Generalization of Motor and Sensory Changes in Motor Learning

This dissertation examines the generalization of motor and sensory changes in motor learning. Chapter two describes the process of intermanual transfer of reach adaptation and proprioceptive recalibration. We exposed participants to a laterally translated cursor while reaching with one hand to three targets, and then we measured reach aftereffects and changes in felt hand position for the trained and untrained hand. We found reach adaptation transfer from right to left hand and no transfer of proprioceptive recalibration. This suggests that the intermanual transfer for motor adaptation is hand-dependant, and proprioceptive recalibration is specific to the trained hand. Chapter three describes the generalization patterns of reach adaptation and proprioceptive recalibration across different distances. Reach aftereffects and changes in estimates of hand position were measured following reach-training with a rotated visual feedback of the hand to a single target distance. We found that reach adaptation and proprioceptive recalibration transfer across near and far novel distances. However, proprioceptive recalibration generalization was significantly smaller at far novel locations. This suggests that, unlike motor adaptation, the extent of sensory changes generalization is distance-dependent. Chapter four describes the contribution of proprioceptive recalibration and updated efference-based sensory predictions in motor adaptation and changes in hand localization. We exposed our participants to only visual-proprioceptive discrepancy by removing volitional movements and having a robot move their hand passively. Then, we examined changes in hand localization in two hand movement conditions, i.e., active (self-generated) and passive (robot-generated). Results showed no significant difference in hand localization changes between active and passive conditions. This suggests changes in hand localization reflect mainly proprioceptive recalibration of the hand rather than updates in efference-based sensorypredictions, and entirely on proprioceptive recalibration when training does not include any volitional movements. Additionally, in Chapter four, we examined how reach adaptation and proprioceptive recalibration generalized across different directions in the workspace. We found that reach aftereffects generalized to neighboring novel targets in a pattern similar to proprioceptive recalibration generalization pattern. This suggests that some of the reach adaptation reflect proprioceptive changes. Our findings provide insight into the characteristics of proprioceptive recalibration and how this process influences motor learning. This should be taken into consideration when designing motor adaptation/learning paradigms, teaching a motor skill or designing a movement rehabilitation protocol.