LONDON -- Neither near death nor neurologic event nor a hallucinogenic-drug trip are prerequisites any more for a surreal out-of-body experience. A little video trickery can induce the feeling of observing the body as if one were another being.
LONDON, Aug. 23 -- Neither near death nor neurologic event nor a hallucinogenic-drug trip are prerequisites any more for a surreal out-of-body experience.
A little video trickery can induce the feeling of observing the body as if one were another being, found investigators here in what might be termed a near-medicine experiment. A dozen participants found it cool.
In addition to near death, out-of-body experiences are sometimes seen in states of altered brain function, such as strokes, partial epileptic seizures, or drug induced hallucinations.
But for 12 healthy volunteers here, inducing the experience was as a simple as fitting them with a pair of head-mounted video goggles similar to those used in virtual-reality displays, said H. Henrik Ehrsson, Ph.D., of University College London. He reported his results in the Aug. 24 issue of Science.
"The invention of this illusion is important because it reveals the basic mechanism that produces the feeling of being inside the physical body," said Dr. Ehrsson, now at the Karolinska Institute in Stockholm.
"This represents a significant advance because the experience of one's own body as the center of awareness is a fundamental aspect of self-consciousness," he added.
In a second study, also published in Science, Olaf Blanke, M.D., Ph.D., of University Hospital in Geneva, Switzerland, and colleagues, described a similar experiment, in which "healthy participants experienced a virtual body as if it were their own and localized their 'selves' outside of their body borders at a different position in space."
The participants in this study felt disoriented, but none reported feeling as if they had left their bodies, the Swiss team reported.
The extracorporeal illusions reveal intriguing information about the mind-body connection, and could have a practical application in medicine, Dr. Ehrsson suggested.
"For example, a surgeon could perform remote surgery, by controlling their virtual self from a different location," Dr. Ehrsson said.
To create his illusion, he sat participants in chairs and fitted them with a pair of head-mounted video goggles similar to those used in virtual-reality displays. The head sets had screens for each eye that were directly connected to video cameras placed two meters behind the volunteer; the left camera displayed an image to left eye, and the right camera displayed to the right eye.
The volunteers saw the images as stereoscopic views of their own backs, as might be seen by an observer sitting behind them.
Dr. Ehrsson then stood beside the participant, within view of the camera, and then simultaneously touched with short plastic rods the actual chest of the participant, and the virtual chest of the image seen in the goggles, by moving the rod to a spot just below the camera's view.
"This was a bizarre, fascinating experience for the participants -- it felt absolutely real for them and was not scary," Dr. Ehrsson said. "Many of them giggled and said 'Wow, this is so weird!"
To test whether they had truly had an out-of-body experience, the participants, after two minutes of the visual stimulus, were administered a questionnaire which asked them to affirm or deny on a seven-point visual analog scale 10 possible perceptual effects.
"Three statements were designed to capture the experience of the illusion, and the other seven served as controls for suggestibility and task compliance," Dr. Ehrsson wrote. "The participants affirmed illusion statements and denied the controls, and the difference in ratings was significant (P<0.0001)."
To test his hypothesis that the out-of-body illusion was caused by the first-person visual perspective in combination with correlated visual and tactile information from the body, and to validate his findings, Dr. Ehrsson then tested the participants' skin conductance response as their virtual bodies were being "hit" by a hammer.
He compared the illusion condition, in which synchronous touches were made, to an asynchronous condition in which the person's real and illusory chests were touched alternatively
He saw that there were significantly greater threat-evoked skin-conductance responses after the illusion condition than after the asynchronous condition (P< 0.013 on the paired t test).
Several of the participants visibly flinched when their illusory bodies were hit with the hammer, but this occurred only in the illusion condition, he noted in supporting material published online. "Before being asked any questions some participants told me that they experienced more fear in the illusion condition."
Dr. Ehrsson said that the illusion reveals that there are two components to the sense of the self being located inside the body.
"First, visual information from the first-person perspective provides indirect information about the location of one's own body in the environment," he wrote.
"The second key factor is the detection of correlated tactile and visual events on the (illusory) body. Multisensory correlations are known to be important for self-attribution of single body parts in near-personal space. Thus, these correlations, in conjunction with the first-person visual perspective, are sufficient to determine the perceived location of one's own whole body."
In the second study, Dr. Blanke and colleagues worked with computer engineers to create a series of simple virtual reality experiments. In these experiments, participants wearing virtual-reality goggles viewed three-dimensional projections of either their own bodies, the body of a dummy, or a simple object such as a column directly in front of them.
The participants watched the back of the image being stroked with a paintbrush either in sync or out of sync with an experimenter stroking the volunteers' backs. Immediately following this, the participants were blindfolded, guided backward, were then asked to return on their own to their original positions.
Those participants who had their backs stroked in sync with the virtual image of themselves or of the dummy consistently overstepped their target in the direction of the image, and went farther off-target than those who were stroked out of sync with their virtual bodies.
In contrast, the volunteers who did not see a virtual image of themselves or of a dummy, or who saw only the simple object, did not consistently overshoot the target.
As with Dr. Ehrsson's experiment, "participants reported varied feelings of 'weirdness' or 'strangeness,' and some found the experiment irritating," Dr. Blanke and colleagues wrote. However, in this study none of the participants reported feelings of either disembodiment or of a change in visuospatial perspective.
"Our results indicate that spatial unity and bodily self-consciousness can be studied experimentally and are based on multisensory and cognitive processing of bodily information," the investigators wrote.
The study by Dr. Blanke and colleagues was supported by the Cogito Foundation, the Fondation de Famille Shandoz, the Fondation Odier and the Swiss National Science Foundation. Conflicts of interest were not disclosed.