When infants catch a rolling ball by intercepting its trajectory, the action is prospectively controlled to take account of the object's speed, direction and path. We complicated this task in two ways: by occluding a portion of the ball's path with a screen, and by sometimes placing a barrier that blocked the ball's path behind the screen. In two experiments we manipulated visual information about the barrier and the ball's trajectory to see how this would aid 9-month-olds' performance. Anticipatory reaching was possible but difficult with a partially occluded trajectory; actually catching the ball was aided by full view of the trajectory although timing of reach onset was not affected. Full sight of the barrier and trajectory through a transparent screen prevented inappropriate reaching, whereas sight of the barrier alone through a 'window' in an opaque screen did not. We interpreted these results as evidence for decreased performance as cognitive load increased with the loss of visual information. In contrast to anticipatory reaching behavior, search for the ball after it disappeared behind the screen was facilitated by the opaque window condition, confirming previous studies that found superior search with opaque versus transparent screens.

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