Somatosensory Changes Accompanying Motor Learning

Abstract

We describe experiments that test the hypothesis that changes in somatosensory function accompany motor learning. We estimated psychophysical functions relating actual and perceived limb position before, and after two kinds of motor learning: directional motor learning (learning to reach in the presence of novel forces applied by a robot), and non-directional learning (learning to reach quickly and accurately to visual targets, without forces). Following force-field learning, sensed limb position shifted reliably in the direction of the applied force. No sensory change was observed when the robot passively moved the hand through the same trajectories as subjects produced during active learning. Perceptual shifts are reflected in subsequent movements: following learning, movements deviate from their pre-learning paths by an amount similar in magnitude and in the same direction as the perceptual shift. After non–directional motor learning in the absence of forces, we observed improvements in somatosensory a...