You may think only aliens could have multiple limbs. But now an experiment conducted by Henrik Ehrsson and his colleagues from Karolinska Institute in Sweden has shown that humans can also feel what it’s like to have a third arm and even flinch if it’s threatened with a knife (see video below). The illusion is perceived when a person’s right arm, and a similar fake arm, are stroked simultaneously when both are in view. For the brain trick to work, the extra arm also has to be lined up with the real one and be placed in an anatomically-appropriate position.
The third arm illusion is similar to the rubber hand illusion, where a person feels like a fake hand is their own when their real arm is hidden from view and stroked at the same time. But the new sensation is different since a person still perceives the real arm as their own and feels like they actually have two of the same limbs. According to the team, it shows that it’s possible to experience a completely different body plan. Using a similar technique, the team previously showed that a person can feel like another body, or that of a mannequin, is their own. Now they’ve just released new video (also see below) that shows the spooky experiments in action.
The team’s new work should be useful for helping disabled people accept a prosthetic limb as their own. But they also foresee futuristic applications, such as people gaining extra artificial limbs to help them get tedious tasks done faster.
Source: New Scientist
