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“Out of body” research attacks philosophical questions

Aug. 24, 2007
Courtesy American Association 
for the Advancement of Science
and World Science staff

Us­ing vir­tu­al real­ity gog­gles to mix up sen­so­ry sig­nals reach­ing the brain, sci­en­tists say they’ve in­duced “out-of-bod­y”-like ex­pe­ri­ences in healthy peo­ple, sug­gest­ing a pos­si­ble ex­plana­t­ion for a phe­nom­e­non of­ten thought to be a fig­ment of the ima­gina­t­ion.

Through the gog­gles, a vol­un­teer views the back of his body, as seen from be­hind by the cam­era. He al­so watches a plas­tic rod mov­ing to­ward a lo­ca­tion just be­low the cam­era, while his real chest is si­mul­ta­ne­ous­ly touched in the cor­re­spond­ing spot. (Im­age cour­te­sy Hen­rik Ehrs­son)


Vol­un­teer par­ti­ci­pants in the re­search had the il­lu­sion of leav­ing their own bod­ies—thanks to the gog­gles plus the sensa­t­ion of their real bod­ies be­ing touched si­mul­ta­ne­ous­ly. Two stud­ies pub­lished in the Aug. 24 is­sue of the re­search jour­nal Sci­ence de­s­cribe the find­ings.

Al­though sci­en­tists were partly in­ter­est­ed in the tour de force of in­duc­ing a dra­ma­tic il­lu­sion, the study had a deeper pur­pose, one of the sci­en­tists in­sisted. 

“I’m in­ter­est­ed in why we feel that our selves are in­side our bod­ies—why we have an ‘in-body ex­pe­ri­ence,’ if you like,” said Hen­rik Ehrs­son of Un­ivers­ity Col­lege Lon­don in the U.K. and the Ka­ro­lin­ska In­sti­tute in Stock­holm, Swe­den, au­thor of one of the stud­ies.

“This has been dis­cussed for cen­turies in phi­los­o­phy, but it’s hard to tack­le ex­pe­ri­men­tal­ly.”

Both Ehrs­son and the sec­ond stu­dy’s au­thors used vi­deo cam­er­as and vir­tu­al real­ity gog­gles to show vol­un­teers im­ages of their own bod­ies from the per­spec­tive of some­one be­hind them. Ex­pe­ri­ment­ers al­so touched the vol­un­teers’ bod­ies, both phys­ic­ally and vir­tu­ally.

“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,” Ehrs­son said.

A dis­con­nect be­tween brain cir­cuits that pro­cess both these types of sen­so­ry in­forma­t­ion may thus ex­plain some out-of-body ex­pe­ri­ences, both stud­ies’ au­thors say. These sensa­t­ions, which gen­er­ally in­volve the feel­ing of dis­em­bod­i­ment and see­ing one’s own body from some­where out­side it, can oc­cur in part through drug use, seizures and oth­er brain dis­tur­bances. They’re al­so re­ported to oc­cur in some near-death ex­pe­ri­ences.

“Brain dys­func­tions that in­ter­fere with in­ter­pret­ing sen­so­ry sig­nals may be re­spon­si­ble for some clin­i­cal cases of out-of-body ex­pe­ri­ences,” Ehrs­son said. “Though wheth­er all out-of-body ex­pe­ri­ences arise from the same causes is still an open ques­tion.”

Both stud­ies used si­m­i­lar se­tups. The sec­ond re­search team, in­clud­ing Olaf Blanke of the Ecole Poly­tech­nique Fédéral de Lau­sanne and the Un­ivers­ity Hos­pi­tal in Ge­ne­va, Switz­er­land, al­so blind­folded vol­un­teers and guid­ed them back­ward af­ter the vir­tu­al real­ity ex­er­cise. When the vol­un­teers were asked to re­turn to their orig­i­nal po­si­tion, they tended to drift to­ward where they had seen their vir­tu­al bod­ies stand­ing.

But in ad­di­tion to sen­so­ry sig­nals, bodily self-con­scious­ness may al­so in­volve a cog­ni­tive di­men­sion: the abil­ity to dis­tin­guish be­tween one’s own body and oth­er ob­jects, Blanke’s team pro­posed. They not­ed that when vol­un­teers viewed a hu­man-sized block in­stead of an im­age of a hu­man body in the vir­tu­al real­ity, they suc­cess­fully re­turned to their start­ing place in the blind­fold test, show­ing no out-of-body il­lu­sion had oc­curred.

“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,” Blanke said.

“We have dec­ades of in­tense re­search on vis­u­al per­cep­tion, but not very much yet on body per­cep­tion,” he added. “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.”


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Using virtual reality goggles to mix up sensory signals reaching the brain, scientists say they’ve induced “out-of-body”-like experiences in healthy people, suggesting a possible explanation for a phenomenon often thought to be a figment of the imagination. Volunteer participants in the research had the illusion of moving outside of their own bodies—thanks to the goggles plus the sensation of their real bodies being touched simultaneously. A pair of studies in the 24 August 2007 issue of the research journal Science describe the findings. Although scientists were partly interested in the tour de force of aspect of inducing an illusion in healthy people, the study had a deeper purpose, one of the scientists insisted. “I’m interested in why we feel that our selves are inside our bodies—why we have an ‘in-body experience,’ if you like,” Henrik Ehrsson of University College London in the U.K. and the Karolinska Institute in Stockholm, Sweden, author of one of the studies. “This has been discussed for centuries in philosophy, but it’s hard to tackle experimentally.” Both Ehrsson and the second study’s authors used video cameras and virtual reality goggles to show volunteers images of their own bodies from the perspective of someone behind them. The researchers also touched the volunteers’ bodies, both physically and virtually. “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,” Ehrsson said. A disconnect between the brain circuits that process both these types of sensory information may thus be responsible for some out-of-body experiences, both studies’ authors say. These sensations, which generally involve the feeling of disembodiment and seeing one’s own body from a location outside the body, can occur in part through drug use, epileptic seizures and other types of brain disturbances. They’re also reported to occur in some near-death experiences. “Brain dysfunctions that interfere with interpreting sensory signals may be responsible for some clinical cases of out-of-body experiences,” Ehrsson said. “Though whether all out-of-body experiences arise from the same causes is still an open question.” Both studies used similar setups. The second research team, including Olaf Blanke of the Ecole Polytechnique Fédéral de Lausanne and the University Hospital in Geneva, Switzerland, also blindfolded volunteers and guided them backward after the virtual reality exercise. When the volunteers were asked to return to their original position, they tended to drift toward where they had seen their virtual bodies standing. But in addition to sensory signals, bodily self-consciousness may also involve a cognitive dimension: the ability to distinguish between one’s own body and other objects, Blanke’s team proposed. They noted that when volunteers viewed a human-sized block instead of an image of a human body in the virtual reality, they successfully returned to their starting place in the blindfold test, showing no out-of-body illusion had occurred. “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,” Blanke said. “We have decades of intense research on visual perception, but not very much yet on body perception,” he added. “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.”