The cost of correcting for error during sensorimotor adaptation

Significance Improving the process of learning from error can play a critical role in applied settings such as rehabilitation. Previous work has generally focused on reward as a variable that may modulate learning. However, in response to an erroneous movement, the nervous system often engages a reflex that corrects for that error, thus expending time and energy. Here, we modulated this cost of error and found that increasing the cost increased how much the brain learned from error. Thus, the landscape of the loss associated with the act of correcting for error regulates the rates of sensorimotor learning. Learning from error is often a slow process. In machine learning, the learning rate depends on a loss function that specifies a cost for error. Here, we hypothesized that during motor learning, error carries an implicit cost for the brain because the act of correcting for error consumes time and energy. Thus, if this implicit cost could be increased, it may robustly alter how the brain learns from error. To vary the implicit cost of error, we designed a task that combined saccade adaptation with motion discrimination: movement errors resulted in corrective saccades, but those corrections took time away from acquiring information in the discrimination task. We then modulated error cost using coherence of the discrimination task and found that when error cost was large, pupil diameter increased and the brain learned more from error. However, when error cost was small, the pupil constricted and the brain learned less from the same error. Thus, during sensorimotor adaptation, the act of correcting for error carries an implicit cost for the brain. Modulating this cost affects how much the brain learns from error.