The Déjà Vu Illusion

The déjà vu illusion occurs when a person has an inappropriate feeling of familiarity in a situation that is objectively unfamiliar or new. The amorphous nature of this experience has made identifying its etiology challenging, but recent advances in neurology and understanding of implicit memory and attention are helping to clarify this cognitive illusion. More specifically, déjà vu may result from (a) a brief change in normal neural transmission speed causing a slightly longer separation between identical messages received from two separate pathways, (b) a brief split in a continuous perceptual experience that is caused by distractions (external or internal) and gives the impression of two separate perceptual events, and (c) the activation of implicit familiarity for some portion (or all) of the present experience without an accompanying conscious recollection of the prior encounter. Procedures that involve degraded or occluded stimulus presentation, divided attention, subliminal mere exposure, and hypnosis may prove especially useful in elucidating this enigmatic cognitive illusion. KEYWORDS—illusion; déjà vu; implicit memory ‘‘Last week, I visited my boyfriend’s new apartment for the first time. As I entered his place, I could have sworn that I had been there in that situation before, and walking through his front door seemed like a repeated action. The experience is so weird and mind-boggling that I usually discard the thought and move on, and it seems to happen at strange times with little importance.’’ This scenario, provided by a college student, typifies the déjà vu illusion, in which there is a jolting confrontation between our subjective sense of familiarity and our objective evaluation of unfamiliarity. For more than 170 years, this most puzzling of memory illusions has intrigued scholars across a broad range of subdisciplines within philosophy, religion, neurology, and psychology. What makes the experience unique is the lack of either a clearly verifiable trigger or an observable response. Unfortunately, systematic scientific exploration of the déjà vu experience has been impeded, in part because of these lacunae, which put the experience off limits during the behaviorist era in psychological research, as well as because a plethora of parapsychological and psychodynamic interpretations of the illusion have been suggested. However, there have been recent efforts to connect the déjà vu illusion to various theories and models of cognitive function (Bernstein & Welch, 1991; Brown, 2003; Hoffman, 1997; Jacoby & Whitehouse, 1989; Seamon, Brody, & Kauff, 1983), and Roediger and McDermott (2000) argued that a better understanding of déjà vu is likely to help clarify our understanding of other more mundane cognitive phenomena. THE DÉJÀ VU EXPERIENCE More than 50 surveys on déjà vu indicate that approximately two thirds of individuals have experienced at least one déjà vu in their lifetime, and these individuals typically report multiple déjà vu experiences. The reported incidence of déjà vu has increased in recent surveys, suggesting a growing cultural awareness and acceptance of the illusion. Déjà vu incidence decreases with age, increases with education and income, and is more common in persons who travel, remember their dreams, and have liberal beliefs (political and religious) compared with those who do not travel, do not remember their dreams, and have conservative beliefs. A déjà vu experience is most likely to be triggered by a general physical context, although spoken words alone sometimes cause the illusion. People experience it mainly when they are indoors, doing leisure activities or relaxing, and in the company of friends; fatigue or stress frequently accompany the illusion. Déjà vu is relatively brief (10 to 30 s), and is more frequent in the evening than in the morning and on the weekend than on weekdays. Personal reactions to déjà vu are more positive than negative, and people typically indicate that they are surprised, curious, or confused when they experience the illusion. Since the 1800s, researchers have offered more than 30 scientifically plausible explanation of déjà vu (Brown, 2003; Neppe, 1983). The interpretations that appear to be the most promising for guiding laboratory research on the illusion explain it as arising from biological dysfunction, divided Address correspondence to Alan S. Brown, Department of Psychology, Dedman College, Southern Methodist University, Dallas, TX 75275; e-mail: [email protected]. CURRENT DIRECTIONS IN PSYCHOLOGICAL SCIENCE 256 Volume 13—Number 6 Copyright r 2004 American Psychological Society perception, and implicit familiarity in the absence of explicit recollection. BIOLOGICAL DYSFUNCTION Early interest in déjà vu stemmed from the observation that some epileptics whose seizures originated in the temporal lobe experienced it during their preseizure aura. Thus, the original question was whether déjà vu reflects seizure activity or other brain pathology. Subsequent research suggests that the illusion does not have diagnostic or clinical significance for epilepsy, but a small spontaneous seizure may cause a déjà vu experience in nonepileptics if it occurs in the area of the brain that processes familiarity (i.e., temporal lobe; Spatt, 2002). From another biological perspective, déjà vu may involve a minimal dysfunction of the neuronal pathways involved in transmitting perceptual information to the higher processing centers. Incoming sensory data follow several different pathways en route to these centers, and a neurochemical event that slightly alters transmission speed in one pathway only (e.g., momentary depletion of neurotransmitter at some neuronal connection) could lead to an illusion of déjà vu. That is, because the brain routinely integrates information received from separate pathways into a unitary experience, a slight delay (or acceleration) in the speed of one pathway relative to another could cause the brain to interpret the data from the two as independent and separate copies of the same experience, even though the two impressions are only milliseconds off. This would then give rise to the sensation that what is happening now has happened before. Similar speculation centers on communication between the two cerebral hemispheres. If incoming information is transmitted directly to the dominant hemisphere, where it is ultimately processed, and a second copy of the information is routed through the nondominant hemisphere prior to traveling to the dominant hemisphere, a slight slowing in those fibers associated with interhemispheric transfer across the corpus callosum could result in déjà vu.