Measures of Implicit and Explicit Adaptation Do Not Linearly Add

Abstract Moving effectively is essential for any animal. That’s why many different kinds of brain processes likely contribute to learning and adapting movement. How these contributions are combined to shape behavior is unknown. Nevertheless, the field of motor adaptation has been working under the assumption that measures of explicit and implicit motor adaptation can simply be added in total adaptation – without testing this assumption. Here we put this additivity assumption to the test in various ways, but we find that measures of implicit and explicit adaptation are not additive. This means that future studies should measure both implicit and explicit adaptation directly. It also challenges us to disentangle how various motor adaptation processes combine when producing movements, and may have implications for our understanding of other kinds of learning as well.(data and code: https://osf.io/kr5eh )