We tested one of the central assumptions of the uncontrolled manifold (UCM) hypothesis, that stability within and orthogonal to the UCM differs in a task-specific way. This was done by exploring the effects of visual feedback on the fast random walk (RW) and slow drifts during multi-finger force production. Healthy participants used the index and middle fingers of both hands to produce an accurate total force magnitude with di...

We address the underexplored role of visual feedback in ensuring stability of pressing force produced in isometric conditions by the two hands. We considered the task as a two-level hierarchy (total force, F TOT , and hand forces, F HAND ) and used the framework of the uncontrolled manifold hypothesis to quantify synergies stabilizing F TOT and F HAND . Young healthy persons performed steady-state forces with visual feedback a...