Abstract
Introduction: Reward expectancies can have profound effects on behavioral choices: primates select the target that is associated with the highest expected reward or value. Previous studies on smooth pursuit eye movements, the eyes’ main response to visual motion, showed that eye velocity dynamically reflects selection in favor of targets with higher expected reward. The current study examined whether reward also modulates basic kinematics of human smooth pursuit: does expecting a higher reward make us track moving objects better? Methods: We recorded eye position in 22 untrained human observers who were instructed to accurately track a small spot of light, moving at constant speed across a computer monitor; luminance contrast of the spot was either high (exp1) or low (exp2). Expected reward was manipulated by using pictures of Canadian 5 or 25 cent coins as cues (presented for 1000 ms preceding stimulus motion) indicating a low or high-reward trial, respectively. The ratio of low- to high-reward trials was 4:1; reward cues were equal in size and luminance. Observers were told that for each high-reward trial 25 cents would be added to their remuneration as a reward for accurate tracking. A control condition without reward cues served as a baseline. Results: We found consistent effects of reward expectation on smooth pursuit in both experiments. In high-reward trials, pursuit was initiated faster (higher acceleration and velocity) and maintained with better accuracy (gain) and lower velocity error. High reward also resulted in smoother pursuit responses with fewer and smaller catch-up saccades. Conclusion: We found adaptive improvements of smooth pursuit as a result of high reward expectation across the entire pursuit response. Reward may increase neuronal sensitivity, thereby boosting the system’s capability of processing visual motion information for pursuit.
