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Mind games: Researchers trick people into thinking they've swapped bodies

Scientists at the Karolinska Institute (K.I.) in Stockholm report that they were able to make people perceive the bodies of mannequins and other people as their own. Their findings, published online this week by PLoS ONE, could help people suffering from body image disorders and be a boon for virtual reality developers to improve the control and realism of their systems and robot makers eager to create appendages that can more easily be remotely controlled.

"Our limbs and body always present themselves in certain orientations because our eyes are fixed to our skull," study co-authors Henrik Ehrsson and Valerie Petkova, both cognitive neuroscientists, write. But they note that if this visual perspective is changed, the mind can be tricked into believing that the body is in a different place, a condition exploited by virtual reality to make a person feel like he or she is flying a plane, driving a car or riding a rollercoaster while simply sitting in front of a computer or movie screen. (See this YouTube video of the experiments from the Associated Press)

In the first experiment, Ehrsson and Petkova fitted the head of a store mannequin with two cameras connected to goggles over study participants eyes that made them see the mannequin’s body from the perspective of the mannequin's head. The researchers then touched the abdomens of subjects and the mannequin (either simultaneously or at different times) with sticks The subjects could see the stick touching the mannequin but could not see the stick touching their own body.

When the experiment ended, participants filled out questionnaires about what they had experienced. Their responses indicated they had "felt" jabs to the mannequin as if their own bodies had been touched.

The researchers also experimented with mounting a camera on another person's head instead of on a mannequin. Ehrsson and Petkova successfully predicted that the participants would feel as though they were in the other person's body if they turned toward one another and shook hands. The researchers found that participants felt the handshake from the perspective of the  other person rather than from their own limbs.

The body-swapping illusion worked even when the two people differed in appearance or were of different sexes, but the researchers were not able to fool their subjects into thinking they were a chair or some other non-humanoid inanimate object.

The results show how easy it is to change the brain's perception of the physical self, Ehrsson, said in a statement.


(Images courtesy of Karolinska Institutet, Stockholm, Sweden)

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