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.

When subjects are presented with distorted visual feedback of their hand during a goal-directed movement (i.e. subjects view a cursor representing their hand that is rotated from their hand’s actual position while reaching in a virtual reality environment), they typically adapt their movements so that the cursor is brought to the target, thus reducing reaching errors. In addition to motor adaptation, it has recently been shown that reaching with distorted visual feedback of the hand results in sensory changes, such that proprioceptive estimates of hand position are shifted in the direction of the visual feedback (Cressman and Henriques 2009). The current study looked to establish how quickly these sensory changes arise while training to reach with distorted visual feedback of the hand. Additionally, by comparing sensory to motor changes across time, we looked to determine the relationship between their underlying processes. Subjects trained to reach to a single visual target while seeing a cursor that was aligned with their actual hand position (50 trials: aligned reach training), or rotated 30° clockwise (CW) relative to their actual hand position (150 trials: rotated reach training). Reach errors and proprioceptive estimates of felt hand position were assessed following the aligned reach training trials and at 7 different times during the rotated reach training trials by having subjects reach to the target without visual feedback, and provide estimates of the position of their hand relative to a visual reference marker respectively. Results revealed a slow change in proprioceptive estimates over the course of reach training with the rotated cursor relative to estimates after the aligned reach training, and in fact, significant sensory changes were not observed until after 70 trials. In contrast, reach adaptation showed a much steeper increase and significant adaptation after a limited number of reach training trials with a rotated cursor. These different time courses suggest that proprioceptive recalibration and reach adaptation arise due to separate neural processes.