Swedish researchers have pulled off an “invisibility cloak” with a twist: it’s the person wearing the cloak who thinks they are invisible. It’s all part of a study looking at ways of treating anxiety.
The invisibility study stems from work on phantom limb syndrome in which amputees still perceive pain and other feelings from the missing limb. Neuroscientists at the Karolinska Institute have previously found it possible to create a form of phantom limb syndrome in non-amputees by placing the subject’s arm out of sight behind a screen, and repeatedly stroking both the arm and the empty (visible) space with a brush at the same time. When they then stopped stroking the arm and instead only stroked the empty space in front of the subject, the subject still “felt” the stroking on their arm.
The researchers decided the next step was to see if that illusion could work for an entire body. They got test subjects to wear a virtual reality headset that was hooked up to a camera pointing down at another spot on the floor. That meant whenever the subject looked down, they would appear to see an empty space beneath them where their body should be.
While the subjects found this odd, they were still aware it was simply an illusion. However, when one researcher began stroking the subject’s torso while another moved a brush beneath the camera, things changed. The introduction of touch meant around 70 per cent the subjects began to perceive what they saw — a brush stroking their invisible torso — as reality.
To check the effect was real, the researchers then ‘stabbed’ the empty space beneath the camera with a knife. The subjects had the same raised heart rate and increased sweating that you’d expect if they really did see a knife coming towards them.
However, it was a different story with emotional rather than physical threats. The subjects were then shown an image of a stern-faced crowd of people looking at them. Some subjects considered to see this while their body appeared to be invisible, while in other cases a mannequin was placed by the other camera so that the subject appeared to be able to see their own body. Those who were still under the invisibility illusion were less anxious about the crowd than those who perceived their body as visible.
The researchers plan to rerun the experiment and introduce moral dilemmas to see if people act differently when they are under the illusion of invisibility.
[Image credit: Staffan Larsson/Karolinska Institutet]