An early Dutch study of déjà vu experiences.

In 1904 and 1906, Heymans reported the results of two prospective questionnaire surveys on déjà vu experiences and depersonalization in a sample of mainly students. Déjà vu experiences appeared to be more frequent than episodes of depersonalization. Emotional sensitivity, unstable mood fluctuations, apathetic episodes and irregular working rhythm emerged as predisposing personality traits. With the exception of the working rhythm, these traits were more prominent among the respondents with episodes of depersonalization than among those with déjà vu experiences. Heymans inferred that these findings supported his hypothesis that déjà vu experiences and depersonalization both resulted from the diminishing or disappearance of a sense of familiarity due to a momentary reduction of psychological energy. A re-analysis of Heymans' data partly confirmed his findings and conclusions as to the predisposing factors. The authors conclude that his studies and his hypothesis have been hitherto undervalued and would deserve more attention.