Biological motion perception in Parkinson's disease
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Parkinson’s disease (PD) disrupts many aspects of visual perception, which has negative functional consequences. How PD affects perception of moving human bodies, or biological motion, is unknown. The ability to accurately perceive others’ motion is related to one’s own motor ability and depends on the integrity of brain areas affected in PD, including superior temporal sulcus and premotor cortex. Biological motion perception may therefore be compromised in PD but also provide a target for intervention, with perceptual training potentially improving motor function. Experiment 1 investigated whether perception of biological motion was impaired in PD (N=26) relative to neurologically-healthy control (NC; N=24) individuals. Participants viewed videos of point-light human figures and judged whether or not they depicted walking. As predicted, PD were less sensitive to biological motion than NC. This deficit was not associated with participants’ own walking difficulties or with other perceptual deficits (contrast sensitivity, coherent motion perception). Experiment 2 evaluated the hypothesis that PD deficits would extend to more socially-complex biological motion. PD (N=23) and NC (N=24) viewed point-light figures depicting communicative and non-communicative (object-oriented) gestures. The PD group was less accurate than NC in describing non-communicative gestures, an effect driven by PD men, who also had difficulty perceiving communicative gestures. Experiment 3 tested the efficacy of perceptual training for PD. Because biological motion perception is associated with motor function, it was hypothesized that perceptual training would improve walking. Individuals with PD were randomized to Gait Observation (N=13; viewing videos of healthy and unhealthy gait) or Landscape Observation (N=10; viewing videos of moving water) and trained daily for one week while gait data were collected with accelerometers. Post-training, only the Gait Observation group self-reported increased mobility, though improvements were not seen in objective gait data (daily activity, walking speed, stride length, stride frequency, leg swing time, gait asymmetry). These studies demonstrate that individuals with PD have difficulty perceiving biological motion (walking and socially-complex gestures). Improving biological motion perception led to enhancement in self-perceived walking ability. Perceptual training that incorporates more explicit learning over a longer time period may be required to effect objective improvements in walking.