Rhythmic Control of a Push-Pull Movement

Rhythmic movement control was investigated in a ‘push-pull’ movement. The subject was asked to move a handle on the smooth rails forward (push) and backward (pull) alternatively between two plates and to synchronize each push and pull movement with periodic sound signals (1 to 5.8 Hz). All subjects synchronized one cycle of the push-pull movement accurately and steadily with two periods of signals over all input frequencies above 2 Hz. As for two components of the movement, i.e., the push and the pull, 9 out of 10 subjects (using the preferred hand) controlled each of them rhythmically so as to deviate equally from the signal towards the opposite directions, but 2.5 and 5 Hz were the exceptional regions at which the rhythmicity disappeared. These characteristics were fundamentally the same as those of finger tapping. It is concluded that the human alternating movement is controlled through the formation of specific rhythm and that this rhythm has intrinsic instabilities around 5, 2.5, … Hz.