Generalization of reach adaptation and proprioceptive recalibration at different distances in the workspace

Studies have shown that adapting one's reaches in one location in the workspace can generalize to other novel locations. Generalization of this visuomotor adaptation is influenced by the location of novel targets relative to the trained location such that reaches made to novel targets that are located far from the trained target direction (i.e., ~22.5°; Krakauer et al. in J Neurosci 20:8916-8924, 2000) show very little generalization compared to those that are closer to the trained direction. However, generalization is much broader when reaching to novel targets in the same direction but at different distances from the trained target. In this study, we investigated whether changes in hand proprioception (proprioceptive recalibration), like reach adaptation, generalize to different distances of the workspace. Subjects adapted their reaches with a rotated cursor to two target locations at a distance of 13 cm from the home position. We then compared changes in open-loop reaches and felt hand position at these trained locations to novel targets located in the same direction as the trained targets but either at a closer (10 cm) or at a farther distance (15 cm) from the home position. We found reach adaptation generalized to novel closer and farther targets to the same extent as observed at the trained target distance. In contrast, while changes in felt hand position were significant across the two novel distances, this recalibration was smaller for the novel-far locations compared to the trained location. Given that reach adaptation completely generalized across the novel distances but proprioceptive recalibration generalized to a lesser extent for farther distances, we suggest that proprioceptive recalibration may arise independently of motor adaptation and vice versa.