Reaching movements in virtual reality depend on the seen avatar arm and not just the acting arm
Virtual reality (VR) offers unique opportunities to study behaviour by allowing the visual environment to be manipulated in ways otherwise impossible in the real world. A central theoretical question is how body-related visual information shapes movement control. Given right-handers' greater dexterity with the right arm, perhaps even seeing a right arm vs. a left arm may engage sensorimotor processes associated with more precise motor control. We examined reaching performance while participants used their own right or left arm to move the manipulandum of a KINARM robot to intercept static targets. Participants wore a VR head-mounted display, calibrated to the robot's physical workspace, in which they saw either the right or left arm holding and moving the manipulandum. The 2 x 2 design allowed for independent manipulation of the controlling arm and virtual arm displayed. As expected, reaches were faster and more accurate when controlled by the right arm. More interestingly, performance was also affected by the seen arm. Participants made straighter reaches when they saw a virtual right arm than a left arm, especially for the right controlling arm. These findings show that precise motor control relies not only on the arm that is actually moved and provides proprioceptive feedback, but also on the visual identity of the arm. The ability to modulate performance using visual features in VR opens new theoretical questions and opportunities for applications such as rehabilitation.