Out of body and in the lab: new experiments stimulate seeing self elsewhere

Two sets of studies published independently in the same issue of the journal Science demonstrate how the illusion of a bodily self outside one's own body can be stimulated in the laboratory. The studies forge ways to better understand both out-of-body and near-death experiences and, perhaps more fundamentally important, the strong degree to which our sense of self is associated with our mind's perception of our physical body.

The studies are similar in many aspects. They both found ways to induce elements of the out-of-body experience in healthy volunteers. They both used head-mounted video displays to provide people with an image of themselves from a different perspective. They used various controls and used the sense of touch by stimulating, in different conditions, both the actual person's body and seemingly the illusory one. In both studies, the volunteers experienced feelings of dissociation from their own bodies--it seemed as if the tactile sensations were in the "other" body.

The first, more detailed study, "Video Ergo Sum: Manipulating Bodily Self-Consciousness," in the August 24 Science is by a Swiss-German team of researchers (Bigna Lenggenhager, Tej Tadi, Thomas Metzinger, and Olaf Blanke). Their investigation of bodily self-consciousness produced an illusion during which healthy participants experienced a virtual body as if it were their own and localized their "selves" outside of their bodies at a different position in space.

They designed their experiment drawing on clinical data in neurological patients reporting out-of-body experiences. These earlier data, they say, suggest that the spatial unity between self and body can be disrupted, leading to the striking experience that one's self is in another physical location.

In one experiment, volunteers viewed the backs of their bodies imaged from a distance of two meters projected onto 3-D video display goggles. Their backs were stroked for one minute, sometimes in synchrony with stimulation of their "virtual" body. The participants were immediately then blindfolded, passively displaced, and then asked to move back to their original position. As hypothesized, they moved closer to their "virtual" body's position.

A second experiment tried to rule out whether this drift toward the virtual body was due to a general motor bias to overshoot the position. Here the researchers instituted fake bodies, virtual fake bodies, real objects, and virtual objects. Once again, there was a sensory drift of position toward one's own virtual body and the fake body when the stroking was synchronous.

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"With the use of virtual reality and multisensory conflict," the Swiss-German researchers say, "we induced an illusion that makes it possible to quantify selfhood by manipulating attribution and localization of the entire body. Our results show that humans systematically experience a virtual body as if it were their own" when visually presented in front of them and stroked synchronously. They say the finding is "corroborated by the participants' mislocalization of their own bodies to a position outside their bodies.... Illusory self-localization to a position outside one's body shows that bodily self-consciousness and selfhood can be dissociated from one's physical body position."

The researchers acknowledge that they have induced only some aspects, not all, of out-of-body experiences. But they speculate that humans' daily experiences of an embodied self and selfhood, and the illusion they report in their study, both rely on mechanisms in the parietal junction of the brain, which is concerned primarily with sensory activities, such as receiving and interpreting information from all parts of the body. They further suggest that "experimentally creating illusions of the globalized, multisensory awareness of selfhood in a controlled manner with virtual-reality technology opens a new avenue for the investigation of the neurobiological, functional, and representational aspects of embodied self-awareness." They urge expansion of such studies into all these areas.

The second study ("The Experimental Induction of Out-of-Body Experiences") was conducted by H. Henrik Ehrsson of the Karolinska Institute in Sweden and the Wellcome Trust Centre for Neuroimaging in London.

Using a similar experimental setup, he likewise demonstrated "a perceptual illusion in which individuals experience that their center of awareness, or 'self,' is located outside their physical bodies and that they look at their bodies from the perspective of another person. The illusion demonstrates [that] the sense of being localized within the physical body can be fully determined by perceptual processes."

Participants were first seated in a chair wearing head-mounted displays showing his or her image as seen from two meters behind. The experimenter then stood beside the participant, in view, and used two plastic rods to touch simultaneously the person's actual chest, which was out of view, and the apparent chest of the "illusory body." After two minutes, the participants answered a questionnaire asking to affirm or deny ten perceptual effects. Three were designed to capture the experience of an illusion and seven served as controls for suggestibility and task compliance. Ehrsson reports that the participants affirmed the illusion statements and denied the controls, and that the difference in ratings was statistically significant.