Interactions: timing and force control of finger-tapping sequences.

This study examined effects of combinations of intertap interval and muscle force on interactions between two factors in sequences of equally paced finger taps. 12 male college students tapped a force plate connected to strain gauges. Subjects firstly tapped the plate at a preferred pace and force for 12 sec. Next, subjects tapped the plate by half or double the preferred pace. A series of finger-tapping tasks the consisted of nine combinations of pace and force. Analysis showed that, although variations in intertap interval were considerably accurately controlled across conditions, those in peak forces were not. Movement timing of tapping sequences hence appeared to be independent of force control. For six of 12 subjects, on the other hand, positive correlations between spontaneous variations in intertap interval and in forces were noted. Then, although motor timing was independent of force control in controls of low pace and weak forces, there were strong interactions between the two factors under high pace conditions.