Visual-proprioceptive conflict resolution when applying contact forces

Although visual feedback dominates over proprioception during voluntary movements, we do not know how the control of contact forces is affected by either sensory system. We asked subjects to perform a planar reaching task while adapting to a visuomotor rotation which induced a conflict between vision and proprioception. After adapting movement control, the subjects’ hand position did not correspond to the displayed position. We found that when asked in that situation to exert an instructed force vector, subjects displayed systematic errors. We were able to account for these by assuming that subjects generated the same joint torques as if the hand were in the displayed rather than in the actual position. This suggests that the visual representation of hand position dominated over the proprioceptive representation. Importantly, this also demonstrated that adaptation being successful at compensating a visual perturbation of movement caused an impairment in the ability to generate contact forces.