In schizophrenia, some other conditions and extreme physical situations, people can feel an unseen presence accompanying them, a ghost. But this ghost has been shown to probably be ourselves. NeuroScienceNews (here) has a review of a new paper, including a video linked below.
The self that we experience is constructed from a number of sources: individual senses, internal body senses, motor prediction. This usually works seamlessly and we feel that we inhabit this self/body. The construct relies on three areas of the brain cooperating. If one of these areas is damaged or the ability to work together is faulty, part of the self may be detached from the rest and then be experienced as a ‘presence’, near but displaced from the rest of the self. “Our brain possesses several representations of our body in space,” added Giulio Rognini. “Under normal conditions, it is able to assemble a unified self-perception of the self from these representations. But when the system malfunctions because of disease – or, in this case, a robot – this can sometimes create a second representation of one’s own body, which is no longer perceived as ‘me’ but as someone else, a ‘presence’.”
The researchers duplicated the effect in the lab with a robotic device which is clearly shown in a video (here).
I have found ghosts interesting since a conversation with my mother many years ago. She did not believe in ghosts or anything like that, but she found that after my father died, she could talk to him. She knew that it was herself talking in his voice in her head. She said that she knew him well enough to know what he would say and how. If fact she encouraged the voice – it was comforting. When she had a problem and want to know what he would advise, if he were alive, she would ask him. It worked best just as she was going to sleep. After a time the effect weakened and then was no longer available. Her grief and her immediate change in responsibility would have affected her, and given her problems that she had not faced before. In trying to figure out what he would have done she made those thoughts into a separate verbal presence. At first, she also thought she could see him out of the corner of her eye, but when she turned there was no one there. She put that down to missing him and changing any little movement, half seen, into him.
I figure there were a number of tiny areas of her brain that were dedicated to monitoring my dad. When he died they were not called on to do any work and eventually started creating sightings of him, like our brains react to sensory deprivation with hallucinations. I have been told that such things are quite common, but people do not mention them for fear of being ridiculed. Also, it is reported that many people hear voices from time to time, but do not report it for fear of being thought mad.
Here is the abstract of the paper (“Neurological and Robot-Controlled Induction of an Apparition”; O. Blanke, P. Pozeg, M. Hara, L. Heydrich, A. Serino, A. Yamamoto, T. Higuchi, R. Salomon, M. Seeck, T. Landis, S. Arzy, B. Herbelin, H. Bleuler, and G. Rognini; Current Biology 2014):
Tales of ghosts, wraiths, and other apparitions have been reported in virtually all cultures. The strange sensation that somebody is nearby when no one is actually present and cannot be seen (feeling of a presence, FoP) is a fascinating feat of the human mind, and this apparition is often covered in the literature of divinity, occultism, and fiction. Although it is described by neurological and psychiatric patients and healthy individuals in different situations, it is not yet understood how the phenomenon is triggered by the brain. Here, we performed lesion analysis in neurological FoP patients, supported by an analysis of associated neurological deficits. Our data show that the FoP is an illusory own-body perception with well-defined characteristics that is associated with sensorimotor loss and caused by lesions in three distinct brain regions: temporoparietal, insular, and especially frontoparietal cortex. Based on these data and recent experimental advances of multisensory own-body illusions, we designed a master-slave robotic system that generated specific sensorimotor conflicts and enabled us to induce the FoP and related illusory own-body perceptions experimentally in normal participants. These data show that the illusion of feeling another person nearby is caused by misperceiving the source and identity of sensorimotor (tactile, proprioceptive, and motor) signals of one’s own body. Our findings reveal the neural mechanisms of the FoP, highlight the subtle balance of brain mechanisms that generate the experience of “self” and “other,” and advance the understanding of the brain mechanisms responsible for hallucinations in schizophrenia.