Reach After-Effects as a Measure of Implicit Learning After Abrupt and Gradual Visuomotor Rotations

Abstract

Humans have an incredible ability to learn new movements and adapt our movements to changing circumstances. Visuomotor adaptation can be observed when subjects reach out to a target holding a cursor with their unseen hand while the visual feedback of the cursor's motion is manipulated. Motor adaptation engages both implicit and explicit learning processes. Some measures of motor adaptation are considered to measure primary implicit learning, such as reach after-effects, which occur when subjects continue to make deviated reaches after the cursor's rotation has been removed. In this study, we look at how a higher contribution of implicit learning influences visuomotor adaptation as measured in reach after-effects and retention. We changed the contribution of implicit learning by introducing the visual feedback of the cursor's rotation either abruptly or gradually. An abrupt change in cursor's motion is more likely to be recognized by subjects, thus, it should evoke more explicit learning and a gradual change should evoke more implicit learning. We expect greater reach after-effects and retention of learned hand movements following gradual rotation training. Participants (N=27) did both a gradual and abrupt version of the same visuomotor adaptation task in a counterbalanced order. Contrary to our expectations, we found no difference between reach after-effects and retention in the two conditions. Perhaps an even larger, more explicit deviation would be necessary to reveal relative contributions of explicit and implicit adaptation to gradually and abruptly introduced visuomotor perturbations.