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Abstract:
Perception of the relative orientation of the self, and objects in the environment, requires integration of visual and vestibular sensory information, and an internal representation of the body's orientation. Here I present and discuss findings on the relative contribution of these cues for orientation perception in Parkinson’s disease (PD; Barnett-Cowan et al., Neuroscience, In Press). The orientation of a line relative to vertical (i.e., subjective visual vertical) and the orientation in which a letter character is perceived as the ‘right way up’ (i.e., the perceptual upright) were measured in PD patients (on- and off-medication) and age-matched controls. Visual, vestibular and body cues were manipulated using a polarized visual room presented in various orientations while observers were upright or lying right-side-down. Patients were more influenced by vision than controls but only when setting a line to vertical. Patients relied less on the internal representation of the body when identifying characters as indicated by a greater influence of vestibular information. Consistent with reports of impaired proprioception among medicated PD patients, our effects were significant only when patients were medicated. I will discuss these results within a framework suggesting that this ‘impaired’ internal representation of the body may reflect physiological impairments in PD.
