When I was a kid, my dad and I plummeted down Niagara Falls together in a beer barrel. Well, maybe not exactly.  In reality, we handed a man five dollars, walked up the steps into a trailer on hydraulic stilts, and sat down in front of a movie screen. The next thing we knew we were careening down a class five rapid in an oak barrel towards our ultimate doom. I vividly remember our thrill ride to this day, because it felt so darn real.

Anyone who has dared to enter one of these virtual reality rides is plainly aware of the obvious mind game being played here. The combination of scenery jostling around on the screen, and the trailer springing the passenger in every which direction, tricks the brain into thinking the body, buckled securely in a padded seat, is experiencing something that in reality is not occurring.

This idea is now being used by scientists to simulate out of body experiences. In a study released this Wednesday in PLoS, entitled, “If I Were You: Perceptual Illusion of Body Swapping,” authors demonstrate that by combining visual and multisensory stimuli (touch or limb position), subjects felt as if they were inside another person’s body. The study, run by Valeria I. Petkova and Henrik Ehrsson of the Karolinska Institutet in Stockholm, Sweden, sites that, “this effect was so strong that people could experience being in another person’s body when facing their own body and shaking hands with it.”

The investigators achieved this illusion by placing a camera at eye level on a mannequin and feeding that visual information into a video head mount worn by the test subject. The subject was told to look downward, and as a result the subject saw the body of the mannequin instead of his or her own.  Next, an experimenter used a rod to simultaneously brush against the abdomen of the both the mannequin and the subject. The subjects reported that they perceived the mannequin body as their own and felt the touch of the rod on the belly of the human sized doll. Interestingly, when the mannequin was threatened with a knife to the abdomen, physiological responses linked to anxiety were significantly heightened in the participants.

Next, experimenters wanted to put the body swap illusion to the ultimate test.  Would the illusion of existing in another’s body persist when the subject sees his or her own body? To test this, the mannequin was replaced by an experimenter, whose eye-level cameras were targeted directly on the subject. This visual information was again fed into the subjects video helmet as the subject and the experimenter were instructed to shake hands. Despite being able to see their own bodies from the shoulders down, the subjects overwhelmingly perceived that they were shaking their own hands from the body of experimenter. Physiological anxiety responses  were higher when the experimenters hand was threatened with a knife than when the subjects own hand was in peril.

The sense of self, or the perception that the body belongs to the self has long been contemplated by philosophers and psychologists. This study demonstrates that the center of self can be moved outside of the physical body by manipulating multisensory information. The body swap illusion could serve as a useful tactic for researching body image or self-identity disorders in psychiatric patients.

Petkova explains that the body swap experience is a pleasurable one, “our subjects experienced this illusion as being exciting and strange, and often said that they wanted to come back and try it again.” This is a technology that could potentially be used to bring increasingly popular avatars to life. For me, living life through a computer representation of myself will never compare to thrill of falling down a virtual waterfall with my dad by my side.

photo credit: http://www.tourneyblog.com/

video credit: associated press/you tube