Gait impairments are prevalent among people with Parkinson’s disease (PD). Instructions to focus on walking can improve walking in PD, but the use of such a cognitive strategy may be limited under dual-task walking conditions, when walking is performed simultaneously with concurrent cognitive or motor tasks. This study examined how dual-task performance of walking and a concurrent cognitive task was affected by instructions in people with PD compared to healthy young and older individuals. Dual-task walking and cognitive task performance was characterized under two sets of instructions as follows: (1) focus on walking and (2) focus on the cognitive task. People with PD and healthy adults walked faster when instructed to focus on walking. However, when focused on walking, people with PD and young adults demonstrated declines in the cognitive task. This suggests that dual-task performance is flexible and can be modified by instructions in people with PD, but walking improvements may come at a cost to cognitive task performance. The ability to modify dual-task performance in response to instructions or other task and environmental factors is critical to mobility in daily life. Future research should continue to examine factors that influence dual-task performance among people with PD. 1. Introduction Gait impairments are common in people with Parkinson’s disease (PD) and are associated with increased disability, reduced quality of life, and increased risk for falls [1–4]. Gait impairments in PD are exacerbated when walking is performed simultaneously with another task [5–9], which is referred to as dual-task walking. People with PD report that walking while performing another task is one of the greatest challenges of daily mobility [10]. They also describe using concentration to monitor and correct walking [10], consistent with James Parkinson’s original observation that, “Walking becomes a task that cannot be performed without considerable attention” [11]. Gait impairments in PD are an important target of therapeutic interventions because of their prevalence and consequences. The use of cognitive processes to consciously attend to and modify gait parameters is a key strategy for gait rehabilitation in PD. For example, people with PD can increase gait speed and stride length when instructed to focus on taking longer strides [12–14]. Such cognitive strategies improve walking under single-task conditions, but the evidence for transfer to dual-task walking conditions is mixed [13, 15]. The ability to improve dual-task walking using cognitive strategies
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