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Ayse Pinar Saygin, Shlomo Bentin, Michal Harel, Geraint Rees, Sharon Gilaie-Dotan; Dissociation between biological motion and shape integration. Journal of Vision 2010;10(7):783. doi: 10.1167/10.7.783.
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© ARVO (1962-2015); The Authors (2016-present)
While studies have pointed to a relationship between form processing and biological motion perception, the extent to which the latter depends on ventral stream integration is unknown. Here, we took advantage of patient LG's neuropsychological profile to address this question. LG has developmental visual agnosia, with severe difficulty in object recognition, but apparently normal motion perception. LG reports recognizing people from the way they move, suggesting he may use biological motion to support perception. In a recent neuroimaging and behavioural study we presented LG's abnormal visual cortical organization (Gilaie-Dotan et al, 2009, Cerebral Cortex). LG exhibited deficits in form processing, normal motion processing, and significant abnormalities in his visual hierarchy. In particular, LG's lateral occipital (LO) region did not show typical object selectivity, while motion sensitive MT+ showed typical activation patterns. Here, LG and age-matched controls performed motion-direction judgments on point light displays depicting either biological or non-biological motion. Using point lights allowed us to investigate structure from motion perception without relying on shape connectivity that assists integration processes. The biological motion stimuli depicted a person walking to the right or to the left (but without translation, as if on a treadmill), whereas non-biological motion consisted of a rectangle moving to either direction. The stimuli were embedded in noise dots in order to obtain sensitivity thresholds, which were calculated adaptively. The noise dots were created by spatially scrambling the target motion. While LG showed a significant deficit in the non-biological motion task, his biological motion performance was clearly within the normal range. His intact biological motion perception was further confirmed in a second experiment using different stimuli and task (Saygin, 2007, Brain). These results suggest that successful biological motion perception can be achieved without strict reliance on the integrity of hierarchical ventral stream integration.
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