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SCIENCE-FOR-THE-PEOPLE  January 2009

SCIENCE-FOR-THE-PEOPLE January 2009

Subject:

Body-swap illusion tricks mind in new study

From:

Mitchel Cohen <[log in to unmask]>

Reply-To:

Science for the People Discussion List <[log in to unmask]>

Date:

Thu, 15 Jan 2009 09:13:31 -0500

Content-Type:

text/plain

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Parts/Attachments

text/plain (112 lines)

Body-swap illusion tricks mind in new study

Dec 2, 7:55 AM (ET)

By KARL RITTER

STOCKHOLM, Sweden (AP) - Shaking hands with yourself is an amusing 
out-of-body experience. The illusion of having your stomach slashed 
with a kitchen knife, not so much.

Both sensations, however, felt real to most participants in a Swedish 
science project exploring how people can be tricked into the false 
perception of owning another body.

In a study presented Tuesday, neuroscientists at Stockholm's renowned 
Karolinska Institute show how they got volunteers wearing virtual 
reality goggles to experience the illusion of swapping bodies with a 
mannequin and a real person.

"We were interested in a classical question that philosophers and 
psychologists have discussed for centuries: why we feel that the self 
is in our bodies," project leader Henrik Ehrsson said. "To study this 
scientifically we've used tricks, perceptual illusions."

It sounded intriguing enough for me to try it, though entering the 
laboratory on Monday, I was having second thoughts.

The first props I saw were two kitchen knives, three naked dummies 
and a prosthetic hand sticking out from behind a curtain.

"You have the right to say stop at anytime if you feel 
uncomfortable," said Ehrsson's colleague, Valeria Petkova, as she 
rubbed my left hand with electrolytic gel and attached electrodes to 
the middle and index fingers.

She assured me I was not in any danger. Still, a nervous tingle 
rushed through my body as she placed the headset over my eyes.

In the first experiment, the goggles were hooked up to CCTV cameras 
fitted to the head of a male mannequin, staring down at its feet. 
Through the headset I saw a grainy image of the dummy's plastic 
torso. I tilted my head down to create the sensation I was looking 
down at my own body.

At that point, it didn't feel very real. But when Petkova 
simultaneously brushed markers against my belly and that of the 
mannequin, the effect started setting in. As my brain processed the 
visual and tactile signals, I had a growing impression that the 
mannequin's body was my own.

That was good fun, until the gleaming blade of a bread knife entered 
my field of vision. Petkova slid it across the dummy's stomach, 
sending shivers down my spine and a pulse of anxiety through the 
electrodes. My heightened stress level was illustrated by a spike in 
a computer diagram shown to me after the experiment.

"Approximately 70-80 percent of the people experience the illusion 
very strongly," Petkova said.

Apparently, I was one of them.

The second experiment was more benign. This time my headset was 
connected to cameras mounted on a round hat that Petkova was wearing. 
We faced each other, extended our right arms and shook hands.

Now that was weird: I was supposed to have the sensation of shaking 
hands with myself. The illusion wasn't perfect as I couldn't quite 
recognize Petkova's grip as my own, even though that's what the 
goggles meant to make me believe.

Perhaps the session was too short. The actual study, in which 87 
volunteers participated, consisted of repeated sessions that 
gradually provided more accurate data. The results were published in 
PLoS One, the online journal of the Public Library of Science.

The principle finding was that under certain conditions a person can 
perceive another body as his or her own, even if it is of an opposite 
gender or an artificial body.

"These findings are of fundamental importance because they identify 
the perceptual processes that make us feel that we own our entire 
body," the study said.

Ehrsson said the study built on a previous experiment known as the 
"rubber hand illusion" in which participants were manipulated to 
experience a rubber hand as their own.

Charles Spence, a professor of experimental psychology at the 
University of Oxford, said the Karolinska study was a "step up" from 
other research on the subject.

"This goes beyond other recent studies, where you've taken ownership 
of rubber hands and rubber legs," said Spence, who was not involved 
with the study.

His only concern was whether there might be any lasting effect on participants.

"The questions is what happens if you did it much longer? If you were 
in there for days and weeks. Would it be like something out of Total 
Recall?" Spence said, referring to the 1990 Arnold Schwarzenegger 
science fiction movie about a virtual vacation that turns into a nightmare.

Ehrsson suggested the findings could be applied in research on body 
image disorders by exploring how people become satisfied or 
dissatisfied with their bodies. Another possible application could be 
developing more advanced versions of computer games such as Second 
Life, he said.

"It could lead to the next generation of virtual reality applications 
in games, where people have the full-blown experience of being the 
avatar," Ehrsson said.

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