It’s the strangest mental phenomena most of us ever experience: the feeling that we’ve already done or seen something that we’re really doing or seeing for the first time.
This week an interesting new aspect of the phenomenon came to light: for the first time, researchers have reported a case of a blind person experiencing déjà vu.
Since déjà vu is French for “already seen,” that might seem like a contradiction in terms. But the blind man in question (and presumably other blind people, since there’s nothing special about him) had déjà vu triggered, not by sight, but by undoing a jacket zipper while hearing a particular piece of music, for example, or hearing a snatch of conversation while holding a plate in a school dining hall.
According to researchers at the University of Leeds, in a study published in the journal Brain and Cognition, this is the first time déjà vu in a blind man has been reported in the scientific literature.
The importance of this is that it puts (or should) the final nail in the coffin of an old theory of déjà vu, called “optical pathway delay,” which is still widely believed. (Partly, probably, because it was featured in Joseph Heller’s novel Catch-22.)
According to the optical pathway delay theory, déjà vu is triggered when images from one eye are delayed, arriving in the brain microseconds after the images from the other eye. But if déjà vu can be triggered through a combination of smell, hearing and touch, that obviously can’t be true.
A couple of years ago, in a book called The Déjà vu Experience: Essays in Cognitive Psychology, Alan S. Brown, a professor of psychology at Southern Methodist University, surveyed what was then know about déjà vu so far. He categorized déjà vu theories into four broad families: dual processing, neurological, memory-related and interruption in perception.
Dual processing theories are based on the idea that memory involves two distinct systems, one of retrieval, and one of familiarity. Déjà vu might occur when the familiarity system is activated but the retrieval system is not, or when the two fire out of sync.
Neurologically inclined theorists point out that people with epilepsy often report déjà vu just before full-blown seizures, so it’s possible some déjà vu experiences are really small, brief seizures involving the part of the brain responsible for determining familiarity. Additional evidence: déjà vu can be elicited by electrically stimulating certain brain regions.
Memory theories suggest déjà vu is triggered by a scene’s similarity to something we’ve seen before but consciously forgotten, whether in reality, a dream, literature or a film.
Interrupted-perception theories hold that déjà vu is caused by a brief interruption in the normal process of perception. Research has shown that things we aren’t even conscious of having seen—because our perception of them was too brief, for example—can nevertheless appear familiar to us later on.
Akira O’Connor, one of the Leeds researchers who authored the new paper, believes that “déjà experiences” (you can’t really call it déjà vu if blind people experience it, can you?) is caused by a disruption in the area of the brain that deals with familiarity—putting him in the “dual processing” camp. (Hmm. Some computers have dual processors. Do they ever suffer from déjà vu?)
O’Connor is currently completing his thesis on the experimental induction of déjà vu through hypnosis. In one of his experiments, students are asked to remember words, then hypnotized to make them forget—then shown the same word again. About half of the students said the experience was similar to déjà vu, and half of those said it was definitely déjà vu.
O’Connor hopes that eventually, scientists may be able to bring on déjà vu on demand, so related brain activity can be scanned and recorded.
However, if you just had the strangest feeling you’ve read a column like this before, don’t go rushing off to England to sign up for O’Connor’s next study. It’s probably just because I wrote a previous column on déjà vu just two years ago and I used the same opening paragraph.
At least…I think I did.