SELF-UNITY successfully met all the major project aims and made significant progress in clarifying the cognitive processes and brain mechanisms that mediate the sense of a unified bodily self.
In Work Package (WP) 1, we developed illusion paradigms to investigate how people perceive their entire body as their own (full-body ownership) and how this experience relates to the ownership of individual body parts (body-part ownership). Our studies found that while the senses of ownership of body parts and the full body are correlated and follow similar rules, full-body ownership is more than the sum of its parts and reflects a global bodily percept. fMRI experiments revealed that body-part and full-body ownership involve different active areas in the premotor, subcortical, and posterior parietal regions, and that part and full-body ownership are associated with different fine-grained activity patterns within these regions, reflecting distinct processes.
In WP2, we conducted behavioral and neuroimaging studies to investigate how the vestibular sense contributes to the sense of bodily self. We found that full-body ownership can be triggered solely by congruent visual and vestibular stimulation, that tactile and vestibular signals work together to promote a unified bodily experience, and that vestibular influences on body ownership are mediated by activated areas in the parietal operculum.
In WP3, e developed novel illusion paradigms to trigger body ownership illusions by stimulating thermoreceptors and nociceptors in the skin—'skin-based interoception.’ We found that signals from these somatosensory receptors, which carry information about the physiological condition of the body, follow the same basic multisensory rules for body ownership as vision and touch. Our neuroimaging findings suggest that the insular and temporal cortices mediate the integration of skin-based interoceptive signals with other bodily-related signals for body ownership.
Finally, in WP4, we developed new “dual-body” and “supernumerary limb” illusions, wherein people simultaneously experience two separate bodies as their own or feel like they have an extra arm. These findings are important because they suggest that the sense of a unified bodily self located in a specific place results from an active and dynamic multisensory integration process. fMRI experiments have pinpointed a specific region in the inferior posterior parietal cortex that may play a critical role in the dual-body illusion and in maintaining a cohesive singular bodily self.
Additionally, we conducted several studies to validate our methods and developed signal detection theory approaches and computational models for bodily illusion experiments to quantify body ownership perception more rigorously, achieving stronger mechanistic and explanatory power. We disseminated our findings through review articles, book chapters, and presentations at numerous scientific conferences (e.g. Society for Neuroscience). We also organized a workshop on bodily illusions and body ownership and shared our findings with the general public through press releases, events, podcasts, and interviews.