Explaining Out-of-body Experiences
September 2007 - Two recent studies published in Science offer insight into how individuals perceive their own bodies and a possible explanation for out-of-body experiences. This phenomenon has been associated with drug use and neurological disorders such as epilepsy but patients were commonly thought to have imagined it.
Researchers suggest that in addition to reducing stigma, the studies use techniques that may facilitate 'teleoperating' training in areas such as remote surgery.
H. Henrik Ehrsson of University College London and Karolinska Institute Stockholm and researchers led by Olaf Blanke of Ecole Polytechique Federale de Lausanne (EPFL) and University Hospital in Geneva both showed volunteers images of their bodies from the perspective of a person viewing them from behind using video cameras and virtual reality goggles. Participants were also simultaneously touched physically and virtually. Both studies conclude that out-of-body experiences thereby induced may result from "multi-sensory conflict" - disconnection between brain circuits responsible for processing both types of information.
Henrik Ehrsson said:
"I'm interested in why we feel that our selves are inside our bodies - why we have an 'in-body experience' if you like. This has been discussed for centuries in philosophy, but it's hard to tackle experimentally."
Participants in Henrik Ehrsson's study looked at recorded images through headsets and saw a plastic rod moving toward a point just below the camera. Their real chests were simultaneously touched in the relevant place. They reported feeling they were located where the camera was and watching a dummy or body belonging to someone else. Volunteers also watched a hammer swing to a point below the camera posing the threat of injury to an invisible part of the virtual body. Researchers measured skin conductance to assess emotional responses such as fear and found that volunteers sensed that their "selves" had moved to the virtual body.
Henrik Ehrsson commented:
"This experiment suggests that the first-person visual perspective is critically important for the in-body experience. In other words, we feel that our self is located where the eyes are."
The second team converted video images into computer simulations similar to holographs which they caution limits comparisons with full out-of-body experiences. After a virtual reality exercise, volunteers were blindfolded and guided backwards. When asked to return to their original position, they tended to gravitate toward the position where they had seen their virtual bodies. However, when participants viewed a human-sized block instead of a body they successfully returned to their original place.
Researchers suggest that this finding indicates that self-consciousness of one's body may involve a cognitive dimension "the ability to distinguish between one's own body and other objects" in addition to sensory signals. Some out-of-body experiences may be related to distorted "full-body perception".
Olaf Blanke said:
"Full-body consciousness seems to require not just the 'bottom up' process of correlating sensory information but also the 'top down' knowledge about human bodies."
"We have decades of intense research on visual perception, but not very much yet on body perception. But that may change, now virtual reality offers a way to manipulate full body perception more systematically and probe out-of-body experiences and bodily self consciousness in a new way."
Henrik Ehrsson concluded:
"Brain dysfunctions that interfere with interpreting sensory signals may be responsible for some clinical cases of out-of-body experiences. Though whether all out-of-body experiences arise from the same causes is still an open question."
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