i ACTION SELECTION IN MOTOR CONTROL: ERROR, REWARD, AND TIME by

ii Each action our bodies execute is the consequence of a complex process of decision making by the brain. At each moment, a multitude of actions are available to the brain to place the body in a more desirable state. How, then, does the brain decide what movement to make, and why? In general, we presented the motor system with tasks where several actions could be used to successfully accomplish a task, and observed what solution healthy people and people with movement disorders adopted. Our goal was to understand the costs and tradeoffs involved in the selection of movement. While many influences likely contribute, we focused on the role of three factors: errors, reward, and time. We found that errors played a dominant role in the selection of action. First, we used error-clamp trials, where we injected artificial redundancy and controlled the errors and rewards produced by each action, to examine the effect of the error on the selection of actions. We found that the policy underlying th