Explaining Why It's Not Just Déjà Vu (All Over Again)

No matter how many times you experience déjà vu in your life, it never ceases to be a bizarre occurrence. While science has pretty much explained all the mystery out of awesome and strange things like the Northern Lights, eclipses, and those Magic Eye posters, it has failed to come up with a thorough explanation for déjà vu. Anne Cleary, a psychologist at Colorado State University, decided to put to the test that strange feeling where you could swear you had already experienced a present situation.

Cleary's theory is that déjà vu is connected to human recognition memory, which allows us to recognize that something happening right now has also happened before. There are two forms of human recognition memory: recollection and familiarity. As you may have guessed (or could you almost swear somebody had told you this before?), recollection memory means you know why a particular moment seems familiar—you can pinpoint the exact time or place when it happened before. For instance, a song comes on in a club and you recognize it because you remember dancing to that same song at a different club the Saturday before. Familiarity-based memory is that nagging feeling that you know something is familiar but can't name why. That would be having a song come on in a club that you know you've heard before but have no idea when or where (perhaps you've had one too many cocktails at that point). The latter is where déjà vu falls.

To test familiarity-based recognition, Cleary gave her subjects a list of celebrity names. Later, they were shown a variety of celebrity photographs. Some of the faces had been on the list of names and some had not. Subjects were asked to identify the people in the photographs and indicate how likely it was that the celebrity's names had been on the earlier list. According to the report, "Even when the volunteers were unable to identify a celebrity by photo, they had a sense of which names they had studied earlier and which they had not. That is, they couldn't identify the source of their familiarity with the celebrity, but they knew the celebrity was familiar to them." Clearly ran the test again using names and photos of famous landmarks in place of celebrities and had similar results. A bit of the memory was there, but, like our friend one too many martinis in at the club, it was hazy and subjects were unable to connect it to the new experience.