With hand on heart: A cardiac Rubber Hand Illusion

Body illusions such as the Rubber Hand Illusion (RHI) have highlighted how multisensory integration underpins the sense of one's own body. Much of this research has focused on senses arising from outside the body (e.g. vision and touch), but sensations from within the body may also play a role. In a pre-registered study, participants completed a cardiac variation of the RHI, where taps to the finger occurred in or out of time with the heartbeat. We replicated the RHI effect, showing that synchronous but not asynchronous taps to the real and rubber hand increased sensations of embodiment over the rubber hand and caused a shift in the perceived hand location. However, there were no significant influences of cardiac timing on embodiment, nor did it interact with visuo-tactile synchrony. An exploratory analysis found a three-way interaction between synchrony, cardiac timing and interoceptive accuracy as measured by a heartbeat counting task, such that greater interoceptive accuracy was associated with lower embodiment ratings in the systole condition compared to diastole, but only during synchronous stimulation. Although our novel methodology successfully replicated the RHI, our findings suggest that the cooccurence of vision and touch with cardiac signals may make little contribution to the sense of one's body.