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)”