Generalization of sensory recalibration in the absence of motor adaptation


Previous work has demonstrated that motor adaptation occurs following reaches with altered visual feedback of the hand. It has also been shown that the sensory system is recalibrated, such that perception of hand position is shifted following training with a visuomotor distortion (Cressman and Henriques, 2009). In the current study we investigated how these changes in the motor and sensory systems are related by comparing how they generalize across the workspace. Subjects trained to reach to a single target (T1) with distorted hand-cursor feedback, such that they saw a cursor that was rotated 30° clockwise relative to their actual hand position. Following reach training trials, subjects reached to (1) the same target with no visual feedback of their hand; (2) the trained target from a novel start position located approximately 20 cm to the right of the trained start position (T2); and (3) a novel target located approximately 20 cm to the left of the trained target, from the trained start position (T3). Subjects were also required to estimate their felt hand position in two dimensions after moving out from both start positions in order to determine the position at which they perceived their hand was aligned with visual markers located at the same locations as the reach targets. Results indicated that subjects adapted their reaches to a greater extent to the trained target T1 than the novel targets (T2 and T3). In contrast, proprioceptive estimates revealed that subjects recalibrated their estimates of felt hand position to a similar extent at all three targets in the direction of the visual feedback provided. Taken together, the differences in generalization patterns for reach adaptation and proprioceptive recalibration suggest that motor and sensory changes arise independently, potentially due to different error signals present during reaches with altered visual feedback of the hand. 

Acknowledgments: Supported by NSERC