Decay of prism aftereffects under passive and active conditions.

In prism adaptation, subjects adapt to new visuospatial coordinates imposed by wedge prisms that laterally displace the visual field. During this process, subjects develop and store new visuomotor coordinates in order to compensate for the displacement of visual stimuli. After the prisms are removed, subjects show an aftereffect in the opposite direction of the original perturbation. The aftereffect is a manifestation of the recently stored information. In the present article, we were interested in studying the properties of the aftereffect. Specifically, we investigated the fate of the aftereffect under active conditions with motor reafferences but without visual input, and during passive conditions without visual or motor reafferences. The results in the motor active condition show that motor reafference (proprioceptive or corollary discharge information) led to a faster, but incomplete, aftereffect decay. The results in the passive condition show a bimodal aftereffect behavior, with a fast decay within the initial minutes, followed by a sustained aftereffect up to 20 min later. These data suggests that two different memory processes may contribute to the aftereffect, one showing a fast decay mainly within 1 min, and another that shows a stable endurance for more than 20 min. Copyright 2004 Elsevier B.V.