According to a new study published in the journal Scientific Reports, the feeling of invisibility changes physical stress response in challenging social situations.

“What is it like to be invisible?” This question has long fascinated man and has been the central theme of many classic literary works, such as the myth of Gyges’ ring in Plato’s dialogue The Republic and the science fiction novel The Invisible Man by H.G. Wells.

Recent studies have suggested that invisibility cloaking of the human body may be possible in the near future. However, it remains unknown how invisibility affects body perception and embodied cognition.

To address these questions, a team of neuroscientists at Karolinska Institutet in Sweden developed a perceptual illusion of having an entire invisible body.

The experiments involved the participant standing up and wearing a set of head-mounted displays. The participant was asked to look down at his/her body, but instead of a real body he/she saw empty space.

To evoke the feeling of having an invisible body, the researchers 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,” explained Dr Arvid Guterstam of the Karolinska Institutet’s Department of Neuroscience, the first author on 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.”

Dr Guterstam and co-authors examined the illusion experience in 125 participants.

To demonstrate that the illusion actually worked, they 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, which suggests that the brain interprets the threat in empty space as a threat directed toward one’s own body.

In another part of the study, the scientists 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,” Dr Guterstam explained.

The results of the study could help in the development of new therapies for social anxiety disorder.

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Arvid Guterstam et al. 2015. Illusory ownership of an invisible body reduces autonomic and subjective social anxiety responses. Scientific Reports 5, article number: 9831; doi: 10.1038/srep09831