Visual and haptic feedback in the control of force.

The ability to control index finger and elbow flexion forces was measured while subjects used either haptic feedback or both haptic and visual feedback to control the forces exerted. Over a 120-s time period subjects were able to control the finger forces ranging from 2 to 6 N to within 1 N using only haptic feedback, and elbow flexion forces to within 4.5 N over a force range of 10-30 N. At the same force amplitude there was no significant difference between the two muscle groups in the precision or accuracy with which the force could be controlled, suggesting that there is not a proximal to distal gradient in force control as has been found for the control of limb movement and position.