How Positioning Wearable Haptic Interfaces on Limbs Influences Virtual Embodiment.

With increasing use of computer applications and robotic devices in our everyday life, and with the advent of metaverse, there is an urgent need of developing new types of interfaces that facilitate a more intuitive interaction in physical and virtual space. In this work, we investigate the influence of the location of haptic feedback devices on embodiment of virtual hands and user load during an interactive pick-and-place task. To do this, we conducted a user study with a 3x2 repeated measure experiment design: feedback position is varied between the distal phalanx of the index finger and the thumb, the proximal phalanx of the index finger and the thumb, and the wrist. These conditions of feedback are tested with the stimuli applied synchronously to the participant in one case, and with an additional delay of 350 ms in the second case. The results show that the location of the haptic feedback device does not affect embodiment, whereas the delay, i.e., whether the feedback is applied synchronously or asynchronously, affects embodiment. This suggests that for pick-and-place tasks, haptic feedback devices can be placed on the user's wrist without compromising performance making the hands to remain free, allowing unobstructed hand visibility for precise motion tracking, thereby improving accuracy.

On the Correlation Between Tactile Stimulation and Pleasantness.

Several studies in the affective haptics research field showed the potential of using haptic technology to convey emotions in remote communications. In this context, it is of interest to simplify the haptic feedback without altering the informative content of the stimulus, with a two-fold advantage. On one side, it would allow the development of affective haptic devices whose technological complexity is limited, hence more compatible with wearability and portability requirements. On the other side, having a simplified set of stimuli would decrease the amount of data to be transmitted, thus improving the overall quality of remote haptic interactions. In this work, we investigated the correlation between the parameters regulating a caress-like stimulation and the perceived pleasantness. This was done by means of two experiments, in which we asked subjects to adjust the temperature and the motion velocity of a set of stimuli in order to find the most pleasant combination. Results indicated that subjects preferred different values of temperature and velocity of the stimulus depending on the proposed tactile stimulation. A small difference in the pleasantness ratings was observed between caresses provided with linear movements and those given as discrete sequences of taps. In particular, participants preferred linear movements set at 34.5 °C and 3.4 cms-1. As regards caress-like stimuli provided with discrete sequences of taps, the preferred temperature and velocity were 33.2 °C and 2.9 cms-1, respectively. The presence of vibration had a little effect on the perceived pleasantness.

Frequency-Dependent Reduction of Cybersickness in Virtual Reality by Transcranial Oscillatory Stimulation of the Vestibular Cortex.

Virtual reality (VR) applications are pervasive of everyday life, as in working, medical, and entertainment scenarios. There is yet no solution to cybersickness (CS), a disabling vestibular syndrome with nausea, dizziness, and general discomfort that most of VR users undergo, which results from an integration mismatch among visual, proprioceptive, and vestibular information. In a double-blind, controlled trial, we propose an innovative treatment for CS, consisting of online oscillatory imperceptible neuromodulation with transcranial alternating current stimulation (tACS) at 10 Hz, biophysically modelled to reach the vestibular cortex bilaterally. tACS significantly reduced CS nausea in 37 healthy subjects during a VR rollercoaster experience. The effect was frequency-dependent and placebo-insensitive. Subjective benefits were paralleled by galvanic skin response modulation in 25 subjects, addressing neurovegetative activity. Besides confirming the role of transcranially delivered oscillations in physiologically tuning the vestibular system function (and dysfunction), results open a new way to facilitate the use of VR in different scenarios and possibly to help treating also other vestibular dysfunctions.

Frequency-dependent tuning of the human vestibular "sixth sense" by transcranial oscillatory currents.

OBJECTIVE: The vestibular cortex is a multisensory associative region that, in neuroimaging investigations, is activated by slow-frequency (1-2 Hz) galvanic stimulation of peripheral receptors. We aimed to directly activate the vestibular cortex with biophysically modeled transcranial oscillatory current stimulation (tACS) in the same frequency range. METHODS: Thirty healthy subjects and one rare patient with chronic bilateral vestibular deafferentation underwent, in a randomized, double-blind, controlled trial, to tACS at slow (1 or 2 Hz) or higher (10 Hz) frequency and sham stimulations, over the Parieto-Insular Vestibular Cortex (PIVC), while standing on a stabilometric platform. Subjective symptoms of motion sickness were scored by Simulator Sickness Questionnaire and subjects' postural sways were monitored on the platform. RESULTS: tACS at 1 and 2 Hz induced symptoms of motion sickness, oscillopsia and postural instability, that were supported by posturographic sway recordings. Both 10 Hz-tACS and sham stimulation on the vestibular cortex did not affect vestibular function. As these effects persisted in a rare patient with bilateral peripheral vestibular areflexia documented by the absence of the Vestibular-Ocular Reflex, the possibility of a current spread toward peripheral afferents is unlikely. Conversely, the 10 Hz-tACS significantly reduced his chronic vestibular symptoms in this patient. CONCLUSIONS: Weak electrical oscillations in a frequency range corresponding to the physiological cortical activity of the vestibular system may generate motion sickness and postural sways, both in healthy subjects and in the case of bilateral vestibular deafferentation. SIGNIFICANCE: This should be taken into account as a new side effect of tACS in future studies addressing cognitive functions. Higher frequencies of stimulation applied to the vestibular cortex may represent a new interventional option to reduce motion sickness in different scenarios.

The Use of Tactile Sensors in Oral and Maxillofacial Surgery: An Overview.

BACKGROUND: This overview aimed to characterize the type, development, and use of haptic technologies for maxillofacial surgical purposes. The work aim is to summarize and evaluate current advantages, drawbacks, and design choices of presented technologies for each field of application in order to address and promote future research as well as to provide a global view of the issue. METHODS: Relevant manuscripts were searched electronically through Scopus, MEDLINE/PubMed, and Cochrane Library databases until 1 November 2022. RESULTS: After analyzing the available literature, 31 articles regarding tactile sensors and interfaces, sensorized tools, haptic technologies, and integrated platforms in oral and maxillofacial surgery have been included. Moreover, a quality rating is provided for each article following appropriate evaluation metrics. DISCUSSION: Many efforts have been made to overcome the technological limits of computed assistant diagnosis, surgery, and teaching. Nonetheless, a research gap is evident between dental/maxillofacial surgery and other specialties such as endovascular, laparoscopic, and microsurgery; especially for what concerns electrical and optical-based sensors for instrumented tools and sensorized tools for contact forces detection. The application of existing technologies is mainly focused on digital simulation purposes, and the integration into Computer Assisted Surgery (CAS) is far from being widely actuated. Virtual reality, increasingly adopted in various fields of surgery (e.g., sino-nasal, traumatology, implantology) showed interesting results and has the potential to revolutionize teaching and learning. A major concern regarding the actual state of the art is the absence of randomized control trials and the prevalence of case reports, retrospective cohorts, and experimental studies. Nonetheless, as the research is fast growing, we can expect to see many developments be incorporated into maxillofacial surgery practice, after adequate evaluation by the scientific community.

A Wearable Haptic Device for the Hand with Interchangeable End-Effectors.

This paper presents a 4-degrees-of-freedom (4-DoF) hand wearable haptic device for Virtual Reality (VR). It is designed to support different end-effectors, that can be easily exchanged so as to provide a wide range of haptic sensations. The device is composed of a static upper body, secured to the back of the hand, and the (changeable) end-effector, placed in contact with the palm. The two parts of the device are connected by two articulated arms, actuated by four servo motors housed on the upper body and along the arms. The paper summarizes the design and kinematics of the wearable haptic device and presents a position control scheme able to actuate a broad range of end-effectors. As a proof of concept, we present and evaluate three representative end-effectors during interactions in VR, rendering the sensation of interacting (E1) with rigid slanted surfaces and sharp edges having different orientations, (E2) with curved surfaces having different curvatures, and (E3) with soft surfaces having different stiffness characteristics. A few additional end-effector designs are discussed. A human-subjects evaluation in immersive VR shows the broad applicability of the device, able to render rich interactions with a diverse set of virtual objects.

Design and Prototyping of an Underactuated Hand Exoskeleton With Fingers Coupled by a Gear-Based Differential.

Exoskeletons and more in general wearable mechatronic devices represent a promising opportunity for rehabilitation and assistance to people presenting with temporary and/or permanent diseases. However, there are still some limits in the diffusion of robotic technologies for neuro-rehabilitation, notwithstanding their technological developments and evidence of clinical effectiveness. One of the main bottlenecks that constrain the complexity, weight, and costs of exoskeletons is represented by the actuators. This problem is particularly evident in devices designed for the upper limb, and in particular for the hand, in which dimension limits and kinematics complexity are particularly challenging. This study presents the design and prototyping of a hand finger exoskeleton. In particular, we focus on the design of a gear-based differential mechanism aimed at coupling the motion of two adjacent fingers and limiting the complexity and costs of the system. The exoskeleton is able to actuate the flexion/extension motion of the fingers and apply bidirectional forces, that is, it is able to both open and close the fingers. The kinematic structure of the finger actuation system has the peculiarity to present three DoFs when the exoskeleton is not worn and one DoF when it is worn, allowing better adaptability and higher wearability. The design of the gear-based differential is inspired by the mechanism widely used in the automotive field; it allows actuating two fingers with one actuator only, keeping their movements independent.

Analysis of postures for handwriting on touch screens without using tools.

The act of handwriting affected the evolutionary development of humans and still impacts the motor cognition of individuals. However, the ubiquitous use of digital technologies has drastically decreased the number of times we really need to pick a pen up and write on paper. Nonetheless, the positive cognitive impact of handwriting is widely recognized, and a possible way to merge the benefits of handwriting and digital writing is to use suitable tools to write over touchscreens or graphics tablets. In this manuscript, we focus on the possibility of using the hand itself as a writing tool. A novel hand posture named FingerPen is introduced, and can be seen as a grasp performed by the hand on the index finger. A comparison with the most common posture that people tend to assume (i.e. index finger-only exploitation) is carried out by means of a biomechanical model. A conducted user study shows that the FingerPen is appreciated by users and leads to accurate writing traits.

Simultaneous control of natural and extra degrees of freedom by isometric force and electromyographic activity in the muscle-to-force null space.

Objective.Muscle activation patterns in the muscle-to-force null space, i.e. patterns that do not generate task-relevant forces, may provide an opportunity for motor augmentation by allowing to control additional end-effectors simultaneously to natural limbs. Here we tested the feasibility of muscular null space control for augmentation by assessing simultaneous control of natural and extra degrees of freedom.Approach.We instructed eight participants to control translation and rotation of a virtual 3D end-effector by simultaneous generation of isometric force at the hand and null space activity extracted in real-time from the electromyographic signals recorded from 15 shoulder and arm muscles. First, we identified the null space components that each participant could control more naturally by voluntary co-contraction. Then, participants performed several blocks of a reaching and holding task. They displaced an ellipsoidal cursor to reach one of nine targets by generating force, and simultaneously rotated the cursor to match the target orientation by activating null space components. We developed an information-theoretic metric, an index of difficulty defined as the sum of a spatial and a temporal term, to assess individual null space control ability for both reaching and holding.Main results.On average, participants could reach the targets in most trials already in the first block (72%) and they improved with practice (maximum 93%) but holding performance remained lower (maximum 43%). As there was a high inter-individual variability in performance, we performed a simulation with different spatial and temporal task conditions to estimate those for which each individual participants would have performed best.Significance.Muscular null space control is feasible and may be used to control additional virtual or robotics end-effectors. However, decoding of motor commands must be optimized according to individual null space control ability.

Emerging of new bioartificial corticospinal motor synergies using a robotic additional thumb.

It is likely that when using an artificially augmented hand with six fingers, the natural five plus a robotic one, corticospinal motor synergies controlling grasping actions might be different. However, no direct neurophysiological evidence for this reasonable assumption is available yet. We used transcranial magnetic stimulation of the primary motor cortex to directly address this issue during motor imagery of objects' grasping actions performed with or without the Soft Sixth Finger (SSF). The SSF is a wearable robotic additional thumb patented for helping patients with hand paresis and inherent loss of thumb opposition abilities. To this aim, we capitalized from the solid notion that neural circuits and mechanisms underlying motor imagery overlap those of physiological voluntary actions. After a few minutes of training, healthy humans wearing the SSF rapidly reshaped the pattern of corticospinal outputs towards forearm and hand muscles governing imagined grasping actions of different objects, suggesting the possibility that the extra finger might rapidly be encoded into the user's body schema, which is integral part of the frontal-parietal grasping network. Such neural signatures might explain how the motor system of human beings is open to very quickly welcoming emerging augmentative bioartificial corticospinal grasping strategies. Such an ability might represent the functional substrate of a final common pathway the brain might count on towards new interactions with the surrounding objects within the peripersonal space. Findings provide a neurophysiological framework for implementing augmentative robotic tools in humans and for the exploitation of the SSF in conceptually new rehabilitation settings.

Design of a Wearable Haptic Device for Hand Palm Cutaneous Feedback.

This study describes the main design and prototyping steps of a novel haptic device for cutaneous stimulus of a hand palm. This part of the hand is fundamental in several grasping and manipulation tasks, but is still less exploited in haptics applications than other parts of the hand, as for instance the fingertips. The proposed device has a parallel tendon-based mechanical structure and is actuated by three motors positioned on the hand's back. The device is able to apply both normal and tangential forces and to render the contact with surfaces with different slopes. The end-effector can be easily changed to simulate the contact with different surface curvatures. The design is inspired by a smaller device previously developed for the fingertips; however, in the device presented in this study, there are significant differences due to the wider size, the different form-factor, and the structure of hand palm. The hand palm represents the support for the fingers and is connected to the arm through the wrist. The device has to be developed taking into account fingers' and wrist's motions, and this requirement constrains the number of actuators and the features of the transmission system. The larger size of the palm and the higher forces challenge the device from a structural point of view. Since tendons can apply only tensile forces, a spring-based support has been developed to keep the end-effector separated from the palm when the device is not actuated or when the force to be rendered is null. The study presents the main design guidelines and the main features of the proposed device. A prototype has been realized for the preliminary tests, and an application scenario with a VR environment is introduced.

Detachable Robotic Grippers for Human-Robot Collaboration.

Collaborative robots promise to add flexibility to production cells thanks to the fact that they can work not only close to humans but also with humans. The possibility of a direct physical interaction between humans and robots allows to perform operations that were inconceivable with industrial robots. Collaborative soft grippers have been recently introduced to extend this possibility beyond the robot end-effector, making humans able to directly act on robotic hands. In this work, we propose to exploit collaborative grippers in a novel paradigm in which these devices can be easily attached and detached from the robot arm and used also independently from it. This is possible only with self-powered hands, that are still quite uncommon in the market. In the presented paradigm not only hands can be attached/detached to/from the robot end-effector as if they were simple tools, but they can also remain active and fully functional after detachment. This ensures all the advantages brought in by tool changers, that allow for quick and possibly automatic tool exchange at the robot end-effector, but also gives the possibility of using the hand capabilities and degrees of freedom without the need of an arm or of external power supplies. In this paper, the concept of detachable robotic grippers is introduced and demonstrated through two illustrative tasks conducted with a new tool changer designed for collaborative grippers. The novel tool changer embeds electromagnets that are used to add safety during attach/detach operations. The activation of the electromagnets is controlled through a wearable interface capable of providing tactile feedback. The usability of the system is confirmed by the evaluations of 12 users.

Integration of a Passive Exoskeleton and a Robotic Supernumerary Finger for Grasping Compensation in Chronic Stroke Patients: The SoftPro Wearable System.

Upper-limb impairments are all-pervasive in Activities of Daily Living (ADLs). As a consequence, people affected by a loss of arm function must endure severe limitations. To compensate for the lack of a functional arm and hand, we developed a wearable system that combines different assistive technologies including sensing, haptics, orthotics and robotics. The result is a device that helps lifting the forearm by means of a passive exoskeleton and improves the grasping ability of the impaired hand by employing a wearable robotic supernumerary finger. A pilot study involving 3 patients, which was conducted to test the capability of the device to assist in performing ADLs, confirmed its usefulness and serves as a first step in the investigation of novel paradigms for robotic assistance.

Design of Personalized Wearable Haptic Interfaces to Account for Fingertip Size and shape.

The size and shape of fingertips vary significantly across humans, making it challenging to design wearable fingertip interfaces suitable for everyone. Although deemed important, this issue has often been neglected due to the difficulty of customizing devices for each different user. This article presents an innovative approach for automatically adapting the hardware design of a wearable haptic interface for a given user. We consider a three-DoF fingertip cutaneous device, composed of a static body and a mobile platform linked by three articulated legs. The mobile platform is capable of making and breaking contact with the finger pulp and re-angle to replicate contacts with arbitrarily-oriented surfaces. We analyze the performance of this device as a function of its main geometrical dimensions. Then, starting from the user's fingertip characteristics, we define a numerical procedure that best adapts the dimension of the device to: (i) maximize the range of renderable haptic stimuli; (ii) avoid unwanted contacts between the device and the skin; (iii) avoid singular configurations; and (iv) minimize the device encumbrance and weight. Together with the mechanical analysis and evaluation of the adapted design, we present a MATLAB script that calculates the device dimensions customized for a target fingertip as well as an online CAD utility for generating a ready-to-print STL file of the personalized design.

Feasibility of TMS in patients with new generation cochlear implants.

OBJECTIVE: The presence of a cochlear implant is being considered an absolute contraindication for experiments and/or treatments. We aimed to verify TMS (Transcranial Magnetic Stimulation) compatibility of a new generation of cochlear implants. METHODS: In a series of experiments, we test if MED-EL cochlear implants -compatible with stable fields of magnetic resonance imaging scanning- are fully resistant even to rapidly varying magnetic fields as those generated by single pulses and low and high-frequency trains of repetitive TMS (rTMS) applied with a figure of eight coil and different magnetic stimulators. RESULTS: With a TMS intensity equal or below 2.2 Tesla (T) the cochlear implant and all its electronic components remain fully functional, even when the combination of frequency, intensity and number of pulses exceeds the currently available safety guidelines. Induced forces on the implant are negligible. With higher magnetic fields (i.e., 3.2 T), one device was corrupted. CONCLUSIONS: Results exclude the risk of electronic damaging, demagnetizing or displacements of the studied cochlear implants when exposed to magnetic fields of up to 2.2 T delivered through a focal coil. SIGNIFICANCE: They open the way to use focal rTMS protocols with the aim of promoting neural plasticity in auditory networks, possibly helping the post-implant recovery of speech perception performance.

A Human Gesture Mapping Method to Control a Multi-Functional Hand for Robot-Assisted Laparoscopic Surgery: The MUSHA Case.

This work presents a novel technique to control multi-functional hand for robot-assisted laparoscopic surgery. We tested the technique using the MUSHA multi-functional hand, a robot-aided minimally invasive surgery tool with more degrees of freedom than the standard commercial end-effector of the da Vinci robot. Extra degrees of freedom require the development of a proper control strategy to guarantee high performance and avoid an increasing complexity of control consoles. However, developing reliable control algorithms while reducing the control side's mechanical complexity is still an open challenge. In the proposed solution, we present a control strategy that projects the human hand motions into the robot actuation space. The human hand motions are tracked by a LeapMotion camera and mapped into the actuation space of the virtualized end-effector. The effectiveness of the proposed method was evaluated in a twofold manner. Firstly, we verified the Lyapunov stability of the algorithm, then an user study with 10 subjects assessed the intuitiveness and usability of the system.

Wearable haptic anklets for gait and freezing improvement in Parkinson's disease: a proof-of-concept study.

BACKGROUND AND OBJECTIVE: In a proof-of-concept study, we aimed to verify whether the wearable haptic anklets, a device that delivers personalized suprathreshold alternating exteroceptive stimulation at the anklets on demand, may improve the quality of walking, including the freezing of gate (FOG), in idiopathic Parkinson's disease (PD) patients. The clinical relevance of the presented device as a walking pacemaker to compensate the disturbed locomotion through the generation of a more physiological internal walking rhythm should be verified in a dedicated clinical trial. METHODS: We tested 15 patients diagnosed as idiopathic PD, during their regular treatment regimen. Patients were evaluated during walking with the device switched on and off, personalized at their most comfortable cadence. Stride velocity, variance, and length, as well as FOG episode duration during walking or turning of 180°, were quantified by an optical high-performance motion capture VICON system. RESULTS: The alternating, rhythmic, sensory stimulation significantly improved either walking velocity or reduced inter-stride variance. Effects were more variable on stride length. The significant reduction of FOG episodes' duration correlated with clinical severity of scales rating gate and balance. No safety problems occurred. CONCLUSIONS: The WEARHAP-PD device, whose Technology Readiness Level (TRL) is 6, significantly improved some walking abilities (walking velocity and stride variance) and reduced the duration of FOG episodes in idiopathic PD patients. Unlike the traditional auditory and visual explicit cues that require the user's allocation of attention for correct functioning, the interaction of the patients with the surrounding environment was preserved, due to the likely implicit processing of haptic stimuli.

Wearable Haptics for Remote Social Walking.

Walking is an essential activity for a healthy life, which becomes less tiring and more enjoyable if done together. Common difficulties we have in performing sufficient physical exercise, for instance the lack of motivation, can be overcome by exploiting its social aspect. However, our lifestyle sometimes makes it very difficult to find time together with others who live far away from us to go for a walk. In this article, we propose a novel system enabling people to have a 'remote social walk' by streaming the gait cadence between two persons walking in different places, increasing the sense of mutual presence. Vibrations provided at the users' ankles display the partner's sensation perceived during the heel-strike. In order to achieve the aforementioned goal in a two users experiment, we envisaged a four-step incremental validation process: i) a single walker has to adapt the cadence with a virtual reference generated by a software; ii) a single user is tasked to follow a predefined time-varying gait cadence; iii) a leader-follower scenario in which the haptic actuation is mono-directional; iv) a peer-to-peer case with bi-directional haptic communication. Careful experimental validation was conducted involving a total of 50 participants, which confirmed the efficacy of our system in perceiving the partners' gait cadence in each of the proposed scenarios.

Caring About the Human Operator: Haptic Shared Control for Enhanced User Comfort in Robotic Telemanipulation.

Haptic shared control enables a human operator and an autonomous controller to share the control of a robotic system using haptic active constraints. It has been used in robotic teleoperation for different purposes, such as navigating along paths minimizing the torques requested to the manipulator or avoiding possibly dangerous areas of the workspace. However, few works have focused on using these ideas to account for the user's comfort. In this article, we present an innovative haptic-enabled shared control approach aimed at minimizing the user's workload during a teleoperated manipulation task. Using an inverse kinematic model of the human arm and the rapid upper limb assessment (RULA) metric, the proposed approach estimates the current user's comfort online. From this measure and an a priori knowledge of the task, we then generate dynamic active constraints guiding the users towards a successful completion of the task, along directions that improve their posture and increase their comfort. Studies with human subjects show the effectiveness of the proposed approach, yielding a 30% perceived reduction of the workload with respect to using standard guided human-in-the-loop teleoperation.

Preventing Undesired Face-Touches With Wearable Devices and Haptic Feedback.

The alarming morbidity of COVID-19 has drawn the attention to the social role of hygiene rules, with a particular focus on the importance of limiting face-touch occurrences. To deal with this aspect, we present No Face-Touch, a system able to estimate hand proximity to face and notify the user whenever a face-touch movement is detected. In its complete setup, the system consists of an application running on the smartwatch and a wearable accessory. Its ease of implementation allows this solution to be ready-to-use and large-scale deployable. We developed two gesture detection approaches compatible with sensors embedded in recent smartwatches, i.e. inertial and magnetic sensors. After preliminary tests to tune target gesture parameters, we tested the two approaches and compared their accuracy. The final phase of this project consisted in exploiting the most robust approach in a daily living scenario during a 6-days campaign. Experimental results revealed the effectiveness of the proposed system, demonstrating its impact in reducing the number of face-touches and their duration.