2. TRAVEL OUT-OF-BODY
The physical sensation of floating outside the body can famously occur during a close brush with death. Now scientists researching the location of the brain’s sense of self have begun inducing the out-of-body experience in the lab. The way to do so occurred to Olaf Blanke—a neurologist and cognitive neuroscientist at the Brain-Mind Institute, part of the École Polytechnique Fédérale de Lausanne in Switzerland—a decade ago while he worked with an epilepsy patient, a 43-year-old woman with drug-resistant seizures who had to be treated with surgery. During the treatment he briefly zapped the temporoparietal junction, a brain region that integrates sound, touch, vision, balance perception, and the sense of location in space. Immediately after, the patient hesitantly said, “I’m ... not really sure I should be telling you this.... I left my body.” At first Blanke did not take the comment seriously. But the woman repeated her claim upon reapplication of the electrode.

Blanke now thinks out-of-body experiences are related to phantom limbs, the sensation reported by many amputees that a missing limb is still attached. He proposes that the feeling of leaving the body represents a broader misperception of not just one limb but the entire physical self. “What you can get wrong for your hand you can also get wrong for the rest,” Blanke says. “When the brain gets it wrong by trying to reconcile what is seen with what is felt, it generates another reality—and two bodily representations of yourself.”

In 2005 Blanke began using virtual reality and robotics to induce out-of-body experiences in healthy subjects whose bodies were entirely intact. In one version of the experiment, he designed a mattress that incorporated a stroking device. A study participant reclined on the mattress, wearing goggles with video screens for lenses, while a computer controlled the machine stroking the person’s back. When the volunteer looked toward the ceiling he saw a computer generated, 3-D image of a body floating.

If the virtual body appeared to receive the same strokes as the real body, participants reported the feeling of floating outside themselves. When he scanned their brains, Blanke found that the test subjects produced the signature brain patterns seen in others reporting an out-of-body state.

DIY: Float outside of yourself
Unless you volunteer for an out-of-body experiment in a neuroscience lab, there is no reliable way to induce the experience on demand. But spontaneous ones can occur. One way to induce the experience, according to reports, is meditation. “In many meditations you avoid moving; the focus is on breathing, and information from the rest of the body is reduced. This seems to be a state that is prone to lead to illusory perceptions,” Blanke says. In one small study, researchers reported that floating in sensory deprivation tanks like those developed in the 1950s (and available to try for a fee in many cities) produced out-of-body experiences in some users.

3. ENTER YOUR AVATAR
Ehrsson and Blanke have both succeeded in triggering a variation on the out-of-body experience in which subjects feel immersed in a representation of another person—in Ehrsson’s case, a figure from live video footage; in Blanke’s, either a video figure or a digital representation often referred to as an avatar. As with other disembodied states, virtual-reality technology is key. Here Ehrsson and his team equip test subjects with head-mounted video display units, large goggles with a small screen over each eye. At the same time, two live video cameras are placed side by side about six feet behind the head of the volunteer. The image from the left video camera is seen through the left-eye display and the image from the right camera is viewed through the right-eye display. Together they produce a 3-D image of the subject’s back.

The result is that when the seated volunteer looks forward, he sees a stereoscopic image of himself, displayed from the perspective of someone behind him. The investigator stands just beside the subject and, using a plastic rod, gently strokes his actual chest while moving a second rod toward where the virtual figure’s chest would be located, right below the camera’s view. After only a few seconds, the majority of participants feel their presence is shifting from their real physical body into that of the illusion.

Blanke’s team conducted a similar experiment but instead used small vibrators connected to a series of lights taped onto the backs of research subjects while cameras filmed them from behind. Looking through the lens of their head-mounted displays, the participants saw a projected image of themselves from the back, appearing to stand six feet ahead. As researchers stroked their real backs, each volunteer saw his avatar image’s back stroked too. Within a few minutes, the research subjects began to feel they had drifted into the avatar body ahead, experiencing the sensation their virtual self was being touched and feeling vibrations as lights flashed.

After Blanke’s avatar illusion was turned off, the volunteers were asked to walk backward several feet and then to return to where they had been standing during the experiment. Most of them moved too far forward, indicating that they had experienced the place where the avatar had been projected as their real location during the test.

DIY: How to heal yourself virtually
Once you can enter an avatar, you can use the technique to soothe physical pain. Researchers have long known that simply viewing an image of an amputee’s intact foot or arm in a mirror can sometimes help relieve phantom pain, as if the brain’s sense of self adjusts its conflicting sensations about the missing limb. Blanke suggests that manipulating whole-body perception with full-body illusions might similarly treat a variety of pain syndromes—making the avatar pick up some of the load.

4. BECOME A LIVING DOLL
Remember old sci-fi movies like Attack of the 50-Foot Woman or the more recent Honey, I Shrunk the Kids? Ehrsson’s team at the Karolinska Institute has reproduced a semblance of their plots by giving test subjects the sensation of swapping bodies with an 11½-inch Barbie doll or a 13-foot-tall mannequin.

As in prior self-perception experiments, participants wore head-mounted displays connected to two video cameras. This time the subjects were positioned in beds on their backs while two cameras sent them images of a tiny doll or an oversize mannequin lying on a bed next to them. The cameras assumed the same perspective as the person, looking down at the doppelgänger. When test participants gazed through their video-connected goggles toward their feet, therefore, their bodies appeared to be the size and shape of the artificial one nearby. A researcher stroked the fake body with a rod while softly touching the real body of the volunteer in exactly the same way. Participants quickly got the bizarre feeling that they were inhabiting the body of the small doll or huge mannequin.

Not content to rely on the participants’ subjective descriptions of their reactions, Ehrsson came up with objective evidence documenting the intensity of the body-projection experience. He measured the volunteers’ evoked skin-conductance response—a change in sweating, and hence electrical conductance, due to stress—while they observed someone threatening or cutting the doll with a knife. Skin conductance rose in step with the apparent level of threat, just as it does when a person faces a genuine possibility of physical harm.

During the time the volunteers felt they were inside the artificial bodies, Ehrsson and his team also asked them to look at blocks across the room and estimate how far away and how large those objects were. Then the subjects were asked to walk over to the blocks with their eyes shut. People who had projected themselves into a small body tended to overestimate how far away and how large the blocks were. For those who experienced themselves in the large fake body, the opposite was true: They thought the blocks were much smaller and closer than they actually were.

Ehrsson suggests that such out-of-body illusions could have practical uses. They might one day allow a surgeon to feel as if he or she were inhabiting a microscopic medical robot, directing operations inside a human patient. Or a worker might project himself into a giant robot, maneuvering it as if it were his own body to make repairs at a nuclear power plant.

DIY: How to get small (or large)
Want to project your body into a race car or a potted plant? Forget it. Your best bet is a humanoid form. Your target object probably needs a trunk, two arms, two legs, and a headlike thing. Even a monkey might work. But if you want to inhabit your cat or dog, the territory is uncharted; scientists have not yet attempted a human-to-animal shift in the lab. Experiments have shown that you cannot swap places with a geometric shape, even if it is stroked in synchrony with your body.

5. THE TOTAL BODY SWAP
In recent experiments, Ehrsson has tried what he describes as the most extreme example of swapping bodies yet: producing out-of-body experiences in volunteers who face their own bodies and shake their own hands, seeming to encounter themselves from the outside.

He devised an experiment in which an investigator wears a specially designed helmet equipped with two video cameras that capture images from the investigator’s viewpoint. A research subject wearing a head-mounted display stands opposite the investigator, but instead of seeing what’s in front of him, the subject sees video of the images passing in front of the investigator’s eyes. To the subject, it feels as if he is looking at himself. Then each subject is told to reach out and shake the right hand of the experimenter for two minutes, until the sensation that he is shaking hands with himself becomes overwhelming. The feeling is that of the classic out-of-body experience: You are standing outside yourself, looking in.

DIY: How to teleport yourself
Even if you aren’t a Trekkie, you probably know the phrase “Beam me up, Scotty” from the vintage Star Trek television show. In that ultimate version of high-speed travel, a person’s atoms are disconnected, transported, and reassembled at the destination of choice. A real-life (but alas, only perceptual) version of beaming is currently under development by Mel Slater, a professor of virtual environments at the ICREA research institute at the University of Barcelona. Unlike the Star Trek approach, Slater keeps bodies intact while transforming their sense of location. The participant needs to wear virtual reality gear: a motion-capture suit and goggles connected to a real-time, 3-D video of a location—a conference, to pick a dull but practical example. People at the conference would see an avatar of the participant or a humanoid robot that embodies the person who has body-swapped in. The next step is adding a sense of touch to the simulation, so a person beaming to a remote location could feel himself hugging or shaking hands with a colleague far away.

Slater’s ultimate goal is nothing less than dissolving “the boundary between the human body and surrogate representations.” If he succeeds, paralyzed people could someday be connected wirelessly to humanoid robots and experience the physical world. A few researchers have already tested implants that can read brain waves of paralyzed people. A head-mounted display connected to a video camera, auditory pickup, and other sensors in the robot would let such patients virtually move about and experience the world, even though their physical bodies are immobile. Says Slater, “They will be embodied in that robot, seeing through its eyes, interacting and talking with people, moving through the world.”