Infants' saccadic behavior during 2-dimensional displays of a bounce

The study examined the saccadic behavior of 4- to 10-month-old infants when tracking a two-dimensional linear motion of a circle that occasionally bounced off a barrier constituted by the screen edges. It was investigated whether infants could anticipate the angle of the circle's direction after the bounce and the circle's displacement from the location of bounce. Seven bounce types were presented which differed in the angle of incidence. Three of the seven bounce types showed physically implausible bounces. Saccades that started before the infant could perceive the bounce and ended after the bounce were analyzed. Infants' saccades matched the circle's displacement with sufficient accuracy to conclude that they made predictive saccades. Only results from two bounce types where the circle's speed was less than 12.5°/s allowed for the possibility that infants made reactive saccades. The infants' anticipated angle was close to the angle of the circle's direction after the bounce. When the circle was moving at 40°/s, the difference between the two aforementioned angles was less than 15°, but it increased as the circle became slower. The effect of age on the saccade targets and other object-tracking measures was small and mostly masked by a large estimation error. Estimates of the saccade amplitude, saccade frequency, and the gaze-circle displacement were similar to those observed for saccades made when no bounce occurred and they were also similar to those reported in previous studies of infant object tracking with similar trajectories but without a barrier.