Pointing movement visually controlled through a video display: adaptation to scale change

This study concerns the adaptation of motor system when the production of m ovement was visually controlled through a video display. The subjects had t o perform a pointing movement in two visual-feedback conditions: they could see the displacement of their hand or only the final location of the hand on the video-screen. By changing the zoom of the camera, the amplitude of t he movement perceived on the screen was increased, decreased or held equal to the actual movement. Results showed that the movement adapted quickly to the apparent distance changes. In the full visual-feedback condition, the adaptation was smaller in magnitude than in the partial visual-feedback con dition. Even though the actual movement was always the same, the subjects t hought they carried out different movements. Therefore, the subjects did no t use kinematic information provided by the kinaesthetic system but essenti ally visual information furnished by the video-screen. Taken together, thes e results show that adaptation to scale changes does not allow the achievem ent of the perception of a single working space but seems rather specific t o each scale.