The Influence of Awareness on Explicit and Implicit Contributions to Visuomotor Adaptation to Different Rotation Sizes

Abstract

Explicit and implicit processes play a role in visuomotor adaptation. (Bond & Taylor, 2015; Werner et al, 2015). The purpose of the current experiment was to investigate the potential contributions of explicit and implicit processes to visuomotor adaptation when awareness was manipulated directly and indirectly. To manipulate the degree of awareness directly, participants were assigned to a Strategy or No-Strategy group, in which they were made aware or remained unaware of the distortion respectively. They were then further subdivided into groups to train with a large (60°), medium (40°) or small (20°) visuomotor distortion, such that participants could become aware of the distortion indirectly with increasing sizes. All participants performed a reaching task to three targets with a cursor that was rotated clockwise relative to their hand by the assigned degrees, and then completed a series of no-cursor reaches without visual feedback to establish the contribution of explicit and implicit processes to visuomotor adaptation. Within the no-cursor reaching trials, the contribution of explicit and implicit processes to visuomotor adaptation were determined by having subjects reach (i) with any strategies they had gained during training (explicit + implicit processes), and (ii) as they did before training with the cursor rotation (implicit processes). Our results showed that the contribution of implicit processes to visuomotor adaptation was greater in the No-Strategy group compared to the Strategy group. Moreover, implicit processes took time to develop, and decayed following a 5-minute break. In contrast, the contribution of explicit processes was greatest in the Strategy group, and increased with rotation size in the No-Strategy group. Explicit contributions also remained consistent over Blocks, as well as when re-tested following a 5-minute break. Thus, the results of the current experiment indicate that there are notable differences in explicit and implicit contributions to visuomotor distortions depending on if, and how participants become aware of the perturbation. The results also highlight the importance of instructions when evaluating reaching performance in aftereffect trials, as they can modulate reaching errors observed.