title: A closer look at mechanisms underlying perceptual differences in Parkinson's freezers and non-freezers.
abstract: Parkinson's disease patients who suffer from freezing of gait (PD-FOG) may have sensory and/or perceptual deficits, although they are difficult to disentangle. This study evaluated whether visuospatial perception or self-motion perception were more impaired in PD-FOG, and whether distance estimation errors might be related to misperception of physical walking (compared to imagined). Finally, cognitive status was evaluated in order to evaluate whether cognitive status predicts any of the perception deficits identified. Nine PD-FOG and 15 PD-nonFOG were tested. In experiment 1, participants were shown a target, then the target was removed, before participants demonstrated the original position of the target in two different feedback conditions (pointing with a laser, or walking to its original position). In experiment 2, participants walked to a target (3, 4.5, 6m) and then imagined walking to that same target. The time to complete both of these tasks was measured and compared. Experiment 1 found a significantly greater judgment error in PD-FOG across both conditions (p=0.013) (compared to PD-nonFOG). Constant error revealed that both groups significantly underestimated during the self-motion condition only (p=0.01). Interestingly, results from experiment 2 demonstrated a significant discrepancy between the time it took to imagine walking compared to their actual movement times, specifically in PD-FOG (p=0.03). This mismatch as well as cognitive status significantly predicted judgment errors during the self-motion condition from experiment 1. Therefore, this study found evidence that PD-FOG have significantly greater sensory-perception deficits compared to PD-nonFOG. These findings have important clinical implications for further understanding FOG and developing new rehabilitative strategies for FOG symptoms.
authors.affiliation: Sun Life Financial Movement Disorders Research and Rehabilitation Centre, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5, Canada; Department of Psychology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: K A
authors.initials: KA
authors.lastname: Ehgoetz Martens
authors.affiliation: Department of Psychology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: C G
authors.initials: CG
authors.lastname: Ellard
authors.affiliation: Sun Life Financial Movement Disorders Research and Rehabilitation Centre, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5, Canada. Electronic address: qalmeida@wlu.ca.
authors.forename: Q J
authors.initials: QJ
authors.lastname: Almeida
mesh_terms: D000368:Aged; D005260:Female; D020233:Gait Disorders, Neurologic / Q000209:etiology / Q000523:psychology; D006801:Humans; D007092:Imagination; D007600:Judgment; D008297:Male; D009039:Motion Perception; D010300:Parkinson Disease / Q000150:complications* / Q000523:psychology*; D013028:Space Perception; D065855:Spatial Processing; D016138:Walking
keywords: Parkinson’s disease; freezing of gait; motor imagery; perception; sensory feedback