Jacob L. Lader¹, Sean O’Bryan^1,2, Joo-Hyun Song¹; ¹Brown University, ²Bard College

Successful motor behavior depends on our ability to adjust movements when the environment changes or when outcomes deviate from expectations. A critical factor in this process is the quality of sensory information. Visual feedback is frequently noisy rather than stable, raising questions about how such noise influences the mechanisms that support sensorimotor adaptation. Explicit and implicit learning contribute to this adaptation in different ways, with explicit learning relying on strategic, cognitive resource-dependent corrections and implicit learning reflecting gradual, automatic adjustments based on sensory prediction errors (SPEs). We evaluated how noisy rotated visual feedback affects these learning processes using two visuomotor adaptation (VMA) tasks designed to emphasize explicit or implicit contributions to reach adaptation. In Exp. 1 (N=43), the delayed-feedback VMA emphasized explicit, strategy-based correction by postponing visual feedback to final reach positions. In Exp. 2 (N=40) the clamped-feedback VMA emphasized implicit learning by presenting cursor motion that followed a fixed trajectory independent of the participant’s reach. In each task, a noisy visual feedback condition was introduced in which rotated feedback varied randomly across trials while maintaining a 45° mean. Since these tasks differ in the cognitive resources they engage, changes in cognitive effort may reveal how participants respond when error information is unreliable. Pupil diameter was recorded continuously to index these demands during adaptation. Visual feedback noise influenced behavior and pupil dilation differently across the two learning contexts. In the delayed-feedback (explicit) task, noise impaired motor adaptation but did not alter pupillary responses, suggesting that noise disrupted strategic correction without increasing cognitive effort. In contrast, in the clamped-feedback (implicit) task, noise did not affect behavior but increased pupillary responses, indicating additional effort to suppress irrelevant feedback. These results demonstrate that visual feedback noise modulates both sensorimotor adaptation and pupil-indexed cognitive effort, with effects that depend on the learning process engaged.