Visual cues signaling object grasp reduce interference in motor learning

Abstract

Recent motor learning studies show that human subjects and nonhuman primates form neural representations of novel mechanical environments and associated forces. Whereas proficient adaptation is seen for a single force field, when faced with multiple novel force environments, movement performance and in particular the ability to switch between different force environments declines. It is difficult to reconcile these findings with the notion that primates can proficiently switch between multiple motor skills. Conceivably, particular kinds of sensory, cognitive, or perceptual contextual cues are required. This study examined the effect of visual feedback on motor learning, in particular, cues that simulated interaction with a virtual object. A robot arm was used to deliver novel patterns of forces (force fields) to the limb during reaching movements. We tested the possibility that subjects transition more easily between novel forces and their sudden absence when they are accompanied by visual cues that relate to object grasp. We used a virtual display system to present subjects with different kinds of visual feedback during reaching, including illusory feedback, indicating grasp of a virtual object during reaching in the force field, and object release in the absence of forces. Throughout the experiment, subjects in fact maintained grasp of the robot. We found that, indeed, the most effective visual cues were those associating the force field with grasp of the virtual object and the absence of the force field with release of the object. Our findings show more broadly that specific visual cues can protect motor skills from interference.