Memories of motor adaptation do not necessarily decay with behavioral unlearning

Motor adaptation reshapes behaviors to habituate novel predictable demands caused by dramatic changes in our body (or environment). In the absence of error signals, behaviors rapidly return to the manner before adaptation. It is still in debate whether this behavioral unlearning is due to memory decay. Recent studies suggested that unlearning may be related to the detection of a context change between adaptation phase and error-absent phase. This context-dependent idea is extended in the present study, which examined the motor adaptation in a ball-tossing task. To facilitate the manipulation of the task and the measurement of the behavior, this tossing task was conducted in a virtual environment. Experiment 1 found that unlearning was more likely to occur when the context in the adaptation phase was less similar to that in the error-absent phase. Experiment 2 further demonstrated that the memory of motor adaptation can bias behavior even after behavioral unlearning. Experiment 3 confirmed that the results in Experiment 1 and 2 were not artifacts. These findings indicate that memories of adaptation are independent of behavioral unlearning, and the contextual similarity between adaptation and error-absent phase determines the unlearning rate.