Impact of optic flow perception and egocentric coordinates on veering in Parkinson's disease

Abstract

Spatial navigation is a complex process requiring integration of visuoperceptual information. The present study examined how visuospatial function relates to navigational veering in Parkinson's disease, a movement disorder in which visuospatial cognition is affected by the degeneration of the basal ganglia and resulting dysfunction of the parietal lobes. We hypothesized that patients whose initial motor symptoms start on the left versus right side of the body (LPD, predominant right-hemisphere dysfunction; RPD, predominant left-hemisphere dysfunction) would display distinct patterns of navigational veering associated with the groups' dissimilar visuospatial profiles. Of particular interest was to examine the association of navigational veering (lateral deviation along the medio-lateral axis) with perception of egocentric coordinates and of radial optic flow patterns, both of which are mediated by the parietal lobes. Thirty-one non-demented Parkinson's disease patients (16 LPD, 15 RPD) and 18 healthy control (HC) adults received visuospatial tests, of whom 23 Parkinson's disease patients and 17 HC also underwent veering assessment. The participants were examined on three visual-feedback navigation conditions: none (eyes closed), natural, and optic flow supplied by a virtual-reality headset. All groups veered to the left when walking with eyes closed, women with Parkinson's disease more so than the other participants. On the navigation assessments with visual feedback, only LPD patients deviated right of centre. On tests of visuospatial function, the perceived midline was shifted rightward in LPD (men and women), increasingly so with the addition of visual input. In contrast, men with RPD showed leftward deviation. RPD patients and HC perceived optic flow in the left hemifield as faster than in the right hemifield, with a trend for the opposite pattern for LPD. Navigational veering in LPD was associated with deviation of the perceived egocentric midline and not with perception of optic flow speed asymmetries, and in RPD it was also associated with visual dependence, though in fact LPD subjects were more visually dependent than those with RPD. Our results indicate that (i) parietal-mediated perception of visual space is affected in Parkinson's disease, with both side of motor symptom onset and gender affecting spatial performance, and (ii) visual input affects veering.

Effects of orthostatic hypotension on cognition in Parkinson disease

“…For this measure, a line presented in one hemifield changes incrementally in size until the participant perceives it to be the same size as a line of constant length in the opposite hemifield. 26 The Line Bisection test was used to determine egocentric reference point, and the Visual Dependence test was used to assess line orientation and angle judgment. 26 Statistical analysis.…”

“…26 The Line Bisection test was used to determine egocentric reference point, and the Visual Dependence test was used to assess line orientation and angle judgment. 26 Statistical analysis. Statistical analysis was performed using SPSS v17.0 (SPSS Inc., Chicago, IL).…”

Insights into the neural control of locomotion from walking through doorways in Parkinson's disease

“…PD impairs the amplitude (Blin, 1991) and timing of walking, but also alters responses to visual inputs (Davidsdottir et al, 2008). For some patients, visual stimuli such as doorways or roads can trigger 'freezing' episodes during which the person feels as if his feet are glued to the floor (Rahman et al, 2008;Schaafsma et al, 2003).…”

Balance in Parkinson's disease patients changing the visual input

“…Fall rates are higher in studies that also include "near falls" 1 . Recent studies have shown that sensory input and sensory motor processing appear to be relevant in clinical issues in PD, such as instability in open spaces, postural control disorientation, or FOG [2][3][4][5][6][7][8] . One of the interesting points about the relationship between the changes in the cues of sensory information and postural control is the possibility to assess postural responses with these changes in order to understand all of the mechanisms involved in balance disorders in patients with PD.…”