Effects of Body Duplication and Split on Body Schema

Visual-tactile synchronization or visual-motor synchronization makes a not innate body feel as if it was one's own body (illusory body ownership). Although recent studies have shown that body ownership can be induced in multiple bodies, it is unclear whether the body ownership is switched between bodies, or we feel that multiple bodies belong to us simultaneously. If the body ownership is induced in multiple bodies simultaneously, we expected the body schema to be extended to correspond to the number of bodies. In this study, we investigated whether body ownership is induced in multiple bodies simultaneously by measuring the body schema when the bodies are replicated and split. Experiment 1 investigated whether two side-by-side virtual bodies moved synchronously with the participant's movements to extend the body schema. In Experiment 2, virtual split bodies in which a virtual body was split into left and right sides were presented. As a result, the body schema was extended only in the split bodies. However, it changed even in the no body ownership condition, suggesting that the appearance of the split bodies simply affected the body schema, not that body ownership of the split bodies occurred at the same time. The results of the questionnaire indicated that the split bodies might be perceived as a single body.