Contrasting effects of adaptation to a visuomotor rotation on explicit and implicit measures of sensory coupling.

We previously investigated sensory coupling of the sensed positions of cursor and hand in a cursor-control task and found differential characteristics of implicit and explicit measures of the bias of sensed hand position toward the position of the cursor. The present study further tested whether adaptation to a visuomotor rotation differentially affects these two measures. Participants made center-out reaching movements to remembered targets while looking at a rotated feedback cursor. After sets of practice trials with constant (adaptation condition) or random (control condition) visuomotor rotations, test trials served to assess sensory coupling. In these trials, participants judged the position of the hand at the end of the center-out movement, and the deviation of these judgments from the physical hand positions served as explicit measure of the bias of sensed hand position toward the position of the cursor, whereas the implicit measure was based on the direction of the return movement. The results showed that inter-individual variability of explicitly assessed biases of sensed hand position toward the cursor position was less in the adaptation condition than in the control condition. Conversely, no such changes were observed for the implicit measure of the bias of sensed hand position, revealing contrasting effects of adaptation on the explicit and implicit measures. These results suggest that biases of explicitly sensed hand position reflect sensory coupling of neural representations that are altered by visuomotor adaptation. In contrast, biases of implicitly sensed hand position reflect sensory coupling of neural representations that are unaffected by adaptation.