The term déjà vu (French: "already seen", also called promnesia) describes the experience of feeling that one has witnessed or experienced a new situation previously. The term was created by a French psychic researcher, Emile Boirac (1851-1917) in his book L' Avenir des Sciences Psychiques. The experience of déjà vu usually accompanied by a compelling sense of familiarity, and also a sense of "eerieness" or "strangeness". The "previous" experience is most frequently attributed to a dream, although in some cases there is a firm sense that the experience "genuinely happened" in the past.
The experience of déjà vu seems to be very common; in formal studies 70% or more of the population report having experienced it at least once . References to the experience of déjà vu are also found in literature of the past, indicating it is not a new phenomenon.
Déjà vu has been subjected in recent years to serious psychological and neurophysiological research. The most likely candidate for explanation, according to scientists in these fields, is that déjà vu is not an act of "precognition" or "prophecy" but is actually an anomaly of memory; it is the impression that an experience is "being recalled" which is false. This is substantiated to an extent by the fact that in most cases the sense of "recollection" at the time is strong, but any circumstances of the "previous" experience (when, where and how the earlier experience occurred) are quite uncertain. Likewise, as time passes, subjects can exhibit a strong recollection of having the "unsettling" experience of déjà vu itself, but little to no recollection of the specifics of the event(s) or circumstances they were "remembering" when they had the déjà vu experience.
A clinical correlation has been found between the experience of déjà vu and disorders such as schizophrenia and anxiety, and the likelihood of the experience increases considerably with subjects having these conditions. However, the strongest pathological association of déjà vu is with temporal lobe epilepsy. This correlation has led some researchers to speculate that the experience of déjà vu is possibly a neurological anomaly related to improper electrical discharge in the brain. As most people suffer a mild (ie. non-pathological) epileptic episode regularly (eg. the sudden "jolt" that frequently occurs just prior to falling asleep), it is conjectured that a similar (mild) neurological aberration occurs in the experience of déjà vu, resulting in an erroneous "memory".
Déjà vu is popularly associated with precognition, clairvoyance or psychic perceptions, and it is frequently cited as evidence for "psychic" abilities in the general population. Non-scientific explanations attribute the experience to a "prophecy" or "vision" (most commonly delivered via a dream), or alternatively to an experience had in a past life (see reincarnation).
Other psychological phenomena have been labelled jamais vu (never seen) and presque vu (almost seen)