While some accept ghosts as a reality, many others are skeptical of the existence of ghosts. Much of the scientific community believes that ghosts, as well as other supernatural and paranormal entities, do not exist. The current tentative consensus among parapsychologists is that ghosts are not the spirits of deceased humans, but psychic imprints which have been left behind, often because of especially strong emotions in the persons who leave the ghost.
Skeptics often explain ghost sightings with the principle of Occam's razor, which argues that explanations should maximize parsimony with the rest of our knowledge, thus making the simplest and most mundane explanation the one which is best. They may suggest that, since few to none of us have ever had an encounter with a ghost, but most or all of us have had an experience of self-delusion or have attributed a false cause to an event, that these options should be preferred in the absence of a great abundance of evidence for supernatural explanations. Skeptics are also keen to note that most ghost sightings happen when our senses are impaired, and that the evidence is unreliable because it doesn't occur when we have full use of our faculties. (It however bears noting that, conversely, spiritualists or theists such as demonologists and other occultists invoking the principle of Occam's razor will come to differing if not opposite conclusions, since, to them, "the rest of our knowledge" provides us with unfathomably vast amounts of positive data regarding the supernatural; ideas like "parsimony" are, by nature, entirely context-dependent.)
Human physiology may play a role in ghost sighting:
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Ghosts are often associated with a chilling sensation, but a natural animal response to fear is hair raising, which can be mistaken for chill.
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Peripheral vision is very sensitive to motion, but does not contain much colour or the ability to sharply distinguish shapes. Any random motion outside the focused view can create a strong illusion of an eerie figure.
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Sound waves with frequencies lower than 20 hertz are called infrasound and are normally inaudible, but British scientists Richard Lord and Richard Wiseman have concluded that infrasound can cause humans to feel a "presence" in the room, or unexplained feelings of anxiety or dread.
Sometimes ghosts are associated with electromagnetic disturbances, which suggests that they might be attributable to the electromagnetic field and not to a presently dead person. Often, videos of paranormal investigators will show them using E-field or B-field detectors and finding "ghostly" results near wall outlets and electrical appliances.
Psychological factors may also relate to ghost sightings. Many people exaggerate their own perceptions, either when visiting a place they believe to be haunted, or when visiting a site which they know unpleasant historical events have occurred. Certain images such as paintings and movies might "program" a person to automatically associate a certain structure or area with ghosts. Also, the psychological phenomenon of pareidolia may cause people to perceive human-like faces or figures in the otherwise mundane surroundings of their environments, particularly in conditions where vision is partly obscured, as in a dark corridor or at night.
