Virtual reality: The images from the cameras were played on screens placed in front of the test subject's eyes, using a head-mounted display, so that when the subject looked down at their body, they saw the mannequin's instead of their own.
Credit: Karolinska Institute/PLoS One
NEW YORK: The mind can be tricked into believing the body of someone else is actually its own, says a new study.
"This shows how easy it is to change the brain's perception of the physical self," said Henrik Ehrsson, a neuroscientist at Karolinska Institute in Stockholm, Sweden. "By manipulating sensory impressions, it's possible to fool the self not only out of its body but into other bodies too."
In addition to helping scientists understand how the brain recognises the body, the research may have future applications in therapy for people who have lost the use of their limbs, as well as in virtual reality and robot technology.
Rubber hand illusion
Previous studies have shown that illusions can trick the mind into swapping a specific body part for their own, such as a prosthetic hand for a real hand in the famous 'rubber hand illusion', which is used to help amputees cope with imagined feelings from phantom limbs.
But, the new study – published today in the open-access journal PloS One – is the first to show that the mind can be tricked into believing the entire body has been swapped.
In the first of several experiments, researchers led by Ehrsson mounted two cameras over the eyes of a mannequin. The images from the cameras were played on screens placed in front of the test subject's eyes, using a head-mounted display, so that when the subject looked down at their body, they saw the mannequin's instead of their own.
The researchers touched the abdomens of the mannequin and the subject simultaneously, which gave a strong impression that the mannequin's body belonged to the subject.
Real body swap
The researchers later used a knife to give the impression that the mannequin's abdomen was being cut, causing an increase in anxiety in the subject. This indicated that they had "taken ownership" of the other body, said the researchers.
Other experiments used a similar camera set-up, but replaced the mannequin with a real person. In one test, the subject and the person with the camera shook hands, which gave the subject a strong impression that they were shaking hands with themselves.
A knife test had a similar affect as with the mannequin experiment: the test subject exhibited a stress reaction when a knife was held to the camera-wearer's arm, but not when it was touching their own arm.
"Important new milestone"
The illusion worked even when the camera holder differed greatly in appearance or was a different gender than the test subject. But it did not work with objects that did not appear human, such as a chair or large block.
"This study extends our knowledge of how the sensory information from our body is mapped onto our conscious perception of our body's interaction with the world," commented Stephen Macknik, Director of the Laboratory of Behavioural Neurophysiology at the Barrow Neurological Institute in the U.S. city of Phoenix, Arizona.
The new research, he said, is not only an "important new milestone", the ideas it presents might eventually be applied clinically to "paraplegics and quadriplegics, to help develop new ways to give them bodily control." Macknik was not a part of the research team.
