Abstract
Higher order motor impairments are rarely investigated in movement disordered populations such as Parkinson's disease (PD). However, individuals with PD have been shown to elicit signs of apraxia with deficits in the spatial and temporal organization of gestures. According to the model of Roy et al (1991), it was hypothesized that both sensory and conceptual systems would contribute to the deficits in PD. The goal of the present study was to evaluate if individuals with PD would be less accurate during imitation of gestures without vision of their limbs, and/or less accurate during gestures that do not involve access to semantics. 48 PD and 16 healthy controls completed a set of imitation tasks involving meaningful and meaningless gestures performed with and without vision. Z-scores were computed for the PD relative to the controls. PD performed worse on meaningless gestures compared to meaningful gestures (p<.001), indicating that access to semantics facilitates performance. While it was predicted that withdrawal of vision would cause a decline in performance, this was only the case for the meaningless gestures (p<.023). Imitation of meaningful gestures was more accurate with vision withdrawn (p<.015). These findings suggest that without access to semantics (meaningless) imitation depends on visual information about the limb. With access to semantics (meaningful) visual information may compete with accessing the stored representation thus leading to degraded performance.Acknowledgments: Heart and Stroke Foundation of Ontario, NSERC