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Dorothy Cowie, Amy Peters, Brian Day; A gateway into the visual control of locomotion: walking through doors in Parkinson's Disease. Journal of Vision 2009;9(8):1121. doi: 10.1167/9.8.1121.
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Freezing of gait (FoG) is a locomotor phenomenon exhibited in a subgroup of patients with Parkinson's Disease. In FoG a patient comes to an involuntary halt while walking, or cannot start walking despite a desire to do so. FoG commonly occurs in certain environmental conditions, including walking through doorways. This suggests a possible perceptual aspect to the phenomenon which we investigated in two ways. First we investigated whether freezing was associated with atypical perceptual processing of door width information. To do this we used a judgment task where participants were asked to judge the width of door they could just walk through (Warren & Whang, 1987). Some groups of PD patients show ‘space compression’ in this task (Lee, 2001), but it has not been investigated in PD patients who ‘freeze’. As a group, PD freezers show some space compression compared with a healthy control group. Additionally, we found greater space compression in patients who showed doorway freezing than patients who did not. Although PD patients have a damaged motor system, this implies that the freezing phenomenon may result from an additional perceptuomotor deficit. Second, using a motion capture system we showed that the presence of a doorway affected gait parameters in freezers. There were changes in step length, heel lift, and step time in the approach to the doorway. These results imply that visual information about upcoming obstacles is used to make motor plans several steps in advance, but that the results of this process are abnormal in PD freezers.
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