Researchers at the Karolinska Institutet have managed to convince people they are inside another person’s body, showing both how our sense of self is an emergent property of the brain, and also how tenuous it really is.

To create the illusion of occupying the dummy’s body, the team stroked the abdomen of the subject and the dummy at the same time while the subject watched the stroking via the cameras on the dummy’s head. As a result, subjects reported a strong feeling that the dummy’s body was their own. The technique is similar to the “rubber hand illusion”, in which a subject can be convinced that a rubber hand is his or her own, but this is the first time the illusion has been extended to a whole body.

The illusion was so convincing that when the researchers threatened the dummy with a knife they recorded an increase in the subject’s skin conductance response - the indicator of stress that polygraph lie detector tests rely on. “This shows how easy it is to change the brain’s perception of the physical self,” said Ehrsson, who led the project. “By manipulating sensory impressions, it’s possible to fool the self not only out of its body but into other bodies too.”

Things got even weirder when the researchers dispensed with the dummy and put the cameras on the head of another person. After carrying out the same double stroking routine the subjects were convinced that they were occupying another person’s body. The illusion persisted even when the other person came over and shook the subject’s hand, producing the sensation of the subject feeling as if they were shaking hands with themselves.