Implicit guidance to dynamic stability in rhythmic ball bouncing

While rhythmically bouncing a ball with a racket appears to be a simple task, it requires precise perceptually-guided coordination between racket and ball to be successful. In this task, subjects manipulate a real table tennis racket to rhythmically bounce a virtual ball to a target height in a 2D virtual environment. Stability analyses of the mathematical model of a bouncing ball showed that dynamic stability is indicated when the racket contacts the ball during the decelerating portion of the racket´s upward movement [1-3]. Dynamically stable performance implies that small errors converge back to stable performance without requiring active corrections, hence constituting a “smart” solution that skilled performers adopt. Previous studies have shown that practice is needed in order to find this dynamically stable solution. This study examined if a suitably designed perturbation could guide novice subjects to hit with negative racket acceleration earlier in practice. The perturbation was applied to racket velocity at contact. Instead of using the actual racket velocity at contact, the calculation used the velocity value 50 ms prior. Results show that humans can be guided to exploit dynamic stability in coordinative behavior early in practice and maintain dynamic stability even when the guidance is removed.