A hallucination is a sensory perception without a source in the external world. The English word "hallucination" comes from the Latin verb hallucinari, which means "to wander in the mind." Hallucinations can affect any of the senses, although certain diseases or disorders are associated with specific types of hallucinations.
It is important to distinguish between hallucinations and illusions or delusions, as the terms are often confused in conversation and popular journalism. A hallucination is a distorted sensory experience that appears to be a perception of something real even though it is not caused by an external stimulus. For example, some elderly people who have been recently bereaved may have hallucinations in which they "see" the dead loved one. An illusion, by contrast, is a mistaken or false interpretation of a real sensory experience, as when a traveler in the desert sees what looks like a pool of water, but in fact is a mirage caused by the refraction of light as it passes through layers of air of different densities. The bluish-colored light is a real sensory stimulus, but mistaking it for water is an illusion. A delusion is a false belief that a person maintains in spite of evidence to the contrary and in spite of proof that other members of their culture do not share the belief. For example, some people insist that they have seen flying saucers or unidentified flying objects (UFOs) even though the objects they have filmed or photographed can be shown to be ordinary aircraft, weather balloons, satellites, etc.
It would be difficult to describe a "typical" hallucination, as these experiences vary considerably in length of time, quality, and sense or senses affected. Some hallucinations last only a few seconds; however, some people diagnosed with Charles Bonnet syndrome (CBS) have reported visual hallucinations lasting over several days, while people who have taken certain drugs have experienced hallucinations involving colors, sounds, and smells lasting for hours. Albert Hoffman, the Swiss chemist who first synthesized lysergic acid diethylamide (LSD), experienced nine hours of hallucinations after taking a small amount of the drug in 1943. In 1896, the American neurologist S. Weir Mitchell published an account of the six hours of hallucinations that followed his experimental swallowing of peyote buttons.
There is not always a close connection between the cause of a person's hallucinations and the emotional response to them. One study of patients diagnosed with CBS found that 30% of the patients were upset by their hallucinations, while 13% found them amusing or pleasant. The environment in which LSD and other hallucinogens are taken may affect an individual's psychological constitution and personal reactions. The writer Peter Matthiessen, for example, noted that his 1960s experiences with LSD "were magic shows, mysterious, enthralling," while his wife "… freaked out; that is the drug term, and there is no better.… her armor had cracked, and all the night winds of the world went howling through." In contrast to those who take hallucinogens, however, a majority of patients with narcolepsy, alcoholic hallucinosis, or post-traumatic disorders finds their hallucinations frightening.
The demographics of hallucinations vary depending on their cause; however, many researchers think that they are underreported for several reasons:
In 2000, one of the few studies of hallucinations in a general Western population reported the following statistics:
There is currently no evidence that hallucinations occur more frequently in some racial or ethnic groups than in others. In addition, gender does not appear to make a difference. The demographics of hallucinations associated with some specific age groups, conditions, or disorders are as follows:
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Author Info: Rebecca Frey PhD, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Neurological Disorders, 2005 |