Using visual feedback to guide movement: Properties of adaptation in changing environments and Parkinson\u27s disease

On a day-to-day basis we use visual information to guide the execution of our movements with great ease. The use of vision allows us to guide and modify our movements by appropriately transforming external sensory information into proper motor commands. Current literature characterizes the process of visuomotor adaptation, but fails to consider the incremental response to sensed errors that comprise a fully adaptive process. We aimed to understand the properties of the trial-by-trial transformation of sensed visual error into subsequent motor adaptation. In this thesis we further aimed to understand how visuomotor learning changes as a function of experienced environment and how it is impacted by Parkinson\u27s disease. Recent experiments in force learning have shown that adaptive strategies can be flexibly and readily modified according to the demands of the environment a person experiences. In Chapter 2, we investigated the properties of visual feedback strategies in response to environments that changed daily. We introduced visual environments that could change as a function of the likelihood of experiencing a visual perturbation, or the direction of the visual perturbation bias across the workspace. By testing subjects in environments with changing statistics across several days, we were able to observe changes in the visuomotor sensitivity across environments. We found that subjects experiencing changes in visual likelihood adopted strategies very similar to those seen in force field learning. However, unlike in haptic learning, we discovered that when subjects experienced different environmental biases, adaptive sensitivity could be effected both within a single training day as well as across training days. In Chapter 3, we investigated the properties of visuomotor adaptation in patients with Parkinson\u27s disease. Previous experiments have suggested that patients with Parkinson\u27s disease have impoverished visuomotor learning when compared to healthy age-matched controls. We tested two aspects of visuomotor adaptation to determine the contribution of visual feedback in Parkinson\u27s disease: visual extent - thought to be mediated by the basal ganglia, and visual direction - thought to be cortically mediated. We found that patients with Parkinson\u27s disease fully adapted to changes in visual direction and showed more complete adaptation compared to control subjects, but adaptation in Parkinson\u27s disease patients was impaired during changes of visual extent. Our results confirm the idea that basal ganglia deficits can alter aspects of visuomotor adaptation. However, we have shown that part of this adaptive process remains intact, in accordance with hypotheses that state visuomotor control of direction and extent are separable processes