- Using virtual reality goggles, a camera and a stick,
scientists have induced out-of-body experiences - the sensation of drifting
outside of one's own body - in healthy people, according to experiments
being published in the journal Science.
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- 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.
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- 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.
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- Usually these sensory streams, which include including
vision, touch, balance and the sense of where one's 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.
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- 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.
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- 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.
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- The new research is a first step in figuring out exactly
how the brain creates this sensation, he said.
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- The out-of-body experiments were conducted by two research
groups using slightly different methods intended to expand the so-called
rubber hand illusion.
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- 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.
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- When the rubber hand is whacked with a hammer, people
wince and sometimes cry out.
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- 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 person's brain sees the fake hand being stroked and feels the
same sensation, the sense of being touched is misattributed to the fake.
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- The new experiments were designed to create a whole body
illusion with similar manipulations.
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- 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.
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- Then Dr. Blanke stroked each person's back for one minute
with a stick while simultaneously projecting the image of the stick onto
the illusory image of the person's body.
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- 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.
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- 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, people's sense of self drifted into the mannequin.
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- A separate set of experiments were carried out by Dr.
Henrik Ehrsson, an assistant professor of neuroscience at the Karolinska
Insitutute in Helsinki.
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- 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?"
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- 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.
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- Using two sticks, Dr. Ehrsson stroked each person's 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.
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- 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.
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- 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.
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- They also reacted emotionally, as if they were watching
themselves get hurt, Dr. Ehrsson said.
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- 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.
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- 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.
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- 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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