Short-term motor learning involves two distinct adaptive processes operating on different timescales. These processes interact to explain various phenomena in motor adaptation, including savings, anterograde interference, spontaneous recovery, and rapid unlearning. The study demonstrates that within minutes, two fast-acting processes drive motor adaptation: one responds weakly to error but retains information well, while the other responds strongly but has poor retention. This two-state system predicts spontaneous recovery if error feedback is clamped at zero after an adaptation-extinction training episode. The researchers used a novel paradigm to confirm this prediction in human motor learning of reaching. They found that the interaction between these processes provides a unifying explanation for several different phenomena in motor adaptation. The results suggest that motor adaptation depends on at least two distinct neural systems with different sensitivity to error and retention rates. The study also shows that the multi-rate model accounts for several well-known phenomena in motor adaptation, including anterograde interference, rapid unlearning, and rapid downscaling. The model predicts that the time constant for adaptation is affected by the specifics of the training regimen. The multi-rate model also explains spontaneous recovery, where motor output temporarily rebounds toward the initial learning level when error is clamped at zero. The findings suggest that multiple learning modules contribute to force-field adaptation within minutes of training. The slow learning module accounts for more than half of the total adaptation by the end of the first learning block, indicating its significant role in short-term motor adaptation. The study also highlights the importance of the cerebellum in motor adaptation, as patients with cerebellar lesions show deficits in motor adaptation rates. The research provides insights into the neural mechanisms underlying motor learning and memory formation, emphasizing the role of different timescales in motor adaptation. The study underscores the complexity of motor learning and the need to understand the interplay between different processes to fully comprehend motor memory formation.Short-term motor learning involves two distinct adaptive processes operating on different timescales. These processes interact to explain various phenomena in motor adaptation, including savings, anterograde interference, spontaneous recovery, and rapid unlearning. The study demonstrates that within minutes, two fast-acting processes drive motor adaptation: one responds weakly to error but retains information well, while the other responds strongly but has poor retention. This two-state system predicts spontaneous recovery if error feedback is clamped at zero after an adaptation-extinction training episode. The researchers used a novel paradigm to confirm this prediction in human motor learning of reaching. They found that the interaction between these processes provides a unifying explanation for several different phenomena in motor adaptation. The results suggest that motor adaptation depends on at least two distinct neural systems with different sensitivity to error and retention rates. The study also shows that the multi-rate model accounts for several well-known phenomena in motor adaptation, including anterograde interference, rapid unlearning, and rapid downscaling. The model predicts that the time constant for adaptation is affected by the specifics of the training regimen. The multi-rate model also explains spontaneous recovery, where motor output temporarily rebounds toward the initial learning level when error is clamped at zero. The findings suggest that multiple learning modules contribute to force-field adaptation within minutes of training. The slow learning module accounts for more than half of the total adaptation by the end of the first learning block, indicating its significant role in short-term motor adaptation. The study also highlights the importance of the cerebellum in motor adaptation, as patients with cerebellar lesions show deficits in motor adaptation rates. The research provides insights into the neural mechanisms underlying motor learning and memory formation, emphasizing the role of different timescales in motor adaptation. The study underscores the complexity of motor learning and the need to understand the interplay between different processes to fully comprehend motor memory formation.