Visuomotor Adaptation: Dependency on Motion Trajectory

In order to pick up an object, its visual location must be converted into the appropriate motor commands. Introducing a discrepancy between the seen and felt locations of the object (e.g., via prism goggles) initially impairs the ability to touch it. The sensory system rapidly adapts to the discrepancy, however, returning perception and performance to near normal. Subsequent removal of the discrepancy leads to a renewed performance decrement - a negative aftereect (NAE). It is generally believed that the process of adaptation consists primarily of \recalibrating" the transformation between the visual and proprioceptive perception of spatial location (Bedford, The psychology of learning and motivation, 1999). According to such a purely perceptual account of adaptation, the movement to reach the object is not important. If, however, the transformation from perception to action is altered, then it will be dependent on motion - i.e. changing motion parameters will reduce or eliminate the NAE (see also Martin et al., Brain, 1996). According to our hypothesis spatial visuomotor information is distributively stored and changed by prism adaptation and it is not based on a centrally organized spatial information system. We conducted seven experiments consisting of four blocks each, in which participants had to touch a cross presented at eye level on a touch screen. In the rst block the participants were introduced and familiarized with the experiment. Blocks two and four were pre and post tests to measure the NAE produced during the dierent experimental conditions in block 3 in which the participants were wearing prism goggles: we tested the eects of dierent trajectories, dierent starting points, weight, vertical generalization and dierent types of feedback. A total transfer from an adapted to a non-adapted condition didn't turn up in any of our experiments, although the trajectories where highly identical in some of them. It rather seems that newly learned spatial information in prism adaptation experiments is stored and retrieved distributively for dierent extremities, for dierent trajectories and for dierent stress/strain conditions (e.g. weight). Furthermore, transfer seems to become weaker with bigger dierences in location. Therefore we conclude that no visual \recalibration" is taking place but a relearning of distributetively organized parameters of visuomotor coordination