The Influence of Top-Down Interpretations on the Full-Body Illusion: An Examination of the Relationship Between the Observer-Self and Self-Body
Kazuki Yamamoto, Ren Sakamoto, Takashi Nakao · 2024
The full-body illusion (FBI) demonstrates the malleability of the sense of body ownership through multisensory integration. Although the impact of bottom-up processes in the FBI is well documented, the role of top-down factors remains unclear. This study investigated how different interpretations of the relationship between the observer-self and a virtual body, considered the self-body in a third-person FBI, influence the occurrence and strength of the FBI. The study is guided by predictive coding theory. We employed a virtual-reality-based third-person perspective FBI paradigm with 66 healthy participants. Participants were randomly assigned to two interpretation conditions: an integration condition (instructed to view the virtual body as their own) and a separation condition (instructed to view the virtual body as a separate body that exists in virtual reality, distinct from their current physical self-body). Both conditions included synchronous and asynchronous visuo-tactile stimulation. The strength of the FBI was measured objectively via skin conductance response (SCR) to a threat stimulus and subjectively using an illusion questionnaire. The results showed that the integration condition experienced a significant occurrence of the FBI, as indicated by a higher SCR in the synchronous versus asynchronous stimulation. Conversely, the separation condition showed no significant difference in SCR, suggesting the absence of the FBI. A comparison of the strength of the FBI between conditions revealed significantly stronger illusions in the integration condition than in the separation condition, supporting the influence of top-down interpretation on the FBI. Our findings provide empirical evidence of the role of top-down interpretations in modulating FBI, extending the predictive coding framework of body ownership. This study contributes to our understanding of body ownership as a complex interplay between sensory inputs and cognitive predictions rather than a purely bottom-up process.