BBC Earth (Asia) - - Science -

Can you imagine be­com­ing con­vinced that a pink, rub­ber hand is your own? Un­likely as it seems, this is the fa­mous ‘rub­ber hand il­lu­sion’. The per­son’s own hand, ly­ing next to a rub­ber hand, is con­cealed from view by a screen. If both hands are stroked si­mul­ta­ne­ously, peo­ple start to feel the touch as though it is on the rub­ber hand.

Bigna Lenggen­hager, at the Univer­sity of Zurich, has man­aged to cre­ate a ‘whole body il­lu­sion’ us­ing vir­tual re­al­ity. She places a cam­era two me­tres be­hind a par­tic­i­pant and gives them a head-mounted dis­play to wear, so they are look­ing at their own back. When the ex­per­i­menter gen­tly strokes the par­tic­i­pant’s back, they can watch as well as feel it. Grad­u­ally the sen­sa­tion shifts to­wards the vir­tual body.

In Swe­den, neu­ro­sci­en­tist Hen­rik Ehrs­son uses a dif­fer­ent method to cre­ate a sim­i­lar ef­fect. A cam­era is again po­si­tioned two me­tres be­hind a par­tic­i­pant, but this time their chest is stroked in syn­chrony with a stick mov­ing up and down in front of the cam­eras. With this method, peo­ple feel they have moved back­wards to­wards the cam­eras. Th­ese may just be tricks but their ef­fect can be pro­found. When the il­lu­sion is strong, body tem­per­a­ture drops, pain is felt less in­tensely, and threat­en­ing the real body with a knife pro­duces a weaker re­ac­tion. The il­lu­sions have been in­duced inside an fMRI scan­ner, re­veal­ing that changes in ac­tiv­ity in the brain’s tem­poropari­etal junc­tion re­flect changes in self-lo­ca­tion. Th­ese il­lu­sions are not the same as full OBEs, yet they re­veal how our sense of be­ing inside our own body can be ma­nip­u­lated. And this may ex­plain how we can some­times be con­vinced that we are out­side our body.

“It may turn out that OBEs are linked with the im­por­tant so­cial skill of be­ing able to un­der­stand some­one else’s per­spec­tive”

group of pa­tients with schizophre­nia to a con­trol group and although the schizophren­ics re­ported more bizarre ex­pe­ri­ences of var­i­ous kinds, the two groups in­cluded the same num­ber of OBErs.

A more pos­i­tive way to un­der­stand OBEs fu­els a re­cent de­bate be­tween those who think they rep­re­sent a fail­ure and oth­ers who say they re­veal a skill. The ear­li­est psy­cho­log­i­cal the­o­ries sug­gested that im­agery might be the rel­e­vant skill but many ex­per­i­ments showed no ob­vi­ous dif­fer­ences in rich­ness or vivid­ness of im­agery. Some small dif­fer­ences were found in the abil­ity to switch view­points, for ex­am­ple be­tween imag­in­ing a scene from eye level or from a bird’s eye view, and OBErs were found more of­ten to dream in bird’s eye view. Th­ese were clues lead­ing to re­cent re­search show­ing the rel­e­vance of what is called ‘per­spec­tive tak­ing’. This is the abil­ity to see things from some­one else’s point of view and is re­lated to em­pa­thy. In­ter­est­ingly, this abil­ity also de­pends on ar­eas of the brain close to the TPJ. So it may turn out that OBEs, far from be­ing a fail­ure, are linked with the im­por­tant so­cial skill of be­ing able to un­der­stand some­one else’s per­spec­tive.

It is still early days for se­ri­ous OBE re­search but now it has be­gun we may find that an ex­pe­ri­ence that was once dis­missed as fan­tasy and ig­nored by main­stream sci­ence is now con­tribut­ing to our un­der­stand­ing of con­scious­ness and the na­ture of self.

LEFT: Ex­per­i­ments with cam­eras and head­sets have al­lowed sci­en­tists to ma­nip­u­late our sense of lo­ca­tion

RIGHT: The brain’s tem­poropari­etal junc­tion (high­lighted with a black cir­cle) is the re­gion that seems to be as­so­ci­ated with OBEs

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