When a ball is rolling on the ground toward an observer, its elements
of texture are successively occluded. The number of the elements of te
xture occluded per unit of time determines the occlusion rate. The aim
of this study was to examine the role of the occlusion rate of ball t
exture and the velocity of the ball in the perception of the time rema
ining before the arrival. if the occlusion rate is used to perceive th
e time to arrival, then timing the initiation of movement should depen
d on occlusion rate. On the other hand, if the optical variable tau is
exclusively used, then no variation is expected. 20 subjects were req
uired to avoid balls rolling directly toward them. Three different bal
l textures and five ball velocities were used, leading to 10 different
occlusion rates. The results showed that the timing of the initiation
of the movement was not modified by variations of occlusion rate. How
ever, the velocity of the avoidance movement increased with occlusion
rate. The role of timing initiation and movement velocity in the contr
ol of the action are discussed, and it is suggested that occlusion rat
e is perceived and taken into account in the control of avoidance move
ments.