“Participants in a recent psychological study will probably never a look at mannequins – or their own bodies – in quite the same way again. Before the study, they knew their ar ms belonged to them and synthetic ones didn ’t, simply because seeing is believing. Now they ’re not so sure. Researchers at Car negie Mellon University in Pittsburgh asked subjects to keep their eyes on a rubber ar m that was sitting on a table in front of them, With the subject ’s left arm hidden from view by a screen, the researchers simultaneously stroked both the rubber hand and the subject ’s hand with a paintbrush. Even though they knew their own hand was being stroked behind the screen, nearly all the subjects experienced the same bizarre sensation: they felt the fake hand was actually their own.

According to Matthew Botvinick, the Ph.D. psychology student who coauthored the study with advisor Jonathan Cohen, awareness of self seems to depend on intricate conversations between the brain and a range of sensory inputs that it constantly receives. If those conversations become garbled by contradictory messages, the brain is even willing to stretch the bounds of where the body ends and the outside world begins in order to draw a coherent picture. “ It ’s like ventriloquism, ” says Botvinick, who was so spooked by the illusion when  he tested it on himself that he let out a yelp and threw the fake hand across the room. “ In the experiment, when something touches the fake hand, you feel it, so the rubber hand  appears to be an object with which you sense. And when there is an object of that kind, it ’s usually part of you. That seems to be one basis of self-identification. ”

To confirm that the subjects were experiencing a true shift in their perception of themselves, researchers asked them to run their right index finger along the underside of the table until it was directly under neath their left one. Those who had experienced the rubber-hand illusion invariably missed their real finger altogether and pointed more closely to the fake hand. “ When you look at your hand, it doesn ’t feel as if your brain might be going through all kinds of complicated computations to arrive at the conclusion that this thing is yours, ” says Botvinick. “ You just know it ’s your hand. ” —Jennifer V n Ezra, in the column “Nexus” in Equinox, no. 99 (July 1998), p. 14.”

Quoted from Norman Swartz, Beyond Experience, 2nd edition, p. 144, freely available  here.

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