August 23, 2007
Scientists Induce Out-of-Body Sensation
By SANDRA BLAKESLEE
NY Times
http://www.nytimes.com/2007/08/23/science/23cnd-body.html?_r=1&hp=&oref=slogin&pagewanted=print
Using virtual reality goggles, a camera and a stick, scientists have
induced out-of-body experiences the sensation of drifting outside of
ones own body in healthy people, according to experiments being
published in the journal Science.
When people gaze at an illusory image of themselves through the goggles and
are prodded in just the right way with the stick, they feel as if they have
left their bodies.
The research reveals that the sense of having a body, of being in a bodily
self, is actually constructed from multiple sensory streams, said Matthew
Botvinick, an assistant professor of neuroscience at Princeton University,
an expert on body and mind who was not involved in the experiments.
Usually these sensory streams, which include including vision, touch,
balance and the sense of where ones body is positioned in space, work
together seamlessly, Prof. Botvinick said. But when the information coming
from the sensory sources does not match up, when they are thrown out of
synchrony, the sense of being embodied as a whole comes apart.
The brain, which abhors ambiguity, then forces a decision that can, as the
new experiments show, involve the sense of being in a different body.
The research provides a physical explanation for phenomena usually ascribed
to other-worldly influences, said Peter Brugger, a neurologist at
University Hospital in Zurich, Switzerland. After severe and sudden
injuries, people often report the sensation of floating over their body,
looking down, hearing what is said, and then, just as suddenly, find
themselves back inside their body.
The new research is a first step in figuring out exactly how the brain
creates this sensation, he said.
The out-of-body experiments were conducted by two research groups using
slightly different methods intended to expand the so-called rubber hand
illusion.
In that illusion, people hide one hand in their lap and look at a rubber
hand set on a table in front of them. As a researcher strokes the real hand
and the rubber hand simultaneously with a stick, people have the vivid
sense that the rubber hand is their own.
When the rubber hand is whacked with a hammer, people wince and sometimes
cry out.
The illusion shows that body parts can be separated from the whole body by
manipulating a mismatch between touch and vision. That is, when a persons
brain sees the fake hand being stroked and feels the same sensation, the
sense of being touched is misattributed to the fake.
The new experiments were designed to create a whole body illusion with
similar manipulations.
In Switzerland, Dr. Olaf Blanke, a neuroscientist at the École
Polytechnique Fédérale in Lausanne, Switzerland, asked people to don
virtual reality goggles while standing in an empty room. A camera projected
an image of each person taken from the back and displayed 6 feet away. The
subjects thus saw an illusory image of themselves standing in the distance.
Then Dr. Blanke stroked each persons back for one minute with a stick
while simultaneously projecting the image of the stick onto the illusory
image of the persons body.
When the strokes were synchronous, people reported the sensation of being
momentarily within the illusory body. When the strokes were not
synchronous, the illusion did not occur.
In another variation, Dr. Blanke projected a rubber body a cheap
mannequin bought on eBay and dressed in the same clothes as the subject
into the virtual reality goggles. With synchronous strokes of the stick,
peoples sense of self drifted into the mannequin.
A separate set of experiments were carried out by Dr. Henrik Ehrsson, an
assistant professor of neuroscience at the Karolinska Insitutute in Helsinki.
Last year, when Dr. Ehrsson was, as he says, a bored medical student at
University College London, he wondered, he said, what would happen if you
took your eyes and moved them to a different part of a room? Would you
see yourself where you eyes were placed? Or from where your body was placed?
To find out, Dr. Ehrsson asked people to sit on a chair and wear goggles
connected to two video cameras placed 6 feet behind them. The left camera
projected to the left eye. The right camera projected to the right eye. As
a result, people saw their own backs from the perspective of a virtual
person sitting behind them.
Using two sticks, Dr. Ehrsson stroked each persons chest for two minutes
with one stick while moving a second stick just under the camera lenses
as if it were touching the virtual body.
Again, when the stroking was synchronous people reported the sense of being
outside their own bodies in this case looking at themselves from a
distance where their eyes were located.
Then Dr. Ehrsson grabbed a hammer. While people were experiencing the
illusion, he pretended to smash the virtual body by waving the hammer just
below the cameras. Immediately, the subjects registered a threat response
as measured by sensors on their skin. They sweated and their pulses raced.
They also reacted emotionally, as if they were watching themselves get
hurt, Dr. Ehrsson said.
People who participated in the experiments said that they felt a sense of
drifting out of their bodies but not a strong sense of floating or
rotating, as is common in full-blown out of body experiences, the
researchers said.
The next set of experiments will involve decoupling not just touch and
vision but other aspects of sensory embodiment, including the felt sense of
the body position in space and balance, they said.
Such mismatches are likely to occur naturally when multi-sensory regions of
the brain are deprived of oxygen after injury or shock. Or they may be
induced during sleep paralysis, the exertion of extreme sports or intense
meditation practices that alter blood flow to specific brain regions.
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