Swedish scientists have created for the first time in the lab a perceptual illusion of having an invisible body among humans.
The experiment involved 125 participants standing up and wearing a set of head-mounted displays.
The participants were then asked to look down at their bodies but instead of their real bodies, they saw empty space.
To evoke the feeling of having an invisible body, scientists touched participants' body in various locations with a large paintbrush while, with another paintbrush held in the other hand, exactly imitating the movements in mid-air in full view of the participants.
"Within less than a minute, the majority of the participants started to transfer the sensation of touch to the portion of empty space where they saw the paintbrush move and experienced an invisible body in that position," explained Arvid Guterstam, lead author from the Karolinska Institutet in Sweden.
In a previous study, the same team showed that the same illusion can be created for a single hand.
"The present study demonstrates that the 'invisible hand illusion' can, surprisingly, be extended to an entire invisible body," he noted.
To demonstrate that the illusion actually worked, the researchers would make a stabbing motion with a knife toward the empty space that represented the belly of the invisible body.
The participants' sweat response to seeing the knife was elevated while experiencing the illusion but absent when the illusion was broken.
"It suggests that the brain interprets the threat in empty space as a threat directed toward one's own body," the authors noted.
In another experiment, the team examined whether the feeling of invisibility affects social anxiety by placing the participants in front of an audience of strangers.
"We found that their heart rate and self-reported stress level during the 'performance' was lower when they experienced the invisible body illusion," Guterstam noted.
The results are interesting because they show that the perceived physical quality of the body can change the way our brain processes social cues.
The results suggest that the feeling of invisibility changes our physical stress response in challenging social situations.
The power of invisibility has long fascinated man and inspired the works of many great authors and philosophers such as renowned science fiction writer H.G. Wells who wrote "The Invisible Man".
Recent advances in materials science have shown that invisibility cloaking of large-scale objects such as a human body might be possible in the not-so-distant future.