The effects of different types of unlearning on savings following visuomotor adaptation

When humans encounter the same disturbance twice, they adapt to it faster during the second exposure. To examine how subconscious learning systems contribute to this savings process, previous studies have suppressed explicit awareness of the perturbation by gradually increasing its magnitude during initial learning. This has produced mixed effects, with some studies demonstrating faster relearning, and others observing no acceleration during relearning. Here, we examined whether these differences might be due to the nature of a de-adaptation period that separates two learning periods. To test this idea, we manipulated the magnitude of washout errors by de-adapting participants abruptly, gradually, or by removing feedback entirely. Empirical analyses indicated that the different classes of washout errors had a profound effect on savings: large washout errors nullified the ability to save, whereas small errors or the absence of error protected savings. Model-based analyses suggested that changes in learning rates were mediated by an increase in sensitivity to error that could be reversed by experience with oppositely oriented washout errors. This suggests that the experience of error produces both a facilitation of learning for similar errors and a reduction in learning for dissimilar errors. The latter can abolish the expression of savings following gradual adaptation.