Publication Details

Philbeck, J. W. (2000). Visually directed walking to briefly glimpsed targets is not biased toward fixation location. Perception, 29 (3), 259-272.


When observers indicate the magnitude of a previously viewed spatial extent by walking without vision to each endpoint, there is little evidence of the perceptual collapse in depth associated with some other methods (eg visual matching). One explanation is that both walking and matching are perceptually mediated, but that the perceived layout is task-dependent. In this view, perceived depth beyond 2 - 3 m is typically distorted by an equidistance effect, whereby the egocentric distances of nonfixated portions of the depth interval are perceptually pulled toward the fixated point. Action-based responses, however, recruit processes that enhance perceptual accuracy as the stimulus configuration is inspected. This predicts that walked indications of egocentric distance performed without vision should exhibit equidistance effects at short exposure durations, but become more accurate at longer exposures. In this paper, two experiments demonstrate that in a well-lit environment there is substantial perceptual anisotropy at near distances (3 - 5 m), but that walked indications of egocentric distance are quite accurate after brief glimpses (150 ms), even when the walking target is not directly fixated. Longer exposures do not increase accuracy. The results are clearly inconsistent with the task-dependent information processing explanation, but do not rule out others in which perception mediates both walking and visual matches.



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