Illusory ownership of re-associated virtual body parts
Body ownership can be induced to fake or virtual bodies (illusory body ownership). Observers feel as though a rubber hand is their own hand through simultaneous and synchronous visual-tactile stimulations; It is the rubber hand illusion . When a virtual avatar’s movement is synchronized with an observer’s movement, the observer feels as if the avatar is their own body (full body illusion) . Thus, visual-motor synchronicity also induces illusory body ownership. Illusory body ownership can be induced even for bodies of a different age  or race . However, the associations between body parts are maintained; For example, the real right hand corresponds to the rubber right hand.Sasaki et al (2017)  created a four-arm interaction by adding two robot arms that were synchronized with the left and right leg movements. In this line, we aimed to investigate if illusory body ownership could be induced by the visual-motor synchronicity of different body parts, and investigate if a body-part remapping can be implemented.
Participants moved their right thumb freely, and observed a virtual right arm through a head-mounted display (HMD: Oculus Rift DK2) for 5 min. The virtual right arm was synchronous or asynchronous with the observers’ actions. A motion capture system (Noitom Perception Neuron) detected the observer’s right thumb movements, and applied them to the virtual arm in the synchronous condition. Two prerecorded motions of an experimenter’s right thumb were applied to motions of the virtual right arm in the asynchronous condition. A virtual knife was presented to measure the SCR (skin conductance response) at the end of each trial. The SCR was measured by BIOPAC MP150. Participants pointed to the position where they felt the tip of their right thumb met with their left index finger under the table (self-localization task). The virtual right arm was presented on the right of the body. After the task, participants were asked to complete a questionnaire regarding body ownership on a seven-level Likert scale from 1 (I did not feel that at all) to 7 (I felt it extremely strongly).
We found that the questionnaire scores were higher in the synchronous condition than in the asynchronous condition. These results suggest that the participants felt as though their own right thumb became the virtual right arm, and illusory body ownership was induced though the synchronization of different body parts. We did not obtain a significant startle response. Self-localization drifted toward the virtual right arm more in the synchronous condition than in the asynchronous condition. It is considered that the right thumb was pulled into the position of the virtual right arm.Our study will enable us to control an arm using a finger with body ownership. Thus, two arms can operate concurrently and independently using a finger and an arm. This may contribute to supporting people with limb deficits.
Kondo, R., Tani, Y., Sugimoto, M., Minamizawa, K., Inami, M. and Kitazaki, M. (2018). Illusory body ownership between different body parts: Synchronization of right thumb and right arm. IEEE Virtual Reality 2018, Reutlingen, Germany, March 18-22.
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Re-association of Body Parts: Illusory Ownership of a Virtual Arm Associated with the Contralateral Real Finger by Visuo-motor Synchrony.Frontiers in Robotics and AI: Virtual Environments, 7:26.Kondo, R., Tani, Y., Sugimoto, M., Minamizawa, K., Inami, M., and Kitazaki, M.ＤＯＩ10.3389/frobt.2020.00026