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Joshua J. New, Brian J. Scholl; The functional nature of motion-induced blindness: Further explorations of the ‘perceptual scotoma’ hypothesis. Journal of Vision 2009;9(8):253. doi: 10.1167/9.8.253.
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Perhaps the most striking phenomenon of visual awareness to be discovered in the last decade is that of motion-induced blindness (MIB). In MIB, fully visible and attended objects may repeatedly fluctuate into and out of conscious awareness when superimposed onto certain global moving patterns. While frequently considered as a limitation or failure of visual perception, we have proposed that MIB may actually reflect a specific functional heuristic in visual processing for identifying and compensating for some visual impairments. In particular, when a small object is invariant despite changes that are occurring in the surrounding visual field, the visual system may interpret that stimulus as akin to a scotoma, and may thus expunge it from awareness. Here we further explore this ‘perceptual scotoma’ hypothesis (New & Scholl, 2008, Psychological Science), reporting several new features of MIB, and responding to some apparent challenges. In particular, we explore the role of moving targets in MIB. Though scotomas can be stationary, some (‘motile scotomas’, or ‘floaters’ consisting of material within the eye) may frequently move. The character of such movements, however, yielded the unique prediction that moving targets in MIB displays may be more likely to perceptually disappear when they are floating downward vs. rising upward through the same positions — a prediction that was robustly confirmed. In additional experiments, we explored the effects of targets in MIB that moved with vs. against smooth horizontal eye movements. Targets moving with fixation (as would a scotoma) disappeared much more readily. Because this effect occurred when both types of moving targets were present in the display at the same time, such effects cannot be explained by appeal to microsaccades or attentional effects. These and other new effects each support the idea that MIB reflects an adaptive visual function.
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