Marco Vicentini

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.

Robot-Assisted Laparoscopic Hysterectomy vs Traditional Laparoscopic Hysterectomy: Five Metaanalyses

To assess differences between laparoscopic hysterectomy performed with or without robot-assistance, we performed metaanalyses of 5 key indices strongly associated with societal and hospital costs, patient safety, and intervention quality. The 5 indexes included estimated blood loss (EBL), operative time, number of conversions to laparotomy, hospital length of stay (LOS), and number of postoperative complications. A search of PubMed, Medline, Embase, and Science citation index online databases yielded a total of 605 studies. After a systematic review, we proceeded with meta-analysis of 14 articles for EBL, with a summary effect of -0.61 (95% confidence interval [CI], -42.42 to 46.20); 20 for operative time, with a summary effect of 0.66 (95% CI, -15.72 to 17.04); 17 for LOS, with a summary effect of -0.43 (95% CI, -0.68 to -0.17); 15 for conversion to laparotomy (odds ratio, 0.50; 95% CI, 0.31 to 0.79 with a random model); and 14 for postoperative complications (odds ratio, 0.69; 95% CI, 0.43 to 1.09 with a random model). In conclusion, compared with traditional laparoscopic hysterectomy, robot-assisted laparoscopic hysterectomy was associated with shorter LOS and fewer postoperative complications and conversions to laparotomy; there were no differences in EBL and operative time. These results confirm that robot-assisted laparoscopy has less deletorious effect on hospital, society, and patient stress and leads to better intervention quality.

Human factors in haptic contact of pliable surfaces

This paper considers relevant human factors to interact with a pliable body in a teleoperation surgical environment. Our aim is to identify the human capabilities, in terms of penetration depth and responsiveness, in a task of pliable surface contact, where surgeons are required to adopt a specific behavior immediately after the contact. A psychophysical experiment is conducted using virtual surfaces rendered with two different force-feedback devices. The results show that impact velocity affects performance in surface contact perception. In a second experiment where different postures are used, we examine whether the previous results hold for the particular ergonomic configuration employed. The results show that posture affects performance especially in expert users. Our findings underscore the importance of understanding the interplay of human perceptual parameters in the surgical teleoperation framework.

Perceptual Issues Improve Haptic Systems Performance

Since its introduction in the early 50s, teleoperation systems have expanded their reach, to address micro and macro manipulation, interaction with virtual worlds and the general field of haptic interaction. From its beginnings, as a mean to handle radioactive materials and to reduce human presence in dangerous areas, teleoperation and haptics have also become an interaction modality with computer generated objects and environments. One of the main goals of teleoperation is to achieve transparency, i.e. the complete perception by the human operator of the virtual or remote environment with which he/she is interacting (Lawrence, 1993). The ability of a teleoperation system to provide transparency depends upon the performance of the master and the slave, and of its control system. Ideally, the master should be able to emulate any environment, real or simulated, from freespace to infinitely stiff obstacles. The design of a transparent haptic interface is a quite challenging engineering task, since motion and sensing capabilities of the human hand/arm system are difficult to match. Furthermore, recent studies are providing more and more evidence that transparency is not only achieved by a good engineering design, but also by a combination of perceptual and cognitive factors that affect the operator ability to actually perceive the stimuli provided. The current knowledge on operator models reflects two separate groups of results. On one hand, there are guidelines for the design of an effective interface, from a human factors points of view, which include perceptual issues related to the cognitive and information processing of the human operators (see Subsection 2.4). On the other hand, there are several operator models related to biomechanical, bandwidth and reaction time issues (see Subsection 2.5). In this work we survey the main human factors that concur to the effectiveness of a haptic interface, and we present a series of psychophysical experiments, which can enrich performance in haptic systems, by measuring the mechanical effectiveness of the interface, providing a measure of the perception of a human operator. In addition the experiments are useful to represent the complex behavior of the human perception capabilities, and to propose new ways for enhancing the transparency of the virtual environment, by proposing suitable force scaling functions. In addition, our experience with psychophysics procedures highlights the needs of non-classical approaches to the problem, but the design of this type of experiments is not trivial, thus the need of a dedicated software tool or library arises. 22

Perception-centric force scaling function for stable bilateral interaction

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.

Overshoot Effect in Stiffness Perception Tasks during Hand Motion with Haptic Device

This study is concerned with the overshoot effect in a task of surface differentiation when both surface stiffness and impact velocity are varied. Psychophysical experiments are conducted using virtual surfaces rendered with a force-feedback device with velocity as visual constraint. We test the force constancy hypothesis formulated by Walker and Tan [12][1] which states that users maintain constant penetration force while exploring haptic virtual surfaces. Data collected during stroking surfaces of varying stiffness partially support this hypothesis and allow to consider the relevance of the impact velocity factor. Our results clearly show that changes in impact velocity affects surface penetration. Our findings underscore the importance of better understanding the interplay of the human perceptual parameters in a haptic framework. Future work will focus on the development of compensation rules for ensuring perceptual accuracy of anatomic haptic virtual environments. This will ensure accurate simulation of the haptic interaction between surgical tools and body organs.

The role of visual-haptic discrepancy in virtual reality environments

Visual-haptic interactions are of utmost importance for VR surgical simulators. We investigate the role of spatial visual-haptic discrepancy by manipulating the presentation order of visual and force feedback. Participants were asked to indicate the nearer wall between a visual and an pliable haptic virtual surface. We factorially manipulated the discrepancy levels (±5, 15, 25 mm) and the stiffness values of the pliable haptic wall, 83 (human fat) and 331 N/m (human skin). Psychophysical curves over depth penetration and latency time inside the wall were estimated. Results showed that haptic and visual walls were indistinguishable among the discrepancy range of 10.57±23.12 mm for 83N/m and -3.07±9.11 mm for 331 N/m. The trend of psychophysical curves show as, in presence of discrepancies or errors between an haptic and a visual surface, the overall perception is influenced by the stiffness of the haptic surface, in according with a weighted summation model, showing a direct relation between the stiffness factor and the weight of the haptic component in the model.

Signal manipulation based on perceptual thresholds enhances surface experience with common haptic device

This paper presents evidences of the performance improvement due to perceptual-based force signal manipulation in an interaction task with an haptic device. We hypothesize that sub-threshold forces become perceivable when a vibration waveform is superimposed onto the force signal. We study the human capabilities in perception of harmonic forces, and we observe lower thresholds for sinusoidal waves than for onset force. Starting from these perceptual findings, we involve a frequency signal instead of a signal amplification to allow the tactile human sensors to sharpen the perception of sub-thresholds forces in a teleoperation task. We report on the results obtained from our experiments and on the method used to reach such goal.

How force perception changes in different refresh rate conditions

In this work we consider the role of different refresh rates of the force feedback physical engine for haptics environments, such as robotic surgery and virtual reality surgical training systems. Two experimental force feedback tasks are evaluated in a virtual environment. Experiment I is a passive contact task, where the hand-grip is held waiting for the force feedback perception given by the contact with virtual objects. Experiment II is an active contact task, where a tool is moved in a direction until the contact perception with a pliable object. Different stiffnesses and refresh rates are factorially manipulated. To evaluate differences in the two tasks, we account for latency time inside the wall, penetration depth, and maximum force exerted against the object surface. The overall result of these experiments shows an improved sensitivity in almost all variables considered with refresh rates of 500 and 1,000 Hz compared with a refresh rate of 250 Hz, but no improved sensitivity is showed among them.

Perceptual factors for interaction modeling using haptic device

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.