How would it feel to be invisible? Neuroscientists at Sweden’s Karolinska Institutet have found out. It can actually changes your physical stress response in challenging social situations, for example.

The history of literature features many well-known narrations of invisibility and its effect on the human mind, 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. Now it’s been studied in the lab.

The experiment

In an open-access article in the journal Scientific Reports, the researchers describe the experiment. The participant is standing up and is wearing a set of head-mounted displays. She is asked to look down at her ody, but instead of her real body she sees empty space. Then the scientist touches the participant’s body in various locations with a large paintbrush while, with another paintbrush held in the other hand, exactly imitates those 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,” says Arvid Guterstam, lead author of the present 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.”

The study examined this illusion experience in 125 participants. To demonstrate that it 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, which suggests that the brain interprets the threat in empty space as a threat directed toward one’s own body.

Therapy for social anxiety

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,” says Arvid Guterstam. “These results are interesting because they show that the perceived physical quality of the body can change the way our brain processes social cues.”

The researches 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.

“Follow-up studies should also investigate whether the feeling of invisibility affects moral decision-making, to ensure that future invisibility cloaking does not make us lose our sense of right and wrong, which Plato asserted over two millennia ago,” says principal investigator Henrik Ehrsson, professor at the Department of Neuroscience.

This research was funded by the Swedish Research Council and the Söderberg Foundation.

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Abstract of Illusory ownership of an invisible body reduces autonomic and subjective social anxiety responses

What is it like to be invisible? This question has long fascinated man and has been the central theme of many classic literary works. Recent advances in materials science suggest that invisibility cloaking of the human body may be possible in the not-so-distant future. However, it remains unknown how invisibility affects body perception and embodied cognition. To address these questions, we developed a perceptual illusion of having an entire invisible body. Through a series of experiments, we characterized the multisensory rules that govern the elicitation of the illusion and show that the experience of having an invisible body reduces the social anxiety response to standing in front of an audience. This study provides an experimental model of what it is like to be invisible and shows that this experience affects bodily self-perception and social cognition.