The symmetry of interlimb transfer depends on workspace locations

We have previously shown that when both arms learn visuo-motor tasks within the shared midline workspace, transfer becomes asymmetrical: initial direction information only transfers from the nondominant to the dominant arm, whereas the final position information only transfers from the dominant to the nondominant arm. We now examine whether symmetry of interlimb transfer depends on the location of workspace provided for the two arms, by investigating the pattern of interlimb transfer when each arm adapts to a 30° rotation at its ipsilateral workspace. All subjects performed center-out reaching movements while adapting to a 30° rotation in the visual display. Half the subjects performed with the nondominant arm first and then the dominant arm, while the other half performed with the dominant arm first and then the nondominant arm. To assess transfer, naïve performance and the performance following opposite arm adaptation were compared for each arm separately. Our results indicate unambiguous transfer that is symmetrical: both arms benefited from opposite arm training in terms of initial direction control. In terms of final position information, neither arm benefited from opposite arm training. This clearly demonstrates that symmetry of interlimb transfer depends on the location of workspace provided for the two arms. Our findings suggest that when visuo-motor tasks are performed within a shared midline workspace, the nondominant controller is selectively inhibited from access to dominant controller information, due to a certain competition between the two limb/hemisphere systems that is introduced by the shared nature of the workspace.