Already Seen, Already Lived: What is Déjà Vu?
"It's déjà vu all over again." Upon hearing this cliché, most people know that it refers to a repetitive, unoriginal situation. They might also be familiar with the meaning of the French phrase "déjà vu": "already seen." Yet only about two thirds of the American population has ever had a déjà vu experience (1), and no scientist in history has been able to definitively explain the phenomenon. What is this sudden, often eerie sensation of having already seen or lived through the present moment, and how does it happen? Recent research on déjà vu, which only a few decades ago was considered unworthy of scientific exploration, has more clearly defined how déjà vu occurs and what is meant by the phrase. "Déjà vu" may actually be a catch-all term for three or four different memory malfunctions, at least one of which can become chronic in people with brain damage.
Defining déjà vu has proved nearly as difficult as describing a déjà vu experience. In 1983, the psychiatrist Vernon Neppe explained the illusion as "any subjectively inappropriate impression of familiarity of a present experience with an undefined past" (3). The words "inappropriate" and "undefined" troubled later researchers in their search for a single cause, because sometimes a "déjà vu" experience actually can be traced back to an experience in the past. Other scientists have found that, in a déjà vu situation, there is a difference between a feeling of "familiarity" and one of "recollection" (4). These discrepancies have caused different categories of phenomena to be created, of which déjà vu is only one.
Arthur Funkhouser, Ph. D., lists three different déjà vu sensations: déjà vécu, déjà senti, and déjà visité (1). According to his research, déjà vécu is what most people experience when they say they have déjà vu. Literally, it means "already lived," which is more accurate because the sensation usually involves all aspects of a scene. Most people undergo an overall feeling of having lived through the moment previously, not only observed it. Another category of déjà vu is déjà senti, or "already felt." Funkhouser describes this feeling as one that does not involve visual stimuli, but is generally triggered by voices. It is a momentary feeling of understanding, which vanishes as quickly as it arises and cannot be specifically recalled afterwards. The third, and most rare, type of déjà vu under this system is déjà visité, or "already visited." This occurs when someone arrives at a location where he or she has never been before, but feels as if he or she knew the layout perfectly. Nineteenth-century author Nathanial Hawthorne described such an experience upon arriving at an abandoned castle in England; much later, he realized his own recognition had stemmed from a description he had read by Alexander Pope (1).
Another study, one by Chris Moulin and Martin Conway, separated déjà vu into two main groups: déjà vécu and, simply, déjà vu. Here, déjà vu refers to a false sense of familiarity, déjà vécu to a false sense of recollection (4). With déjà vu, some familiar object or situation sparks a familiarity sensation, but the person is unaware of what sparked it. An untraceable sense of having been somewhere or seen something before results. This explanation accounts for why most people report being in very ordinary places when they experience déjà vu. Déjà vécu, on the other hand, creates a stronger impression because the person has a "sense of self in the past" (4). He or she feels as if they are actually living through the past a second time. This is a feeling of recollection without a feeling of having any memory to base it on. The difference lies in the fact that during déjà vu, the person feels that if only he or she could recall the correct memory, he or she would know why the situation seemed familiar. Funkhouser does not recognize this distinction between familiarity and recollection, but focuses instead on how we sensually perceive the déjà experience. He would probably group Martin and Conway's déjà vu with déjà vécu, and they would probably group his déjà visité and déjà senti with déjà vu.
Now that we have a better idea of what we mean by déjà vu, what causes it? Psychology professor Alan Brown devised four possible different kinds of causes (2). He recognized that more than one might be true, as there can be more than one cause for a stomachache (3), and does not distinguish which may cause which type of déjà vu. These theories, he hopes, will serve as hypotheses for later experiments. The first explanation, called dual processing, is based on the theory that there are two systems for memory recognition in the brain (2). One is for familiarity, the other for retrieval of information. When the familiarity system is working but the retrieval system is not, or is a split-second slower, we may experience some kind of déjà vu.
The second theory is the neurological theory, which suggests that déjà vu is caused by small misfirings of nerves in the parahippocampal cortex, an area that helps with recognition (2). These sudden spastic nerve activations are akin to mini-seizures; the fact that epileptics often report having déjà vu before going into full-blown seizures supports the neurological theory. Brown's third hypothesis proposes that some aspect of a real memory or dream triggers déjà vu, but the person is unable to place that memory (2). Hawthorne's experience with déjà visité supports this theory. The last theory is called "double perception." Here, a person is interrupted while glancing at something new; when he or she returns to the new thing, it seems strangely familiar. This might happen if someone were driving through a town for the first time on a cell phone, not paying attention to the surroundings. On the way back, because the person is now able to focus, he or she may experience déjà vu because of the "inattentional blindness" experienced the first time (2).
For most people who have déjà vu, the experience is only momentary and occurs infrequently. However, rare cases have been reported in which a patient experiences déjà vu many times a day, or even constantly. Moulin and Conway termed this condition "persistent déjà vécu" (4), because sufferers have a false sense of recollection and believe that their memories are real. Because they are convinced that they are actually "remembering the present," these people are called anosagnostic (3). One of the patients in Moulin and Conway's study was referred to a memory specialist when he complained of his problem; he insisted that he had already been, although he had not. Other sufferers refuse to read books or watch television and sports because they believe they already know every outcome (4).
How can déjà vécu become a real conviction of having "already lived" for those who undergo it all the time? The answer lies in the fact that episodic memory is "content addressable" (4), meaning that a cue will cause it to rise up. A cue could be an object, a scent, or a sound connected with a memory. When we sense the cues, some memories become more accessible than others, but the memories might not be useful to the brain. People could constantly live in a state of recollection if we were unable to stem the tide of these cues, choosing which ones to use. Moulin and Conway theorize that persistent déjà vécu sufferers do have this problem, so they feel as if they are always remembering. In order to rationalize this feeling, they perform "recollective confabulation" (4). This means that when they are asked to explain why they think something is familiar, they fabricate reasons to fill in the gap between what they "remember" and what they are living through "again." For example, one of the test subjects told his wife that he remembered seeing a coin lying in a certain spot on the street because he had put it there for her to find (4). When these patients are told the truth, that the sensation of memory is separate from any real memory (3), they are most often relieved. While the déjà vécu does not disappear, they are more able to continue with their lives in spite of it.
During only the past week or so as I researched and wrote this report, I have heard four or five friends, on different occasions, mention that they had "just had déjà vu." Since, for unclear reasons, one is more likely to have déjà vu if one is a political liberal (2), is between about 15 and 30 (3), is fatigued (3), and has a higher educational background (4), this makes sense. In any case, déjà vu is not an uncommon occurrence, and people consider it worth mentioning when it happens. Yet, in the end, there is still very little definite information about this phenomenon, which affects us so often and so deeply. Sensing that sometimes one cannot trust one's own mind is an unsettling experience, certainly for those who live with persistent déjà vécu, but also for those of us who déjà vu surprises. Knowing how déjà vu happens helps to satisfy our conscious minds when it happens. Sometimes, though, in our unconscious, no amount of rational explanation will dispel that eerie feeling.
1. Funkhouser, Arthur. "Three Types of Déjà Vu." Scientific and Medical Network Review 1995. <http://home.cc.umanitoba.ca/~mdlee/dejavu.htm>
2. Glenn, David. "The Tease of Memory." The Chronicle of Higher Education July 2004: Volume 60, Issue 46, pg. A12. <http://chronicle.com/ free/v50/i46/46a01201.htm> [Or search on Google: "David Glenn Chronicle Deja Vu" and click on first result.]
3. Ratliff, Evan. "Déjà Vu, Again and Again." The New York Times July 2006.
4. Moulin, Christopher J.A., and Conway, Martin A., et. al. "Disordered memory awareness: Recollective confabulation in two cases of persistent déjà vecu. " Neuropsychologia Volume 43, Issue 9, pgs. 1362-1378. [Science Direct]. <http://www.sciencedirect.com/>