Abstract
Multiple processes contribute to sensorimotor adaptation. Explicit processes provide rapid, flexible compensation for sensorimotor perturbations, whereas implicit processes are characterized by a slower, nearly invariant response profile. Implicit processes operate outside of cognitive control and are therefore not expected to be sensitive to changes in attentional demands. However, it has been suggested that implicit and explicit processes interact in a push-pull manner, that is, deficits in one are offset by contributions from the other. From this perspective, increasing attentional demands should restrict the contributions of explicit processes, thereby enhancing implicit contributions. This suggests that implicit adaptation may counterintuitively be enhanced when attention is allocated to a secondary task. Participants performed a visuomotor rotation task with clamped visual feedback to isolate implicit adaptation. Under clamped feedback, the cursor indicated the radial position of the hand but was independent of the movement direction. Instead, the cursor followed a fixed path rotated 45° off target. The instructions were to ignore the task-irrelevant feedback and move directly to the target. Participants were randomly assigned to a single or dual task group. The single task group only performed the visuomotor rotation task; the dual task group concurrently performed the visuomotor rotation task and a secondary visual detection task. Visual stimuli were the same across groups. The hand angle relative to the target was computed to measure adaptation. Both groups showed implicit adaptation under clamped feedback characterized by a monotonic increase in hand angle and prolonged aftereffects. The dual task group showed a small, but consistent, increase in implicit adaptation, as indicated by greater hand angle under clamped feedback and stronger aftereffects. We suggest that the increase in implicit adaptation under divided attention is consistent with the idea that implicit and explicit processes operate in a push-pull manner. Further experiments are required to confirm this hypothesis.