Evaluation of force and torque magnitude discrimination thresholds on the human hand-arm system

This article reports on experiments about haptic perception aimed at measuring the force/torque differential thresholds applied to the hand-arm system. The experimental work analyzes how force is sent back to the user by means of a 6 degrees-of-freedom haptic device. Our findings on force perception indicate that the just-noticeable-difference is generally higher than previously reported in the literature and not constant along the stimulus continuum. We found evidence that the thresholds change also among the different directions. Furthermore, asymmetries in force perceptions, which were not described in previous reports, can be evinced for most of the directions. These findings support our claim that human beings perceive forces differently along different directions, thus suggesting that perception can also be enhanced by suitable signal processing, that is, with a manipulation of the force signal before it reaches the haptic device. We think that the improvement of the user perception can have a great impact in many applications and in particular we are focusing on surgical teleoperation scenarios.