Dual adaptation to opposing visuomotor rotations with similar hand movement trajectories

Abstract

This research explored specific contextual cues that might facilitate human motor learning. Using a dual adaptation task, humans performed manual reaches to visual targets while experiencing a 30° clockwise or counterclockwise rotation, which randomly alternated between trials, of a seen cursor representing their unseen hand. Groups had different cues to distinguish between rotations: 'Cue' (colours and shapes), 'Workspace' (target locations) and 'Workspace with Cue' (combination of cues). Importantly, the workspace groups required similar hand movement trajectories to accurately acquire pairs of targets. Our data show that only the 'Workspace' and 'Workspace with Cue' groups, but not 'Cue' group, adapted to both rotations concurrently (dual adaption). These findings suggest that colour and shape cues, even when integrated with the end-effector and targets, do not facilitate dual adaptation. However, target separation is sufficient to facilitate dual adaptation, even when hand movement trajectories are similar. Interestingly, adaptation was less complete when required hand trajectories were completely overlapping for pairs of targets (versus being similar), suggesting an important role for the motor system as well. Nonetheless, the location of targets and consequent differences in motor planning may play a larger role in facilitating adaptation than previously thought.