Virtual Hand Research Articles

Effect of Physical and Virtual Feedback on Reach-to-Grasp Movements in Virtual Environments

Object grabbing is a common interaction task in virtual environments, where the virtual and physical feedback of both the hand and the targeted object may impact its performance. To investigate these effects, we first designed a comparative study where subjects were required to reach and grasp a physical cylinder under four conditions: 1) no virtual hand and no virtual cylinder; 2) virtual cylinder without virtual hand; 3) virtual hand and cylinder; and 4) real environment. The results showed that the subjects performed with different kinematic patterns in all three virtual conditions compared to the real environment. Additionally, we found that this difference is not due to the environment or depth illusion. We performed another experiment to examine the effects of physical cylinder feedback on reach-to-grasp movement. We found that the subjects performed similarly to the physical environment only in the condition with a virtual hand and a virtual cylinder. These results suggest that feedback with virtual hand and virtual targeted object would result in similar kinematic patterns in virtual environments as in physical environments, which implies design guidelines in virtual environments for rehabilitation in patients with motor deficits.

Virtual Reality-Induced Dissociative Symptoms: A Retrospective Study.

Objective: The use of virtual reality (VR) has been increasing worldwide, as devices are becoming more sophisticated and provide an escape from reality during the COVID-19 lockdown. This recent rise in the use of VR leads to new side effects being reported, such as dissociative symptoms that may or may not constitute a mental health concern. This retrospective study investigated the prevalence and intensity of dissociative symptoms in VR users, as well as some potential predisposing conditions that may trigger them, and their impact on the subjects' wellbeing. Materials and Methods: We conducted a survey (n = 358) that was posted on VR Facebook groups. This survey was approved by the University of Lisbon Medical Faculty's IRB, and comprised a modified version of the Clinician-Administered Dissociative State Scale (CADSS) and questions regarding potential risk factors known to induce dissociative disorders or experiences. Results: Data analysis revealed that 83.9% participants reported dissociative symptoms, with varying intensity according to CADSS (). Significant correlations were found between CADSS score and the time spent playing, the use of software applications (apps) that involve virtual hands or hand tracking, history of previous dissociative experiences, traumatic childhood events, avoidant coping strategies, and psychiatric disorders. Nonetheless, most participants categorized the symptoms as nonanxiogenic (85.8%) and minute lasting (77.4%). Conclusion: In conclusion, this study revealed that although VR can induce dissociative experiences, they seem to be short lasting and nonthreatening to the individual's wellbeing and might be predicted or attenuated by managing other known risk factors for dissociative phenomena.

Hafnia Hands: A Multi-Skin Hand Texture Resource for Virtual Reality Research

We created a hand texture resource (with different skin tone versions as well as non-human hands) for use in virtual reality studies. This makes it easier to run lab and remote studies where the hand representation is matched to the participants’ own skin tone. We validate that the virtual hands with our textures align with participants’ view of their own real hands and allow to create VR applications where participants have an increased sense of body ownership. These properties are critical for a range of VR studies, such as of immersion.

3D hand pose and shape estimation from RGB images for keypoint-based hand gesture recognition

Estimating the 3D pose of a hand from a 2D image is a well-studied problem and a requirement for several real-life applications such as virtual reality, augmented reality, and hand gesture recognition. Currently, reasonable estimations can be computed from single RGB images, especially when a multi-task learning approach is used to force the system to consider the shape of the hand when its pose is determined. However, depending on the method used to represent the hand, the performance can drop considerably in real-life tasks, suggesting that stable descriptions are required to achieve satisfactory results. In this paper, we present a keypoint-based end-to-end framework for 3D hand and pose estimation and successfully apply it to the task of hand gesture recognition as a study case. Specifically, after a pre-processing step in which the images are normalized, the proposed pipeline uses a multi-task semantic feature extractor generating 2D heatmaps and hand silhouettes from RGB images, a viewpoint encoder to predict the hand and camera view parameters, a stable hand estimator to produce the 3D hand pose and shape, and a loss function to guide all of the components jointly during the learning phase. Tests were performed on a 3D pose and shape estimation benchmark dataset to assess the proposed framework, which obtained state-of-the-art performance. Our system was also evaluated on two hand-gesture recognition benchmark datasets and significantly outperformed other keypoint-based approaches, indicating that it is an effective solution that is able to generate stable 3D estimates for hand pose and shape.

The dynamic boundaries of the Self: Serial dependence in the Sense of Agency

The feeling of control over one's actions, termed the Sense of Agency (SoA), delineates one's experience as an embodied self. Although this embodied experience is typically perceived as stable over time, recent theoretical accounts highlight the experience-dependent and dynamic nature of the embodied self. In this study we examined how recent experiences modulate SoA (i.e., serial dependence), and disambiguated the unique contributions of previous stimuli and choices on subsequent SoA judgments. In addition, we examined whether these effects persist across different domains of perceptual alteration. We analyzed two independent datasets of the Virtual Hand (VH) task (N = 100 participants) in which a sensorimotor conflict is introduced between the presented visual feedback and the actual movement performed. In Dataset 1, which included only temporal alterations, we found that previous stimuli recalibrate current perception, increasing the likelihood of the current choice to be different than the previous choice. Whereas previous choices induce a repetition bias increasing the likelihood to repeat choices across trials. Thus, previous external stimuli and self-generated choices exert opposing influences on SoA. We replicated these findings in Dataset 2, in which the VH task was tested with alterations in both temporal and spatial domains. In addition, we discovered that previous stimuli from a different perceptual domain exert a recalibration effect similar to stimuli from the same domain. Thus, SoA is constantly shaped by our previous subjective choices and objective stimuli experienced even across different perceptual domains. This highlights how SoA may act as unifying construct organizing our experience of the self over time and across perceptual experiences.

Virtual Reality Pre-Prosthetic Hand Training With Physics Simulation and Robotic Force Interaction

Virtual reality (VR) rehabilitation systems have been proposed to enable prosthetic hand users to perform training before receiving their prosthesis. Improving pre-prosthetic training to be more representative and better prepare the patient for prosthesis use is a crucial step forwards in rehabilitation. However, existing VR platforms lack realism and accuracy in terms of the virtual hand and the forces produced when interacting with the environment. To address these shortcomings, this work presents a VR training platform based on accurate simulation of an anthropomorphic prosthetic hand, utilising an external robot arm to render realistic forces that the user would feel at the attachment point of their prosthesis. Experimental results with non-disabled participants show that training with this platform leads to a significant improvement in Box and Block scores compared to training in VR alone and a control group with no prior training. Results performing pick-and-place tasks with a wider range of objects demonstrates that training in VR alone negatively impacts performance, whereas the proposed platform has no significant impact on performance. User perception results highlight that the platform is much closer to using a physical prosthesis in terms of physical demand and effort, however frustration is significantly higher during training.

Midfrontal Theta Transcranial Alternating Current Stimulation Facilitates Motor Coordination in Dyadic Human-Avatar Interactions.

Synchronous interpersonal motor interactions require moment-to-moment prediction and proactive monitoring of the partner's actions. Neurophysiologically, this is highlighted by an enhancement of midfrontal theta (4-7 Hz) oscillations. In this study, we explored the causal role of midfrontal theta for interpersonal motor interactions using transcranial alternating current stimulation (tACS). We implemented a realistic human-avatar interaction task in immersive virtual reality where participants controlled a virtual arm and hand to press a button synchronously with a virtual partner. Participants completed the task while receiving EEG-informed theta (Experiment 1) or beta (control frequency, Experiment 2) tACS over the frontal midline, as well as sham stimulation as a control. Results showed that midfrontal theta tACS significantly improved behavioral performance (i.e., reduced interpersonal asynchrony) and participants' motor strategies (i.e., increased movement times and reduced RTs), whereas beta tACS had no effect on these measures. These results suggest that theta tACS over frontal areas facilitates action monitoring and motor abilities supporting interpersonal interactions.

A novel tablet-based application for assessment of manual dexterity and its components: a reliability and validity study in healthy subjects

BackgroundWe developed five tablet-based tasks (applications) to measure multiple components of manual dexterity. Aim: to test reliability and validity of tablet-based dexterity measures in healthy participants.MethodsTasks included: (1) Finger recognition to assess mental rotation capacity. The subject taps with the finger indicated on a virtual hand in three orientations (reaction time, correct trials). (2) Rhythm tapping to evaluate timing of finger movements performed with, and subsequently without, an auditory cue (inter-stimulus interval). (3) Multi-finger tapping to assess independent finger movements (reaction time, correct trials, unwanted finger movements). (4) Sequence tapping to assess production and memorization of visually cued finger sequences (successful taps). (5) Line-tracking to assess movement speed and accuracy while tracking an unpredictably moving line on the screen with the fingertip (duration, error). To study inter-rater reliability, 34 healthy subjects (mean age 35 years) performed the tablet tasks twice with two raters. Relative reliability (Intra-class correlation, ICC) and absolute reliability (Standard error of measurement, SEM) were established. Task validity was evaluated in 54 healthy subjects (mean age 49 years, range: 20–78 years) by correlating tablet measures with age, clinical dexterity assessments (time taken to pick-up objects in Box and Block Test, BBT and Moberg Pick Up Test, MPUT) and with measures obtained using a finger force-sensor device.ResultsMost timing measures showed excellent reliability. Poor to excellent reliability was found for correct trials across tasks, and reliability was poor for unwanted movements. Inter-session learning occurred in some measures. Age correlated with slower and more variable reaction times in finger recognition, less correct trials in multi-finger tapping, and slower line-tracking. Reaction times correlated with those obtained using a finger force-sensor device. No significant correlations between tablet measures and BBT or MPUT were found. Inter-task correlation among tablet-derived measures was weak.ConclusionsMost tablet-based dexterity measures showed good-to-excellent reliability (ICC ≥ 0.60) except for unwanted movements during multi-finger tapping. Age-related decline in performance and association with finger force-sensor measures support validity of tablet measures. Tablet-based components of dexterity complement conventional clinical dexterity assessments. Future work is required to establish measurement properties in patients with neurological and psychiatric disorders.

The relative contribution of five key perceptual cues and their interaction to the sense of embodiment.

A range of perceptual cues drive the Sense of Embodiment (SoE) with an external object, such as a virtual arm that looks like one’s own or can be controlled like one’s own. Since most experiments test one or two cues at a time, it is difficult to establish their relative contribution and possible interaction. This work aims at investigating the importance of five key perceptual cues (field of view, visuo-proprioceptive synchronicity, tactile feedback, visual human likeness, and connectedness) and their potential interaction in a single, full-factorial experiment. Participants touched a target dot, which changed position after a hit, for 1 min in a virtual environment seen through a head-mounted display. Participants’ arm and hand motions were mapped to a virtual arm and hand. All perceptual cues had two levels: SoE supportive and SoE suppressive. Twenty-eight participants completed the task in all possible combinations. We recorded Task Performance and self-ratings of Sense of Ownership and Sense of Agency. Results showed that visuo-proprioceptive synchronicity had the largest effect on all three measures. The relative importance of the remaining four cues differed for the three dependent variables. The cues did not have significant interactive effects. We conclude that when designing an interface for maximum supportive embodiment, visuo-proprioceptive synchronicity is the most important perceptual cue. The extent to which other supportive cues can improve the embodiment experience depends on the considered variables, but generally, the more other supportive cues can be added, the better.

Exploring the Effect of Personality Traits in VR Interaction: The Emergent Role of Perspective-Taking in Task Performance

In this work we explore the effect of personality traits on user interaction in virtual reality (VR), on the less widely studied aspect of task performance during object manipulation. We conducted an experiment measuring the performance of 39 users interacting with a virtual environment using the virtual hand metaphor to execute a simple selection and positioning task, with or without virtual obstacles. Our findings suggest concrete correlations between user personality traits and behavior data. Perspective-taking, in particular, seems to be strongly affecting task performance, highlighting the need for further research. Besides the wider implications of our results in relation to the effect of personality on how users experience VR, our main contribution lies in identifying specific traits that should be taken into account when designing experiments involving users performing such tasks. The study of these traits may also significantly advance our understanding of personality traits as part of the user model in a wider range of VR applications, including those offering personalization and recommendation functionality.

Exodex Adam-A Reconfigurable Dexterous Haptic User Interface for the Whole Hand.

Applications for dexterous robot teleoperation and immersive virtual reality are growing. Haptic user input devices need to allow the user to intuitively command and seamlessly “feel” the environment they work in, whether virtual or a remote site through an avatar. We introduce the DLR Exodex Adam, a reconfigurable, dexterous, whole-hand haptic input device. The device comprises multiple modular, three degrees of freedom (3-DOF) robotic fingers, whose placement on the device can be adjusted to optimize manipulability for different user hand sizes. Additionally, the device is mounted on a 7-DOF robot arm to increase the user’s workspace. Exodex Adam uses a front-facing interface, with robotic fingers coupled to two of the user’s fingertips, the thumb, and two points on the palm. Including the palm, as opposed to only the fingertips as is common in existing devices, enables accurate tracking of the whole hand without additional sensors such as a data glove or motion capture. By providing “whole-hand” interaction with omnidirectional force-feedback at the attachment points, we enable the user to experience the environment with the complete hand instead of only the fingertips, thus realizing deeper immersion. Interaction using Exodex Adam can range from palpation of objects and surfaces to manipulation using both power and precision grasps, all while receiving haptic feedback. This article details the concept and design of the Exodex Adam, as well as use cases where it is deployed with different command modalities. These include mixed-media interaction in a virtual environment, gesture-based telemanipulation, and robotic hand–arm teleoperation using adaptive model-mediated teleoperation. Finally, we share the insights gained during our development process and use case deployments.

The vivid tactile experience from vision and auditory: Clues from multisensory channel integration

<p id=C9>Virtual reality creates an immersive experience for users by providing visual, auditory, and tactile information. However, tactile feedback still faces many technical bottlenecks, which limit natural interaction in the virtual reality environment. Pseudo-haptic technology based on multi-sensory illusion can enhance and enrich tactile perception with the help of information from other channels, which is one of the effective ways to optimize tactile perception in the virtual reality environment. In order to explore the problem in a more targeted way, the study focuses on roughness perception among different dimensions of tactile perception. We first discuss the relationship between visual, auditory, and tactile perception in roughness information integration and further analyze visual and auditory factors affecting roughness perception. <p id=C10>In the process of roughness perception, the channel with less noise and more reliable information will have a higher weight. By evaluating the roughness under every single channel (visual、auditory and tactile) condition,and each double-channel（visual-tactile and auditory-tactile) condition, previous studies have quantified the high weight of visual and auditory channels in roughness perception. It further verifies that roughness perception results from integrating tactile, visual, and auditory information. Therefore, it has excellent potential to manipulate visual and auditory factors to induce or enhance roughness perception in the virtual reality environment. <p id=C11>For visual factors, the texture of the surface, light or shadow, and the control display rate (CDR) may affect the perception of roughness. ①When the texture density of the object surface increase, the perceived roughness will increase accordingly; ②Since the angle of incidence influence the shadow of the surface texture, thus affecting the perception of roughness; ③ When the glossiness of surface decrease, the perceived roughness increase; ④Reducing the CDR of the virtual hand or presenting a vibratory virtual hand will increase the users perception of the roughness. <p id=C12>For auditory factors, manipulating loudness and pitch/frequency can change the roughness perception: increasing loudness in the entire frequency of sound or increasing loudness in a high, medium, or low frequency band of sound can improve the roughness perception. There is a strong correlation between pitch/frequency and roughness perception. According to current research, we speculated that there might be an inverted U-shaped curve between pitch/frequency change and roughness perception. <p id=C13>In the future, in order to optimize the tactile roughness experience in virtual reality environment, studies can be carried out from the following aspects: Firstly, it is necessary to explore the differences between every single channel (visual, auditory, and tactile) information in the virtual reality environment and real environment respectively, since single channel information is the prerequisite for multi-sensory channel information in the virtual reality environment. Secondly, from the practical point of view, we can choose the channel more suitable to the current scene or task and provide sufficient information timely with emphasis. Thirdly, the difference of single-channel information in virtual reality will lead to information mismatch between different channels. Therefore, it is necessary to explore further how the brain integrates the originally different and mismatched multi-channel sensory information. Finally, most studies explored the usability of relevant sensory information on roughness perception from the perspective of single-channels or double-channels. Therefore, in the future, it is of significant importance to explore the information integration and processing rules of three channels in virtual reality.

Shared mechanisms underlie mental imagery and motor planning

Many studies have associated mental imagery with motor control mechanisms by showing mutually active brain areas and functions, as well as similar temporal patterns of imagining and executing the same motor actions. One of the main conjectured mutual mechanisms is the Cerebellar forward-model, commonly believed to generate sensory predictions as part of both motor control and mental imagery processes. Nevertheless, trials to associate one’s overall individual mental and motor capacities have shown only mild and inconsistent correlations, hence challenging the mutual mechanism assumption. We hypothesized that one cause to this inconsistency is the forward-model’s dominance in the motor-planning stage only when adapting to novel sensorimotor environments, while the inverse-model is gradually taking the lead along the adaptation, and therefore biasing most attempts to measure motor-mental overlapping functions and correlate these measurements under regular circumstances. Our current study aimed to tackle and explore this gap using immersive virtual embodiment, by applying an experience of a fundamental sensorimotor conflict, thereby manipulating the sensory prediction mechanism, and presumably forcing an increased involvement of the forward-model in the motor planning stage throughout the experiment. In the study, two groups of subjects (n = 48) performed mental and manual rotation within an immersive, motion-captured, virtual reality environment, while the sensorimotor dynamics of only the test group were altered by physical-virtual speed re-mapping making the virtual hand move twice as fast as the physical hand controlling it. Individual mental imagery capacities were assessed before and after three blocks of manual-rotation, where motor planning durations were measured as the time until motion onset. The results show that virtual sensorimotor alteration extremely increases the correlation of mental imagery and motor planning (r = 0.9, p < .0001) and leads to higher mental imagery performance improvement following the physical blocks. We particularly show that virtual embodiment manipulation affects the motor planning stage to change and functionally overlap with imagery mechanisms, rather than the other way around, which supports our conjecture of an increased sensory-prediction forward-model involvement. Our results shed new light on the embodied nature of mental imagery, support the view of the predictive forward-model as a key mechanism mutually underlying motor control and imagery, and suggest virtual sensorimotor alteration as a novel methodology to increase physical-mental convergence. These findings also suggest the applicability of using existing motion-tracked virtual environments for continuous cognitive evaluation and treatment, through kinematic analysis of ongoing natural motor behaviors.

Development and Testing of a Portable Virtual Reality-Based Mirror Visual Feedback System with Behavioral Measures Monitoring.

Virtual Reality (VR) is a technology that has been used to provide the Mirror Visual Feedback (MVF) illusion to patients with promising results. In the present work, the goal is to design, develop and test a portable VR-based MVF system that monitors behavioral information about the performance of a simple motor task. The developed application runs in a stand-alone VR system and allows the researcher to select the real and virtual hands used to perform the motor task. The system was evaluated with a group of twenty healthy volunteers (12 men and 8 women) with ages between 18 and 66 years. Participants had to repetitively perform a motor task in four different experimental conditions: two mirror conditions (performing real movements with the dominant and with the non-dominant hand) and two non-mirror conditions. A significant effect of the experimental condition on embodiment score (p < 0.001), response time (p < 0.001), performance time (p < 0.001), trajectory length (p < 0.004) and trajectory maximum horizontal deviation (p < 0.001) was observed. Furthermore, a significant effect of the experimental moment (initial, middle and final parts of the training) on the performance time was observed (p < 0.001). These results show that the monitored parameters provide relevant information to evaluate the participant’s task performance in different experimental conditions.

Observing Product Touch: The Vicarious Haptic Effect in Digital Marketing and Virtual Reality

Retail is rapidly evolving to construct virtual environments for consumers. Online product images, videos, and virtual reality (VR) interfaces enliven consumer experiences and are a source of product information. Because consumers are unable to physically touch products in these digital environments, this research examines vicarious touch, or the observation of a hand in physical contact with a product in a digital environment. Across eight studies, the authors use images, GIFs, and VR to show that vicarious touch affects consumers’ psychological ownership and product valuation due to the active nature of product touch, which results in a felt sense of body ownership of the virtual hand. This is termed the “vicarious haptic effect.” Results demonstrate that it is not enough to show a hand in an advertisement; the hand must be touching a product. The vicarious haptic effect is strongest for people who become highly stimulated by an immersive VR experience (i.e., measured via the elevation in heart rate). The vicarious haptic effect is attenuated if the viewed interaction does not represent a diagnostic hand movement. The authors discuss theoretical and managerial implications for digital product presentation to encourage feelings of product ownership and valuation.

Judgments of agency are affected by sensory noise without recruiting metacognitive processing.

Acting in the world is accompanied by a sense of agency, or experience of control over our actions and their outcomes. As humans, we can report on this experience through judgments of agency. These judgments often occur under noisy conditions. We examined the computations underlying judgments of agency, in particular under the influence of sensory noise. Building on previous literature, we studied whether judgments of agency incorporate uncertainty in the same way that confidence judgments do, which would imply that the former share computational mechanisms with metacognitive judgments. In two tasks, participants rated agency, or confidence in a decision about their agency, over a virtual hand that tracked their movements, either synchronously or with a delay and either under high or low noise. We compared the predictions of two computational models to participants' ratings and found that agency ratings, unlike confidence, were best explained by a model involving no estimates of sensory noise. We propose that agency judgments reflect first-order measures of the internal signal, without involving metacognitive computations, challenging the assumed link between the two cognitive processes.

Hand dominance in the performance and perceptions of virtual reach control

PurposeEfforts to optimize human-computer interactions are becoming increasingly prevalent, especially with virtual reality (VR) rehabilitation paradigms that utilize engaging interfaces. We hypothesized that motor and perceptional behaviors within a virtual environment are modulated uniquely through different modes of control of a hand avatar depending on limb dominance. This study investigated the effects of limb dominance on performance and concurrent changes in perceptions, such as time-based measures for intentional binding, during virtual reach-to-grasp. MethodsParticipants (n = 16, healthy) controlled a virtual hand through their own hand motions with control adaptations in speed, noise, and automation. ResultsA significant (p < 0.01) positive relationship between performance (reaching pathlength) and binding (time-interval estimation of beep-sound after grasp contact) was observed for the dominant hand. Unique changes in performance (p < 0.0001) and binding (p < 0.0001) were observed depending on handedness and which control mode was applied. ConclusionsDevelopers of VR paradigms should consider limb dominance to optimize settings that facilitate better performance and perceptional engagement. Adapting VR rehabilitation for handedness may particularly benefit unilateral impairments, like hemiparesis or single-limb amputation.

Hand Sign Recognition System Based on EIT Imaging and Robust CNN Classification

Hand sign recognition is gaining importance in human-human and in human-machine communication and interaction. Electrical Impedance Tomography (EIT) is thereby very interesting as it provides information on impedance changes in depth of the Section of the arm, which infers muscle contractions. This paper introduces an EIT imaging system for hand sign recognition and monitoring having a low complexity and including an electronic interface with 8 electrodes placed on the forearm, a Gauss-Newton image reconstruction algorithm, a robust CNN based hand sign classification and a virtual hand model for visualization. A database has been collected for EIT measurements in pole mode taken by eight subjects performing the American sign language numbers from 0 to 9. The overall imaging system is validated using a water tank system, where conductive objects can be changed in properties and positions. The correspondence between the reconstructed images and the expected muscle behavior for the hand signs is investigated. A robust Convolutional Neural Network (CNN) classification algorithm was implemented and optimized by implementing an Adam optimizer and conducting a dedicated study to avoid overfitting. The results obtained by CNN are compared to the results by a Support Vector Machine (SVM), and a Softmax classifier. They show a classification accuracy of 95.94%, 75.61%, and 62.9% respectively. In term of subject dependency, the system using the CNN model shows a higher performance, as the accuracy decreases only by 0.72% while increasing the number of subjects from one to eight. Finally, for visualization, a 3D virtual hand model is designed and controlled based on detected hand signs.

Feasibility study of immersive virtual prism adaptation therapy with depth-sensing camera using functional near-infrared spectroscopy in healthy adults

Prism Adaptation (PA) is used to alleviate spatial neglect. We combined immersive virtual reality with a depth-sensing camera to develop virtual prism adaptation therapy (VPAT), which block external visual cues and easily quantify and monitor errors than conventional PA. We conducted a feasibility study to investigate whether VPAT can induce behavioral adaptations by measuring after-effect and identifying which cortical areas were most significantly activated during VPAT using functional near-infrared spectroscopy (fNIRS). Fourteen healthy subjects participated in this study. The experiment consisted of four sequential phases (pre-VPAT, VPAT-10°, VPAT-20°, and post-VPAT). To compare the most significantly activated cortical areas during pointing in different phases against pointing during the pre-VPAT phase, we analyzed changes in oxyhemoglobin concentration using fNIRS during pointing. The pointing errors of the virtual hand deviated to the right-side during early pointing blocks in the VPAT-10° and VPAT-20° phases. There was a left-side deviation of the real hand to the target in the post-VPAT phase, demonstrating after-effect. The most significantly activated channels during pointing tasks were located in the right hemisphere, and possible corresponding cortical areas included the dorsolateral prefrontal cortex and frontal eye field. In conclusion, VPAT may induce behavioral adaptation with modulation of the dorsal attentional network.

A Virtual Reality Application of the Rubber Hand Illusion Induced by Ultrasonic Mid-air Haptic Stimulation

Ultrasonic mid-air haptic technologies, which provide haptic feedback through airwaves produced using ultrasound, could be employed to investigate the sense of body ownership and immersion in virtual reality (VR) by inducing the virtual hand illusion (VHI). Ultrasonic mid-air haptic perception has solely been investigated for glabrous (hairless) skin, which has higher tactile sensitivity than hairy skin. In contrast, the VHI paradigm typically targets hairy skin without comparisons to glabrous skin. The aim of this article was to investigate illusory body ownership, the applicability of ultrasonic mid-air haptics, and perceived immersion in VR using the VHI. Fifty participants viewed a virtual hand being stroked by a feather synchronously and asynchronously with the ultrasonic stimulation applied to the glabrous skin on the palmar surface and the hairy skin on the dorsal surface of their hands. Questionnaire responses revealed that synchronous stimulation induced a stronger VHI than asynchronous stimulation. In synchronous conditions, the VHI was stronger for palmar stimulation than dorsal stimulation. The ultrasonic stimulation was also perceived as more intense on the palmar surface compared to the dorsal surface. Perceived immersion was not related to illusory body ownership per se but was enhanced by the provision of synchronous stimulation.