Intercepting moving objects during self-motion

It is generally assumed that in catching a fly ball, an efficient strategy for dealing with the horizontal component of the ball's trajectory is for t he observer to keep the angular position of the ball constant with respect to his head. That strategy is called the constant bearing angle or CBA stra tegy. Maintenance of angular constancy results in the simultaneous arrival of both observer and ball at the landing spot. The authors analyzed the app roach behavior of 26 subjects in a ball-interception task with straight pat hs for both the subjects and the ball. Subjects moved at a velocity that ma intained a close-to-constant horizontal angular position of the ball with r espect to the end effector throughout the approach phase rather than a cons tant bearing angle with respect to their head. Velocity adaptations occurre d as a function of the changes in the angular velocity of the ball in such a way that a positive or negative angular velocity was canceled. Thus, an a ctor following the CBA strategy does not need to know where and when the ba ll will arrive (i.e., a predictive strategy), because reliance on the CBA s trategy ensures that he will make the appropriate adaptations that enable h im to arrive at the right place in the right time.