Abstract
Learning in sensorimotor adaptation tasks has been historically viewed as solely an implicit learning phenomenon. However, recent findings suggest that implicit adaptation is heavily constrained, calling into question its utility in motor learning, and the theoretical framework of sensorimotor adaptation paradigms. These inferences have been based on results from single bouts of training, thus, it is possible that implicit adaptation processes supersede explicit re-aiming strategies over repeated practice sessions. We tested this by dissociating the contributions of explicit re-aiming strategies and implicit adaptation over five consecutive days of training. Implicit adaptation plateaued at a value far short of complete learning. We sought to determine if these constraints on implicit adaptation extend to another sensorimotor task, mirror reversal. Implicit adaptation was inappropriate for mirror reversal and became suppressed during training. We suggest that the implicit adaptation process studied in sensorimotor adaptation paradigms cannot support long-term motor skill learning.
Significance Statement Adaptation to visually perturbed movements has been used as a model for understanding motor control and, potentially, motor skill acquisition. Learning in these tasks has traditionally been interpreted as the result of implicit adaptation processes, as evidenced by aftereffects following exposure. However, recent research has revealed multiple learning processes involved in motor learning and, when isolated, implicit adaptation processes are highly constrained. In this set of studies, we find that implicit adaptation cannot fully account for learning in adaptation tasks, such as the visuomotor rotation and mirror reversal tasks, even following several days of training. In fact, implicit adaptation can be counterproductive to learning. These findings question the utility of implicit adaptation processes to motor learning more broadly.
Footnotes
The authors declare no competing interests, financial or otherwise.
Experiment 2 Results updated to clarify purpose of model. Discussion updated with cleaner theoretical analysis of the differences in the underlying computational demands of mirror and rotation (including Lillicrap et al., 2013). A Significance Statement was added.