Predictive eye movements when hitting a bouncing ball.

Predictive eye movements targeted toward the direction of ball bounce are a feature of gaze behavior when intercepting a target soon after it has bounced. However, there is conjecture over the exact location toward which these predictive eye movements are directed, and whether gaze during this period is moving or instead "lies in wait" for the ball to arrive. Therefore, the aim of this study was to further examine the location toward which predictive eye movements are made when hitting a bouncing ball. We tracked the eye and head movements of 23 novice participants who attempted to hit approaching tennis balls in a virtual environment. The balls differed in time from bounce to contact (300, 550, and 800 ms). Results revealed that participants made predictive saccades shortly before the ball bounced in two-thirds of all trials. These saccades were directed several degrees above the position at which the ball bounced, rather than toward the position at which it bounced or toward a position the ball would occupy shortly after the bounce. After the saccade, a separation of roles for the eyes and head ensured that gaze continued to change so that it was as close as possible to the ball soon after bounce. Smooth head movements were responsible for the immediate and ongoing changes in gaze to align it with the ball in the lateral direction, while eye movements realigned gaze with the ball in the vertical direction from approximately 100 ms after the ball changed its direction of motion after bounce. We conclude that predictive saccades direct gaze above the location at which the ball will bounce, presumably in order to facilitate ball tracking after the bounce.