Adaptation and spatial generalization to a triaxial visuomotor perturbation in a virtual reality environment.

We explored visuomotor adaptation and spatial generalization of three-dimensional reaching movements performed in a virtual reality environment. We used a multiphase learning paradigm. First, subjects performed reaching movements to six targets without visual feedback (VF) (pre-exposure phase). Next, participants aimed at one target with veridical VF (baseline phase). Immediately after, they were required to adapt their movements to a triaxial visuomotor perturbation (horizontal, vertical, and sagittal translations) between actual hand motion and VF of hand motion in the virtual environment (learning phase). Finally, subjects aimed at the same targets as in the baseline (aftereffect) and pre-exposure phases (generalization) without VF (post-exposure phase). The results revealed spatial axis-dependent visuomotor adaptation capacities. First, subjects showed smaller intertrial variability along the horizontal compared to the sagittal and vertical axes during the baseline and learning phases. Second, although subjects were unaware of the visual distortion, they adapted their movements to each component of the triaxial perturbation. However, they showed reduced learning rate and less persistent adaptation (aftereffect) along the vertical than the horizontal and sagittal axes. Similarly, subjects transferred the newly learned visuomotor association to untrained regions of the workspace, but their average level of generalization was smaller along the vertical than the horizontal and sagittal axes. Collectively, our results suggest that adapting three-dimensional movements to a visual distortion involves distinct processes according to the specific sensorimotor integration demands of moving along each spatial axis. This finding supports the idea that the brain employs a modular decomposition strategy to simplify complex multidimensional visuomotor tasks.