Motor Performance and Induced Muscular Tension

Abstract

Forty-six subjects were each tested on a ball-snatch task at five different preliminary tension levels (0, 5, 10, 15, and 20 pounds). It was hypothesized that motor performance would follow an inverted U-curve trend with increases in muscular tension. Reaction time followed the hypothesized trend; 15 pounds of tension produced the fastest response. Movement time, however, was not facilitated; instead there was a linear trend toward slower speed with increasing tension.     

Guiding movements with internal representations: a reach-and-grasp task

We investigated participants' ability to use internal representations of the environment to guide prehensile movements, when visual feedback was not available. Reaching and grasping performed with concurrent visual feedback was compared to conditions in which participants actively formed spatial images and passively encoded images from visual presented information. Movement times, the proportion of time spent after peak velocity and peak apertures, were greater when concurrent visual feedback was unavailable. Movement times increased as a function of premovement occlusion length, with passively encoded images resulting in shorter movement durations than actively formed images. The findings indicated that participants adapted their movement trajectories to compensate for the degradation of stored spatial information, when concurrent visual feedback was not available.     

The effects of task constraints on the organization of interception movements

In the light of the intensity coupling effects reported in the literature, subjects' capacities for independently controlling the absolute velocity of their movement at the point of interception was evaluated by asking them to learn to propel orthogonally approaching balls, varying in their speed of approach, into target boxes placed at various distances from the interception point. As required for successful accomplishment of the task, movement velocity was found to be adapted to the distance to be covered, with the near target giving rise to lower velocities and the far target giving rise to higher velocities even when the conditions were presented in random order. Nevertheless, even though target distance accounted for a substantial proportion of the total variance, a small but significant effect of ball approach speed on movement velocity was found, suggesting that intensity coupling is a persistent but modulable phenomenon in interception tasks.