Traveling outside your own body is as easy as a video illusion, according to new research. Simply sit in front of two cameras filming your back. Place a special headset over your eyes; it will display the images from the left camera to your left eye and the right camera to your right eye. Then enlist a friend to simultaneously stroke your chest and perform a similar motion just below the cameras' fields of view. Within a minute, you will suddenly be overcome by the strange sensation that you are sitting where the cameras are rather than in your own body.
For a quicker, less powerful jaunt outside your bodily confines, try the double-mirror trick: Position two mirrors facing each other and then lean toward one so that two thirds of your face is reflected in it. Scratch your cheek and stare deep into the hall of mirrors you have created, past your original reflection, past the image of your back, and settle on the third reflection—your own face but slightly obscured. Within seconds, you won't recognize that reflection as you, says neuroscientist Eric Altschuler of the University of Medicine & Dentistry of New Jersey in Newark, who reported the phenomenon in the April issue of Perception.
Admittedly, neither of these illusions precisely match the classic example of the out-of-body experiences reported by patients near death who say they floated out of their bodies but were able to continue observing scenes from above or elsewhere in the room. But two studies published this week in Science show how the self and body can be disconnected, using video cameras.
"We found a method to change the perceived location of the body in space even if that means that one is located outside the physical body," cognitive neuroscientist Henrik Ehrsson of the Karolinska Institute in Stockholm says. "They see themselves sitting in the middle of the room, but they feel themselves sitting in a corner of the room."
He tested seven men and 11 women using the headset and camera method. All of the subjects reported feeling whisked across the room when stroked. "I felt as though I was outside my body and looking at myself from the back," one volunteer offered; others spontaneously giggled or otherwise expressed amusement when subjected to the odd effect.
In an attempt to test the strength of the illusion, Ehrsson threatened the illusory bodies of eight men and four women with a hammer. All of the subjects flinched or winced in alarm and the electrical currents in their skin jumped even though Ehrsson had explicitly promised not to hurt any of them at the beginning of the session. " You can't think [the illusion] away, it's not a high-level cognitive thing," he says. "It's a perceptual illusion and you don't have ulterior [(intellectual)] control."
In similar work, Olaf Blanke of the Brain Mind Institute at the Swiss Federal Institute of Technology in Lausanne and his colleagues persuaded subjects that they were not standing where they really were by simultaneously stroking their backs and projecting a virtual reality image into headgear of them standing two meters (2.2 yards) in front of their true location.
The nine women and five men were moved from their original spot and, when asked to return to it, moved toward the virtual location by an average of 24 centimeters (9.4 inches). [see video] Other subjects shown a mannequin of a blonde woman (instead of virtual images of themselves) also drifted in her direction and even those fed an image of a simple metal block moved slightly toward it. "We believe that the almost [statistically] significant drift in the object condition is actually a relevant result and needs to be tested in further experiments," Blanke says.
The illusion is delicate: If the strokes were applied with a different rhythm than the ones displayed in the video or if a subject moved his or her own hand, the feeling would be dispelled. But the findings suggest that our consciousness of a self that is contained in our body is based on the brain processing and correlating inputs from the various senses, the researchers report. "All of these illusions are all about the integration of all available data and the brain coming up with one interpretation," Ehrsson says.
These results further indicate, Blanke says, that self-consciousness begins with the awareness of a self in a particular body. "This research gives us the first building block of how the first-person perspective could naturally emerge," says Thomas Metzinger of the University of Mainz in Germany, a member of Blanke's team. "Can you be conscious without any experience of your body at all?"
"The constant checking that everything is in register is crucial for the sense of a unified corporeal self," or a sense of a self within a particular body, Altschuler adds. "The perception of the corporeal self is in some sense an illusion that is dependent on this registration. If you don't have that, then you become disembodied."
Because the effect is simple and seems to be universal, it may be possible to use it for things like telesurgery (enabling surgeons to operate intuitively from a distance) or for space exploration (allowing controllers to manipulate robots as if they were on distant moons or planets). "We don't really know the constraints," Ehrsson notes. "How much tactile information is necessary? How much delay [between the visual signal and the feeling] is allowed?"
The techniques could also be used to put people into the computer-generated virtual avatars, either for therapy (as in body-image modification for anorexics) or for enhancing game experiences, an application Ehrsson is currently studying.
It remains unclear, researchers say, whether consciousness can be transferred from person to person or even person to object as Blanke's metal box experiment hints. The brain functions underlying the illusion also remain a mystery; preliminary research and clinical reports of epileptics and patients with brain damage point to networks that link the temporal and parietal lobes of the brain. Blanke plans to do neuroimaging studies to try to map the brain circuits involved.
And matching these out-of-body illusions with the actual out-of-body episodes experienced by as many as one in 10 people will also be key, researchers note. Ehrsson says that at least one of his patients reported feeling the same way after the lab test as she did after a spontaneous out-of-body occurrence.
"The advantage of what these guys have done," says neuroscientist Vilayanur Ramachandran of the University of California, San Diego, "is that they have shown a simple way of producing out-of-body experiences in normal people." Getting out of the body may be as simple as tricking the brain.