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W. Drew Bromfield, Christopher Taylor, Jason Gold; Efficiencies for parts and wholes in biological motion perception. Journal of Vision 2012;12(9):461. doi: 10.1167/12.9.461.
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While some previous studies have examined how well humans can process certain subsets of points in a point-light walker (PLW) stimulus (e.g., Mather, Radford & West, 1992; Troje & Westoff, 2006), none has explored whether differences in information content exist across subsets of points within PLW stimuli. As a result, it is difficult to draw strong conclusions about the relative ability of human observers to process points located at one part of the body (e.g. the feet) relative to another (e.g. the hands). To begin to address this issue, we employed ideal-observer analysis to compute the efficiency with which human observers use information when processing different parts of PLW stimuli. Specifically, we measured both human and ideal observer contrast energy thresholds for left-right walking discrimination of PLW stimuli in 7 related conditions: a set of 3 ‘isolated’ conditions in which the stimuli contained only feet, hands or knees; a set of 3 complementary ‘missing’ conditions in which the stimuli were missing their feet, hands or knees; and a ‘complete’ condition in which the stimuli contained all body points. Ideal observer thresholds did not vary significantly across conditions, indicating that the amount of information carried by PLW stimuli does not depend on whether a given body location is either isolated or missing. For human observers, average efficiencies (ideal threshold/human threshold) were similar across each of the ‘missing’ conditions as well as the ‘complete’ condition, and were also similar across each of the ‘isolated’ conditions. However, absolute efficiencies were over a factor of 2 greater in the ‘isolated’ conditions relative to the ‘missing’ and ‘complete’ conditions. While it remains unclear why efficiency is so much greater for isolated body locations, our results show that human observers process the information contained in the hands, feet and knees with approximately equal efficiency.
Meeting abstract presented at VSS 2012
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