The frequently heard coach's advice, "Keep your eye on the ball", may not be the best approach, suggests a new study on page 1236 of this issue*. The authors used the cricket batsman's challenge (how to react to a fast-approaching ball) to address how athletes use visual cues to produce rapid and accurate motor responses. Previous theories proposed that a batsman must use direct visual measurements, such as image expansion or the rate of change of binocular disparity, to predict the ball's trajectory. However, given that the batsman has only a fraction of a second to monitor such visual cues, it has been controversial whether these parameters could be measured accurately enough to guide the correct response.
Land and McLeod took a new approach to this problem by monitoring the eye movements of batsmen as the ball was approaching, to determine what type of visual information they were actually collecting. The authors monitored the eye movements of three cricket batsman of widely varying skill, and found that, in general, they made a similar sequence of eye movements. Their eyes followed the ball's trajectory for a short period after release, then made a saccade below the ball to the site where it would be predicted to bounce. They then fixated again on the ball as it bounced, and followed its upward trajectory for approximately 200 ms afterward. The parameters that best distinguished most skilled from least skilled batsmen were the speed and variability of the initial saccade. The best batsman had the shortest delay between the ball's release and saccade initiation, and also used different saccade timing and magnitude for different ball trajectories. Therefore, the cricket batsman prepares his response to an oncoming ball by quickly assessing its predicted trajectory and directing visual attention to appropriate regions of the visual field with a precisely timed sequence of eye movements.
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