Dual-Processing Explanations (Part 2)

Perception and memory

Another dual-process interpretation, proposed by Bergson, is that perception and memory are simultaneous events and that “memory is never posterior to the formation of perception; it is contemporaneous with it. Step by step, as perception is created, the memory of it is projected beside it, as the shadow falls beside the body” (as cited in Carrington, 1931, p. 303; cf. Tulving, 1968). People’s cognitive resources are generally focused on the perception of an ongoing event, but distraction, inattention, or fatigue can lead to memory and perception momentarily enfolding in on each other.

Bergson likened this to two soldiers marching in tight formation: If the first one pauses for a moment, the two will bump into each other. Thus, if storage of information occasionally occurs the moment it is perceived, it could give rise to inappropriate recognition or deja vu.

Dual consciousness

Hughlings-Jackson (1888) suggested that people have two varieties of consciousness: normal, which processes information from the outside world, and parasitic, which monitors the thoughts and reflections of the inner, mental world. When the activity of the normal consciousness is diminished by distraction, fatigue, or seizure (in TLEs), evaluating the familiarity of incoming sensory experiences must depend on the more primitive internal consciousness, which operates from mentally generated images.

The result is a momentary misreading of a new experience as old, leading to deja vu. Rather than dominant and recessive states of consciousness, Wigan (1844) proposed two more equal and coordinated states. Only one is usually operational at any given moment, and it is the occasional activation of the second system simultaneous with the first that results in a déjà vu experience.

Only one brain has been used in the immediate preceding part of the scene—the other brain has been asleep, or in an analogous state nearly approaching it. When the attention of both brains is roused to the topic, there is the same vague consciousness that the ideas have passed through the mind before.

We have no means of knowing the length of time that had elapsed between the faint impression received by the single brain, and the distinct impression received by the double brain. It may seem to have been many years. (Wigan, 1844, pp. 84–85)”

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.

Another Anomalous

Two sets of outcomes suggest that belief in, or acceptance of, the deja vu experience has increased across recent decades. Gallup and Newport (1991) found that from 1978 to 1990, the amount of people who believed in the deja vu experience nearly doubled from 30% to 55%. In addition, the General Social Survey showed an increase in the reported lifetime incidence of deja vu from 59% in the 1970s (McCready & Greeley, 1976) to 68% in the 1980s (NORC, 1984, 1988, 1989).

This societal increase in the belief in, and reporting of, deja vu experiences may account for the decrease in reported deja vu incidence with age. To be more specific, older cohorts matured during an era in which belief in deja vu was not as accepted as it is today.

Aside from the anomalous decrease in lifetime incidence of deja vu with age, there is also an age-related decline in the frequency of deja vu among experients. A gradual increase in the cultural awareness of, and comfort with, deja vu may contribute to this age trend, and future surveys should require participants to define the term, as well as evaluate the personal and cultural acceptability of deja vu.

Another possible reason why older adults experience fewer incidents of deja vu is that they may be less sensitive to the qualities of their own cognitive experiences. That is, older adults are less accurate in identifying the sources of information (Brown, Jones, & Davis, 1995) and less likely to spontaneously use source information in making memory evaluations (Multhaup, 1995), thus making them less aware of the type of source memory mismatch that spontaneously leads to deja vu.

Finally, older adults tend to be more settled in their routine physical surroundings, making them less likely to encounter those new settings that could elicit deja vu experiences.

Paradoxes of age-related Deja experience

Chapman and Mensh (1951) presented age-related data on mean number of deja vu experiences per year. These data show a sharp decline with age and indicate that teenage experients showed a comparable deja vu frequency to those in their 20s but that the percentage of experients was simply lower among teenagers. Richardson and Winokur (1967) compared younger (<45 years) and older (45+ years) patients and found a distinct age-related drop in the incidence of deja vu in the past year in both the neurosurgery (younger = 44%; older = 16%) and the psychiatric (younger = 42%; older = 13%) groups.

Finally, the age-related decline in deja vu found by the NORC surveys (1984,1988, 1989) was similar within each frequency category (once or twice, several times, often). Apparently, the number of déjà vu experiences per year drops off across the adult age span more sharply than the number of individuals who claim to have had an incidence of deja vu in their lifetime.

All analyses presented above suggest that the age composition of samples used in deja vu survey research can dramatically affect estimates of deja vu incidence. Aside from this measurement issue, there are two logical paradoxes in these data.

First, teenage samples have the greatest number of deja vu experiences per experient, yet appear to have a lower percentage of experients than samples of those in their 20s. Does this indicate that one has to reach a certain developmental level before experiencing deja vu? Although no survey research has addressed the question of when a person first experiences deja vu, several have suggested the cognitive maturation necessary for deja vu is not fully in place until 8 or 9 years old (Crichton-Browne, 1895; Kohn, 1979; Neppe, 1983e). Furthermore, one may notice a deja vu only after hearing or reading about it, and this awareness may not happen until the mid-teen years.

The second logical issue is that the lifetime incidence of déjà vu drops off dramatically in older adults. It is important to separate this issue from the frequency of deja vu, which also drops off with age. Individuals in their 60s were once in their 20s; therefore, it is logically inconsistent that fewer 60-year-olds than 20-year-olds report ever having had a deja vu. The function plotting whether one has ever experienced a deja vu should either increase or remain flat with increasing age, but it certainly should not decrease. Is there a memory problem: Do these experiences occur only during youth and then are forgotten over time? Is there a response bias: Do older adults feel less comfortable admitting to having a deja vu experience? Is there a cohort effect: Has societal awareness and acceptance of deja vu increased across the past 50 years?

Age Related Deja

The most consistent finding in the deja vu literature is that the incidence with which it is experienced decreases with age (Bernhard-Leroy, 1898; Brauer et al., 1970; Chapman & Mensh, 1951; J. C. Dixon, 1963; Dugas, 1894; Gallup & Newport, 1991; M. A. Harper, 1969; Kohr, 1980; Kraepelin, 1887; Krijgers Janzen, 1958; Levin, 1993; MacCurdy, 1925; McCready & Greeley, 1976; Oberndorf, 1941; Palmer, 1979; Richardson & Winokur, 1967; Sander, 1874; Sno et al., 1994; Stanford, 1982; Zuger, 1966; although M. A. Harper, 1969; Lalande, 1893; and Neppe, 1983d, found no age difference).

Whereas many evaluations were based on personal observations, there have been several convincing empirical demonstrations of this trend. Three studies extensively evaluated changes in lifetime déjà vu experience across a broad age range. Chapman and Mensh (1951) assessed deja vu incidence in 11 different 5-year age spans (from 15–19 through 65–69). They discovered a systematic decline in the lifetime deja vu incidence with increasing age. The only anomaly in this trend is the lower rate found with teenagers.

Richardson and Winokur (1967) modeled their research after Chapman and Mensh, and queried patients admitted to a hospital for neurosurgical and psychiatric treatment. The age trends for both of their groups were similar to that found by Chapman and Mensh: a systematic decline in deja vu lifetime incidence across the adult age span, with the exception of a lower incidence for teenagers.

The third extensive evaluation of age-related data comes from the combined results of three surveys by the NORC (1984, 1988, 1989), including 3,885 individuals across ages 18–89 with an average sample size of 274 for each age block (range 70 to 488). The NORC incidence stayed steady at around 75% to 80% from the teen years to the early 40s, but declined systematically from there.

Palmer (1979) discovered that the lifetime incidence of deja vu was 83% for those under age 30 but dropped to 52% for those over 50, whereas Zuger (1966) found that the incidence dropped from 72% in those aged 25 years and under to 61% in individuals older than 25. Finally, Sno et al. (1994), Chapman and Mensh (1951), and Kohr (1980) all found similar negative correlations between age and deja vu incidence (–.22, –.23, and –.32, respectively).

What Is Triggering Deja Experience?

There are surprisingly scant data on the precise nature of the deja vu experience. Most surveys only ask about incidence, and among those probing the various dimensions of the experience, the data are either unavailable (Sno et al., 1994) or based on very small samples (Neppe, 1983e).

Brown et al. (1994) and Neppe (1983e) both found that the deja vu experience was primarily triggered by the visual scene and lasted for only a few seconds. Neppe (1983e) discovered that the experience was associated with mild stress or anxiety and was not accompanied by substantial changes in thinking or emotion. Brown et al. (1994) also noted that the primary psychological reaction was surprise and that participants’ time sense seemed to slow down.

There are obvious limitations in deriving such information from retrospective designs. Aside from the difficulty of remembering the personal details of a brief experience that may have happened months or years ago, one’s memory of the deja vu is most likely dominated by the perceptual experience which seems to be duplicated rather than details of one’s physical state and psychological reaction.

In prospective research (Heymans, 1904, 1906), most deja vu experiences occurred in the evening, in the company of others, while listening, in a state of fatigue, and following unpleasant or confusing mental activity or physical exertion or excessive alcohol consumption. However, no descriptive summary statistics were provided on the contextual and behavioral correlates (cf. Sno & Draaisma, 1993).

Frequency of Deja

Frequency of deja vu has been measured in three different ways. The absolute measure is how many total deja vu experiences the respondent has had. Kohr (1980) found that 14% had one or two lifetime experiences, 19% had three or four, 23% had five to eight, and 44% had nine or more. Though the highest percentage of experients had nine or more deja vu experiences, this sample consisted of members of a paranormal club.

Using a rougher cut, Palmer (1979) found that 98% of those who had deja vu have had more than one experience. Both investigations suggest that if one has experienced deja vu, it is highly likely that one has had

multiple experiences.

Deja vu frequency has also been evaluated by the following relative categories: seldom or rare, occasional, and often or frequent. The General Social Survey (NORC, 1984, 1988, 1989) revealed that most respondents fell in the seldom (44%) and occasional (44%) categories, with fewer claiming frequent (12%) deja vu. These percentages are close to the those found by Leeds (1944; 44% seldom, 39% occasional, 18% frequent) and by McCready and Greeley (1976; 49% seldom, 41% occasional, 10% frequent). Both Green (1966) and Brauer, Harrow, and Tucker (1970) discovered that 16% of respondents claimed frequent deja vu, a percentage close to that found in the other three studies.

Finally, a temporal evaluation can be made of either one’s last deja vu experience (past week? past month?) or how often one experiences a deja vu (every week? every month?). For the present analysis, these two questions were considered comparable; if an individual’s last deja vu was in the past week, it was assumed that his or her incidence was weekly.

Among investigations with a wide age range, there was moderate consistency in percentages of experients claiming monthly deja vu: 10% in Chapman and Mensh (1951), 10% in M. A. Harper (1969), and 19% in Neppe (1979). This percentage was considerably higher (54%) for Brown, Porter, and Nix (1994), but this was probably due to their young age sample (see Age Differences section).

The percentage of respondents claiming deja vu at least every year was more variable across studies: 14% in Heymans (1904), 21% in M. A. Harper (1969), 40% in Richardson and Winokur (1967, sample of neurosurgery patients), 71% in Chapman and Mensh (1951), 84% in Neppe (1983e), and 94% in Brown et al. (1994).

How many people have deja experience?

The percentage of individuals experiencing at least one déjà vu in their lifetime was studied across 41 surveys, with surveys separated by the authors’ use of clinical and nonclinical samples and listed in decreasing order of deja vu incidence within each set.

Over all outcomes, the mean incidence was 67%, and the median incidence was 66%. For the 32 nonclinical outcomes, the mean incidence was 68%, and median incidence was 70%; for the 9 clinical outcomes, the mean was 55%, and the median incidence was 65%. Thus, it appears that about two thirds of individuals have experienced at least one deja vu in their life.

It is interesting that many behavioral scientists writing informally about the deja vu experience describe it as common and universal (Angell, 1908; Carrington, 1931; Chapman & Mensh, 1951; Conklin, 1935; Critchley, 1989; M. A. Harper, 1969; James, 1890; MacCurdy, 1925; Maudsley, 1889; Murphy, 1951; Titchener, 1928;Wilson, 1929). Most of these writers are well educated, and the evidence suggests that the experience is more common among this subgroup of individuals.

The frequency-of-occurrence statistics were calculated using those individuals who have experienced a deja vu, or experients, as a base. Thus, if 60% of respondents have experienced a deja vu and 20% reported deja vu once a month, this is reported as a monthly rate of 33% (20%/60%) among experients.

Deja: Personality Disorder

The combined reporting of deja vu and depersonalization experiences highlights a consistent theme in earlier investigations of deja vu. Many researchers assumed that deja vu was a symptom of a mood or personality disorder, rather than a routine cognitive dysfunction, and were primarily interested in documenting the relationship between deja vu and other moderate to severe psychological disturbances (e.g., depersonalization), psychopathology (e.g., schizophrenia), and ongoing personal dispositions (e.g., mood fluctuations, working rhythms, emotional sensitivity; cf. Heymans, 1904, 1906).

Leeds (1944) also used a prospective procedure in evaluating the intensity and duration of 144 of his personal deja vu experiences spanning a 12-month period. (An average of one every 2.5 days!) This extraordinary frequency motivated his self-analysis, and although Leeds provided summary information on his deja vuexperiences, this is not included in the present review because of the anomalous frequency of his episodes.

Two groups of individuals traditionally have been identified as having an atypically high incidence of deja vu experiences: TLEs and people with schizophrenia. In the case of schizophrenia, attempts have been made to link the deja vu experience to psychopathology (Cutting & Silzer, 1990; Sno, Schalken, & de Jonghe,1992), but it is difficult to determine whether the experience of people in this subgroup is similar to that of individuals lacking such pathology. Neppe (1983e) suggested that deja vu among people with schizophrenia may be of much longer duration (hours, not seconds) and associated with intense depersonalization, mak-

ing it qualitatively different from that experienced by nonclinical individuals.

With respect to TLEs, deja vu is part of the aura preceding the seizure in some, and this phenomenon has been studied with retrospective anecdotal reports (Cole & Zangwill, 1963; Gloor, 1990; M. Harper & Roth, 1962; Krijgers Janzen, 1958; Neppe, 1980), personal experiential reports (Hughlings-Jackson, 1888; Leeds, 1944;Wohlgemuth, 1924), and brain stimulation (Adachi et al., 1999; Bancaud, Brunet-Bourgin, Chauvel, & Halgren, 1994; Gupta, Jeavons, Hughes, & Covanis, 1983; Weinand et al., 1994).

Depersonalization of Deja Experience

A final issue with the survey research is the potential unreliability of the self-report data on this particular topic. M. A. Harper (1969) suggested that the incidence of deja vu may simply be “an artefact of the interview situation and measures only the willingness of an individual to admit to an experience which may be universal” (p. 70; cf. Chapman & Mensh, 1951).

As an experimental caution, M. A. Harper (1969) compared oral and written administrations of the same deja vu questions to the same respondents and discovered only a 78% correspondence between whether the individual claimed to have experienced a deja vu through written versus oral queries (written response yielded a lower incidence).

The infrequency of deja vu experiences presents problems for remembering the specific physical and psychological details surrounding the deja vu. This difficulty can be addressed by prospective survey, but only Heymans (1904, 1906) has used this methodology.

In two separate studies, originally written in Dutch and translated into English by Sno and Draaisma (1993), college students recorded the details of each deja vu they experienced during an academic year. In the first investigation, 6 of 42 students (14%) had a total of 13 deja vu experiences during the 9-month period.

The incidence of deja vu in the second study is not available because deja vu and depersonalization experiences were reported in combination: 31 of 88 respondents (35%) reported one or both experiences during the academic year.

Another Bias on Deja Evaluation

The problem of an inadequate and restricted sample is particularly disappointing in Neppe’s (1983e) book, one of the most extensively documented survey projects on deja vu. Although he included five groups—people with schizophrenia, people with temporal lobe epilepsy (TLEs), people with non-temporal lobe epilepsy, paranormal experients (people who believe in the paranormal), and controls—his control group consisted of 10 people who did not believe in paranormal phenomena (i.e., paranormal nonexperients).

Only 5 of these 10 controls had ever had a deja vu experience; thus, an extensive series of descriptive statistics and analyses was based on 5 persons. Though Neppe (1983e) admitted that data from this control group were not generalizable, it is unfortunate that such a great effort was expended on presenting the results from so few individuals.

Another bias is created by the context of the deja vu question, which is often embedded among items evaluating paranormal phenomena such as out-of-body experiences, belief in poltergeists, psychokinesis, channeling, spirit possession, thought control, telekinesis, hauntings, past-life experiences, lucid dreams, ESP, and hallucinations (Gaynard, 1992; Green, 1966; Greyson, 1977; Kohr, 1980; McClenon, 1988; Palmer, 1979; Ross & Joshi, 1992).

Note, however, that Ross and Joshi (1992) removed the deja vu question from their analysis of 15 other questions on the paranormal because the reported deja vu incidence was too high to be considered paranormal.

A particularly unfortunate example of this bias is in the General Social Survey by the National Opinion Research Center (NORC) at the University of Chicago. The NORC uses exceptional sampling procedures in their surveys, yet accompany the deja vu question with four others evaluating parapsychological phenomena, namely ESP, clairvoyance, contact with the dead, and out-of-body experiences.

Similarly, a Gallup poll (Gallup & Newport, 1991) positioned the deja vu item in a set of questions about belief in the following realms of the paranormal: ESP, astrology, ghosts, clairvoyance, witches, and devils. Although Gallup and Newport (1991) acknowledged that most psychologists do not consider deja vu to be a psychic or paranormal phenomenon, they clearly implied this to their survey participants.

Herbal Medicine

Herbal Medicine is the therapeutic use of plants to safely assist the body in healing various disease conditions. Regarded as the oldest known form of medicine, herbs have a history stemming from most ancient cultures of the world, including the Greeks, Romans, Chinese as well as India and Egypt. Still today, it is the primary form of medicine for most of the worlds population.

Herbal medicine originally formed the basis for modern pharmaceutical medications. By isolating a herbs active ingredient, synthesized drugs can be formed. Although orthodox medicine prefers to ignore their true origins within herbal medicine.

Herbs act to nourish and support the body’s organs, restore and strengthen damaged tissue as well as detoxify and eliminate waste. Conditions more commonly treated with herbal medicine include skin disorders, hormonal problems, digestive imbalance, infections, penis girth, as well as nervous system issues such as anxiety, stress, and depression.

According to the Kinsey Institute’s data published back in the late 1940s, the average penis length is 5.5 - 6 inches and the average penis width (circumference) is 4 - 5 inches.

Many women and men will tell that it is not only the length of the penis, but the penis size that matters in the long run. In many ways, this is true. The majority of the nerves that are stimulated during penetration (both the vaginal and anal varieties) are located close to the entrance of the vagina and anus. This makes length less important and width that much greater a factor since it is the stretching of the vaginal or anal walls that stimulates the nerves.

One might be asked how to increase penis size using herbs. There is an invigorating herbal formula that helps men to attain larger and thicker penis sizes called MXMAN. This natural penis enlargement formula not only increases the penis length but also increases the girth for enormous sexual pleasure.

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