Eye-hand coordination while pointing rapidly under risk.

Humans make rapid, goal-directed movements to interact with their environment. Saccadic eye movements usually accompany rapid hand movements, suggesting neural coupling, although it remains unclear what determines the strength of the coupling. Here, we present evidence that humans can alter eye-hand coordination in response to risk associated with endpoint variability. We used a paradigm in which human participants were forced to point rapidly under risk and were penalized or rewarded depending on the hand movement outcome. A separate reward schedule was employed for relative saccadic endpoint position. Participants received a monetary reward proportional to points won. We present a model that defines optimality of eye-hand coordination for this task depending on where the hand lands relative to the eye. A comparison of the results and model predictions showed that participants could optimize performance to maximize gain in some conditions, but not others. Participants produced near-optimal results when no feedback was given about relative saccade location and when negative feedback was provided for large distances between the saccade and hand. Participants were sub-optimal when given negative feedback for saccades very close to the hand endpoint. Our results suggest that eye-hand coordination is flexible when pointing rapidly under risk, but final eye position remains correlated with finger location.