Visual sampling during walking in people with Parkinson's disease and the influence of environment and dual-task.

Visuospatial dysfunction may play a crucial role in gait disturbance in Parkinson's disease (PD), in particular how visual exploration of the environment is integrated into gait control. In this study, we tested the hypothesis that people with PD would visually sample their environment less frequently than controls when walking under different levels of environmental complexity and dual-task. We also explored associations between saccadic outcomes and clinical measures. Visual sampling (saccadic frequency) and gait were measured concurrently for 21 people with PD and 12 age-matched controls during a series of walking tasks using electrooculography (EOG) synchronised with 3D motion analysis (VICON). Participants walked under four environmental conditions during single and dual-task. Saccade frequency and task duration were measured. PD participants took longer to complete all tasks than controls (p =.004). Environment and dual-task impacted on saccadic frequency especially for PD. For both groups, saccadic frequency increased when approaching a turn compared with straight walking. Prior to turning, PD made less frequent early preparatory saccades than controls (p =.012). Under dual-task conditions, people with PD made less frequent saccades than controls when walking straight ahead (p =.040) and in preparation for a turn (p =.032). Increased saccadic frequency was related to poorer attention, cognition and spatial memory in controls and people with PD for single-task conditions but not dual-task conditions. Impaired visual sampling may contribute to the gait disorder in PD, especially when navigating through complex environments and when distracted.