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.

In this paper a force scaling function for an haptic system is the output of the psychophysics experiments that have been carried out with the aim of better understanding the human perception capabilities. The experimental work consists in measuring the differential thresholds of force perception applied to the hand-arm system. These findings support our claim that the human perception of forces and torques depends on force intensity and works differently along different directions, thus suggesting that perception can be enhanced by suitable scaling. We have identified a scaling function for each direction and we have shown that this variable scalings can be safely embedded in a passivity based teleoperation system in order to improve the feeling perceived by the user during the interaction with remote environments.

In this paper a perceptual model of the interaction with pliable surface is presented. The aim of this work is to evaluate those human factors most relevant to surface contact task in a bilateral teleoperation system characterized by a low stiffness environment. Three psychophysical experiments are conducted using an high performance haptic device and a virtual environment. In the first experiment we measure the capability of the human hand in terms of absolute force detection. The second experiment takes into account the time required by the neuro-muscular-skeletal system to stabilize the hand displacement in the presence of an external force. In the third one, a task of surface detection is involved to measures the smallest penetration depth that can be used to reliably perceive the contact surface. These perceptual factors are evaluated to build a perceptual model of a surface detection task. Results show the effectiveness of our model, which can be useful in applications where it is crucial to be aware of the interplay among perceptual factors.