Absence of after-effects for observers after watching a visuomotor adaptation.

We tested whether observational practice would elicit after-effects in a normal environment following observation of an actor performing in a perturbed visuomotor environment. Two actor groups (with and without vision of the hand) practised reaching to visual targets with the cursor rotated 30 degrees to the actual hand movement. An observer group viewed this adaptation. Observers demonstrated significant learning when they subsequently performed the aiming task in the perturbed environment. However, different from both actor groups, observers did not show after-effects in the normal visuomotor condition. Our findings imply that there is a qualitative difference in the processes between observational and physical practice and suggest that physical exposure is required to update an internal model of the visuomotor environment.