Déjà vu is that creepy feeling that you're living through a moment for the second time, as if retreading the path of an earlier existence. Now Alan Brown and Elizabeth Marsh believe they've found a way to simulate the déjà vu sensation in the laboratory - a finding that could help us understand why the phenomenon occurs.
Twenty-four participants were presented with dozens of symbols that had been carefully chosen, with the help of a pilot study, to be either entirely novel, rarely encountered, or highly familiar (e.g. the division symbol). The participants' task was simply to state for each symbol whether they'd seen it prior to the experiment.
A vital twist was that some of the symbols were preceded by an exceedingly brief flash - too quick to be detected consciously - of the same or a different symbol.
The take-home finding was that a brief flash of an entirely novel symbol before its subsequent, longer presentation, significantly increased the likelihood that a participant would wrongly claim to have seen that symbol prior to the experiment. Indeed, novel symbols not preceded by a subliminal flash were judged to be familiar just three per cent of the time, compared with 15 per cent of the time when preceded by a subliminal flash of the same symbol.
The relevance of these findings to the déjà vu effect were highlighted by post-test questioning of the participants, in which 50 per cent of them reported having experienced déjà vu during the study and 79 per cent said they'd sometimes been confused about whether or not they'd seen a symbol before.
The researchers said their experimental paradigm was analogous to a person glancing fleetingly at an unfamiliar street scene, being distracted by a poster in a window, before returning their gaze to the street and experiencing a strange sense of having been there before. The experiment provides "a possible mechanism for common illusions of false recognition," they concluded.
Brown, A., & Marsh, E. (2009). Creating Illusions of Past Encounter Through Brief Exposure. Psychological Science, 20 (5), 534-538. DOI: 10.1111/j.1467-9280.2009.02337.x