Open Collections

Abstract

Sensorimotor adaptation enables us to recalibrate movements to changes in body and environment, a process studied in visuomotor rotation tasks involving reaching movements with rotated cursor feedback. Adaptation is thought to arise primarily through sensory prediction errors but is also impacted by target errors and reinforcement mechanisms. A challenge for researchers has been to isolate how these processes impact adaptation. Learning from sensory prediction errors has been linked to cerebrocerebellar loops, encoding the discrepancy between predicted and actual sensory feedback. Cortical circuits have been associated with target errors, which represent the direction and magnitude of errors to a reaching target. Supplementing sensory feedback with reward aids motor performance via mesolimbic reward circuitry. A concern with attempts to distinguish across these 3 processes relates to how reward has been manipulated in these tasks. Some researchers have provided extrinsic rewards (e.g., money), whereas others relied on intrinsic rewards (i.e., target success). The latter combines the vectorial target error and a non-vectorial reward. For my thesis, we tested whether target error and reward make dissociable contributions to adaptation across two experimental studies. In Experiment 1, we instructed participants to ignore a clamped feedback cursor that either hit (no target error) or missed (target error) one of four reaching targets. Some participants received performance-based rewards when they accurately reached to the intended target, thereby not adapting to the cursor. We predicted that adaptation, reflected by reaching errors opposing the clamp, should be lower in reward groups. Surprisingly, reaching errors increased when rewards were given. To further investigate this surprising result, we modified the reaching task in Experiment 2, such that participants performed reaches to a single target and clamped and non-clamped trials were interleaved throughout adaptation trials. Rewards now attenuated compensatory reach adjustments, confirming our original prediction. A key finding of this work is that target error and rewards make dissociable contributions to adaptation. Further, depending on reward outcome at the previous trial, reward appears to modulate the solution the motor system computes to compensate for a sensory error.