Fast corrective responses in redundant motor control are shaped by intrinsic constraints of movement patterns

In real-world motor tasks, body movements unfold in a high-dimensional space, whereas task errors are defined in a lower-dimensional space. How such low-dimensional errors propagate across redundant motor degrees of freedom to generate rapid corrective responses remains poorly understood. To address this question, we developed a redundant bimanual task in which participants manipulated a virtual stick with both hands to move its tip to a visual target. Visual perturbations either displaced the stick tip (end-effector relevant errors) or altered the tilt angle of the stick without affecting the tip position (end-effector irrelevant errors), allowing us to dissociate errors defined in task space from those arising in redundant dimensions. Participants rapidly corrected both types of perturbations using highly stereotyped movement patterns. Corrections to end-effector relevant errors consistently involved coordinated changes across redundant dimensions, and even perturbations that did not affect task success elicited systematic corrective responses. Together, these results demonstrate that fast corrective responses in redundant motor control are not generated by flexible re-optimization, but are instead shaped by intrinsic coordination constraints that govern how visual errors propagate through the motor system.