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Abstract:
Visual backward masking occurs when perception of a briefly presented target is impaired by a mask presented 30-100 ms after the target. One account of this masking argues that top-down feedback from higher to lower visual brain areas along the visual pathway is involved. Top-down processing helps visual recognition in challenging situations, such as a very short viewing duration of the target, as follows. First, the bottom-up sensory inputs arising from the target generate an initial hypothesis about the target's character; second, the brain's internal model of the visual world generates a synthesized visual input consistent with this hypothesis; third, top-down feedback compares this synthesized input with the actual bottom-up visual input; fourth, the initial hypothesis is strengthed or weakened when synthesized and actual inputs have a good or poor match, respectively. Accordingly, a mask can interrupt this process when the bottom-up input from the subsequently presented mask rather than the target is compared with the top-down synthesized input. Zhaoping (2017) recently proposed that top-down processing for object recognition is weaker in the peripheral visual field. This predicts that visual backward masking is weaker peripherally. We report psychophysical experiments to test this prediction, using various target-mask presentation intervals and visual viewing eccentricities.
