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James Thompson, Elizabeth Hussey; Evidence for object-centered coding of biological motion. Journal of Vision 2009;9(8):619. doi: 10.1167/9.8.619.
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It has recently been shown that prolonged or repeated viewing of particular biological motion patterns, such as male or female gait, produce strong adaptation effects selective to the adapted gait pattern. We previously reported that such gait-specific adaptation depends on the configuration of the adapter and test stimuli - an adapter that is configured with an intact body shape can produce adaptation of both an intact test stimulus and an apart stimulus, while an adapter with the arms and legs separated from the torso does not produce adaptation of an intact test stimulus (Hussey & Thompson, 2008). In this study we examined the effects of inversion in gait-specific adaptation. As in our previous study, participants (N=11) viewed an animated figure walking with a gait that consisted of a spatiotemporal morph between gait styles captured from two different human actors. The walking figure was configured either as upright or inverted. We determined the point of subjective equality (PSE) between the two gaits for upright and inverted test walkers, before and after 2mins (plus 5secs/trial top-up) adaptation to one of the gaits. Participants adapted to upright and inverted figures in sessions separated by at least 48hrs. Results revealed strong within-stimulus adaptation, with the upright walker adapting the upright test walker, and the inverted walker adapting the inverted test walker. In contrast to our previous findings of configuration-dependent gait adaptation, however, we found that the upright and inverted adapters produced similar levels of adaptation of the upright test stimulus (36% vs 30%, n.s.). Both upright and inverted adapters also produced similar levels of adaptation in the inverted test stimulus (30% vs 37%, n.s.). Combined with our previous results, these findings suggest an object-centered visual coding of specific gaits that is dependent on the intrinsic relationship between body parts, rather than a viewer-centered, orientation-dependent coding.
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