Psychology photo

You’re all alone in a room, when all of a sudden your senses start tingling. Though you can’t hear or see anyone around, you have this indescribable perception of a human presence lurking nearby. It just feels like someone is there.

This ghostly phenomenon, referred to as a “feeling of a presence” or FoP, has been reported across cultures, especially in individuals under extreme conditions — from mountaineers to shipwreck survivors. FoP is also a common symptom of patients with certain neurological and mental health issues — for example, schizophrenic patients may encounter this feeling on a daily basis. And now, researchers think they may know where the mysterious feeling comes from.

Neuroscientists in Switzerland had a hunch that FoP originates from damage or confusion in three areas of the brain. So they created a robot capable of giving healthy people this unnerving sensation, by sending mixed-up signals to the brain. Apparently the robot was so good at its job, two of the study participants were too freaked out to finish the experiment.

But first, to find these faulty brain regions, the researchers studied 12 patients with different neurological conditions stemming from epilepsy, stroke, migraine, and tumors. These study participants all feel FoP for seconds or minutes at a time, and the researchers were able to trace this feeling to damage in three areas of their brains: the temporoparietal, insular, and frontoparietal cortex. These areas are important for processing movement and spatial positioning.

FoP is the result of confusion over the signals your body sends to your brain when you move around. That would mean the “ghosts” people feel are actually themselves.

Most importantly, the researchers noticed the patients all shared a similar sensation during their experiences with FoP. If the patient was standing, he or she had a sense that the nearby “ghost” or “presence” was also standing. If the patient was sitting, then the presence was also sitting. The patients and their ghosts also shared the same posture and movements. This gave the researchers an idea: Maybe FoP is the result of confusion over the source and identity of the body’s sensorimotor signals — the signals your body sends to your brain when you move around. That would mean the ghosts people feel are actually themselves.

“The feeling of a presence is the misattribution of signals in the brain,” lead researcher Dr. Giulio Rognini, from the École polytechnique fédérale de Lausanne in Switzerland, tells Popular Science. “Their own signals are coming from the body, but they’re not properly integrated by the brain. So instead of the movements being properly attributed to themselves, they’re misattributed to another person.”

To test this idea, the researchers created a robot that messed with people’s sensorimotor signals. With their eyes covered, otherwise healthy participants pushed against a lever in front of them, which relayed signals to a poking device behind them. Each time they pushed they lever, the robot behind them poked them in the back. Essentially, it gave the participants the experience of feeling as though they were reaching in front of them and touching themselves in the back. You can check out a video of someone using the robot below:

Then in a second part of the experiment, the researchers added in a delay to the poking. When participants pushed on the lever, the robot waited half a second or more to poke them in the back. This mix-up in timing gave people a very distinct – and sometimes very strong – feeling that someone else was standing behind them, poking them. Participants even reported feeling as though their bodies drifted backwards toward the presence.

“When we perturb this system through robotic simulation, a second representation of our body is formed; it’s not felt as ‘me’ or ‘my body’, but it is felt as a presence of another,” Rognini says. “It is generated when the prediction of the consequences of a movement and the act of the consequences of this movement mismatch.” This mismatch can also explain why healthy people experience FoP from time to time; it’s just a matter of momentary sensory confusion in the brain.

Rognini notes that they hope to one day use their sensory confusion robot in a completely opposite manner, in order to help those with schizophrenia. “Instead of creating this conflict, we want to use this robotic simulation to remove this conflict to help schizophrenic patients to restore balance. We could make them better at distinguishing themselves from someone else.”

The study was published today in Current Biology.