Passive vs. active control of rhythmic ball bouncing: the role of visual information.

The simple task of bouncing a ball on a racket offers a model system for studying how human actors exploit the physics and information of the environment to control their behavior. Previous work shows that people take advantage of a passively stable solution for ball bouncing but can also use perceptual information to actively stabilize bouncing. In this article, we investigate (a) active and passive contributions to the control of bouncing, (b) the visual information in the ball's trajectory, and (c) how it modulates the parameters of racket oscillation. We used a virtual ball bouncing apparatus to manipulate the coefficient of restitution alpha and gravitational acceleration g during steady-state bouncing (Experiment 1) and sudden transitions (Experiment 2) to dissociate informational variables. The results support a form of mixed control, based on the half-period of the ball's trajectory, in which racket oscillation is actively regulated on every cycle in order to keep the system in or near the passively stable region. The mixed control mode may be a general strategy for integrating passive stability with active stabilization in perception-action systems.