Transition from an antiphase error-correction mode to a synchronization mode in mutual hand tracking.

Proactive motion in hand tracking and in finger bending, in which the body motion occurs prior to the reference signal, has been previously reported when a periodic target signal was shown to the subjects at relatively high frequencies. These phenomena indicate that the human sensory-motor system tends to choose an anticipatory mode rather than a reactive mode, when the target motion is relatively fast. The present research was undertaken to study what kind of mode appears in the sensory-motor system when two persons were asked to track the hand position of the partner at various mean tracking frequency. The experimental results showed that a transition from a mutual error-correction mode to a synchronization mode occurred in the same region of the transition frequency with the one from a reactive error-correction mode to a proactive anticipatory mode reported previously in the target tracking experiments of the single subjects. Present research indicated that synchronization of body motion occurred only when both of the pair subjects operated in a proactive anticipatory mode. We also presented mathematical models to explain the behavior of the error-correction mode and the synchronization mode.