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Karin Wittinghofer, Markus Lappe; Position and size invariance in the mechanisms of biological motion perception. Journal of Vision 2012;12(9):651. doi: 10.1167/12.9.651.
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Biological motion, the perception of a moving human figure from point-light stimuli, may be derived from the analysis of sequences of body posture by body selective neurons in the ventral visual system. These neurons are likely to show position and size invariance to their preferred stimuli. We investigated biological motion perception from sequences of point-light images that changed in position or size from frame to frame. In the size change condition, stimulus size changed randomly between 1.59 and 7.31 deg from frame to frame. In the position change condition, stimulus size was 1.59 deg, and stimulus position was random on a circle of radius 3.18 deg. In one experiment, 150 naive subjects verbally described their spontaneous percept of one such stimulus. 60,5 % of the subjects correctly recognized biological motion despite the variability of the size and position of the individual frames. In a control condition, in which the same posture was used in all frames only 16 % reported seeing a human figure. In a second experiment, 11 subjects discriminated facing and moving direction of the walkers in a psychophysical experiment. Correct recognition rates were 91 % for the facing discrimination and 69 % for the walking direction discrimination. We conclude that biological motion can be perceived even from stimuli that vary unnaturally in size and position, consistent with an involvement of size and position invariant form recognition mechanisms in the ventral visual system.
Meeting abstract presented at VSS 2012
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