Despite our body will not stay stable because there are various internal and/or external fluctuation, we can perform several physical activities with higher accuracy. This would imply that our motor system is equipped with some mechanism for compensating these perturbations automatically. Recently, several visuomotor studies demonstrated that visual background motion during target reaching induces a reflexive manual response with ultra-short latency (manual following response). Although the function is still unclear, this is assumed to be a candidate of automatic compensating system for the motor error caused by body fluctuation because visual background motion varied according to the self (body) motion in the real world.
　To make a better understanding of motor-error compensation mechanism in sport, we examined the adaptive inhibition of the quick visuomotor response which occurs when the response was evoked iteratively. In a first experiment, participants required correctly reaching to visual target represented on the screen (240 trials), and were perturbed by the visual background motion which would evoke a quick response of reaching arm. In next experiment, the participants were asked to perform a visualmotion discrimination-reaction task which using visual background motion (120 trials), following reaching task (60 trials). And then, they asked to perform additional reaching task (60 trials). The changes in the amplitudes of manual response throughout each experiment were compared. In the result, the mean amplitude was significantly decreased with the repetition of reaching in the first experiment, but not in the second experiment. The results obviously suggested that the frequency of exposure to the background visual motion is not a determinative factor for the inhibition of the response amplitude. Rather, top-down suppression by higher brain area might be responsible for the amplitude inhibition.

DESCENTE SPORTS SCIENCE Vol. 34/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE