Whose body is it anyway? 4: Body swap
Transcript of Whose body is it anyway? 4: Body swap
21 March 2009 | NewScientist | 37
VOLUNTEER
VIDEO DISPLAY
GOGGLES
RESEARCHER
VIDEO
CAMERA
Under normal circumstances, your sense
of self is firmly anchored inside your body.
Sometimes, though, something goes
awry, the connection between body
and self breaks down and you have an
out-of-body experience.
Such moments occur when brain
function is disturbed, such as after a
stroke or epileptic seizure, or while on
drugs. In 2007, however, two research
teams independently reported ways of
inducing an out-of-body experience in
the lab in normal healthy people.
The techniques differ slightly, but both
involve feeding volunteers video images
of themselves from an unusual perspective
while applying tactile stimulation,
somewhat like the rubber hand illusion.
In the first set-up, a team led by Olaf
Blanke at the Swiss Federal Institute of
Technology in Lausanne got volunteers
to stand about 2 metres in front of a video
camera while wearing goggles, which
displayed the video images, converted
into a holographic-like 3D projection. This
meant that the volunteers could see a
version of their own backs. When they
stoked the volunteers’ backs, many
reported a weird feeling that they were
somehow inside the virtual body in front
of them ( Science, vol 317, p 1096 ).
The volunteers also experienced
“proprioceptive drift” towards the virtual
body: they felt as if they were standing in
the position of their virtual self. When the
researchers turned off the display, moved
their volunteers backwards and asked
them to return to their original position,
many overshot towards where they felt
their virtual body had stood.
Last year Blanke’s team also reported
inducing a feeling of out-of-body
levitation by repeating the experiment
with volunteers who were lying down
( Consciousness and Cognition, DOI:
10.1016/j.concog.2008.11.003 )
Nevertheless, Blanke points out that they
have not yet recreated the entire out-of-
body experience: “It remains an ‘as-if’
feeling, but we’re trying to refine it.”
Ehrsson’s team have done something
similar , with seated volunteers filmed
from behind while a researcher stands
to the side of them stroking the
volunteer’s chest and a space just in front
of the camera (illustrated above). The
volunteers see their own backs, feel the
stroking but also see somebody stroking
a position just behind them. This
strongly creates the illusion that they are
outside their own bodies, says Ehrsson
(Science, vol 317, p 1048).
What’s more, when Ehrsson tried
swinging a hammer at the previously
stroked airspace, it elicited a strong
stress response in the volunteer.
3
Leave your body behind
If leaving your own body behind or having an
extra or virtual arm is not enough for you, how
about switching bodies with someone else? In late
2008, Ehrsson and his colleague Valeria Petkova
described an experimental set-up that creates
this freaky illusion.
They got two people to stand facing one another,
one wearing a pair of head-mounted video cameras
and the other wearing goggles with the images
from the cameras projected inside. The pair were
then asked to reach out and shake each other’s
right hand and, as they held their grip, to apply
a synchronised series of squeezes.
For the goggle-wearer, this creates an uncanny
feeling of occupying the camera-wearer’s body:
where they would normally see their own torso and
their own arm and hand reaching out, they see their
partner’s. Within a couple of minutes about 70 per
cent of participants feel as if their partner’s arm –
and by extension the body attached to it – is their
own. And when the experimenters brandish a knife
over the participants’ wrists, the goggle-wearers
stress response was greatest when it is closer to
their partner’s wrist ( PLoS ONE, vol 3(12), p e3832 ).
Ehrsson says the illusion is highly convincing: “The
first time I experienced the body-swapping illusion
with Valeria I almost started screaming because it
was such a surreal and striking experience to shake
hand with myself using a different body.” ■
4 Body swap
To experience the rubber hand
illusion, you’ll need a fake hand
of some kind – an inflated rubber
glove will often do the trick – a flat
piece of cardboard and two small
paintbrushes. Place the hand on a
table in front of you and conceal your
real hand behind the cardboard.
Now get somebody to stroke
and tap the fake hand and real hand
using identical movements of the
paintbrushes. Look at the fake hand
for a while until the illusion kicks in.
HOW TO TURN A RUBBER HAND INTO A ‘REAL’ ONE