The first case study of a blind man suffering d�j� vu has overturned traditional theories about how the effect occurs. It was previously thought that d�j� vu was triggered when images from one eye arrived in the brain a few microseconds after images from the other eye - causing a feeling that something was being seen for the second time. But University of Leeds researchers have just reported about a blind person experiencing d�j� vu through smell, hearing and touch.

Researchers Akira O'Connor and Chris Moulin, from the university's Institute of Psychological Sciences have just had their paper on non-visual d�j� vu published in the journal Brain and Cognition. In the article, they discuss how mundane experiences - undoing a jacket zip while hearing a particular piece of music; hearing a snatch of conversation while holding a plate in the school dining hall - triggered d�j� experiences in the blind subject.

"Optical pathway delay is a quite antiquated theory, but still widely believed - and was the basis for the d�j� vu sequences in Joseph Heller's novel Catch-22. But this provides strong evidence that optical pathway delay is not the explanation for d�j� vu. The findings are so obvious, so intuitive, that it's remarkable this research has never been done before," said O'Connor.

The researchers hope to work with other visually impaired people, to assess how common the effect is. They'd also like to take the research further: "It would be really neat to do some neuro-imaging on people during genuine spontaneous d�j� vu experiences - but it's very difficult to get them to have them on demand," mused O'Connor.

O'Connor is also experimenting with the induction of d�j� vu through hypnosis. "We now believe that d�j� experiences are caused when an area of the brain that deals with familiarity gets disrupted," he said. In one experiment, subjects were asked to remember words, then hypnotized to make them forget the words - and then shown the same word again to induce a feeling that they have seen it before. Around half said this brought on a sensation similar to d�j� vu.