WORLD
Scientists create illusion of having three arms
Baku, February 24 (AZERTAC). If two hands are better than one, then imagine what you could do with three. In a new study, Swedish researchers were able to trick participants` brains into believing their body had an extra arm.
Brain scientists at the Karolinska Institutet in Stockholm conducted five different experiments on 154 healthy men and women, in the paper published in the February issue of the online journal PLoS ONE. To create the impression of having a third arm, participants sat with their right arm resting on a table and their left arm hidden from view, behind a screen.
Known to neuroscientists as "the supernumerary hand illusion," researchers used two different paintbrushes to stroke the skin on the index and middle fingers of the participant`s real right hand and false one at the exact same time for a minute or two. During this process, participant`s were told to look at the artificial limb.
After each brushing session, volunteers completed a questionnaire. Participants reported that they felt the touch of the brush on both the real and fake hand. They also described feeling as if they had two right hands and both limbs felt like a part of their body.
In another experiment, the researchers held a knife close to the volunteer`s hand and the rubber hand as if it might pierce the skin. They wanted to see if the body and mind perceived the knife as a threat. The same stress response was seen in both the real hand and the prosthetic one. (The reserachers measured the amount of sweat coming from the skin as a measure of emotional arousal of the nervous system; the same response to the threat of the knife was seen whether it was close to touching the real hand or the fake one.)