Researchers at Sweden's Karolinska Institute conducted 11 experiments in which they created a perpetual illusion were the participants, with two arms and hands, felt as if they had an invisible hand.
The participants were made to sit in a chair with their right hand hidden behind a screen and the researchers touched that hand with a paintbrush while they used another brush to imitate the movements mid-air in view of the participants. In another experiment, the researchers made stabbing motions towards the area where the participants believed their phantom arm was situated.
"We discovered that most participants, within less than a minute, transfer the sensation of touch to the region of empty space where they see the paintbrush move, and experience an invisible hand in that position. Previous research has shown that non-bodily objects, such as a block of wood, cannot be experienced as one's own hand, so we were extremely surprised to find that the brain can accept an invisible hand as part of the body", lead researcher Arvid Guterstam said.