In a first, scientists have created a perceptual illusion of having an invisible body among humans in the lab and found the feeling of invisibility changes our physical stress response in challenging social situations.
The experiment by neuroscientists from Sweden's Karolinska Institutet involved the participant standing up and wearing a set of head-mounted displays.
The participant was then asked to look down at her body, but instead of her real body she saw empty space.
To evoke the feeling of having an invisible body, a scientist touched the participant's 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 participant.
"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," said Arvid Guterstam, lead author of the study.
"We showed in a previous study 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," said Guterstam.
The study examined the illusion experience in 125 participants.
To demonstrate that the illusion actually worked, the researchers would make a stabbing motion with a knife towards 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, which suggests that the brain interprets the threat in empty space as a threat directed towards one's own body.
In another part of the study, the researchers 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 immediately prior had experienced the invisible body illusion compared to when they experienced having a physical body," Guterstam said.
The researchers hope that the results of the study will be of value to future clinical research, for example in the development of new therapies for social anxiety disorder.
The research was published in the journal Scientific Reports.
