Goal uncertainty attenuates sensorimotor adaptation

Implicit sensorimotor adaptation-the automatic correction of movement errors-is driven by a perceptual prediction error, the mismatch between the perceived movement outcome and its intended goal. Although perceptual uncertainty is known to attenuate adaptation, the impact of goal uncertainty on adaptation remains unknown. We used a visuomotor adaptation task that isolates implicit adaptation (n = 180), manipulating goal uncertainty by varying how precisely the goal's midpoint could be identified. Display format was varied independently to control for the objective size and luminance of visual features, and targets were hidden at movement onset, ensuring that identical visual input at the moment the error was experienced. We found that goal uncertainty significantly attenuated implicit adaptation, independent of low-level visual and kinematic features. Together, these results demonstrate that a precise internal representation of the goal is critical for sensorimotor adaptation, motivating a fundamental revision of motor learning models to explicitly incorporate goal uncertainty as a key determinant of performance.NEW & NOTEWORTHY Implicit adaptation depends not only on feedback uncertainty but also on goal uncertainty. In a large-scale online visuomotor rotation study (n = 180), increasing spatial ambiguity in the target midpoint-while keeping visual input constant-systematically attenuated implicit adaptation. These results call for a revision of standard models of motor adaptation, positioning the precision of the motor goal as a fundamental component in modulating motor learning.