Interference underlies attenuation upon relearning in sensorimotor adaptation

Abstract

Savings refers to the gain in performance upon relearning. In sensorimotor adaptation, savings is tested by having participants adapt to perturbed feedback and, following a washout block during which the system resets to baseline, presenting the same perturbation again. While savings has been observed with these tasks, we have shown that the contribution from implicit adaptation, a process that uses errors to recalibrate the sensorimotor map, is attenuated upon relearning (Avraham et al., 2021). Here, we test the hypothesis that this attenuation is due to interference arising from the different relationship between the movement and the feedback during washout. Removing the perturbation at the start of the washout block typically results in a salient error signal in the opposite direction to that observed during learning. We first replicated the finding that implicit adaptation is attenuated following a washout period that introduces salient opposite errors. When we eliminated feedback during washout, relearning was no longer attenuated, consistent with the interference hypothesis. Next, we created a scenario in which the perceived errors during washout were not salient, falling within the range of motor noise. Nonetheless, attenuation was still prominent. Inspired by this observation, we tested participants with an extended initial experience with veridical feedback and found that this was sufficient to attenuate adaptation during the first learning block. This effect was context-specific and did not generalize to other movements. Taken together, the implicit sensorimotor adaptation system is highly sensitive to memory interference from a recent experience with a discrepant action-outcome contingency.

Significant statement Relearning refers to the situation in which a previously learned, but forgotten task, is re-introduced. Typically, performance is facilitated upon relearning. One exception is implicit adaptation, an error-based process in which the sensorimotor system compensates for external perturbations: For implicit adaptation, relearning is attenuated, a phenomenon at odds with models of motor learning that assume that error sensitivity increases with practice. Here, we demonstrate that attenuation upon relearning is the result of interference between competing memories. We show that the adaptation system is sensitive to interference when multiple memories are associated with similar movements. Indeed, interference is not limited to a memory of competing errors but is also observed during initial learning after prolonged experience with non-perturbed movements.