Conclusions

Deja vu is experienced by a majority of the population, and occurs about once a year in experients. The incidence decreases with age but increases with education and socioeconomic class.

Deja vu is more common under conditions of stress and fatigue, and it is experienced more frequently by persons who travel.

Societal acceptance of the phenomenon appears to have increased over recent decades. Though deja vu historically has been linked to temporal lobe epilepsy and schizophrenia, this association has not been convincingly demonstrated.

Explanations of the phenomenon have included (a) momentary alteration in the normal operation of two usually coordinated cognitive processes; (b) neurological dysfunction (seizure, slowed synaptic transmission); (c) implicit memory activation based on familiarity of processing, object, or gestalt configuration; and (d) unattended perception (under distraction) followed immediately by a fully aware perception.

Although the deja vu experience occupies a solid position in the popular culture, the community of research psychologists has been largely silent on the topic. It is hoped that the use of more sophisticated research techniques to help elucidate this illusion of recognition will change this situation and that the findings from such research efforts could expand the field’s understanding of routine memory functions. As Roediger and McDermott (2000) suggested, “distortions of memory provide a fertile ground for studying interesting and important psychological phenomena” (p. 123).

Attentional Explanations (Part 3)

Inattentional blindness

Related to this interpretation of the deja vu, recent research suggests that individuals often miss objects that are clearly visible if they are focused on some other object in the visual array. This inattentional blindness, extensively investigated by Mack and Rock (1998), could explain how an initial brief perception of objects in a scene can go undetected.

When an extraneous visual stimulus (e.g., shape, object, word) accompanies a target stimulus (e.g., cross) to which the participant is instructed to respond (e.g., Which line of the cross is longer?), the individual often misses seeing the extraneous stimulus. When the target stimulus is in the periphery and the extraneous (ignored) stimulus is in the center of the visual field (fovea), inattentional blindness is more likely than when the target stimulus is in the fovea and the extraneous stimulus is in the periphery. Individuals who fail to report the extraneous (e.g., word) stimulus still process it, as reflected in significant priming on a subsequent word stem completion task (Mack & Rock, 1998).

Such a paradigm, in which the stimulus is above threshold but unattended (rather than subthreshold), better models people’s natural perceptual experience (Merikle et al., 2001) and provides a more realistic framework for studying the deja vu experience. For example, one may enter a room talking on a cell phone or thinking about an upcoming meeting while looking directly at a particular stimulus, and moments later this same stimulus is consciously perceived and elicits a déjà vu. Perhaps one of the most blatant examples of inattention to suprathreshold stimuli is the “time gap” experience, in which one’s entire perceptual experience over several minutes (e.g., during highway driving) is unrecallable (Reed, 1979).

It is possible that an inhibitory mechanism underlies the inattentional blindness effect. In elaborating on Poetzl’s (1917/1960) earlier speculation, N. F. Dixon (1971) suggested that during an initial brief stimulus exposure there is “a rapid fragmentation of the sensory information, wherein ‘inhibition by interference’ causes parts of the stimulus field to interfere with the development of other parts” (p. 106). Thus, certain elements in the stimulus array may suppress or block the perception of other elements, similarly to lateral inhibition in the visual system (cf. Martindale, 1981). In a second glance at the scene immediately after the first, the initially inhibited portion of the visual scene is disinhibited and now matches the present perception. The possibility that inhibition–disinhibition underlies deja vu is supported by the fact that both inhibitory processes and deja vu frequency decrease with age.

The magnitude of negative priming interference, for which a response which is actively inhibited on one trial is more difficult to generate on the immediately succeeding trial, is much smaller with older than younger adults (Hasher, Stoltzfus, Zacks, & Rypma, 1991). If the visual inhibition of parafoveal elements similarly decreases with age, this would reduce the likelihood that inhibited features would later disinhibit and lead to a deja vu.

Attentional Explanations (Part 2)

Perceptual fluency

This model for the déjà vu experience was evaluated by Jacoby and Whitehouse (1989), who discovered that when a test word was briefly presented (and masked) at subthreshold levels immediately prior to presentation on a recognition test, individuals were more likely to call the word “old” compared with a word not briefly preceded by itself. They attributed this illusion that the word had occurred on a prior list to its facilitated processing (perceptual fluency) engendered by the immediately prior subliminal presentation. This fluency bias supposedly precipitates the common experience of having a word appear to “jump out from the page” when reading (Jacoby & Dallas, 1981, p. 333).

Similarly, when a primed perceptual element suddenly and forcefully stands out, and source identification is lacking, this may precipitate a déjà vu. Jacoby and Whitehouse related this finding directly to the deja vu phenomenon, but the paradigm is lacking the element of “this could not have happened here before.” In this type of experimental setting, participants logically can misattribute the word to having occurred in the prior experimental list rather than being convinced that they could not have experienced this word before.

There has been debate over whether participants in this particular paradigm are consciously aware of the masked prime word (Bernstein & Welch, 1991; Joordens & Merikle, 1992; Watkins & Gibson, 1988), but this issue does not undermine the potential relevance of this paradigm for modeling the deja vu phenomenon. In fact, a supraliminal perceptual experience corresponds to Titchener’s (1928) illustration above, and modifying the Jacoby-Whitehouse design to have a divided attention manipulation, rather than subliminal presentation, may better model the deja vu experience. Merikle, Smilek, and Eastwood (2001) summarized the literature on perception without awareness and indicated that there are numerous investigations that suggest that stimuli presented either subliminally or supraliminally (but unattended) consistently have a potential to influence subsequent behavior.

Attentional Explanations (Part 1)

The fourth framework for interpreting déjà vu is that an ongoing stream of perceptual experience is divided into two separate perceptions through distraction or inattention. A brief initial perception of a scene under diminished attention is followed immediately by a second perception under full attention. The second impression matches that experienced moments earlier under degraded attention, and the individual does not consciously identify the prior experience as moments old but rather attributes it to a more distant past. Many researchers have espoused different versions of this interpretation (Conklin, 1935; Heymans, 1904; Lalande, 1893; Osborn, 1884; Wigan, 1844), and Titchener (1928) provided the following, oft-cited illustration:

You are about to cross a crowded street, and you take a hasty glance in both directions to make sure of a safe passage. Now your eye is caught, for a moment, by the contents of a shop window; and you pause, though only for a moment, to survey the window before you actually cross the street. . . . The preliminary glance up and down, which ordinarily connects with the crossing in a single attentive experience, is disjointed from the crossing; the look at the window, casual as it was, has been able to disrupt the associative tendencies. As you cross, then, you think “Why, I crossed this street just now”; your nervous system has severed two phases of a single experience, both of which are familiar, and the latter of which appears accordingly as a repetition of the earlier. (pp. 187–188)

Leeds (1944) called this phenomenon split-perception and proposed that an eye blink could possibly divide these two successive perceptions. Mayer and Merckelbach (1999) even suggested that this type of double take may be part of routine perception. The first second of information processing may be a platform from which a “quick and dirty” unconscious processing can have important effects on subsequent reactions to the stimuli around us. Though Mayer and Merckelbach related their speculation to anxiety disorders, their ideas have clear relevance to the déjà vu phenomenon.

Finally, Krijgers Janzen (1958) speculated that an initial and unattended eidetic image matches a regular perception moments later. He argued that all people experience eidetic imagery occasionally and that regular eidetic imagers would experience déjà vu more frequently than individuals who have eidetic images infrequently.

Memory Explanations (Part 5)

Gestalt familiarity

When the overall perceptual configuration of the present stimulus array is similar to one experienced previously, this gestalt correspondence could trigger a deja vu (Reed, 1974). Recall the example of the first visit to a friend’s home as an illustration; it is not the grandfather clock in the corner of your friend’s living room that is familiar, rather the familiarity comes from the fact that the room has a layout similar to the one in your aunt’s house: a sofa to the right of the love seat with a stairway to the left going up the wall, a grandfather clock against the back wall, and an Oriental rug on the floor. None of the elements in the newly entered living room is identical to one from the previous context, but the particular configuration of elements fits the same template. Sno and Linszen (1990) suggested that different scenes and individuals often overlap in many structural details, and when perception is degraded the general framework of a prior experience may overlap considerably with the present one. Using similar logic, Levitan (1969) suggested that in recognizing an entire scene or setting, people automatically break it down into simpler perceptual forms such as cubes, triangles, circles—a process similar to what cubist painters did. This is also related to Biederman’s (1987) notion that all perceptual experience can be reduced to a relatively small set of geons, which represent the range of all primitive perceptual forms. Thus, the untoward sense of familiarity eliciting deja vu in an unfamiliar setting may arise because the arrangement of the reduced perceptual forms matches those from a prior experience.

Gloor (1990) also used this gestalt analogy and tied his speculation to deja vu experiences in the preseizure aura of TLEs. Drawing on the parallel distributed processing model of Rumelhart and McClelland (1986), Gloor suggested that the erratic firing of neurons in the temporal lobe prior to the seizure gives rise to spurious matches between the present visual scene and prior visual experiences. For both Sno and Linszen (1990) and Gloor, perceptual degradation was more likely to precipitate such configural matches. Assuming that fatigue or stress are associated with such reduced perceptual precision, this fits with the earlier suggestion of an association between fatigue and deja vu.

Memory Explanations (Part 4)

Single-element emotional association

Another framework for interpreting a deja vu is that some aspect of the present situation triggers an affective response which then elicits a deja vu. Under this interpretation, the strange feeling accompanying a deja vuis not elicited by the unsettling contrast between implicit familiarity and explicit source memory failure. Instead, the feeling is evoked by a conditioned emotional association to a particular stimulus.

Under most circumstances, a person can identify the particular stimulus (seeing a person, hearing a name, smelling a perfume) that elicits an emotional reaction. When this implicit emotional reaction cannot be connected to its source, the person misidentifies the emotional arousal as familiarity to an unfamiliar setting and a deja vu results (Pagliaro, 1991; Siomopoulos, 1972). Thus, the implicit affective (emotional) response is immediately reinterpreted in a cognitive (familiarity) manner. To illustrate, imagine you enter a hotel you have never been in before, and a couch in the corner of the lobby is identical to one that was in your grandparents’ house. You experience a strong implicit (and positive) emotional reaction to the item of furniture without explicitly recognizing the item as the source of your affective response. Baldwin (1889) suggested that the emotional reaction must reach a certain level of intensity before it forces the inappropriate feeling of familiarity, and Siomopoulos (1972) speculated that implicit emotional associations to objects may persist long after conscious recollection has disappeared. In support of this possibility, Johnson, Kim, and Risse (1985) demonstrated that in patients with Korsakoff’s amnesia, an affective response to a stimulus could be acquired in the absence of explicit memory.

MacCurdy (1928) speculated that there are always two components of a nominal recognition response: an initial affective reaction, followed immediately by the familiarity (cf. Zajonc, 1980). Although these two stages usually follow in quick and seamless succession, and are essentially indistinguishable as separate processes, deja vu results when the initial affective stage is not succeeded by a clear second-stage memory match. Fleminger (1991) similarly suggested that the affective and cognitive channels of information processing usually work in concert but that deja vu results from “aberrant activity in the pathway responsible for affective interpretation of percepts” (p. 1418). Linn (1953) further speculated that it is not an affective response, in general, that triggers a deja vu. Rather, anxiety evoked by some aspect of the present situation disrupts the normal functioning of the reticular activating system. Thus, Linn (1953) assumed that a change in arousal precipitates a deja vu, rather than a specific affect associated with a stimulus.

These emotion-based interpretations of the deja vu experience are related to the subliminal mere exposure research, in which unfamiliar stimuli exposed at levels well below perceptual threshold (i.e., 5 ms) are later preferred over nonexposed stimuli even though participants are unable to recognize these exposed stimuli as old (Bornstein, 1992; Kunst-Wilson & Zajonc, 1980). In fact, Seamon et al. (1983) specifically related their research on subliminal mere exposure to deja vu:

In deja vu, stimuli are recognized as familiar without recognition of the basis of their familiarity. Essentially, the same outcome was observed in this study: people liked familiar stimuli without recognizing the basis for their familiarity. In this respect, the finding of target selection by affect in the absence of recognition is similar to the well-known, but poorly understood, phenomenon. (p. 188)

This parallel with subliminal mere exposure may be strained because what is typically measured in this research is preference or liking—a modest affective response, at best. What is needed is a way to experimentally evoke the type of intense affective reaction characteristic of a deja vu. Both number of exposures and test delay are directly related to preference (Bornstein, 1989), so perhaps a large number of subliminal exposures and long input-to-test delay could intensify the affective response to a level capable of eliciting a deja vu.

Memory Explanations (Part 3)

Extending the single-element position in a different direction, Sno and Linszen (1990) proposed a holographic explanation of deja vu (see also Meurs & Fies, 1993). If memories are stored as holograms (cf. Pribram, 1969), then each memory involves a unique pattern of neural activation involving the entire cortex. That is, a memory (first kiss, favorite song) is not based on physical storage but on a unique wave form pattern of neural activation. If any perceptual element in a new scene overlaps with an element of a previous memory, then this has the potential to reactivate the entire old memory (Kafka, 1989). If only the implicit familiarity component of that prior experience is reactivated, a deja vu results. However, if both implicit and explicit components are reactivated, the present setting simply reminds the person of a prior experience.

The single-element interpretation of a deja vu is also related to the Poetzl (1917/1960) phenomenon, in which elements of a briefly presented stimulus appear later as a response in an unstructured generation task such as free association, day dreaming, or doodling (cf. N. F. Dixon, 1971). Whereas later extensions of this research evaluated a psychoanalytic theory of dreams, Poetzl’s work was experimentally oriented and involved subthreshold presentations of simple stimuli, or brief suprathreshold presentations of complex visual scenes. The Poetzl phenomenon occurs when these stimulus elements are not immediately accessible (remembered) but appear later in subsequent free associations to word or pictorial stimuli (Allers & Teler, 1924/1960; Erdelyi, 1970; Haber & Erdelyi, 1967; Shevrin & Fritzler, 1968; Silverman & Silverman, 1964). Although usually evaluated through recall procedures, the Poetzl phenomenon could occur with recognition as well, and could underlie the deja vu experience.

The above interpretations focus on a single element; however, it is possible that several familiar elements are involved in a déjà vu experience (Findler, 1998; Fleminger, 1991; Wohlgemuth, 1924). Wohlgemuth (1924) presented an extensive analysis of a personal deja vu experience and found that three elements in the setting duplicated aspects of three separate episodic memories. He speculated that these multiple single elements summated to create an unusually strong feeling of familiarity, whereas none of the individual elements’ contextual associations was sufficiently strong to reach threshold, or competition among the separate contextual associations blocked access to any specific episodic memory. This mechanism is similar to that proposed by Hintzman (1988) in his MINERVA model of memory.

Memory Explanations (Part 2)

Single-element familiarity

A deja vu experience may be triggered by one element of the present setting that is objectively familiar but unrecognized because it is experienced in a new and changed context. The familiarity elicited by the one unidentified object is misinterpreted as a response to the entire setting, resulting in deja vu. To illustrate, suppose that you visit a friend’s home for the first time, and the grandfather clock in the corner is identical to one in your aunt’s home. While you experience a familiarity reaction to this element, you are unable to connect your response to the “old” object and misattribute the familiarity to the entire new setting, resulting in a deja vu. This interpretation was proposed in earlier writings on the deja vu experience (Banister & Zangwill, 1941a; Boirac, 1876; Boring, Langfeld, & Weld, 1935; Bourdon, 1894; Conklin, 1935; Humphrey, 1923; James, 1890; Lapie, 1894; Leeds, 1944; Oberndorf, 1941) and has been resurrected in more recent speculation (Jordan, 1986; Levitan, 1969; Reed, 1979; Sno & Linszen, 1990; Zeidenberg, 1973).

MacCurdy (1925) called this phenomenon restricted paramnesia: the experience in which an element of the present setting is familiar but its prior identity is obscure. Banister and Zangwill (1941a, 1941b) used hypnotic suggestion to test this notion that a previously encountered but “forgotten” stimulus can be misidentified as familiar. They did not intend to create a deja vu, but wanted simply to evaluate whether participants could misattribute a hypnotically forgotten stimulus to the wrong setting. On the first day, participants studied pictures and odors during a normal waking state. On Day 2 they were hypnotized and presented with additional picture and odor stimuli, followed by a posthypnotic suggestion to forget these Day-2 stimuli. On Day 3, participants were tested with a mixture of new and old stimuli, and most participants (3 out of 5) misidentified some Day-2 stimuli as having been presented on Day 1. Although Banister and Zangwill (1941a, 1941b) emphasized that their study supported the possibility of such paramnesias, they noted that the relationship between their study and deja vu was “conjectural” and said that the results “throw little light on the origin of deja vu” (Banister & Zangwill, 1941b, p. 51). Despite this disclaimer, hypnotic procedures may hold some promise for an experimental paradigm to elicit déjà vu if accompanied by a sufficiently unique context within which to later experience the subsequently forgotten stimuli.

Also related to the single-element hypothesis is Whittlesea and Williams’s (1998) extension of the processing fluency theory of familiarity. Jacoby and Dallas (1981) demonstrated that when information is reexperienced, it is processed more easily and rapidly than in the first encounter, and this fluid reprocessing gives rise to a sense of oldness concerning the stimulus. Whittlesea and Williams argued that in the real world, the processing fluency basis of familiarity occurs primarily when the object or person is encountered in an unexpected context. In theory, meeting your spouse in your own kitchen should engender considerable processing fluency because of repeated exposures, leading to a strong familiarity response. However, this does not occur. In fact, such encounters curiously elicit no sense of familiarity. In contrast, if you unexpectedly spot your spouse sitting in the middle of your class as you lecture, this would arouse an intense and immediate sense of familiarity. Similarly, seeing your mail carrier at your front door arouses no sense of familiarity, but seeing him or her at the movie theater evokes a strong sense of familiarity due to the novel context (Reed, 1979). Applying this interpretation to deja vu, if an individual experiences a single familiar (but unrecognized) element in an unfamiliar context, the fluent reprocessing of this one element may elicit a deja vu experience specifically because the context is different.

Memory Explanations (Part 1)

An extensive literature documents that an individual’s response to a particular stimulus can be altered by a prior encounter in the absence of explicit (episodic) recollection of this previous experi-
ence (cf. Roediger & McDermott, 1993; Schacter, 1987). Speculation concerning implicit familiarity as a foundation for a deja vu was originally proposed more than a century ago by Osborn (1884), who suggested that individuals process a considerable amount of information without paying full conscious attention to it and that the subsequent reprocessing of this information may occasionally give rise to a sensation of subjective familiarity in the absence of recollection. What sets the deja vu experience apart from other implicit memory responses is an inordinately strong impression of familiarity in the absence of explicit recollection.

Not all models in this section provide a clear explanation of what causes this intense familiarity, but they do present reasonable frameworks within which the deja vu experience can be interpreted.

Conflict in source monitoring processes

According to the source monitoring framework (SMF; Johnson, Hashtroudi, & Lindsay, 1993; Mitchell & Johnson, 2000), as events are experienced, various features are encoded (perceptual, spatial, emotional, semantic details, temporal information, ongoing cognitive operations), depending on the processing that occurs. Remembering is a mental activity in which current mental experiences are attributed to past events on the basis of their qualitative characteristics and on the individual’s general knowledge and beliefs. Although deja vu has not been specifically interpreted within the SMF, it is relatively straightforward to do so. For example, suppose that you are excited about a first trip to Seattle, enter the airport terminal on your arrival, and have a strong deja vu experience. You know that you never have been in Seattle, but the terminal seems incredibly familiar.

According to the SMF, a deja vu experience could arise from the conflict in two types of source monitoring processes. That is, your attribution based on your general knowledge (of never having been in Seattle) is in conflict with the heuristic attribution that is most natural as based on qualities of the mental experience, which imply it is familiar from past perception. Such familiarity could arise from a number of different types of past events encoded in memory. Perhaps you have seen this airport setting in a movie, television documentary, or picture in a magazine, but your current mental experience does not include this additional information that would allow you to identify the source of the familiarity. If you had a sense of familiarity but could identify its source (e.g., a magazine article on the plane), you would not have a deja vu experience. If you could not identify the source of the familiarity but also thought it was likely that you might have been in Seattle before after all, you also might not have a deja vu experience.

Duplication of processing

Osborn (1884) suggested that it may not be the content of the memory that is duplicated in a deja vu but rather the particular cognitive processing that occurred on a prior occasion:

If at any time in our past lives we passed in actual experience or in imagination over a mental track, say a b c d e , and if to-day [sic] this track is again traversed, although the former experience itself may have been long forgotten, we have a sense that it has been through the mind before. . . . If the mind passes over only part of the former track, say b c d,we sometimes, in the dim recognition which arises, believe we have been over the whole before. (pp. 480–481)

This interpretation can account for why the strong familiarity essential to deja vu can occur in a completely novel setting.  Osborn’s position is similar to the theory of transfer appropriate processing (Kolers, 1973; Kolers & Roediger, 1984; Morris, Bransford, & Franks, 1977; Roediger, Weldon, & Challis, 1989), in which retrieval success depends on the correspondence between the way the information is processed during input and retrieval. If similar mental procedures occur on both occasions, then recollection probability is high. If the processes are dissimilar, the likelihood of remembering the information is low. Thus, if the processing of the new information duplicates the mental procedures that occurred with a prior but unrelated experience, an unexpected sense of familiarity and deja vu may result, even though the stimulus elements in both situations are different.

Neurological Explanations (Part 2)

Neural transmission delay

Another class of neurological interpretations assumes that the deja vu experience results from a momentary delay in neuronal transmission from the perceptual organ to the higher order processing centers of the brain. In one version, there is a slight increase in the normal time taken to transmit the message, due to a synaptic dysfunction, and this slight slowing in the routine processing time (several milliseconds) is misinterpreted as representing that the information is old (Grasset, 1904). Anjel (1896) noted that the fatigued state often accompanying deja vu may underlie this neural slowing, temporarily elongating the time between sensation and perception. The logic behind this position is vague and unspecified, and it seems at odds with research on perceptual fluency. More specifically, individuals interpret faster (easier) processing of information as indicating that the item has been experienced before (Jacoby, 1988; Jacoby et al., 1988). Thus, slower processing should imply that the information is new, not old.

Another version of this transmission delay interpretation involves two neuronal pathways rather than one and has more logical explanatory appeal than the single-pathway version. In the visual system, sensory information traverses multiple pathways between the sensory organ and the higher cortical centers (Goodale & Milner, 1992; Milner & Goodale, 1995; Schneider, 1969). In most instances, the information is first received cortically from the primary and then from the secondary pathway (Weizkrantz, 1986). When the normally brief difference in processing time between the two tracks becomes lengthened, the usually seamless integration of the two messages into a single perception becomes disrupted and is experienced as two separate messages (Comfort, 1977). The brain interprets the second version, through the slowed secondary track, as a separate perceptual experience, and thus the inappropriate feeling of oldness derives from the match with the first input processed moments earlier.

Another version of this dual-pathway speculation assumes that the primary perceptual pathway goes directly to the dominant hemisphere while the secondary pathway routes first through the nondominant and then to the dominant hemisphere (Ephron, 1963; Humphrey, 1923). When the delay of information from the nondominant to the dominant hemisphere is slightly extended, a deja vu results (Maudsley, 1889; Osborn, 1884; Weinand et al., 1994). A simpler version of this position is that the two hemispheres normally receive the same information simultaneously, but a slight delay of information to one hemisphere results in a déjà vu (Humphrey, 1923; Wigan, 1844). Weinand et al. (1994) and Ephron (1963) proposed that the preseizure electrical disturbance confined to one hemisphere may cause the slight temporal delay in the secondary pathway, resulting in deja vu. Ephron also speculated that a lesion in the nondominant hemisphere could occasionally slow information transmission from the nondominant to the dominant hemispheres, an interpretation he suggested could be tested during neurosurgical procedures through local anesthesia of the corpus callosum.

A final neurological interpretation of deja vu, also involving two perceptual pathways, assumes that the primary rather than the secondary pathway is delayed, causing the information from the secondary pathway to arrive slightly before that received from the primary pathway. Information from the primary pathway is routinely interpreted by the individual as the initial perception, so when this information arrives after the secondary pathway information it feels familiar because a “memory” match already exists, only milliseconds old (Comfort, 1977; Ephron, 1963).

Neurological Explanations (Part 1)

A number of researchers have suggested that a deja vu experience results from a neurological dysfunction involving seizure or a change in the speed of normal neural transmission.

Seizure

Because deja vu is part of the preseizure aura in some TLEs, a logical extension is that deja vu in nonepileptic individuals results from a small temporal lobe seizure (Penfield, 1955; Stevens, 1990). In earlier research, Hughlings-Jackson (1888) attempted to determine whether deja vu was diagnostic of seizure activity, epilepsy, and brain pathology, and Maudsley (1889) suggested that those most susceptible to deja vu have a higher likelihood of developing epilepsy. Such speculation is supported by the fact that stimulation of the amygdala and hippocampus in TLEs can cause a deja vu experience (Bancaud et al., 1994; Gloor et al., 1982; Halgren et al., 1978).

However, the weight of evidence argues against deja vu being more common in people with epilepsy or being diagnostic of seizure pathology (M. A. Harper, 1969; Neppe, 1983e; Richardson & Winokur, 1967). In fact, estimates of the percentage of TLEs with deja vu as part of their aura is generally quite low (< 1% to 6%; Gupta et al., 1983; Lennox & Cobb, 1933; Mullan & Penfield, 1959; Sengoku, Toichi, & Murai, 1997; Weinand et al., 1994), and studies reporting a higher incidence (11% to 86%) usually include TLEs with intractable seizures undergoing medical procedures to correct this problem (Cole & Zangwill, 1963; Gloor et al., 1982; Halgren et al., 1978; M. Harper & Roth, 1962; Neppe,1983c). A variant of this position is that a more general, right hemisphere dysfunction results in deja vu, a conclusion stemming from the consistent observation that TLEs with deja vu have a higher probability of seizure activity originating in the right hemisphere (Cole & Zangwill, 1963; Cutting & Silzer, 1990; Gupta et al., 1983; Jackson, 1880; Mullan & Penfield, 1959; Weinand et al., 1994).

Halgren et al. (1978) used brain stimulation procedures to duplicate a number of components of the preseizure aura in TLEs, among them the deja vu experience. They speculated that during a typical seizure, a similar type of increased electrical “outflow” from the hippocampal gyrus, an area so intimately involved in encoding and retrieval, may be misinterpreted as a sensation of familiarity. Bancaud et al. (1994) supported such speculation and added that because the lateral temporal lobe receives major inputs from the visual and auditory cortices the nonspecific seizure activity in the temporal lobe combined with current sensory input results in an inappropriate feeling of familiarity.

Dual-Processing Explanations (Part 1)

The first category of deja vu explanations is based on a disruption in the normal operation of two separate but interactive cognitive processes. At the core of each speculation, two mnemonic processes that generally operate in concert occasionally become asynchronous, or one process becomes activated in the absence of the other.

Familiarity and retrieval.

Gloor (1990) proposed that retrieval and familiarity are independent cognitive functions that usually operate in a coordinated manner, with recall accompanied by a sense of familiarity concerning the information retrieved. However, these two processes occasionally operate independently of each other. Thus, retrieval can be activated in the absence of familiarity, which causes an ostensibly familiar setting to become momentarily unfamiliar (jamais vu). Conversely, a familiarity response may become activated in the absence of retrieval (deja vu).

This issue is also related to a large literature concerning the possible independence of recall and familiarity (Gardiner & Parkin, 1990; Tulving, 1985) and the process dissociation procedure (Jacoby, 1991).

Encoding and retrieval.

De Nayer (1979) proposed a tape recorder metaphor for deja vu. Under normal conditions, memory encoding and retrieval operate in a manner similar to the record and play heads (respectively) on a tape recorder: Either the record (encode) or play (retrieve) head can be on but not both at once. On rare occasions, the tape machine in a person’s memory has both the record and play heads active simultaneously during a new experience, creating a false sense of familiarity for the newly encoded experience. Though this interpretation is intriguing, it is not well developed and remains at the nascent metaphoric level.

Most cognitive psychologists would assume that retrieval of information (from semantic memory) is an important component of successful encoding. In addition, it appears to be at odds with Pashler’s (1994) research on the bottleneck model of attention, in which a single, central processor is required for memory encoding, memory retrieval, and response selection. From this perspective, encoding and retrieval can never occur in parallel. Furthermore, other models suggest that memory is the outcome of whatever processing occurred during input (Johnson, 1983; Kolers & Roediger, 1984) rather than being attributed to specific encoding or retrieval operations.

Explanations of Deja Vu

For more than a century, researchers have proposed a variety of explanations for the deja vu experience. Many are framed within the psychodynamic and parapsychological perspectives, and the interested reader should consult Neppe (1983e) or Sno and Linszen (1990) for further details on these explanations.

Scientific interpretations of the deja vu experience fall into four categories: dual processing, neurological, memory, and attentional. The dualprocessing explanations assume that two cognitive processes that normally operate in synchrony become momentarily uncoordinated or out of phase. Neurological explanations suggest that deja vu represents a brief dysfunction in the nervous system involving either a small seizure or alteration in the normal time course of neuronal transmission. Memory interpretations assume that some aspect of the present setting is objectively familiar but that the source of familiarity has been forgotten. Finally, attentional interpretations posit that an initial perception under distraction is followed immediately by a second perception under full attention.

With respect to ultimately explaining the deja vu experience, the dual-processing and neurological positions are less useful than the attentional and memory explanations. The dual-processing interpretations have deep historical roots, but they are less clearly and precisely formulated and are grounded more in the theoretical-philosophical than in the empirical realm. The neurological positions are more logically compelling and molecular, but a laboratory test of these explanations may be problematic with today’s technology.

The attentional and memory interpretations of déjà vu make clear connections with current cognitive findings, and a number of possible empirical tests emanates from these two perspectives.

Related Phenomena to Deja

Several other recognition dysfunctions have been related to the deja vu experience. Jamais vu can be considered the opposite of deja vu in that it involves encountering an objectively familiar stimulus that momentarily feels unfamiliar (Burnham, 1903; Conklin, 1935; Critchley, 1989; Cutting & Silzer, 1990; Hughlings-Jackson, 1888; Neppe, 1983e; Reed, 1974; Sno, 2000).

Jamais vu is related to both word alienation, when an ordinary word suddenly looks unfamiliar (Heymans, 1904, 1906; Sno & Draaisma, 1993), and semantic satiation (Amster, 1964; Kounios, Kotz, & Holcomb, 2000), when the repeated (massed) presentation causes a word to momentarily lose its connotative meaning. Jamais vu is much rarer than deja vu (Findler, 1998; Reed, 1974; Sno, 2000), but Heymans (1904, 1906) presented data suggesting that the two recognition dysfunctions of deja vu and jamais vu may be related.

Also related to deja vu is the Capgras syndrome (Capgras & Re ´boul-Lachaux, 1923), a condition in which an individual believes that someone familiar (friend, relative) has been replaced by an imposter. This most studied of the delusional misidentification syndromes does not occur in neurologically and psychiatrically healthy adults but is associated with either schizophrenia or organic brain damage (Critchley, 1989) involving the right hemisphere (Fo ¨ rstl, Almeida, Owen, Burns, & Howard, 1991).

Déjà vu may also be related to reduplicative paramnesia, whereby an individual believes that the present situation is one that has been duplicated from the past (Hakim, Verma, & Greiffenstein, 1988; Langdon & Coltheart, 2000). The typical episode of reduplicative paramnesia involves a hospitalized patient mistakenly convinced that the present hospital is the same one that he or she had been in earlier (in a different geographical location). As with the Capgras syndrome, this recognition dysfunction is confined to individuals with (delusional) psychopathology usually associated with brain injury involving the frontal lobe (Benson & Stuss, 1990) and is unaltered by providing patients with clear evidence to the contrary (Langdon & Coltheart, 2000).

Two other rare misidentification syndromes, Fre ´goli syndrome (Courbon & Fail, 1927) and intermetamorphosis (Courbon & Tusques, 1932), have also been connected with deja vu by Berrios (1995). Both involve the belief that a familiar (intermetamorphosis) or unfamiliar (Fre ´goli syndrome) individual has been replaced by a familiar friend or relative.

Psychopathology of Deja Experience

Some suggest that the incidence of deja vu is more common among people with schizophrenia than among the population in general (Cutting & Silzer, 1990; Kirshner, 1973; Neppe, 1983e; Richardson & Winokur, 1967, 1968). However, it is difficult to determine whether their deja vu experience is similar to that of nonschizophrenic individuals because schizophrenia involves a variety of cognitive distortions (M. A. Harper, 1969). Sno, Schalken, and de Jonghe (1992) suggested that there is a continuum of deja vu, ranging from brief and fleeting in those without to chronic and prolonged in those with schizophrenia.

Taking a more general look at deja vu and psychopathology, M. A. Harper (1969) did not find any general relationship between deja vu frequency and neurotic traits (and phobias) or psychiatric health. In fact, deja vu appeared to be less common in neurotic individuals.

Richardson and Winokur (1968) examined the incidence of deja vu across 10 subtypes of psychopathology (depression, schizophrenia, personality disorder, etc.) and found a higher deja vu incidence only for individuals with personality disorder and situational reaction. They concluded that deja vu might be diagnostic of personality disorder, but the high variability in sample size across subtypes and the problematic sampling procedures make this conclusion suspect.

In a comparison of seven subtypes of neuropathology (brain, meninges, cerebral vessels, spinal cord, etc.), Richardson and Winokur (1968) found no difference in the incidence of deja vu. However, deja vu has been found to be more common in those who have suffered head injury with loss of consciousness (M. A. Harper, 1969) in addition to being associated with amphetamine psychosis (Ellinwood, 1968), influenza medications (amantadine and phenylpropanolamine; Taiminen & Ja ¨a ¨skela ¨inen, 2001), abuse of toluene-based solvents (Takaoka, Ikawa, & Niwa, 2001), withdrawal from medications prescribed for bipolar disorder (carbamazepine, clonazepam; Garbutt & Gillette, 1988), and herpes simplex encephalitis (Yamashita, Yoshida, Yoneda, Mori, & Yamadori, 1994).

Deja Experience by Dreams

Some individuals report that their deja vu experiences appear to duplicate a prior dream, and it is possible that dreams provide the fragmentary memories later duplicated during the deja vu (cf. Baldwin, 1889).

When Zuger (1966) asked his respondents whether they (a) experienced deja vu and (b) remembered their dreams, a striking relationship emerged: All 10 respondents who reported no dream memory also reported no deja vu experiences, and all 36 respondents who reported deja vu also reported remembering their dreams (9 reported dream recall but no deja vu). Thus, there appears to be a strong relationship between remembering dreams and experiencing deja vu. Palmer (1979) discovered a significant correlation between deja vu and dream frequency among older adults but not among college students.

However, the lack of correlation among students may be due to restriction of range because the college group reported a high number of both experiences. Hence, although Zuger speculated that the déjà vu experience is actually a dream state intruding into waking consciousness, it is also likely that dream memory fragments may trigger a deja vu when similar situations are reencountered while awake.

Deja Experience by Stress, Fatigue, Anxiety, and Illness

Earlier anecdotal reports linked deja vu with physical or psychological distress, suggesting that “it occurs most frequently after periods of emotional stress, or in the state of extreme mental fatigue” (Titchener, 1924, p. 187) or “when one is in a let-down state, and far from alert and keen” (Woodworth, 1940, p. 357).

This speculation has received considerable support (Anjel, 1886; Arlow, 1959; Conklin, 1935; de Nayer, 1979; Groh, 1968; Heymans, 1904, 1906; Krijgers Janzen, 1958; Leeds, 1944; MacCurdy, 1925; Murphy, 1951; Oberndorf, 1941; Osborn, 1884; Richardson & Winokur, 1967, 1968; Schneck, 1962; Siomopoulos, 1972; Smith, 1913; West, 1948; Yager, 1989).

In prospective research, Leeds (1944) found that his own deja vu experiences were more likely when fatigued, and Heymans (1904, 1906) noted that fatigue was associated with the majority of deja vu episodes reported by his students.

A further point of interest is Linn’s (1954) assertion that deja vu was frequently experienced by soldiers going into battle. Indeed, marching through new terrain under the heightened stress of anticipating combat may present an ideal set of circumstances for eliciting deja vu experiences. This may also relate to the higher incidence of deja vu in travelers (see Travel Frequency section), as trips are often moderately to highly stressful experiences.

Deja Experience by Travel Frequency

Logically, those individuals who travel should have more opportunities to experience a deja vu because they encounter objectively new physical locations more often than those who do not travel.

Several investigations support this speculation. Chapman and Mensh (1951) discovered that people who did not travel had an 11% incidence of deja vu, whereas those who made one to four trips a year had a 31% incidence, and people who took five or more trips per year had a 32% incidence of deja vu.

Richardson and Winokur (1967) found a similar relationship with both neurosurgery (11% incidence for nontravelers, 41% among those making one to four trips a year, and 44% for those taking five or more trips per year) and psychiatric patients (33% for nontravelers, 48% among those making one to four trips, and 45% for those taking five or more trips per year).

Thus, those who travel have more deja vu experiences than those who do not, but the amount of travel seems to make little difference. This association of deja vu with travel is probably interrelated with educational and socioeconomic differences, in that those in the upper class and with more education are more likely to travel.

Deja Experience by Education and Socioeconomic Class

A positive relationship between the deja vu experience and both education level and socioeconomic class has been noted in both anecdotal and empirical evaluations (Chapman & Mensh, 1951; Crichton-Browne, 1895; Gallup & Newport, 1991; M. A. Harper, 1969; Kohr, 1980; MacCurdy, 1925; Neppe, 1979, 1983e; Palmer, 1979; Richardson & Winokur, 1967, 1968).

Chapman and Mensh (1951) compared six different “occupation” groups and declared that better educated persons (their definition; professional = 45%, student = 42%, clerical = 41%) had a higher deja vu incidence than less educated individuals (skilled = 33%, housewife = 31%, unskilled = 28%). Richardson and Winokur (1967) used similar classifications and found a higher incidence of déjà vu in the “clerical, professional, and student groups (47% to 73%)” compared with the “unemployed (retired), unskilled, housewife and skilled groups (25% to 43%)” (p. 624).

Comparing a number of different occupational levels, Palmer (1979) found the highest incidence of deja vu among professionals (80%) and the lowest incidence among blue collar workers (50%). With respect to education level, Chapman and Mensh (1951) found a systematic increase in deja vu incidence across years of education (education years: < 9 = 20%, 9–12 = 44%, 13+ = 50%). Richardson andWinokur (1967) found a similar relationship between years of education and deja vu incidence in both neurosurgery (education years: < 9 = 12%, 9–12 = 42%, 13+ = 68%) and psychiatric (education years: < 9 = 23%, 9–12 = 46%, 13+ = 56%) patients.

Comparing five levels of educational achievement, Palmer (1979) noted the lowest incidence of deja vu (48%) at the bottom rung (grade school only) and the highest incidence of deja vu (81%) among those with a graduate degree. In addition, both Chapman and Mensh and Kohr (1980) found positive correlations (.16 and .10, respectively) between education and deja vu.

Thus, all investigations show a direct relationship between déjà vu incidence and years of schooling. Of course, education and socioeconomic class are highly related, and no one has separated the independent contributions of each variable.

Deja Experience by Gender

Many investigations have compared deja vu incidence in male and female participants, but no consistent gender difference has emerged.

Some have found a higher incidence among women and girls (Gaynard, 1992; Myers & Grant, 1972), others have reported a higher incidence among men and boys (Green, 1966; NORC, 1984, 1988, 1989; Richardson & Winokur, 1967, sample of neurosurgery patients), and some have found no gender difference (Bernhard-Leroy, 1898; Chapman & Mensh, 1951; M. A. Harper, 1969; Kohr, 1980; Leeds, 1944; Palmer, 1979; Richardson & Winokur, 1967, sample of psychiatric patients; Sno et al., 1994).

Thus, deja vu is not clearly gender related in any obvious way.