In an experiment that could explain why some people see ghosts, participants were made to feel as though they saw phantoms around them and that ghosts were touching their backs with invisible fingers. The illusion was so real that some test subjects begged for it to stop.

Scientists from Switzerland's Ecole Polytechnique Federale de Lausanne have shown that it's possible to induce the illusion of seeing and feeling an apparition by creating a situation wherein a person momentarily loses track of their body's location in space and time.

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The researchers were investigating the strange sensation that somebody is nearby, but no one is actually present and cannot be seen. Scientists call this a "feeling of presence," or FoP for short. It's a psychological phenomenon that's been recorded throughout history, leading to various beliefs in the supernatural or divine. Though well documented, scientists aren't exactly sure how the phenomenon is triggered by the brain.

Making Ghosts

That said, scientists do suspect that certain regions of the brain are responsible for this illusion, including the temporoparietal, insular, and frontoparietal cortex.

To reproduce FoP, the researchers set up an interesting experiment. An EPFL release explains:

The researchers first analyzed the brains of 12 patients with neurological disorders – mostly epilepsy – who have experienced this kind of "apparition." MRI analysis of the patients's brains revealed interference with three cortical regions: the insular cortex, parietal-frontal cortex, and the temporo-parietal cortex. These three areas are involved in self-awareness, movement and the sense of position in space (proprioception). Together, they contribute to multisensory signal processing, which is important for the perception of one's own body.

The scientists carried out a "dissonance" experiment. Blindfolded participants performed movements with their hand in front of their body. Behind them, a robotic device reproduces their movements, touching them on the back in real time. The result is a kind of spatial discrepancy, but because of the synchronized movement of the robot, the participant's brain is able to adapt and correct for it.

Next, the neuroscientists introduced a temporal delay between the participant's movement and the robot's touch. Under these asynchronous conditions, distorting temporal and spatial perception, the researchers were able to recreate the ghost illusion.

The participants were not aware of the experiment's purpose. After several minutes of this delayed touching, several subjects reported a strong "feeling of presence," even counting up to four "ghosts" where there were non. For some, the feeling was so strong that they asked the researchers to stop the experiment.

Image: EPFL.

"Our experiment induced the sensation of a foreign presence in the laboratory for the first time," noted study author Olaf Blanke. "It shows that it can arise under normal conditions, simply through conflicting sensory-motor signals. This confirms that it is caused by an altered perception of their own bodies in the brain."

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The sensorimotor robot was also able to induce FoP experimentally in healthy subjects.

This research could help us understand why people suffering from emotional stress or injury see apparitions, as well as offering a deeper understanding of the brain mechanisms responsible for hallucinations and schizophrenia.

Check out the entire study at Current Biology: "Neurological and Robot-Controlled Induction of an Apparition".

Top image: Arman Zhenlikeyev/Shutterstock.

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