Measuring the effects through time of the influence of visuomotor and visuotactile synchronous stimulation on a virtual body ownership illusion

Previous studies have examined the experience of owning a virtual surrogate body or body part through specific combinations of cross-modal multisensory stimulation. Both visuomotor (VM) and visuotactile (VT) synchronous stimulation have been shown to be important for inducing a body ownership illusion, each tested separately or both in combination. In this study we compared the relative importance of these two cross-modal correlations, when both are provided in the same immersive virtual reality setup and the same experiment. We systematically manipulated VT and VM contingencies in order to assess their relative role and mutual interaction. Moreover, we present a new method for measuring the induced body ownership illusion through time, by recording reports of breaks in the illusion of ownership ("breaks") throughout the experimental phase. The balance of the evidence, from both questionnaires and analysis of the breaks, suggests that while VM synchronous stimulation contributes the greatest to the attainment of the illusion, a disruption of either (through asynchronous stimulation) contributes equally to the probability of a break in the illusion

Acquisition of ownership illusion with self-disownership in neurological patients

The multisensory regions in frontoparietal cortices play a crucial role in the sense of body and self. Disrupting this sense may lead to a feeling of disembodiment, or more generally, a sense of disownership. Experimentally, this altered consciousness disappears during illusory own-body perceptions, increasing the intensity of perceived ownership for an external virtual limb. In many clinical conditions, particularly in individuals with a discontinuous or absent sense of bodily awareness, the brain may effortlessly create a convincing feeling of body ownership over a surrogate body or body part. The immediate visual input dominates the current bodily state and induces rapid plastic adaptation that reconfigures the dynamics of bodily representation, allowing the brain to acquire an alternative sense of body and self. Investigating strategies to deconstruct the lack of a normal sense of bodily ownership, especially after a neurological injury, may aid the selection of appropriate clinical treatment

Body ownership illusion through virtual reality as modulator variable for limbs rehabilitation after stroke: a systematic review

Stroke is the leading cause of motor impairments and generates distortion of body representation. Hence, stroke can modulate the sense of embodiment, namely the feeling of being inside the body (ownership), in the place where the body is located (location), and moving the body according to its own intentions (agency). A growing number of studies have adopted virtual reality (VR) to train motor abilities. However, the impact of the body illusion on the rehabilitation outcome is not fully understood. The present systematic review investigates the modulating role of the body illusion elicited by VR on motor rehabilitation in post-stroke patients after embodying a virtual avatar. The research was led in the main databases—PubMed, Scopus, PsychINFO, and Web of Science—and four studies matched the inclusion criteria (e.g., to have a sample of adult post-stroke patients, to use VR as an instrument for motor rehabilitation, to adopt the paradigm of the body illusion as a modulator for motor rehabilitation, to test the sense of body illusion outcome). Research outcomes demonstrated that two studies adopted the immersive and two the non-immersive embodied VR; three studies focused on the upper limb, and one on lower limb rehabilitation. Two studies compare VR training with traditional therapy, and two are pilot studies with only one experimental group. The studies demonstrated the feasibility of the body illusion as an accelerator for motor rehabilitation compared to the non-embodied condition, and as a positive correlator of the rehabilitation outcome. The finding should be taken with caution due to the limited studies included; however, they are encouraging to justify further research efforts in this area

The Perspective Matters! Multisensory Integration in Ego-Centric Reference Frames Determines Full-Body Ownership

Recent advances in experimental science have made it possible to investigate the perceptual processes involved in generating a sense of owning an entire body. This is achieved by full-body ownership illusions which make use of specific patterns of visual and somatic stimuli integration. Here we investigate the fundamental question of the reference frames used in the process of attributing an entire body to the self. We quantified the strength of the body-swap illusion in conditions where the participants were observing this artificial body from the perspective of the first or third person. Consistent results from subjective reports and physiological recordings show that the first person visual perspective is critical for the induction of this full-body ownership illusion. This demonstrates that the multisensory integration processes producing the sense of corporeal self operates in an ego-centric reference frame

Learning empathy through virtual reality : Multiple strategies for training empathy-related abilities using body ownership Illusions in embodied virtual reality

Several disciplines have investigated the interconnected empathic abilities behind the proverb “to walk a mile in someone else’s shoes” to determine how the presence, and absence, of empathy-related phenomena affect prosocial behavior and intergroup relations. Empathy enables us to learn from others’ pain and to know when to offer support. Similarly, virtual reality (VR) appears to allow individuals to step into someone else’s shoes, through a perceptual illusion called embodiment, or the body ownership illusion. Considering these perspectives, we propose a theoretical analysis of different mechanisms of empathic practices in order to define a possible framework for the design of empathic training in VR. This is not intended to be an extensive review of all types of practices, but an exploration of empathy and empathy-related phenomena. Empathy-related training practices are analyzed and categorized. We also identify different variables used by pioneer studies in VR to promote empathy-related responses. Finally, we propose strategies for using embodied VR technology to train specific empathy-related abilities

Eye-Tracking and Virtual Reality-based Attentional Bias Modification Training to Improve Mirror Exposure Therapy: preliminary findings from a multiple case study with Anorexia Nervosa patients

Attentional bias modification training (ABMT) is an effective technique for reducing the dysfunctional body-related attentional bias (AB) that may be responsible for reducing the effectiveness of mirror exposure therapy (MET), which has been proposed as an effective treatment for anorexia nervosa ( AN). This multiple-case study provides evidence of the usefulness of incorporating ABMT into virtual reality ( VR) and eye-tracking (ET)-based MET to improve its efficacy in the treatment of four female adolescents with AN. Over five exposure sessions, patients were immersed in a virtual environment and were embodied in a real-size body virtual avatar reflected in a mirror that gradually increased body mass index (BMI) until reaching a healthy BMI in the last session. In every session, the participants completed the ABMT followed by the MET. This augmentation of MET using VRET-based ABMT achieved promising results for targeting AN symptomatology by reducing body dissatisfaction, drive for thinness, weight-related body parts anxiety, body checking behaviors, fear of gaining weight, and anxiety, and increasing body appreciation. Two patients who did not show a reduction in fear of gaining weight during the sessions also showed high anxiety levels, which could have affected its reduction. To advance this preliminary study and evaluate the effectiveness of incorporating ABMT into MET, a controlled clinical trial will be conducted

Sensory integration through the scope of body ownership

Sensory integration is the process by which the brain combines distinct sensory modalities, such that the merged information can be efficiently used to interact with the environment. Body ownership is an example of a subjective experience that emerges through sensory integration. The mechanisms of sensory integration are not yet fully understood. By employing illusions such as the body ownership illusion, where a person falsely perceives an artificial limb as part of their body, brain processes governing sensory integration can be investigated. In this PhD project, a virtual reality platform capable of eliciting a body ownership illusion via accurately timed visuo-tactile stimulation was developed, and used as a tool for studying sensory integration. A threat perception experiment, and an experiment inducing visuo-tactile stimulation with temporal delay were conducted using this platform. Biophysical and behavioural results from this study showed that threat perception and body ownership are not necessarily correlated, but can be viewed as parallel processes within the context of embodiment, and can be observed in distinct neural correlates of brain activity. Based on the results from these studies, it is proposed that the experience of body ownership is not an all-or-nothing, binary experience, but instead, can be considered as a graded experience and having multiple levels

The relationship between virtual body ownership and temperature sensitivity.

In the rubber hand illusion tactile stimulation seen on a rubber hand, that is synchronous with tactile stimulation felt on the hidden real hand, can lead to an illusion of ownership over the rubber hand. This illusion has been shown to produce a temperature decrease in the hidden hand, suggesting that such illusory ownership produces disownership of the real hand. Here we apply immersive virtual reality (VR) to experimentally investigate this with respect to sensitivity to temperature change. Forty participants experienced immersion in a VR with a virtual body (VB) seen from a first person perspective. For half the participants the VB was consistent in posture and movement with their own body, and in the other half there was inconsistency. Temperature sensitivity on the palm of the hand was measured before and during the virtual experience. The results show that temperature sensitivity decreased in the consistent compared to the inconsistent condition. Moreover, the change in sensitivity was significantly correlated with the subjective illusion of virtual arm ownership but modulated by the illusion of ownership over the full virtual body. This suggests that a full body ownership illusion results in a unification of the virtual and real bodies into one overall entity - with proprioception and tactile sensations on the real body integrated with the visual presence of the virtual body. The results are interpreted in the framework of a"body matrix" recently introduced into the literature

Drumming in immersive virtual reality: the body shapes the way we play

It has been shown that it is possible to generate perceptual illusions of ownership in immersive virtual reality (IVR) over a virtual body seen from first person perspective, in other words over a body that visually substitutes the person's real body. This can occur even when the virtual body is quite different in appearance from the person's real body. However, investigation of the psychological, behavioral and attitudinal consequences of such body transformations remains an interesting problem with much to be discovered. Thirty six Caucasian people participated in a between-groups experiment where they played a West-African Djembe hand drum while immersed in IVR and with a virtual body that substituted their own. The virtual hand drum was registered with a physical drum. They were alongside a virtual character that played a drum in a supporting, accompanying role. In a baseline condition participants were represented only by plainly shaded white hands, so that they were able merely to play. In the experimental condition they were represented either by a casually dressed dark-skinned virtual body (Casual Dark-Skinned - CD) or by a formal suited light-skinned body (Formal Light-Skinned - FL). Although participants of both groups experienced a strong body ownership illusion towards the virtual body, only those with the CD representation showed significant increases in their movement patterns for drumming compared to the baseline condition and compared with those embodied in the FL body. Moreover, the stronger the illusion of body ownership in the CD condition, the greater this behavioral change. A path analysis showed that the observed behavioral changes were a function of the strength of the illusion of body ownership towards the virtual body and its perceived appropriateness for the drumming task. These results demonstrate that full body ownership illusions can lead to substantial behavioral and possibly cognitive changes depending on the appearance of the virtual body. This could be important for many applications such as learning, education, training, psychotherapy and rehabilitation using IVR

Drift and ownership toward a distant virtual body.

In body ownership illusions participants feel that a mannequin or virtual body (VB) is their own. Earlier results suggest that body ownership over a body seen from behind in extra personal space is possible when the surrogate body is visually stroked and tapped on its back, while spatially and temporal synchronous tactile stimulation is applied to the participant's back. This result has been disputed with the claim that the results can be explained by self-recognition rather than somatic body ownership. We carried out an experiment with 30 participants in a between-groups design. They all saw the back of a VB 1.2 m in front, that moved in real-time determined by upper body motion capture. All felt tactile stimulation on their back, and for 15 of them this was spatially and temporally synchronous with stimulation that they saw on the back of the VB, but asynchronous for the other 15. After 3 min a revolving fan above the VB descended and stopped at the position of the VB neck. A questionnaire assessed referral of touch to the VB, body ownership, the illusion of drifting forwards toward the VB, and the VB drifting backwards. Heart rate deceleration (HRD) and the amount of head movement during the threat period were used to assess the response to the threat from the fan. Results showed that although referral of touch was significantly greater in the synchronous condition than the asynchronous, there were no other differences between the conditions. However, a further multivariate analysis revealed that in the visuotactile synchronous condition HRD and head movement increased with the illusion of forward drift and decreased with backwards drift. Body ownership contributed positively to these drift sensations. Our conclusion is that the setup results in a contradiction-somatic feelings associated with a distant body-that the brain attempts to resolve by generating drift illusions that would make the two bodies coincide