Table 1.

Experimental conditions

	Master finger(s)	Direction	Conditions
Flexion	I, M, R, L, IMRL	−Z = +n	5
RUdeviation	I, M, R, L, IMRL	±X = ±t	10
		Total	15

The master fingers (index I, middle M, ring R, and little L) were those that were explicitly instructed to produce force. For the flexion and radial/ulnar deviation (RUdeviation) tasks, subjects produced maximal force in either the normal (n) or tangential (t) direction, respectively (see Fig. 1). The five-flexion tasks included four single-finger tasks and two multi-finger tasks. The RUdeviation tasks were the same except that they were performed in +t and −t directions separately. Two repetitions of each of the 15 conditions were performed, yielding 30 trials per subject