Patients suffering from neurological or psychiatric conditions have often reported 'feeling a presence' watching over them. Now, researchers have succeeded in recreating these ghostly illusions in the lab.
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 then carried out a "dissonance" experiment in which blindfolded participants performed movements with their hand in front of their body. Behind them, a robotic device reproduced their movements, touching them on the back in real time. The result was a kind of spatial discrepancy, but because of the synchronized movement of the robot, the participant's brain was 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.