Aug 27, 2008

Attentional Explanations (Part 3)

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Inattentional blindness

Related to this interpretation of the deja vu, recent research suggests that individuals often miss objects that are clearly visible if they are focused on some other object in the visual array. This inattentional blindness, extensively investigated by Mack and Rock (1998), could explain how an initial brief perception of objects in a scene can go undetected.

When an extraneous visual stimulus (e.g., shape, object, word) accompanies a target stimulus (e.g., cross) to which the participant is instructed to respond (e.g., Which line of the cross is longer?), the individual often misses seeing the extraneous stimulus. When the target stimulus is in the periphery and the extraneous (ignored) stimulus is in the center of the visual field (fovea), inattentional blindness is more likely than when the target stimulus is in the fovea and the extraneous stimulus is in the periphery. Individuals who fail to report the extraneous (e.g., word) stimulus still process it, as reflected in significant priming on a subsequent word stem completion task (Mack & Rock, 1998).

Such a paradigm, in which the stimulus is above threshold but unattended (rather than subthreshold), better models people’s natural perceptual experience (Merikle et al., 2001) and provides a more realistic framework for studying the deja vu experience. For example, one may enter a room talking on a cell phone or thinking about an upcoming meeting while looking directly at a particular stimulus, and moments later this same stimulus is consciously perceived and elicits a déjà vu. Perhaps one of the most blatant examples of inattention to suprathreshold stimuli is the “time gap” experience, in which one’s entire perceptual experience over several minutes (e.g., during highway driving) is unrecallable (Reed, 1979).

It is possible that an inhibitory mechanism underlies the inattentional blindness effect. In elaborating on Poetzl’s (1917/1960) earlier speculation, N. F. Dixon (1971) suggested that during an initial brief stimulus exposure there is “a rapid fragmentation of the sensory information, wherein ‘inhibition by interference’ causes parts of the stimulus field to interfere with the development of other parts” (p. 106). Thus, certain elements in the stimulus array may suppress or block the perception of other elements, similarly to lateral inhibition in the visual system (cf. Martindale, 1981). In a second glance at the scene immediately after the first, the initially inhibited portion of the visual scene is disinhibited and now matches the present perception. The possibility that inhibition–disinhibition underlies deja vu is supported by the fact that both inhibitory processes and deja vu frequency decrease with age.

The magnitude of negative priming interference, for which a response which is actively inhibited on one trial is more difficult to generate on the immediately succeeding trial, is much smaller with older than younger adults (Hasher, Stoltzfus, Zacks, & Rypma, 1991). If the visual inhibition of parafoveal elements similarly decreases with age, this would reduce the likelihood that inhibited features would later disinhibit and lead to a deja vu.