The Bodily Illusion in Adverse Conditions: Virtual Arm Ownership During Visuomotor Mismatch

Classically, body ownership illusions are triggered by cross-modal synchronous stimulations, and hampered by multisensory inconsistencies. Nonetheless, the boundaries of such illusions have been proven to be highly plastic. In this immersive virtual reality study, we explored whether it is possible to induce a sense of body ownership over a virtual body part during visuomotor inconsistencies, with or without the aid of concomitant visuo-tactile stimulations. From a first-person perspective, participants watched a virtual tube moving or an avatar’s arm moving, with or without concomitant synchronous visuo-tactile stimulations on their hand. Three different virtual arm/tube speeds were also investigated, while all participants kept their real arms still. The subjective reports show that synchronous visuo-tactile stimulations effectively counteract the effect of visuomotor inconsistencies, but at slow arm movements, a feeling of body ownership might be successfully induced even without concomitant multisensory correspondences. Possible therapeutical implications of these findings are discussed

Pain During Illusory Own Arm Movement: A Study in Immersive Virtual Reality

Previous studies have demonstrated that the vision of one’s own body, or of external embodied limbs, can lead to pain relieving outcomes. Analgesic effects have also been related to the vision of illusory limb movements. Nonetheless, whether these two processes can be put together to obtain a summatory analgesic effect is not yet clear. The aim of this work was to investigate if it is possible to combine the analgesic effects of looking at one’s own body with those deriving from the illusion that one’s own limb is moving. Thirty-eight healthy participants underwent four visual conditions in immersive virtual reality while their heat pain thresholds were measured. In different conditions the subject watched from a first-person perspective: i) a still virtual arm, ii) a moving virtual arm, iii) a still non-corporeal object, and iv) a moving non-corporeal object. All participants were asked to keep their arms completely still during the visual exposures. After each condition, participants answered questions about their illusory experience. Our results show that the vision of the ‘own’ body significantly increased participants’ pain threshold as compared to the vision of the non-corporeal object. However, no statistically significant analgesic effect of vision of the virtual arm movement was found. The implications and limitations of this study are discussed

Altered visual feedback from an embodied avatar unconsciously influences movement amplitude and muscle activity

Evidence suggests that the sense of the position of our body parts can be surreptitiously deceived, for instance through illusory visual inputs. However, whether altered visual feedback during limb movement can induce substantial unconscious motor and muscular adjustments is not known. To address this question, we covertly manipulated virtual body movements in immersive virtual reality. Participants were instructed to flex their elbow to 90° while tensing an elastic band, as their virtual arm reproduced the same, a reduced (75°), or an amplified (105°) movement. We recorded muscle activity using electromyography, and assessed body ownership, agency and proprioception of the arm. Our results not only show that participants compensated for the avatar’s manipulated arm movement while being completely unaware of it, but also that it is possible to induce unconscious motor adaptations requiring significant changes in muscular activity. Altered visual feedback through body ownership illusions can influence motor performance in a process that bypasses awareness