Prominent theories highlight the importance of bodily perception for self-consciousness, but it is currently not known whether bodily perception is based on interoceptive or exteroceptive signals or on integrated signals from these anatomically distinct systems. In the research reported here, we combined both types of signals by surreptitiously providing participants with visual exteroceptive information about their heartbeat: A real-time video image of a periodically illuminated silhouette outlined participants’ (projected, “virtual”) bodies and flashed in synchrony with their heartbeats. We investigated whether these “cardio-visual” signals could modulate bodily self-consciousness and tactile perception. We report two main findings. First, synchronous cardio-visual signals increased self-identification with and self-location toward the virtual body, and second, they altered the perception of tactile stimuli applied to participants’ backs so that touch was mislocalized toward the virtual body. We argue that the integration of signals from the inside and the outside of the human body is a fundamental neurobiological process underlying self-consciousness.
Experimental setup for the body conditions. Participants (a) stood with their backs facing a video camera placed 200 cm behind them (b). The video showing the participant’s body (his or her “virtual body”) was projected in real time onto a head-mounted display. An electrocardiogram was recorded, and R peaks were detected in real time (c), triggering a flashing silhouette outlining the participant’s virtual body (d). The display made it appear as though the virtual body was standing 200 cm in front of the participant (e). After each block, participants were passively displaced 150 cm backward to the camera and were instructed to walk back to the original position.