Proprioceptive recalibration following prolonged training and increasing distortions in visuomotor adaptation

Reaching with misaligned visual feedback of the hand leads to reach adaptation (motor recalibration) and also results in partial sensory recalibration, where proprioceptive estimates of hand position are changed in a way that is consistent with the visual distortion. The goal of the present study was to explore the relationship between changes in sensory and motor systems by examining these processes following (1) prolonged reach training and (2) training with increasing visuomotor distortions. To examine proprioceptive recalibration, we determined the position at which subjects felt their hand was aligned with a reference marker after completing three blocks of reach training trials with a cursor that was rotated 30° clockwise (CW) for all blocks, or with a visuomotor distortion that was increased incrementally across the training blocks up to 70°CW relative to actual hand motion. On average, subjects adapted their reaches by 16° and recalibrated their sense of felt hand position by 7° leftwards following the first block of reach training trials in which they reached with a cursor that was rotated 30°CW relative to the hand, compared to baseline values. There was no change in these values for the 30° training group across subsequent training blocks. However, subjects training with increasing levels of visuomotor distortion showed increased reach adaptation (up to 34° leftward movement aftereffects) and sensory recalibration (up to 15° leftwards). Analysis of motor and sensory changes following each training block did not reveal any significant correlations, suggesting that the processes underlying motor adaptation and proprioceptive recalibration occur simultaneously yet independently of each other.