Start hesitation in patients with Parkinson's disease (PD) occurs predominantly during distractive and conflictual situations. The aim of this study was to investigate how differently an auditory stimulus (AS) influences execution function and execution time during a cognitively demanding stepping task in PD patients as compared to healthy controls. PD patients and healthy controls stepped forward in response to a visual imperative stimulus of an arrow. We applied a Simon task that comprised congruent and incongruent conditions. Direction and location of the arrow matched in the congruent condition, while they didn't in the incongruent condition. AS were randomly and simultaneously presented with the visual stimulus. An error in the direction of an anticipatory postural adjustment (APA), termed an APA error, and temporal parameters (reaction onset of APA and APA duration) were analyzed. As a result, the AS increased the APA error rate in the control group regardless of the condition, but they did not influence it in the PD group. The AS also speeded the reaction onset in both groups regardless of the condition. The APA duration was prolonged by the AS for the control group, while it was unaffected by the AS for the PD group in both conditions. These findings indicate that AS could facilitate a step initiation, conceivably by facilitating a stimulus identification process and increasing attentional control of stepping behavior, without influencing a decision-making process even in a cognitively demanding condition in patients with PD.
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