And as with the rubber hand, stroking the real and artificial stomachs out of time ruined the effect and broke the illusion. The recruits' responses to a questionnaire showed that they sensed the touch of the rod on the mannequin's stomach and, more importantly, that the mannequin's body was their body. The volunteer felt the movement on their own body while seeing the same movement on the artificial stomach. The experimenter then used a short rod to simultaneously stroke the volunteer's stomach and the mannequin's. The duo gave 32 young adults a mannequin's-eye-view of the world, by asking them to wear head-mounted displays connected to cameras mounted on a mannequin's head. The delusion is so powerful that the person can shake hands with their own real body without breaking the spell.

Petkova and Ehrsson have now taken these illusions to a new extreme, tricking people into thinking that an entire body, rather than just a mere hand, is their own. So is point-of-view - in a previous experiment, Ehrsson showed that he could induce an out-of-body experiment in the lab by combining the simultaneous stroking of the rubber-hand illusion with virtual reality headsets to show people views of their own backs. The illusion shows that timing is important. The most famous of these involves a rubber hand - by stroking it at the same time as a person's real hand (which is hidden from view), you can convince them that the rubber one is actually theirs. The sense of bodily ownership can even be deceived in normal, healthy people, through the use of illusions. But some people do suffer from brain damage that prevents them from accurately recognising their own limbs, or causes them to experience out-of-body experiences. The idea that our bodies are part of ourselves is so obvious and permanent that it seems ridiculous to consider any other alternative.

Body swap fiction