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.
It’s called “déjà vu,” French for “already seen,” and although nobody doubts it exists–surveys indicate that about two-thirds of adults have had at least one déjà vu experience–it hasn’t been subjected to much scientific scrutiny, mainly because nobody knew how to study it.
That’s beginning to change. In a new book, The Déjà vu Experience: Essays in Cognitive Psychology, Alan S. Brown, a professor of psychology at Southern Methodist University surveys what we know about déjà vu so far, with an eye to moving research forward.
Brown categorizes déjà vu theories into four broad families. One group of theories involves “dual processing.” Experiments in the 1990s indicated memory involves two distinct systems, one of retrieval, and one of familiarity. “Dual processing” theories suggest déjà vu occurs when the familiarity system is activated but the retrieval system is not, or when the two fire out of sync.
A second group of déjà vu theories postulate a neurological cause. 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 is at the core of a third group of theories, which 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. A single familiar element–a tea cup with the same pattern as a tea cup in a movie you once saw–might be enough to produce the feeling.
The fourth family of theories suggest that déjà vu is caused by a brief interruption in the normal process of perception. One of the first laboratory attempts to provoke something similar to déjà vu was based on this idea. In 1989, cognitive psychologists Larry L. Jacoby and Kevin Whitehouse of Washington University in St. Louis showed subjects a long list of words on a screen. A day or week later the subjects were shown another long list of words, half of which had also been in the first list, and were asked to identify which ones they had seen the first time around.
The researchers discovered that flashing a word very briefly (for just 20 milliseconds) shortly before it made its official appearance on the screen during the second round often caused subjects to say they’d seen it in the first list–demonstrating things we don’t actually notice consciously can appear familiar later on.
This is being demonstrated even more dramatically in new experiments that Dr. Brown and a colleague, Dr. Elizabeth Marsh, a psychologist at Duke University, are now carrying out. The researchers show college students a sheaf of photographs of various places at Duke and Southern Methodist, one at a time, and have them look for a small black or white cross. A week or so later, they’re shown the campus photographs again, along with many photographs not in the first round, and asked, “Have you seen this place before?” and “Have you been to this place before?”
Drs. Brown and Marsh expected that the initial look at the photos would imprint on the students’ memories unconsciously. That seems to be holding up. In a preliminary run involving 81 students, some Duke students who had never been to Dallas believed they had been to the campus shown in photos taken at Southern Methodist, while many Southern Methodist students thought they had been to the campus shown in the Duke photos, even though they really hadn’t.
The next step is to repeat the experiment with a three-week lag between showings of the photos.
This is a long way from pinning down the precise mechanism behind déjà vu, of course, but the nobody expects a definitive answer for a long time. In fact, Dr. Brown predicts that ultimately there will prove to be several mechanisms at work, perhaps different for different people and in different situations.
Wow. Haven’t I written that exact same sentence once before?
Sources:
“The Tease of Memory” by David Glenn, The Chronicle of Higher Education
“Déjà Vu: If It All Seems Familiar, There May Be a Reason,” by Benedict Carey, New York Times (registration required)
