Above: Image courtesy of Matthew Liem
Fast Fact: About two thirds of people experience déjà vu at some point in their lifetimes, usually more than once.Your new friend invites you over to her place for a party. You have never been to her house before, but when you get there, everything about the situation, from the way your friend greets you at her door to the decor in the entryway, seems eerily familiar. “Strange, I just had a feeling of déjà vu.” But just as quickly, the feeling passes and you enter the house.
Déjà vu, the strange feeling of having experienced a situation before, has happened to most of us at some point in our lives. But what exactly causes it? The mystery of déjà vu has long intrigued scientists, who have come up with a few possible explanations.
Fast Fact: Déjà vu becomes less common as people age. It is more frequent in people who are more educated, who travel more, and who remember their dreams.One explanation has to do with how your brain receives information. Sensory information—what you see, feel, hear, etc.—travels through different pathways to get to your brain, where the information normally gets processed as one experience. But if the information travelling along one of these pathways is delayed for even the tiniest fraction of a second, it is treated as two separate copies of the same experience. As a result, you feel like you have experienced the situation before.
Another explanation has to do with distraction. Let's say you're walking down the street while deep in conversation on your phone. There is a store window in your peripheral vision. After hanging up the phone, you look directly at the store window and get a feeling of déjà vu. On a subconscious level, your brain has already seen and processed the image of the store window, even if you do not consciously remember seeing it before.
Fast Fact: In French, “déjà vu” literally means “seen before.”Finally, a third way of explaining déjà vu is that you are, in fact, experiencing something familiar. You just can't remember what that thing is. For example, you may see a lamp in a store window that looks just like the lamp your aunt used to have in her living room when you were a child. You may not remember that your aunt owned the lamp, but your brain does. As a result, the experience feels familiar, even if you can't explain why.
Even when you are armed with all of these explanations, déjà vu still often feels like a mind-boggling experience. So scientists continue to study déjà vu, in the hopes of shedding more light on this strange phenomenon.
The Psychology of Déjà Vu (Discover Magazine)
http://discovermagazine.com/2005/sep/psychology-of-deja-vu#.UNtaG6wpjiE Explaining Why It’s Not Just Deja Vu (All Over Again) (Popular Science)
Sno, HN, et al. 1994. The Inventory for Déjà Vu Experiences Assessment. The Journal of Nervous and Mental Disease. 182: 27-33. Brown, AS. 2004. The Déjà Vu Illusion. Current Directions in Psychological Science. 13: 256-259.