The Interaction Between Position Sense and Force Control

Several daily life tasks require us to coordinate the motion and the force produced by both hands, using our position sense as well as sense of effort. However, the interaction between these in bimanual tasks is not extensively investigated. In this work we focused on bimanual tasks where subjects were require either (1) to place the hands in a same position (identical configuration in joint space) under different loading conditions, or (2) to produce an equal isometric force with the two hands with different arms configurations. The hand motion and force required for accomplishing the task were constrained to the vertical direction. In the first task, the difference between the hands positions was greater when the two hands were loaded with different weights. Conversely, in the second task, when subjects were asked to exert small equal forces with both hands, the systematic difference between left and right hand force was not influenced by symmetric or asymmetric arm configurations, but by the absolute position of the left arm, regardless of the right arm position.