Symmetric Movement Leads to Asymmetric Grip Forces in a Bimanual Peg-in-Hole Task

Mechanically uncoupled bimanual tasks, where each hand manipulates an object independently, present unique challenges compared to unimanual tasks. When the two objects must be controlled such that they precisely interact, both hands must account for the combined motor noise and variability when coordinating their movements. Here, we investigated the motion, variability, and grip forces immediately prior to insertion of both hands during a simulated bimanual peg-in-hole task, where participants completed the task in both possible hand configurations for the peg and hole. By using three different peg diameters, we introduce a range of difficulty levels to the task. Participants moved both hands symmetrically in the task due to experimental constraints of the motion, with increased duration and corrective movements as the task difficulty increased. However, we found that grip force before insertion was consistently elevated in the left hand compared to the right hand. This asymmetry is evident despite similar forces acting on each object within the simulated environment, resulting in comparable forces acting on the two hands. Overall, we found a strong asymmetry in grip force before insertion, independent of the manipulated object and symmetry of the movements.