Have you ever gotten that creepy feeling that there’s someone behind you? And then you turn around, and find that you’re alone. It’s eerie, like maybe you’ve just missed seeing a ghost. Now researchers in Switzerland have just discovered how to induce that feeling in study subjects in a lab, using a robot that messed with the way their brains interpret bodily signals.
Science writer Ed Yong describes the robot setup on National Geographic:
[The set-up involved] two robots—a master that sits in front of a volunteer, and a slave that sits behind. You stick your right index finger in the master and move it around. These movements are sent to slave, which prods you in the back, using the same pressure, timing, and pattern. Meanwhile, the master also gives you tactile feedback through your fingertip. As a result, you feel that you’re stroking your own back, even though your arm is stretched out in front of you.
It’s a neat trick. But things got really interesting when the team added a short delay—a half-second difference between the volunteers moving the master, and the slave prodding them in return.
Suddenly, five participants felt that there was someone in the room, standing behind them and touching them … . This is the first time that anyone has been able to deliberately recreate that feeling in a lab.
That unsettling feeling comes from a mix-up in the brain’s sensorimotor signals, which usually help us understand where our bodies are physically located. The researchers hope that their work will help lead them to new treatments for people with schizophrenia and other psychiatric problems, who frequently experience delusions and hallucinations like this. You can watch the study authors talk about their research in the video below.