The effect of conflicting sensorimotor memories on optimal force strategies was explored. Subjects operated a virtual object controlled by a physical handle to complete a simple straight-line task. Perturbations applied to the handle induced a period of increased error in subject accuracy. After two blocks of 33 trials, perturbations switched direction, inducing increased error from the previous trials. Subjects returned after a 24-hour period to complete a similar protocol, but beginning with the second context and ending with the first. Interference from the first context on each day caused an increase in initial error for the second (P < 0.05). Following the rest period, subjects showed retention of the sensorimotor memory from the previous day through significantly decreased initial error (P = 3x10-6). However, subjects showed an increase in forces for each new context resulting from a sub-optimal motor strategy. Higher levels of total effort (P < 0.05) and a lack of separation between force values for opposing and non-opposing digits (P > 0.05) indicated a strategy that used more energy to complete the task, even when rates of learning appeared identical or improved. Two possible mechanisms for this lack of energy conservation have been proposed.

The interaction between visual fixations during planning and performance in a

dexterous task was analyzed. An eye-tracking device was affixed to subjects during

sequences of null (salient center of mass) and weighted (non salient center of mass) trials

with unconstrained precision grasp. Subjects experienced both expected and unexpected

perturbations, with the task of minimizing object roll. Unexpected perturbations were

controlled by switching weights between trials, expected perturbations were controlled by

asking subjects to rotate the object themselves. In all cases subjects were able to

minimize the roll of the object within three trials. Eye fixations were correlated with

object weight for the initial context and for known shifts in center of mass. In subsequent

trials with unexpected weight shifts, subjects appeared to scan areas of interest from both

contexts even after learning present orientation.