The Real Hand Illusion: Inducing disownership of the biological limb in virtual reality and the involvement of the right parietal cortex

Abstract

‘What does it mean to own a body?’ is a fundamental question regarding the nature of the self. The bottom-up perceptual and higher order processes of how we distinguish what is our own body from the environment have been of great interest in recent years. The now classical ‘rubber hand illusion’ revealed how embodiment of a like life rubber hand can be achieved through manipulating visuo-tactile information. However, the RHI and subsequent iterations have often failed to replicate the phenomenology of disorders such as Xenomelia and Somatoparaphrenia, where individuals do not report ownership of a limb(s), rather than the misattribution of ownership to an extrabodily object. Therefore, we have developed the ‘Real Hand Illusion’, which endeavours to reduce ownership of one’s own biological limb through a virtual reality illusion. Participants viewed their hand being stroked by a paintbrush in the virtual environment, in the illusory condition, there was a 400ms visual latency leading to a disruption of multisensory integration. Feelings of ownership were reduced in the illusory condition as measured by a self-report questionnaire generated by the researchers. We also sought to investigate whether right parietal regions are involved in the processing of multisensory data, as has been suggested through clinical cases of individuals with body ownership disorders. Electrical stimulation of the P4 region using tDCS successfully modulated feelings of ownership. Cathodal stimulation conditions resulted in significantly higher sensations of ownership than anodal conditions. We have therefore developed a novel virtual paradigm which more closely reflects the phenomenology of disorders such as Xenomelia. We have also provided further evidence for the involvement of right sided parietal regions in processing multisensory information, and subsequently leading to feelings of ownership.