Once the illusion of the invisible body was created, the researchers tried two different experiments. The first one measured the sweating of skin and increased heart rate in response to a knife threatening the empty space representing the body, said Arvid Guterstam, a former doctoral student in cognitive neuroscience who is now at the University of Washington.

“We were measuring that the illusion actually works,” Guterstam said. “The brain should react with automatic stress response when sharp object is approaching. We showed you have an increased stress response and similar to illusion of having mannequin body.”

In the second experiment, the researchers created an invisible body in front of a crowd of strangers in the room. In both instances, the body exhibited a stress reaction.