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 human participants (males and females) manipulated a virtual stick with both hands to move its tip to a visual target. By shifting the tip position (task-relevant perturbation) or rotating the stick with the tip position fixed (task-irrelevant perturbation), we separated task-space errors from redundant-dimension errors. Participants rapidly corrected both types of perturbations using highly stereotyped movement patterns. Corrections to task-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 shaped by intrinsic coordination constraints that govern how visual errors propagate through the motor system. Significance Statement The motor system can correct a movement error within 200 ms of its occurrence. However, the compensatory movement pattern is not uniquely determined because of the many degrees of freedom in the body. How does the motor system rapidly select and execute an appropriate corrective pattern? Our bimanual stick-tip reaching task, in which participants controlled a cursor located at the tip of a virtual stick, allowed us to dissociate tip-displacing errors from stick-rotation errors. Tip displacements triggered fast corrections, but surprisingly, rotation-only perturbations also evoked rapid responses and biased the tip along its usual coordination between tip motion and stick tilt. Our findings show that fast corrections are constrained by intrinsic coordination patterns, limiting the ability to ignore goal-irrelevant perturbations.