Concurrent adaptation to opposing visuomotor rotations by varying hand and body postures.

When reaching towards objects, the human central nervous system (CNS) can actively compensate for two different perturbations simultaneously (dual adaptation), though this does not simply occur upon presentation. Dual adaptation is made more difficult when the desired trajectories and targets are identical and hence do not cue the impending perturbation. In cases like these, the CNS requires contextual cues in order to predict the dynamics of the environment. Not all cues are effective at facilitating dual adaptation. In two experiments, we investigated the efficacy of two contextual cues that are intrinsic to the CNS, namely hand as well as body posture in concurrently adapting to two opposing visuomotor rotations. For the hand posture experiment, we also look at the role of extended training. Participants reached manually to visual targets with their unseen hand represented by a cursor that was rotated either 30° clockwise or counterclockwise, determined randomly on each reach. Each rotation was associated with a distinct hand posture (a precision or power grip, respectively) in one experiment and a distinct body rotation (10° leftward or rightward turn of the seat, respectively, while fixating straight) in the second experiment. Critically, the targets (and thus, the required cursor trajectories) were identical in both rotations. We found that how people held the tool or oriented their body while reaching is sufficient for concurrently adapting separate visuomotor mappings such that over time, reach errors significantly decrease. Extended practice did not lead to further benefits though. These findings suggest that when the required cursor movements are identical for different visuomotor mappings, dual adaptation is still possible given sufficient intrinsic contextual cues.