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Travis McKinney, Kelly Chajka, Mary Hayhoe; Pro-active gaze control in squash. Journal of Vision 2008;8(6):111. doi: 10.1167/8.6.111.
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In the natural world, the brain must handle inherent delays in visual processing, particularly during dynamic tasks, such as athletics. A possible solution to visuo-motor delays is prediction of a future state of the environment based on the current state and properties of the environment learned from experience (Wolpert, 2007). We tracked the eye movements of four skilled squash players, recording simultaneously from two players wearing RIT lightweight wearable eye-trackers. Performance for the four players was similar. When it was a player's turn to hit the ball, he mostly pursued the ball, but made an anticipatory saccade to the front wall, arriving 152 +/− 28 msec before contact with the wall, with an accuracy of 9.2 +/− 1.6 deg. After the ball bounced off the front wall, the player resumed pursuit within 184 msec. If the ball was on a trajectory to hit the side or back wall, players made an anticipatory saccade ahead of the ball to a point in space where the ball would pass approximately 220 msec later. The accuracy of this saccade was 2.6 deg in two subjects. This reveals a complex, highly accurate spatial prediction when both player and object move rapidly. In all trials, players stopped pursuit and held gaze stable in space about 160 msec before hitting the ball. At this time, no useful visual feedback about the ball can occur, and holding gaze may help provide a stable reference frame for the swing or allow preparation of the next eye movement. These data suggest that prediction of future state, based on current ball trajectory and experience with the ball is important for programming saccades. Such experience-based prediction may, in general, be a good strategy for gaze deployment.
Wolpert, D (2007) Probabilistic models in human sensorimotor control. Human Movement Science, 26, 511-524.
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