Invariant errors reveal limitations in motor correction rather than constraints on error sensitivity

Implicit sensorimotor adaptation is traditionally described as a process of error reduction, whereby a fraction of the error is corrected for with each movement. Here, in our study of healthy human participants, we characterize two constraints on this learning process: the size of adaptive corrections is only related to error size when errors are smaller than 6°, and learning functions converge to a similar level of asymptotic learning over a wide range of error sizes. These findings are problematic for current models of sensorimotor adaptation, and point to a new theoretical perspective in which learning is constrained by the size of the error correction, rather than sensitivity to error. Kim et al. report a study of implicit sensorimotor adaptation using task-irrelevant clamped visual feedback and find that learning is constrained primarily by the size of the error correction rather than sensitivity to error. The results present a challenge to current models of adaptation and suggest a new framework to guide new models of this process.