Abstract
Reaching with a visuomotor distortion in a virtual environment leads to reach adaptation in the trained hand, and in the untrained hand. In the current study we asked if reach adaptation in the untrained (right) hand is due to transfer of explicit adaptation (EA; strategic changes in reaches) and/or implicit adaptation (IA; unconscious changes in reaches) from the trained (left) hand, and if this transfer changes depending on instructions provided. We further asked if EA and IA are retained in both the trained and untrained hands. Participants (n = 60) were divided into 3 groups (Instructed (provided with instructions on how to counteract the visuomotor distortion), Non-Instructed (no instructions provided), and Control (EA not assessed)). EA and IA were assessed in both the trained and untrained hands immediately following rotated reach training with a 40° visuomotor distortion, and again 24 hours later by having participants reach in the absence of cursor feedback. Participants were to reach (1) so that the cursor landed on the target (EA + IA), and (2) so that their hand landed on the target (IA). Results revealed that, while initial EA observed in the trained hand was greater for the Instructed versus Non-Instructed group, the full extent of EA transferred between hands for both groups and was retained across days. IA observed in the trained hand was greatest in the Non-Instructed group. However, IA did not significantly transfer between hands for any of the three groups. Limited retention of IA was observed in the trained hand. Together, these results suggest that while initial EA and IA in the trained hand are dependent on instructions provided, transfer and retention of visuomotor adaptation to a large visuomotor distortion are driven almost exclusively by EA.
Highlights
Reaching with altered visual feedback of the hand’s position in a virtual reality environment leads to motor adaptation in the trained hand and in the untrained hand [1,2,3,4]
The phenomenon of intermanual transfer of visuomotor adaptation has been studied in the lab by having participants reach to visual targets with a single hand while seeing a cursor on a screen that is misplaced relative to their actual hand position
While all participants were designated as aware of the visuomotor distortion based on their verbal responses, it is evident that their knowledge regarding the nature of the visuomotor distortion varied greatly between participants and across groups of participants
Summary
Reaching with altered visual feedback of the hand’s position in a virtual reality environment leads to motor adaptation in the trained hand and in the untrained hand [1,2,3,4]. The phenomenon of intermanual transfer of visuomotor adaptation has been studied in the lab by having participants reach to visual targets with a single hand while seeing a cursor on a screen that is misplaced relative to their actual hand position (e.g., the cursor’s trajectory is rotated relative to actual hand motion). Initial findings led to the proposal that intermanual transfer of visuomotor adaption arises because the underlying processes are effector independent [see 11] Both hands have shared access to a sensorimotor map that has been updated implicitly (i.e., unconsciously) through error-based motor learning, such that motor commands have been adapted to minimize the difference between predicated and actual sensory feedback experienced [12]. These results suggest that the two hands do not have the same access to the new sensorimotor mapping and/or that additional learning processes [see 13] may differentially contribute to visuomotor adaptation in the trained and untrained hands
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