Roll of Rhythmic Component in Proactive Controll of Human Hand

Evolutionally, the strategy of catching prey should have been important to survive in constantly changing environment. Prediction mechanism should have developed to compensate the delay of sensory-motor system. In previous study, "proactive control" was found, in which motion of hands preceded the virtual moving target. The results implied that the positive phase shift of the hand motion represents the proactive nature of the visual-motor control system to minimize the transient error of the hand motion when the target changes unexpectedly. In our study, visual target moves in circle (13cm in diameter) in computer screen, and each subject is asked to keep track with the target motion in circle by the motion of a cursor. As frequency of target increases, rhythmic component in velocity of cursor was found in spite of the fact that velocity of target is constant. The generation of rhythmic component cannot be explained by only feedback mechanism for the phase shift of target and cursor in sensory-motor system. Therefore, it implies that rhythmic component was generated to predict the velocity of target, which is feed forward mechanism in sensory-motor system. In this research, we discuss the generation of rhythmic component and its roll in feed forward mechanism.