Abstract
Motor adaptation relies on implicit and explicit learning systems. Although the extent of implicit reach aftereffects is explored, less is known about the rate it emerges in visuomotor adaptation Here, we measured the time courses of implicit reach aftereffects, measured after every single training trial, as a function of the size of the perturbation, and as a function of delay in terminal feedback. Using exponential fits to the data, we found that the asymptotes of implicit reach aftereffects increased with larger rotation sizes, while the relative rates of change decreased. However, in absolute terms, the first trial elicited ~2.5° of change in all conditions, suggesting the rate of change in response to the perturbation was independent of size. Aiming trials to measure explicit awareness in late training demonstrated a greater explicit contribution for larger perturbations. Therefore, we explored the effect of continuous aiming compared to only aiming at the end, which elucidated a higher rate but lower extent of implicit adaptation for a 45° rotation. Also, the continuous aiming group exhibited 80% greater explicit strategy use, with the onset of cognitive strategy emerging only slightly faster than implicit aftereffects. Despite studies suggesting that feedback delay leads to only cognitive strategy, we found that intervening reach aftereffects again emerged quite quickly and to a similar extent as that produced without delay. These results show that the unconscious component of learning, when directly tested during classical visuomotor adaptation, is quite robust and quickly emerges across various visuomotor adaptation paradigms.
