Jun 13, 2008

Paradoxes of age-related Deja experience

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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?