What would it feel like to be, in some sense, a brain without a body? Now a handful of people in Sweden can tell you.
These invisible people didn’t actually disappear. No magic capes, evil rings or cloaking devices were involved, and other people could still see them. But they believed to an extent that their bodies had vanished, thanks to an elaborate psychological trick. And it seems that losing your body may have a positive side effect. “The experience of having an invisible body seems to reduce stress, specifically the stress we feel when standing in front of strangers,” says Arvid Guterstam, a cognitive neuroscientist at the Karolinska Institutet, whose team describes the finding this week in Scientific Reports.
That people can be fooled this way isn’t entirely surprising. Though powerful, the brain has its limits, and piecing together the information gathered by the senses requires some guesswork and filling in blanks. That means even our day-to-day experience of reality can be thought of as a trick of the mind. “Almost everything we perceive is an illusion based on partial information,” says Susana Martinez-Conde, a neuroscientist at SUNY Downstate Medical Center. “Most of the time the brain does a pretty good job, but sometimes it really gets it wrong.”
Investigating why the brain sometimes falters can reveal how it gets things right the rest of the time. Consider the classic illusion of the rubber hand: Stroke a person's hand while it's hidden under a table and, at the same time, stroke a prosthetic hand in plain sight. The hand’s owner will begin to think of the prosthetic as part of their body. Scans conducted during this illusion have highlighted the brain regions involved in the confusion, helping scientists identify neurons whose job it is to combine data from different senses.
Extraordinary circumstances outside of the laboratory can also distort our relationships with our bodies. Amputees talk about phantom limbs extending from the stumps where their arms or legs used to be. And damage to the spine has been known to give rise to the sensation of a second body projecting out at an angle from the neck, hovering in empty space.
Inspired by these cases of ghostly flesh, the new illusion started with virtual reality goggles. Bespectacled volunteers who were completely intact looked down and saw not their bellies and legs but only empty space—a live feed recorded by a nearby camera pointed at the floor. That wouldn’t be much of a trick on its own. But Guterstam then stroked each volunteer’s stomach with an unseen paintbrush while waving a second brush under the camera, where it could be seen dancing alone. If the pair of brushes moved in the same patterns at the same time, things got strange.
Faced with contradictory information—the feel of the bristles against their torsos clashing with the sight of a brush touching nothing—many people experienced the uncanny sensation that their body had become transparent. This spell proved powerful. When those who succumbed to it watched a knife being thrust through the empty space, their skin reacted. Its electrical conductance jumped, which the researchers interpreted as a stress reaction to this threat against the invisible self. Volunteers who saw a knife but did not experience the invisibility illusion had a much smaller reaction.
“It’s interesting that they can turn the body off, and the self seems to continue,” says Patrick Haggard of the University College London Institute of Cognitive Neuroscience. “This suggests our sense of self might be less dependent on the material body than has been previously proposed.”
Hoping to put this illusion to good use, the researchers tried one last experiment. Goggled volunteers looked up from the empty space to the surprising sight of a crowd of people staring at them—not an actual audience there in the room, but a convincing image of a virtual crowd. This wasn’t very pleasant, as reported in surveys and indicated by increases in heart rate. But the participants seemed to experience a little less stress, on average, if under the influence of the invisibility illusion.
“It’s not a dramatic difference, but it’s a difference that can’t be explained by chance,” says Guterstam.
Virtual reality might thus be a tool for treating social anxiety, an intense fear of social situations accompanied by physical symptoms such as a pounding heart, sweating and shaking. A common treatment for those suffering from the disorder is cognitive behavioral therapy, in which someone is exposed to increasingly difficult social situations. Being able to turn invisible, at least in one’s own mind, could help people to cope with this process, the study authors suggest.
Though the preliminary data is intriguing, the illusion is still a long way from therapeutic use, says Lorimer Moseley, a cognitive neuroscientist at the Sansom Institute for Health Research at the University of South Australia. He has already challenged the reported benefits of other illusions, including the ability of the rubber hand trick to ease the pain that amputees often feel in their phantom limbs. Moseley is eager to put this new trick to the test. “It’s discoveries like these that plant a seed in the minds of people like me,” he says.
Ultimately, Guterstam hopes to tackle a more philosophical concern: how being invisible influences moral decisions. It’s a favorite topic of fiction writers: H.G. Wells’ invisible man invents an especially concealing paint only to become a thief and a terrorist. Comic book superheroes, on the other hand, often use their unusual gift to make the world a better place. And with the proliferation of cloaking materials being investigated in labs worldwide, fact may be catching up to fiction, which raises some ethical quandaries. “Does gaining the power of invisibility corrupt human moral nature? We have a new tool to answer this question,” Guterstam says.