Déjà vu is commonly described as the feeling of having seen something before. In fact, some scientists have long thought that one type of the phenomenon occurs when the image of a scene through one eye arrives at the brain before the image from the other eye.
But researchers have now found a blind man who experiences déjà vu through smell, hearing and touch.
The man had déjà vu when undoing a jacket zipper while hearing a particular piece of music, and also while hearing a snatch of conversation while holding a plate in the school dining hall.
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The discovery is reported in the December issue of the journal Brain and Cognition.
"It is the first time this has been reported in scientific literature," said Akira O'Connor of the University of Leeds. "It’s useful because it provides a concrete case study which contradicts the theory of optical pathway delay. Eventually we would like to talk to more blind people, though there’s no reason to believe this man’s experiences are abnormal or different to those of others."
O'Connor said déjà vu is such a convincing sensation that it feels almost inexplicable to the person who has it.
"And because it feels so subjective, psychology, in striving for objectivity, has tended to shy away from it," he said. "But psychologists have gone some way to illuminating things like the 'tip of my tongue' sensation when you can’t think of a particular word. We just wanted to get to the same sort of understanding for déjà vu."
O'Connor and his colleague Chris Moulin also study déjà vu through hypnosis. They believe the experience is caused when an area of the brain that deals with familiarity gets disrupted.
In one experiment they do, students are asked to remember words, then hypnotized to make them forget. When shown the same word again, they describe feeling as if they've seen it before. About half of test subjects say the sensation is similar to déjà vu, and about half of those say it is definitely déjà vu.
"It would be really neat to do some neuro-imaging on people during genuine spontaneous déjà vu experiences," O'Conner said, "but it’s very difficult to get them to have them on demand."
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