Visual feedback from a virtual body modulates motor illusion induced by tendon vibration

Leveraging Tendon Vibration to Enhance Pseudo-Haptic Perceptions in VR

Pseudo-haptic techniques are used to modify haptic perception by appropriately changing visual feedback to body movements. Based on the knowledge that tendon vibration can affect our somatosensory perception, this article proposes a method for leveraging tendon vibration to enhance pseudo-haptics during free arm motion. Three experiments were performed to examine the impact of tendon vibration on the range and resolution of pseudo-haptics. The first experiment investigated the effect of tendon vibration on the detection threshold of the discrepancy between visual and physical motion. The results indicated that vibrations applied to the inner tendons of the wrist and elbow increased the threshold, suggesting that tendon vibration can augment the applicable visual motion gain by approximately 13% without users detecting the visual/physical discrepancy. Furthermore, the results demonstrate that tendon vibration acts as noise on haptic motion cues. The second experiment assessed the impact of tendon vibration on the resolution of pseudo-haptics by determining the just noticeable difference in pseudo-weight perception. The results suggested that the tendon vibration does not largely compromise the resolution of pseudo-haptics. The third experiment evaluated the equivalence between the weight perception triggered by tendon vibration and that by visual motion gain, that is, the point of subjective equality. The results revealed that vibration amplifies the weight perception and its effect was equivalent to that obtained using a gain of 0.64 without vibration, implying that the tendon vibration also functions as an additional haptic cue. Our results provide design guidelines and future work for enhancing pseudo-haptics with tendon vibration.

Interactive Virtual Ankle Movement Controlled by Wrist sEMG Improves Motor Imagery: An Exploratory Study

Virtual reality (VR) techniques can significantly enhance motor imagery training by creating a strong illusion of action for central sensory stimulation. In this article, we establish a precedent by using surface electromyography (sEMG) of contralateral wrist movement to trigger virtual ankle movement through an improved data-driven approach with a continuous sEMG signal for fast and accurate intention recognition. Our developed VR interactive system can provide feedback training for stroke patients in the early stages, even if there is no active ankle movement. Our objectives are to evaluate: 1) the effects of VR immersion mode on body illusion, kinesthetic illusion, and motor imagery performance in stroke patients; 2) the effects of motivation and attention when utilizing wrist sEMG as a trigger signal for virtual ankle motion; 3) the acute effects on motor function in stroke patients. Through a series of well-designed experiments, we have found that, compared to the 2D condition, VR significantly increases the degree of kinesthetic illusion and body ownership of the patients, and improves their motor imagery performance and motor memory. When compared to conditions without feedback, using contralateral wrist sEMG signals as trigger signals for virtual ankle movement enhances patients' sustained attention and motivation during repetitive tasks. Furthermore, the combination of VR and feedback has an acute impact on motor function. Our exploratory study suggests that the sEMG-based immersive virtual interactive feedback provides an effective option for active rehabilitation training for severe hemiplegia patients in the early stages, with great potential for clinical application.

Does Embodying a Divine Avatar Influence Moral Decisions? An Immersive Virtual Reality Study

The term Proteus effect refers to the changes in attitudes and behavior induced by the characteristics of an embodied virtual agent. Whether the effect can extend to the moral sphere is currently unknown. To deal with this issue, we investigated if embodying virtual agents (i.e., avatars) with different characteristics modulate people's moral standards differentially. Participants were requested to embody an avatar resembling the Christian God in His anthropomorphic appearance or a control human avatar and to perform a text-based version of incidental and instrumental dilemmas in a virtual environment. For each participant, we recorded (1) chosen options (deontological vs. utilitarian), (2) decision times, (3) postdecision feelings, and (4) physiological reactions (skin conductance response and heart rate). We found that embodying God vs. a control avatar did not change the performance in the moral dilemma task, indicating that no strong Proteus effect was at play in our experimental conditions. We interpreted this result by examining the constraints and limitations of our task, reasoning about the necessary conditions for eliciting the Proteus effect, and discussing future developments and advances in the field. Moreover, we presented compelling effects concerning dilemma type, chosen option, personality traits, and religion affiliation, thus supporting and extending literature on decision making in moral dilemmas.

Michelangelo Effect in Virtual Sculpturing: Prospective for Motor Neurorehabilitation in the Metaverse

We investigated the Michelangelo effect, i.e. the facilitatory effect of a virtual art therapy in motor rehabilitation (Iosa et al. 2021), with a novel virtual reality paradigm in which users are engaged in motor exercises with 3D sculptures. In particular, thirty young adults were immersed in a virtual environment where they could sculpt, by using the real hands, some famous sculptures in the history of art, such as the David of Michelangelo, the Venus of Milo and the statue of Laocoon and His Sons, and their control stimuli, i.e. statues in very low resolution or cubes. We recorded the kinematics (length, the time to complete each trial, mean normalized jerk) and questionnaire answers (objective and subjective beauty, User Satisfaction Evaluation Questionnaire and Nasa Task Load Index). In general, we found that the perception of subjective and objective beauty was higher when sculpting the statues than control stimuli, the judgment of usability of the system was high. The perceived fatigue was not higher when sculpting the statues despite the longer time spent in completing the task that with respect to the control stimuli. Moreover, we found that the interaction with the experimental statues affected the fluidity and symmetry of hands movements. Finally, we discuss this evidence regarding the art therapy and neuroaesthetics principles for motor rehabilitation in the Metaverse with VR, including the possible role of virtual embodiment (illusory feeling to have a virtual body) for boosting the efficacy of the clinical applications.

Combined EEG and immersive virtual reality unveil dopaminergic modulation of error monitoring in Parkinson's Disease

Detecting errors in your own and others' actions is associated with discrepancies between intended and expected outcomes. The processing of salient events is associated with dopamine release, the balance of which is altered in Parkinson's disease (PD). Errors in observed actions trigger various electrocortical indices (e.g. mid-frontal theta, error-related delta, and error positivity [oPe]). However, the impact of dopamine depletion to observed errors in the same individual remains unclear. Healthy controls (HCs) and PD patients observed ecological reach-to-grasp-a-glass actions performed by a virtual arm from a first-person perspective. PD patients were tested under their dopaminergic medication (on-condition) and after dopaminergic withdrawal (off-condition). Analyses of oPe, delta, and theta-power increases indicate that while the formers were elicited after incorrect vs. correct actions in all groups, the latter were observed in on-condition but altered in off-condition PD. Therefore, different EEG error signatures may index the activity of distinct mechanisms, and error-related theta power is selectively modulated by dopamine depletion. Our findings may facilitate discovering dopamine-related biomarkers for error-monitoring dysfunctions that may have crucial theoretical and clinical implications.

Embodying the avatar of an omnipotent agent modulates the perception of one's own abilities and enhances feelings of invulnerability

Immersive virtual reality can give people the illusion of owning artificial bodies (i.e., avatars) and controlling their actions. Tellingly, people appear to adhere to the newly embodied entities not just on the basis of physical traits but also behaving accordingly with the hallmarks of the represented characters. In two studies we pushed the limits of this process by testing if one's own sense of power could be affected by embodying the anthropomorphic representation of the Christian God, that is considered an omnipotent entity. A human Muscled and a Normotype avatar were used as controls. Results showed that participants embodying the God-avatar: (i) reacted to a threatening event compromising their physical safety by exhibiting a lower skin conductance response and heart rate deceleration compared to the Normotype-control avatar (Study 1); (ii) estimated they had more physical abilities compared to both the Normotype-control and the Muscled-control avatars (Study 2). Taken together, our findings suggest that embodying an omnipotent agent may exert an influence on people's perception of their own limits and capabilities, nourishing feelings of physical invulnerability and strength. Our study indicates that effectively embodying virtual role models may boost achievements and have translational implications in the field of empowerment.

Reduced ownership over a virtual body modulates dishonesty

Although studies suggest that even higher-order functions can be embodied, whether body awareness may bias moral decisions toward (dis)honesty remains underinvestigated. Here, we tested if the Sense of body Ownership (SoO) and the magnitude of monetary rewards influence the tendency to act immorally. Through a virtual body, participants played a card game in which they could lie to others to steal high or low amounts of money. To manipulate SoO, the virtual body was seen and controlled from a first-person perspective, with hands attached or detached, or from a third-person perspective. In third-person perspective, SoO was significantly reduced and more egoistic lies were produced in high reward conditions. Thus, SoO reduction and high monetary reward facilitate dishonest behavior, likely by separating the self from the dishonest actions performed through the disowned body. Because most future interactions will likely occur in a digital metaverse, our results may have crucial societal impact.

Wearing same- and opposite-sex virtual bodies and seeing them caressed in intimate areas

Immersive virtual reality enables people to undergo the experience of owning an artificial body and vicariously feeling tactile stimuli delivered to it. However, it is currently unknown how such experiences are modified by the sexual congruency between the human and the artificial agent. In two studies, heterosexual men (Experiment 1) and women (Experiment 2) embodied same-sex and opposite-sex avatars and were asked to evaluate the experience (e.g., pleasantness, erogeneity) of being touched on social or intimate areas of their virtual body by a male or female avatar. Electrocardiogram and galvanic skin response were also recorded. Moreover, participants' implicit and explicit gender biases were examined via a gender-potency implicit association test and the Ambivalent Sexism Inventory. When embodying a same-sex avatar, men and women rated caresses on intimate areas from an avatar of the opposite sex as more pleasant and erogenous. Conversely, body swap-that is, wearing an opposite-sex avatar-enhanced participants' perceptions of pleasantness and erogeneity for caresses on intimate areas from a same-sex toucher. This effect was stronger in men than in women. Furthermore, physiological correlates of enhanced processing of arousing stimuli predicted behavioural outcomes during the body swap illusion. Wearing an opposite-sex avatar affects one's own body representations and may have important implications on people's attitudes and implicit reactivity to touch-mediated interactions. Men seem more susceptible to this type of body swap illusion. Our paradigm may induce profound changes of cross-sex perspective-taking and provide novel tools for promoting empathy and comprehension of sex-related diversity.

How to lose a hand: Sensory updating drives disembodiment

Body representations are readily expanded based on sensorimotor experience. A dynamic view of body representations, however, holds that these representations cannot only be expanded but that they can also be narrowed down by disembodying elements of the body representation that are no longer warranted. Here we induced illusory ownership in terms of a moving rubber hand illusion and studied the maintenance of this illusion across different conditions. We observed ownership experience to decrease gradually unless participants continued to receive confirmatory multisensory input. Moreover, a single instance of multisensory mismatch – a hammer striking the rubber hand but not the real hand – triggered substantial and immediate disembodiment. Together, these findings support and extend previous theoretical efforts to model body representations through basic mechanisms of multisensory integration. They further support an updating model suggesting that embodied entities fade from the body representation if they are not refreshed continuously.

"eLoriCorps Immersive Body Rating Scale": Exploring the Assessment of Body Image Disturbances from Allocentric and Egocentric Perspectives

The first objective of this study was to test the convergent and discriminant validity between the “eLoriCorps Immersive Body Rating Scale” and the traditional paper-based figure rating scale (FRS). The second objective was to explore the contribution of the egocentric virtual reality (VR) perspective of eLoriCorps to understanding body image disturbances (BIDs). The sample consisted of 53 female and 13 male adults. Body size dissatisfaction, body size distortion, perceived body size, and ideal body size were assessed. Overall, outcomes showed good agreement between allocentric perspectives as measured via VR and the FRS. The egocentric VR perspective produced different results compared to both the allocentric VR perspective and the FRS. This difference revealed discriminant validity and suggested that eLoricorps’ egocentric VR perspective might assess something different from the traditional conception of body dissatisfaction, which an allocentric VR perspective generally assesses. Finally, the egocentric VR perspective in assessing BIDs deserves to be studied more extensively to explore the possibility of finding two types of body image distortion: (a) an egocentric perceptual body distortion, referring to internal body sensation affected by intra-individual changes, and (b) an allocentric perceptual body distortion, referring to external body benchmarks constructed by inter-individual comparison occurring in a given cultural context.