Fractionated reaction time as a function of magnitude of force in simple and choice conditions.

The present study examined whether varying magnitude of force required to perform an isometric response influences fractionated reaction time in simple and choice conditions and whether reaction time and premotor time to initiate the response are shorter when force is selected freely by the subject than when it is selected by the experimenter. 20 subjects were required to react and produce a designated peak force as quickly and accurately as possible by squeezing a handle after a reaction signal. Four different magnitudes of force were 30, 50, and 70% of the maximum grip strength of the subjects and subject-selected magnitude of force. Reaction time and premotor time did not change across the range of forces examined in both simple and choice reaction-time conditions regardless of whether a desired force was selected by the experimenter or by the subject. These findings suggest that programming an isometric response may require a constant amount of time.