by beeps, the researchers asked test subjects to determine whether there was one or two flashes.

However, unknown to the subjects, the number of flashes mismatch that of beeps in some trials. When the subjects were shown the flash accompanied by one beep, everyone correctly stated that they had seen one flash. But when they were shown the flash with two very quick beeps spaced about 50 milliseconds apart, the subjects all erroneously reported that they had seen two flashes.

What's more, test subjects who were told that there was actually only one flash still continued to perceive two flashes when they heard two beeps.

According to Shimojo, a professor of biology at Caltech, the effect works only if the beeps are very rapid. When they are, "there's no way within the time window for vision to tell whether there's a single or double flash," he says.

According to Shams, a postdoctoral scholar working in Shimojo's lab and lead author of the paper, the results contribute to a shift in our view of visual processing from one "that is independent of other modalities, toward one that is more intertwined with other modalities, and can get as profoundly influenced by signals of other modalities as it influences them."

Contact: Robert Tindol (626) 395-3631