SYDNEY: A blind man who feels like he has ‘already seen’ some unfamiliar situations is challenging the long-held belief that déjà vu involves sight, according to a new U.K. study.
“Hearing and touch and smell often seem to intermingle in the déjà vu experiences,” said the study subject, whose name has not been made public. “It is almost like photographic memory, without sight obviously … as if I was encountering a mini-recording in my head, but trying to think ‘Where have I come across that before?’.”
Déjà vu, French for ‘already seen’, is the illusionary feeling that one has previously witnessed or experienced a new situation, and has been reported to occur in up to 96 per cent of the population.
One explanation for déjà vu is that images from one eye are delayed, arriving in the brain microseconds after images from the other eye – causing the feeling that they are being seen for the second time.
“Optical pathway delay is a quite antiquated theory, but still widely believed,” said lead author Akira O’Connor of the University of Leeds. The researchers, reporting in the December edition of the journal Brain and Cognition, concede the subject’s experiences could be explained if non-optical pathways are also delayed, but this would require several senses to be delayed at once.
The team thinks it’s more likely for a single common factor to be behind all déjà vu experiences. “[This study] provides strong evidence that optical pathway delay is not the explanation for déjà vu.”
This supports the theory that déjà vu is caused by faulty activation of the temporal lobe, resulting in a false sense of familiarity, said the researchers. The temporal lobes are found on the sides of the brain and are important in memory and recognition.
Neuroscientists have used electrodes implanted in the temporal lobe to trigger ‘dreamy states’ where participants find everything familiar, said O’Connor.
“Exactly how and why we might get such inappropriate activation in this area of the brain is unclear, but it may just be a mistaken neuronal firing in the same way as these mistaken firings lead to muscle twitches et cetera,” he said.
The subject’s déjà vu was triggered by mundane experiences, like undoing a jacket zip while hearing a particular piece of music, or in the hall of a school cafeteria. “[The déjà vu] was from the point that I said ‘yes please’, and felt the plate, and heard the retort from one of the members of staff to one of the other people on the table, that I suddenly thought ‘I’m sure I’ve done this before’,” said the subject, according to the study.
He described his experiences of déjà vu as “curious, in some cases enjoyable … and weird,” reported the study.
To ensure the subject was really describing déjà vu, not a similar phenomenon like ‘on-the-tip-of-the-tongue’, the researchers rated his experience on a scale of ‘dissociative experiences’, and found it matched déjà vu.
Similar to sighted people, he first remembered experiencing déjà vu around the age of eight, and the number of episodes of déjà vu declined as he aged.
“We have no reason to believe that it was inaccurate as we have heard many anecdotal stories of blind individuals experiencing déjà vu,” said O’Connor.
Due to the subjective nature of the sensations, the researchers want to talk to more blind subjects to confirm the case.
“It would be really neat to do some neuro-imaging on people during genuine spontaneous déjà vu experiences, but it’s very difficult to get them to have them on demand,” said O’Connor.