Processes within the subspaces leading to changes in performance and keeping it unchanged

We explored processes within and orthogonal to the solution space (uncontrolled manifold, UCM) as superposition of fast random walk (RW) and slow drifts during multi-finger force production. Healthy participants performed two-hand (using the index and middle fingers per hand) accurate total force production task with different initial sharing of the force between the hand. After 5 s, visual feedback was manipulated - kept for both force and sharing, for only one of those variables, or turned off. The subjects tried to continue "doing what they have been doing" for 55 s. Trajectories both along and orthogonal to the UCM for total force showed fast RW and slow drifts. The diffusion plots confirmed persistent RW within the first 0.2 s and anti-persistent RW after 0.5 s. Persistent RW was similar across visual feedback conditions and larger orthogonal to the UCM. Its Hurst index correlated between the UCM and orthogonal to the UCM direction across participants. Anti-persistent RW depended strongly on visual feedback. Drift magnitude and characteristic time depended strongly on visual feedback, being similar along and orthogonal to the UCM. We conclude that RW destabilizes the state of the system thus encouraging exploration of nearby states over short time intervals and contributes to its stability over larger time intervals. Visual feedback plays a more important role in structuring stability of performance compared to the explicit task formulation. RW exploration promises new insights into the organization of stability in abundant systems and a potential biomarker for clinical studies. HighlightsO_LIStability during a multi-element action is structured in a feedback-specific way; C_LIO_LIRandom walk and drift characteristics of force depend not on the task but on salient feedback; C_LIO_LIRandom walk destabilizes steady state within a short range and stabilizes it within a long range; C_LIO_LIThe control of an action encourages exploration but limits its range. C_LI