December 4, 2008

Scientists create body swapping illusion

Swedish neuroscientists say they have demonstrated, for the first time, that people can perceive another body to be their own.

Valeria Petkova and Dr. H. Henrik Ehrsson of the Karolinska Institute in Stockholm, Sweden, conducted five experiments, during which participants wore a head-mounted video display that showed high-fidelity, stereoscopic images taken from cameras in the eyes of a life-sized, male mannequin.

Asked to tilt their heads downward, the participants saw the mannequin's body respond but not their own. Responses to a questionnaire showed that participants perceived the mannequin's body as their own when a rod simultaneously stroked the abdomen of the participant and the mannequin, the researchers said. And when experimenters threatened the mannequin with a knife, participants displayed a physiological response to the threat.

The scientists said the illusion was so strong that people could experience being in another person's body when facing their own body and shaking hands with it.

The scientists concluded that to create the illusion, there had to be (1) a continuous match between visual and tactile cues about the body; (2) the use of a sufficiently humanoid body; and (3) images corresponding to what one would see from the eyes of the other body.

The study is detailed in the online journal PLOS One.