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:
- Fear of being thought "crazy" or mentally ill
- Gaps in research. For example, some types of hallucinations are associated with disorders that primarily affect the elderly, who are often underrepresented in health surveys
- Fear of being reported to law enforcement for illegal drug use
In 2000, one of the few studies of hallucinations in a general Western population reported the following statistics:
- Of a total sample of 13,000 adults, 38.7% reported hallucinations: 6.4% had hallucinations once a month, 2.7% once a week, and 2.4% more than once a week.
- Of the subjects, 27% reported having hallucinations in the daytime. In this group, visual (3.2%) and auditory (0.6%) hallucinations were closely associated with diagnoses of psychotic or anxiety disorders.
- Of the subjects, 3.1% reported haptic (tactile) hallucinations; most of these subjects were current drug users.
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:
- Children. Hallucinations are rare in children below the age of eight. About 40% of children diagnosed with schizophrenia , however, have visual or auditory hallucinations.
- Eye disorders. About 14% of patients treated in eye clinics for glaucoma or age-related macular degeneration report visual hallucinations.
- Alzheimer's disease (AD). About 40–50% of patients diagnosed with AD develop hallucinations in the later stages of the disease.
- Drug use. Hallucinogens are the third most frequently abused class of drugs (after alcohol and marijuana) among high school and college students. Various surveys report that about 7% of people in the United States over the age of 12 have taken LSD at least once; that 5% of high school seniors admit to using MDMA (Ecstasy); and that 20–24% of college students use MDMA. The highest rate of hallucinogen abuse is found in Caucasian males between the ages of 18 and 25.
- Normal sleep/wake cycles. Sleep researchers in Great Britain and the United States have reported that 30–37% of adults experience hypnagogic hallucinations, which occur during the passage from wakefulness into sleep, while about 10–12% report hypnopompic hallucinations, which occur as a person awakens. Hallucinations related to ordinary sleeping and waking are not considered an indication of a mental or physical disorder.
- Migraine headaches. About 10% of patients diagnosed with migraine headaches experience visual hallucinations prior to the onset of an acute attack.
- Adult-onset schizophrenia. According to the National Institute of Mental Health (NIMH), about 75% of adults diagnosed with schizophrenia experience hallucinations, most commonly auditory or visual. The auditory hallucinations may be command hallucinations, in which the person hears voices ordering him or her to do something. For example, the man who killed a Swedish politician in September 2003 told the police that voices in his head told him "to attack."
- Temporal lobe epilepsy (TLE). About 80% of patients diagnosed with TLE report gustatory and olfactory hallucinations as well as auditory and visual hallucinations.
- Narcolepsy. Frequent hypnagogic hallucinations are considered one of four classic symptoms of narcolepsy, and are experienced by 60% of patients diagnosed with the disorder.
- Post-traumatic stress disorder (PTSD). Studies of combat veterans diagnosed with PTSD have found that 50–65% have experienced auditory hallucinations. Visual, olfactory, and haptic hallucinations have been reported by survivors of rape and childhood sexual abuse.
The neurologic causes of hallucinations are not currently completely understood, although researchers have identified some factors in the context of specific disorders, and have proposed various hypotheses to explain hallucinations in others. There does not appear to be a single causal factor that accounts for hallucinations in all people who experience them.
Research subjects who have undergone sleep deprivation experiments typically begin to hallucinate after 72–96 hours without sleep. It is thought that these hallucinations result from the malfunctioning of nerve cells within the prefrontal cortex of the brain. This area of the brain is associated with judgment, impulse control, attention, and visual association, and is refreshed during the early stages of sleep. When a person is sleep-deprived, the nerve cells in the prefrontal cortex must work harder than usual without an opportunity to recover. The hallucinations that develop on the third day of wakefulness are thought to be hypnagogic hallucinations that occur during "microsleeps," or short periods of light sleep lasting about one to ten seconds.
Post-traumatic memory formation
Hallucinations in trauma survivors are caused by abnormal patterns of memory formation during the traumatic experience. In normal situations, memories are formed from sensory data, organized in a part of the brain known as the hippocampus, and integrated with previous memories in the frontal cortex. People then "make sense" of their memories through the use of language, which helps them to describe their experiences to others and to themselves. In traumatic situations, however, bits and pieces of memory are stored in the amygdala, an almond-shaped structure in the brain that ordinarily attaches emotional significance to memories, without being integrated by the hippocampus and interpreted in the frontal cortex. In addition, the region of the brain that governs speech (Broca's area) often shuts down under extreme stress. The result is that memories of the traumatic event remain in the amygdala as a chaotic wordless jumble of physical sensations or sensory images that can re-emerge as hallucinations during stressful situations at later points in the patient's life.
In 1973, a British researcher named Cogan categorized hallucinations into two major groups that he called "irritative" and "release" hallucinations. Irritative hallucinations result from abnormal electrical discharges in the brain, and are associated with such disorders as migraine headaches and epilepsy. Brain tumors and traumatic damage to the brain are other possible causes of abnormal electrical activity manifesting as visual hallucinations.
Hallucinations have also been reported with a number of infectious diseases that affect the brain, including bacterial meningitis, rabies, herpes virus infections, Lyme disease , HIV infection, toxoplasmosis, Jakob-Creuzfeldt disease, and late-stage syphilis.
Release hallucinations are most common in people with impaired eyesight or hearing. They are produced by the spontaneous activity of nerve cells in the visual or auditory cortex of the brain in the absence of actual sensory data from the eyes or ears. These experiences differ from the hallucinations of schizophrenia in that those patients experiencing release hallucinations are often able to recognize them as unreal. Release hallucinations are also more elaborate and usually longer in duration than irritative hallucinations. The visual hallucinations of patients with CBS are an example of release hallucinations.
Neurotransmitters are chemicals produced by the body that carry electrical impulses across the gaps (synapses) between adjoining nerve cells. Some neurotransmitters inhibit the transmission of nerve impulses, while others excite or intensify them. Hallucinations in some conditions or disorders result from imbalances among these various chemicals.
NARCOLEPSY Narcolepsy is a disorder characterized by uncontrollable brief episodes of sleep, frequent hypnagogic or hypnopompic hallucinations, and sleep paralysis. Between 1999 and 2000, researchers discovered that people with narcolepsy have a much lower than normal number of hypocretin neurons, which are nerve cells in the hypothalamus that secrete a neurotransmitter known as hypocretin. Low levels of this chemical are thought to be responsible for the daytime sleepiness and hallucinations of narcolepsy.
PRESCRIPTION MEDICATIONS Hallucinations have been reported as side effects of such drugs as ketamine (Ketalar), which is sometimes used as an anesthetic but has also been used illegally to commit date rape; paroxetine (Paxil), an SSRI antidepressant; mirtazapine (Remeron), a serotonin-specific antidepressant; and zolpidem (Ambien), a sleep medication. Ketamine prevents brain cells from taking up glutamate, a neurotransmitter that governs perception of pain and of one's relationship to the environment. Paroxetine alters the balance between the neurotransmitters serotonin and acetylcholine.
Hallucinations in patients with Alzheimer's disease are thought to be a side effect of treatment with neuroleptics (antipsychotic medications), although they may also result from inadequate blood flow in certain regions of the brain. The antiretroviral drugs used to treat HIV infection may also produce hallucinations in some patients.
HALLUCINOGENS AND DRUGS OF ABUSE Like the hallucinations caused by prescription drugs, hallucinations caused by drugs of abuse result from disruption of the normal balance of neurotransmitters in the brain. Hallucinations in cocaine and amphetamine users, for example, are associated with the overproduction of dopamine, a neuro-transmitter associated with arousal and motor excitability. LSD appears to produce hallucinations by blocking the action of the neurotransmitters serotonin (particularly serotonin-2) and norepinephrine. Phencyclidine (PCP) acts like ketamine in producing hallucinations by blocking the reception of glutamate.
People who have used LSD sometimes experience flashbacks, which are spontaneous recurrences of the hallucinations and other distorted perceptions caused by the drug. Some doctors refer to this condition as hallucinogen persisting perception disorder, or HPPD.
There are two types of alcohol withdrawal syndromes characterized by hallucinations. Alcoholic hallucinosis typically occurs after abrupt withdrawal from alcohol after a long period of excessive drinking. The patient hears threatening or accusing voices rather than "seeing things," and his or her consciousness is otherwise normal. Delirium tremens (DTs), on the other hand, is a withdrawal syndrome that begins several days after drinking stops. A patient with the DTs is disoriented, confused, depressed, feverish, and sweating heavily as well as hallucinating, and the hallucinations are usually visual.
MOOD DISORDERS Visual hallucinations occasionally occur in patients diagnosed with depression , particularly the elderly. These hallucinations are thought to result from low levels of the neurotransmitter serotonin. The hallucinations that occur in patients with Parkinson's disease appear to result from a combination of medication side effects, depressed mood, and impaired eyesight.
The auditory hallucinations associated with schizophrenia may be the end result of a combination of factors. These hallucinations have sometimes been attributed to unusually high levels of the neurotransmitter dopamine in the patient's brain. Other researchers have noted abnormal patterns of brain activity in patients with schizophrenia. In particular, these patients suffer from dysfunction of a mechanism known as corollary discharge, which allows people to distinguish between stimuli outside the self and internal intentions and thoughts. Electroencephalograms (EEGs) of patients with schizophrenia that were taken while the patients were talking showed that corollary discharges from the frontal cortex of the brain (where thoughts are produced) failed to inform the auditory cortex (where sounds are interpreted) that the talking was self-generated. This failure would lead the patients to interpret internal speech as coming from external sources, thus producing auditory hallucinations. In addition, the brains of patients with schizophrenia appear to suffer tissue loss in certain regions. In early 2004, some German researchers reported a direct correlation between the severity of auditory hallucinations in patients with schizophrenia and the amount of brain tissue that had been lost from the primary auditory cortex.
The differential diagnosis of hallucinations can be complicated, but in most cases taking the patient's medical history will help the doctor narrow the list of possible diagnoses. If the patient has been taken to a hospital emergency room, the doctor may ask those who accompanied the patient for information. The doctor may also need to perform a medical evaluation before a psychiatric assessment of the hallucinations can be made. The medical evaluation may include laboratory tests and imaging studies as well as a physical examination, depending on the patient's other symptoms. If it is suspected that the patient is suffering from delirium, dementia , or a psychotic disorder, the doctor may assess the patient's mental status by using a standard instrument known as the mini-mental status examination (MMSE) or the Folstein (after the clinician who devised it). The MMSE yields a total score based on the patient's appearance, mood, cognitive skills, thought content, judgment, and speech patterns. A score of 20 or lower usually indicates delirium, dementia, schizophrenia, or severe depression.
Hallucinations in elderly patients may require specialized evaluation because of the possibility of overlapping causes. The American Association for Geriatric Psychiatry lists hallucinations as an indication for consulting a geriatric psychiatrist. In addition, elderly patients should be routinely screened for visual or hearing impairments.
Hallucinations are treated with regard to the underlying disorder. Depending on the disorder, treatment may involve antipsychotic, anticonvulsant, or antidepressant medications; psychotherapy; brain or ear surgery; or therapy for drug dependence. Hallucinations related to normal sleeping and waking are not a cause for concern.
The prognosis of hallucinations depends on the underlying cause or disorder.
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National Institute of Mental Health (NIMH) Office of Communications. 6001 Executive Boulevard, Room 8184, MSC 9663, Bethesda, MD 20892-9663. (301) 443-4513 or (866) 615-NIMH; Fax: (301) 443-5158. [email protected] <http://www.nimh.nih.gov>.
Rebecca Frey, PhD
A false perception of sensory vividness arising without the stimulus of a corresponding sense impression. In this it differs from illusion, which is merely the misinterpretation of an actual sense perception. Visual and auditory hallucinations are the most common, but hallucinations of the other senses may also be experienced. Human figures and voices most frequently form the subject of a hallucination, but in certain types other classes of objects may be seen, as, for instance, the rats and insects of delirium tremens.
Although hallucination is often associated with various mental and physical diseases, it may nevertheless occur spontaneously while the agent shows no departure from full vigor of body and mind. It may also be induced (i.e., in hypnotism ) in a high percentage of subjects. The essential difference between sane and insane hallucinations is that in the former case the agent can, by reflection, recognize the subjective nature of the impression, even when it has every appearance of objectivity, whereas in the latter case the patient cannot be made to understand that the vision is not real.
Until the early twentieth century, hallucinatory percepts were regarded merely as intensified memory images; however, the most intense of ordinary representations do not possess the sensory vividness of the smallest sensation received from the external world. It follows that other conditions must be present besides the excitement of the brain, which is the correlate of representation. The seat of excitement is the same in actual sense perceptions and in memory images, but in the former the stimulus is peripherally originated in the sensory nerve, whereas in the latter it originates in the brain itself.
When a neural system becomes highly excited—a state which may be brought about by emotion, ill health, drugs, or a number of other causes—it may serve to divert from their proper paths any set of impulses arising from the sense organs. Because any impulse ascending through the sensory nerves produces an effect of sensory vividness—normally, a true perception—the impulses thus diverted gives to the memory image an appearance of actuality not distinguishable from that produced by a corresponding sense impression—a hallucination.
In hypnosis a state of cerebral dissociation is induced, whereby a neural system may be abnormally excited and hallucination thus readily engendered. Drugs, especially hallucinogens, which excite the brain, also induce hallucinations.
In 1901 the British physician Sir Henry Head demonstrated that certain visceral disorders produce hallucinations, such as the appearance of a shrouded human figure. The question of whether there is any relationship between the hallucination and the person it represents is, and has long been, a vexing one. Countless well-authenticated stories of apparitions coinciding with a death or some other crisis are on record and would seem to establish some causal connection between them. In former times apparitions were considered to be the doubles or "ethereal bodies" of real persons, and Spiritualists believe that they are the spirits of the dead (or, in some instances, of the living) temporarily forsaking the physical body.
The dress and appearance of the apparition does not necessarily correspond with the actual dress and appearance of the person it represents. Thus a man at the point of death, in bed and wasted by disease, may appear to a friend miles away as if in ordinary health and wearing familiar clothing. Nevertheless, there are notable instances where some remarkable detail of dress is reproduced in the apparition. It seems clear, however, that it is the agent's general personality that is, as a rule, conveyed to the percipient, and not, except in special cases, his or her actual appearance.
It has been suggested that those images that do not arise in the subliminal consciousness of the agent may be telepathically received by him or her from other minds. A similar explanation has been offered for the hallucinatory images that many people can induce by crystal gazing or staring into a pool of water, a drop of ink, or a magic mirror in search of information about scenes or people they know nothing about.
Collective hallucination is a term applied to hallucinations shared by a number of people. There is no firm evidence, however, of the operation of any agency other than suggestion or telepathy.
Hallucination and Psychical Research
One of the most succinct definitions of hallucination occurs in Phantasms of the Living (2 vols., 1886), by Edmund Gurney, F. W. H. Myers, and Frank Podmore: "percepts which lack, but which can only by a distinct reflection be recognised as lacking, the objective basis which they suggest." If the sensory perception coincides with an objective occurrence or counterpart, the hallucination is called veridical, (truth-telling), as in the phantasm of the dying. If the apparition is seen by several people at the same time, the case is called collective veridical hallucination.
In the years following the foundation of the Society for Psychical Research (SPR), London, the hallucination theory of psychic phenomena was in great vogue. If no other explanation was available the person who had had a supernormal experience was told it was a hallucination, and if several people testified to the same occurrence it was said that the hallucination of one was communicated to the others. Sir William Crookes counters that idea in his Researches in the Phenomena of Spiritualism (1870): "The supposition that there is a sort of mania or delusion which suddenly attacks a whole roomful of intelligent persons who are quite sane elsewhere, and that they all concur, to the minutest particulars, in the details of the occurrences of which they suppose themselves to be witnesses, seems to my mind more incredible than even the facts which they attest."
Charles Richet, in Thirty Years of Psychical Research (1923), omits hallucination completely in his discussion of metapsychical phenomena (a term for paranormal). He believed that hallucination should be reserved to describe a morbid state when a mental image is exteriorized without any exterior reality. According to Richet,
"It is extremely rare that a person who is neither ill, nor drunk, nor hypnotised should, in the walking state, have an auditory, visual, or tactile illusion of things that in no way exist. The opinion of alienists that hallucination is the chief sign of mental derangement, and the infallible characteristic of insanity seems to me well grounded. With certain exceptions (for every rule there are exceptions) a normal healthy individual when fully awake does not have hallucinations. If he see[s] apparitions these correspond to some external reality or other. In the absence of any external reality there are no hallucinations but those of the insane and of alcoholics."
An instance recounted by Sir John Herschel did not conform to Richet's idea. He had been watching with some anxiety the demolition of a familiar building. On the following evening, in good light, he passed the spot where the building had stood. "Great was my amazement to see it," he wrote, "as if still standing, projected against the dull sky. I walked on, and the perspective of the form and disposition of the parts appeared to change as they would have done if real."
In the case of hauntings where a ghost is seen, Gurney suggests that a person thinking of a given place that is at the time actually experienced in sense perception by others may be imparting into the consciousness of the others a thought existing in his own.
Of course, data provided by a registering apparatus or photography may rule out the hallucination theory as applied to hauntings, provided that there is some proper scientific control. Similarly, if objects are displaced, as in poltergeist cases, the theory of hallucination is no longer tenable. As Andrew Lang writes in Cock Lane and Common Sense (1896), "Hallucinations cannot draw curtains, or open doors, or pick up books, or tuck in bedclothes or cause thumps."
The things seen during a psychic experience of an otherwise normal person should also be distinguished from the hallucinations of the mentally deranged, of the sick, drunk, or drugged. The latter are not veridical, nor telepathic, nor collective. In the "Census of Hallucinations," published in the Proceedings of the SPR (1894), the committee excluded, as far as possible, all pathological subjects. J. G. Piddington (see Proceedings, vol. 19), in testing this census for cases that would show the same nature as hallucinations arising from visceral diseases, concluded that there was not a single case in the census report that fell into line with the visceral type.
In hypnotic hallucinations the hypnotized subject may see apparitions if so suggested and may not see ordinary people who are in the same room. But the subject may hear the noises they make, see the movement of objects they touch, and be frightened by what appears to be poltergeist phenomena. If the suggestion is posthypnotic the subject may also see a phantom shape when given a signal or at a prescribed time.
The visions seen by some people on the verge of sleep were called " hypnagogic hallucinations" by F. W. H. Myers. The afterimages on waking from sleep he named "hypnopompic hallucinations." A comprehensive study of both classes of phenomena was published by G. E. Leaning in the Proceedings of the SPR, (vol. 35, 1926).
The difference between hallucination and illusion is that there is an objective basis for the illusion, which is falsely interpreted. In hallucination, although more than one sense may be affected, there is no external basis for the perception.
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A hallucination (ha-LOO-sin-A-shun) is something that a person perceives as real but that is not actually caused by an outside event. It can involve any of the senses: hearing, smell, sight, taste, or touch.
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Multiple personality disorder
A good magician can make audience members think that they are seeing something they really are not, such as an animal disappearing into thin air or a bouquet appearing from under a handkerchief. These tricks are often referred to as optical illusions. The magician knows how to perform the illusion so that the viewer’s eyes and brain are likely to misinterpret what is really happening.
Hallucinations are different from illusions. During a hallucination, the person is not reacting to something real in the outside world. The brain creates its own stimulation instead of relying on input from the five senses. In other words, the entire experience takes place right inside the brain. In her book Mapping the Mind, science writer Rita Carter defines hallucinations as “exceptionally intense self-generated sensory experiences.”
Dreams are the most common types of hallucinations that people experience on a regular basis. While dreaming, people may think that what they are seeing and hearing is real, but actually it is all in their heads. One frequently occurring “dream hallucination” is the sensation of falling, followed immediately by a jerking reflex that wakes the person up. Hallucinations also commonly occur when a person experiences extremely high fever or when an anesthetic* starts to wear off after surgery.
- * anesthetic
- (an-es-THET-ik) is a medicine that decreases the sensation of pain.
How can the brain create sights, sounds, feelings, and even tastes and smells that seem so real? For a variety of reasons, the areas of the brain responsible for interpreting sensory input can become activated on their own. When a person dreams, for example, these areas of the brain are still working even though the person is asleep and not processing stimuli from the environment.
People who have undergone amputation* help researchers understand what may happen in the brain when it hallucinates. Many of these patients report that they feel like the missing body part is still there, even though they know the arm, leg, hand, or other body part is gone. For example, it is not uncommon for people who lose a leg to try to stand up and walk after their surgery. Feeling like an amputated limb is still present is called phantom limb syndrome, and there are two main theories
- * amputation
- (am-pyu-TAY-shun) is the removal of a limb or other appendage of the body.
about why it happens. It may be that the nerve cells in the brain area that used to receive signals from that limb go into overdrive and stimulate themselves because that input has disappeared. Another theory is that the brain is programmed for a body where everything is intact and in the right place so that when certain signals are missing, spontaneous nerve cell activity takes over. In either case, the brain is compensating for the lack of sensory input.
That the brain may compensate for a lack of sensory input helps to explain why people who experience vision or hearing loss or who are placed in solitary confinement often experience hallucinations (they start “seeing things” or “hearing things”). Under such circumstances, the different areas of the brain that were used to receiving signals through the senses start to stimulate themselves into action. This also explains why people tend to “see” ghosts at night instead of during the day; the brain is more likely to create the vision of ghosts when other visual stimuli are absent. In other words, people’s minds tend to play more tricks on them at twelve midnight than at twelve noon.
Too much stimulation can also result in hallucinations. Excessive anxiety*, intense emotions, certain drugs, and even some mental disorders can essentially flood the brain with too much sensory input. In these cases, the brain’s circuits get jammed and it cannot concentrate on making sense of the person’s real environment; instead, the brain starts generating its own sensations. For example, people who experience the death of a loved one often report hallucinations in which they see that person or hear his or her voice. Similarly, people who undergo the terrible trauma of abuse sometimes report later visions of their abuser. Hallucinogenic drugs* such as LSD and Ecstasy are artificial sources of overstimulation. They excite the central nervous system* so much that certain areas of the brain produce visions, sounds, and feelings that are not based in reality. Some hallucinogenic drug users continue to experience bizarre visions and sounds even long after they stop using the drug. Researchers have found that subjecting people to constant loud noise and bright lights can also produce hallucinations.
- * anxiety
- can be experienced as a troubled feeling, a sense of dread, fear of the future, or distress over a possible threat to a person’s physical or mental well-being.
- * hallucinogenic drugs
- are substances that cause a person to have hallucinations.
- * central nervous system
- refers to the brain and the spinal cord, which coordinate the activity of the entire nervous system.
Perhaps the most disturbing hallucinations are those that can accompany psychotic disorders* such as schizophrenia*. People with schizophrenia lose touch with aspects of reality, which affects their thinking and behavior. They often report hearing voices that tell them that they are bad or that they should act in a certain way. Experts who work with these patients have found evidence that these voices actually belong to the patient; patients may be generating “speech” in one part of their brain then experiencing it as sound in another part. People with schizophrenia also tend to see disturbing visions. Medications can help with hallucinations caused by schizophrenia, and in some cases, people can be trained to recognize and even control their hallucinations. This level of improvement usually requires intensive therapy.
- * psychotic disorders
- (sy-KOT-ik) are mental disorders, such as schizophrenia, in which the sense of reality is so impaired that a person can not function normally. People with psychotic disorders may experience delusions, hallucinations, incoherent speech, and agitated behavior, but they usually are not aware of their altered mental state.
- * schizophrenia
- (skit-so-FREE-nee-ah) is a serious mental disorder that causes people to experience hallucinations, delusions, and other confusing thoughts and behaviors, which distort their view of reality.
Anxiety and Anxiety Disorders
Carter, Rita. Mapping the Mind. Berkeley: University of California Press, 2000. See especially Chapter 5, “A World of One’s Own.”
Siegel, Ronald K. Fire in the Brain: Clinical Tales of Hallucination. New York: Penguin, 1993.
A hallucination is a false perception occurring without any identifiable external stimulus and indicates an abnormality in perception. The false perceptions can occur in any of the five sensory modalities. Therefore, a hallucination essentially is seeing, hearing, tasting, feeling, or smelling something that is not there. The false perceptions are not accounted for by the person’s religious or cultural background, and the person experiencing hallucinations may or may not have insight into them. Therefore, some people experiencing hallucinations may be aware that the perceptions are false, whereas others may truly believe that what they are seeing, hearing, tasting, feeling, or smelling is real. In cases when the person truly believes the hallucination is real, the individual may also have a delusional interpretation of the hallucination.
Hallucinations must be distinguished from illusions, which are misperceptions of actual external stimuli. In other words, an illusion is essentially seeing, hearing, tasting, feeling, or smelling something that is there, but perceiving it or interpreting it incorrectly. An example of an illusion might be hearing one’s name called when the radio is playing. There is an external auditory stimulus, but it is misperceived. True hallucinations do not include false perceptions that occur while dreaming, while falling asleep, or while waking up. Unusual perceptual experiences one may have while falling asleep are referred to as hypnagogic experiences. Unusual perceptual experiences one may have while waking up are referred to as hypnopompic experiences. Hallucinations also do not include very vivid experiences one may have while fully awake (e.g., especially vivid daydreaming or imaginative play).
Hallucinations are a symptom of either a medical (e.g., epilepsy), neurological, or mental disorder. Hallucinations may be present in any of the following mental disorders: psychotic disorders (including schizophrenia, schizoaffective disorder, schizophreni form disorder, shared psychotic disorder, brief psychotic disorder, substance-induced psychotic disorder ), bipolar disorder , major depression with psychotic features, delirium , or dementia. Auditory hallucinations, in particular, are common in psychotic disorders such as schizophrenia.
Use of certain recreational drugs may induce hallucinations. These drugs include amphetamines and cocaine , hallucinogens (e.g., lysergic acid diethylamide or LSD), phencyclidine (PCP), and cannabis or marijuana. Visual hallucinations are commonly associated with substance use. Individuals may report false perceptions of little people or animals (sometimes referred to as Lilliputian hallucinations). In addition, withdrawal from some recreational drugs—including alcohol, sedatives , hypnotics, or anxiolytics—can produce hallucinations. Withdrawal from alcohol, for instance, commonly causes visual hallucinations, especially at nighttime.
Hallucinations are categorized according to which sensory modality is involved and are categorized as either mood-congruent or mood-incongruent. The types of hallucinations are:
- auditory: The false perception of sound, music, noises, or voices. Hearing voices when there is no auditory stimulus is the most common type of auditory hallucination in mental disorders. The voice may be heard either inside or outside one’s head and is generally considered more severe when coming from outside one’s head. The voices may be male or female, recognized as the voice of someone familiar or not recognized as familiar, and may be critical or positive. In mental disorders such as schizophrenia, however, the content of what the voices say is usually unpleasant and negative. In schizophrenia, a common symptom is to hear voices conversing and/or commenting. When someone hears voices conversing, they hear two or more voices speaking to each other (usually about the person who is hallucinating). In voices commenting, the person hears a voice making comments about his or her behavior or thoughts, typically in the third person (e.g., “isn’t he silly”). Sometimes the voices consist of hearing a “running commentary” on the person’s behavior as it occurs (“she is showering”). Other times, the voices may tell the person to do something (commonly referred to as “command hallucinations”).
- gustatory: A false perception of taste. Usually, the experience is unpleasant. For instance, an individual may complain of a persistent taste of metal. This type of hallucination is more commonly seen in some medical disorders (e.g., epilepsy) than in mental disorders.
- mood-congruent hallucination: Any hallucination whose content is consistent with either the depressive or manic state the person may be in at the time. Depressive themes include guilt, death, disease, personal inadequacy, and deserved punishment. Manic themes include inflated sense of self-worth, power, knowledge, skills, and identity and may include belief in a special relationship with a famous person or deity. For example, a depressed person may hear voices saying that he or she is a horrible person, whereas a manic person may hear voices saying that he or she is an incredibly important person.
- mood-incongruent hallucination: Any hallucination whose content is not consistent with either the depressed or manic state the person is in at the time, or is mood-neutral. For example, a depressed person may experience hallucinations without any themes of guilt, death, disease, personal inadequacy, or deserved punishment. Similarly, a manic person may experience hallucinations without any themes of inflated self-worth, power, knowledge, skills, or identity or a special relationship to a famous person or deity.
- olfactory hallucination: A false perception of odor or smell. Typically, the experience is very unpleasant. For example, the person may smell decaying fish, dead bodies, or burning rubber. Sometimes, those experiencing olfactory hallucinations believe the odor emanates from them. Olfactory hallucinations are more typical of medical disorders than mental disorders.
- somatic/tactile hallucination: A false perception or sensation of touch or something happening in or on the body. A common tactile hallucination is feeling like something is crawling under or on the skin (also known as formication). Other examples include feeling electricity through one’s body and feeling like someone is touching one’s body while no one is there. Actual physical sensations stemming from medical disorders (perhaps not yet diagnosed) and hypochondriacal preoccupations with normal physical sensations are not thought of as somatic hallucinations.
- visual hallucination: A false perception of sight. The content of the hallucination may be anything (e.g., shapes, colors, and flashes of light) but are typically people or human-like figures. For example, one may perceive a person standing before them when no one is there. Sometimes an individual may experience the false perception of religious figure (e.g., the devil, or Christ). Perceptions that would be considered normal for an individual’s religion or culture are not considered hallucinations.
Illusion —A misperception or misinterpretation in the presence of a real external stimulus.
The treatment approach to hallucinations depends on the accompanying mental disorder. For example, in the case of schizophrenia, antipyschotics may be used to address aural hallucinations, although cognitive behavioral therapy also shows some efficacy in reducing aural hallucinations in people with schizophrenia.
American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th edition, text revised. Washington, DC: American Psychiatric Association, 2000.
Kaplan, Harold I., M.D., and Benjamin J. Sadock, M.D. Kaplan and Sadock’s Synopsis of Psychiatry: Behavioral Sciences, Clinical Psychiatry. 8th edition. Baltimore: Williams and Wilkins.
Arehart-Treichel, Joan. “Hallucinations respond to innovative use of CBT.” Psychiatric News (2004): 46.
National Library of Medicine. “Hallucinations.” <http://www.nlm.nih.gov/medlineplus/ency/article/003258.htm>.
Jennifer Hahn, PhD
Hallucinations are false or distorted sensory experiences that appear to be real perceptions. These sensory impressions are generated by the mind rather than by any external stimuli, and may be seen, heard, felt, and even smelled or tasted.
A hallucination occurs when environmental, emotional, or physical factors such as stress, medication, extreme fatigue, or mental illness cause the mechanism within the brain that helps to distinguish conscious perceptions from internal, memory-based perceptions to misfire. As a result, hallucinations occur during periods of consciousness. They can appear in the form of visions, voices or sounds, tactile feelings (known as haptic hallucinations), smells, or tastes.
Patients suffering from dementia and psychotic disorders such as schizophrenia frequently experience hallucinations. Hallucinations can also occur in patients who are not mentally ill as a result of stress overload or exhaustion, or may be intentionally induced through the use of drugs, meditation, or sensory deprivation. A 1996 report, published in the British Journal of Psychiatry, noted that 37% of 4,972 people surveyed experienced hypnagogic hallucinations (hallucinations that occur as a person is falling to sleep). Hypnopomic hallucinations (hallucinations that occur just upon waking) were reported by 12% of the sample.
Causes and symptoms
Common causes of hallucinations include:
- Drugs. Hallucinogenics such as ecstasy (3,4-methylenedioxymethamphetamine, or MDMA), LSD (lysergic acid diethylamide, or acid), mescaline (3,4,5-trimethoxyphenethylamine, or peyote), and psilocybin (4-phosphoryloxy-N, N-dimethyltryptamine, or mushrooms) trigger hallucinations. Other drugs such as marijuana and PCP have hallucinatory effects. Certain prescription medications may also cause hallucinations. In addition, drug withdrawal may induce tactile and visual hallucinations; as in an alcoholic suffering from delirium tremens (DTs).
- Stress. Prolonged or extreme stress can impede thought processes and trigger hallucinations.
- Sleep deprivation and/or exhaustion. Physical and emotional exhaustion can induce hallucinations by blurring the line between sleep and wakefulness.
- Meditation and/or sensory deprivation. When the brain lacks external stimulation to form perceptions, it may compensate by referencing the memory and form hallucinatory perceptions. This condition is commonly found in blind and deaf individuals.
- Electrical or neurochemical activity in the brain. A hallucinatory sensation—usually involving touch—called an aura, often appears before, and gives warning of, a migraine. Also, auras involving smell and touch (tactile) are known to warn of the onset of an epileptic attack.
- Mental illness. Up to 75% of schizophrenic patients admitted for treatment report hallucinations.
- Brain damage or disease. Lesions or injuries to the brain may alter brain function and produce hallucinations.
Aside from hypnogogic and hypnopompic hallucinations, more than one event suggests a person should seek evaluation. A general physician, psychologist, or psychiatrist will try to rule out possible organic, environmental, or psychological causes through a detailed medical examination and social history. If a psychological cause such as schizophrenia is suspected, a psychologist will typically conduct an interview with the patient and his family and administer one of several clinical inventories, or tests, to evaluate the mental status of the patient.
Occasionally, people who are in good mental health will experience a hallucination. If hallucinations are infrequent and transitory, and can be accounted for by short-term environmental factors such as sleep deprivation or meditation, no treatment may be necessary. However, if hallucinations are hampering an individual's ability to function, a general physician, psychologist, or psychiatrist should be consulted to pinpoint their source and recommend a treatment plan.
Hallucinations that are symptomatic of a mental illness such as schizophrenia should be treated by a psychologist or psychiatrist. Antipsychotic medication such as thioridazine (Mellaril), haloperidol (Haldol), chlorpromazine (Thorazine), clozapine (Clozaril), or risperidone (Risperdal) may be prescribed.
In many cases, chronic hallucinations caused by schizophrenia or some other mental illness can be controlled by medication. If hallucinations persist, psychosocial therapy can be helpful in teaching the patient the coping skills to deal with them. Hallucinations due to sleep deprivation or extreme stress generally stop after the cause is removed.
National Alliance for the Mentally Ill (NAMI). Colonial Place Three, 2107 Wilson Blvd., Ste. 300, Arlington, VA 22201-3042. (800) 950-6264. 〈http://www.nami.org〉.
Aura— A subjective sensation or motor phenomenon that precedes and indicates the onset of a neurological episode, such as a migraine or an epileptic seizure.
Hypnogogic hallucination— A hallucination, such as the sensation of falling, that occurs at the onset of sleep.
Hypnopompic hallucination— A hallucination that occurs as a person is waking from sleep.
Sensory deprivation— A situation where an individual finds himself in an environment without sensory cues. Also, (used here) the act of shutting one's senses off to outside sensory stimuli to achieve hallucinatory experiences and/or to observe the psychological results.
Such variety has naturally frustrated any attempt at providing a clear classification of the phenomenon. Attempts to distinguish the various forms of hallucination according to their origins, their content, their intensity, and the condition of their hosts have been largely unsuccessful. Most psychiatrists in Europe and North America have now adopted a fairly broad definition of the phenomenon, simply relying upon the distinction between illusion, which resulted from the misinterpretation of an existing external object, and hallucination, in which the false perception is generated without any reference to the outside world. Even this definition, which was introduced by the French psychiatrist J. E. D. Esquirol in the early nineteenth century, fails to account for such borderline phenomena as synaesthesia in which the sensations provoked by an object become confused, so that the subject may taste colours or see sounds.
Alongside this ongoing contest over the definition and classification of hallucination there exists a more fundamental struggle over the meaning and significance of the phenomenon. Artists and mystics have long criticized the modern medicalization of hallucinations, portraying the process as a secularizing attempt to pathologize religious or spiritual experience. Certainly popular attitudes to hallucination have been transformed across the last thousand years. In the Platonic tradition of classical philosophy, the subjective vision was celebrated as a form of privileged insight beyond the phenomenal experience of the external world. Likewise in the Christian and Jewish religions the objective quality of the inner hallucination had long been regarded as a proof of its spiritual reality, although its origin could have been either demonic or divine.
These Platonic and Christian traditions were united in the work of the Primitive Church fathers. Their writing held up the visionary experience as a charism, a gift from God which allowed individuals to perceive some object which was normally invisible to men. This conception was further refined by St Augustine, who divided visions into three classes: the corporeal, in which an apparition of an object was presented before the individual's eyes through either natural or spiritual means; the imaginative, in which an image was supernaturally created in the host's mind; and the intellectual, in which sense of personal assurance was created directly by God, without recourse to implanted words or images.
This framework for interpreting the hallucinatory experience persisted into the nineteenth century. Many romantic writers, such as Coleridge and Wordsworth, complained that normal vision enslaved the mind to the mundane world of material object. In contrast, they proposed a ‘Spiritual Optics’ (to borrow Thomas Carlyle's phrase) in which the inner eye would be awakened to the creative inspiration of the spirit. Such a programme sat unhappily with contemporary medical investigations in this field. In the late eighteenth and early nineteenth centuries, many writers commented upon the correlation between hallucination, injury, and disease. This correlation suggested that the hallucination had a somatic basis, originating in either the disordered operations of the peripheral nerves or an aberrant psychological process in the brain.
This interpretation of hallucination as a symptom of organic nervous disorder persisted throughout the nineteenth century. In 1881 the Italian psychiatrist, August Tamburini, presented a coherent neurological model for the experience, arguing that hallucination was produced through a pathological excitement or epilepsy in the higher sensory centres of the brain. This materialist account did little to diminish the mystical celebration of hallucination. Writers influenced by spiritualism and the Swedish mystic Emanuel Swedenborg accepted the scientific identification of hallucination with organic disturbance, arguing that this identity provided strong evidence for the objective reality of visions.
The mystical assessment of the significance of hallucinations was undermined by a series of psychological surveys at the end of the nineteenth century. During the 1880s the statistician, Francis Galton, circulated questionnaires on mental imagery to schools and acquaintances. From the responses he was able to demonstrate a gradation between hallucination and the familiar acts of visualization which occurred in everyday life. Galton suggested that hallucination was not a distinct experience, but rather that it represented an extreme point on two axes representing the strength of the mental image and its resistance to conscious control. This statistical erosion of the boundary between normal visualization and pathological hallucination was reinforced in a more wide-scale survey published by the Society for Psychical Research (SPR) in 1892. The SPR's ‘Census of Hallucinations’ discovered 1684 cases of waking hallucination amongst 17 000 respondents. Further analysis suggested that hallucination was most prevalent amongst women, children, and the insane, although the experience could occur in almost any individual.
In the twentieth century the hallucinatory experience seems to have lost its spiritual significance. The popular use of hallucinogenic drugs, such as LSD and psilocybin, and increased understanding of the chemical mechanisms of their actions, has encouraged a more instrumental attitude towards the visionary experience. Hallucination is no longer seen as a gratuitous event except in pathological cases such as fever or schizophrenia. Rather it is a state which can be induced directly through chemical, electrical, or mechanical means. As the neurosurgeon Wilder Penfield demonstrated, intense mental images may be created through the electrical stimulation of a subject's brain. Likewise hallucinations of movement (see proprioception) can be induced at a particular joint through the mechanical vibration of the muscles attached to it. Through such technical advances the meaning and cultural significance of hallucination has been transformed. The vision, which once revealed the mind of God to men, is now seen as a symptom revealing the disordered mind of man to others.
Berrios, G. E. (1995). The history of mental symptoms. Cambridge University Press, Cambridge.
Critchley, M. (1987). Hallucinations and their impact upon art. Carnegie Press, Preston.
See also illusions.
Halcion see Triazolam
Haldol see Haloperidol
A hallucination is a false perception occurring without any identifiable external stimulus and indicates an abnormality in perception. The false perceptions can occur in any of the five sensory modalities. Therefore, a hallucination essentially is seeing, hearing, tasting, feeling, or smelling something that is not there. The false perceptions are not accounted for by the person's religious or cultural background, and the person experiencing hallucinations may or may not have insight into them. Therefore, some people experiencing hallucinations may be aware that the perceptions are false, whereas others may truly believe that what they are seeing, hearing, tasting, feeling, or smelling is real. In cases when the person truly believes the hallucination is real, the individual may also have a delusional interpretation of the hallucination.
Hallucinations must be distinguished from illusions, which are misperceptions of actual external stimuli. In other words, an illusion is essentially seeing, hearing, tasting, feeling, or smelling something that is there, but perceiving it or interpreting it incorrectly. An example of an illusion might be hearing one's name called when the radio is playing. There is an external auditory stimulus, but it is misperceived. True hallucinations do not include false perceptions that occur while dreaming, while falling asleep, or while waking up. Unusual perceptual experiences one may have while falling asleep are referred to as hypnagogic experiences. Unusual perceptual experiences one may have while waking up are referred to as hypnopompic experiences. Hallucinations also do not include very vivid experiences one may have while fully awake (such as especially vivid daydreaming or imaginative play).
Hallucinations are a symptom of either a medical (e.g., epilepsy), neurological, or mental disorder. Hallucinations may be present in any of the following mental disorders: psychotic disorders (including schizophrenia , schizoaffective disorder , schizophreniform disorder , shared psychotic disorder , brief psychotic disorder , substance-induced psychotic disorder ), bipolar disorder , major depression with psychotic features, delirium , or dementia . Auditory hallucinations, in particular, are common in psychotic disorders such as schizophrenia.
Use of certain recreational drugs may induce hallucinations, including amphetamines and cocaine, hallucinogens (such as lysergic acid diethylamide or LSD), phencyclidine (PCP), and cannabis or marijuana. For example, visual hallucinations are commonly associated with substance use. Individuals may report false perceptions of little people or animals (sometimes referred to as Lilliputian hallucinations). In addition, withdrawal from some recreational drugs can produce hallucinations, including withdrawal from alcohol, sedatives, hypnotics, or anxiolytics. Withdrawal from alcohol, for instance, commonly causes visual hallucinations, especially at nighttime.
Hallucinations are categorized according to which sensory modality is involved and, in addition, are categorized as either mood-congruent or mood-incongruent. The types of hallucinations are:
- Auditory: The false perception of sound, music, noises, or voices. Hearing voices when there is no auditory stimulus is the most common type of auditory hallucination in mental disorders. The voice may be heard either inside or outside one's head and is generally considered more severe when coming from outside one's head. The voices may be male or female, recognized as the voice of someone familiar or not recognized as familiar, and may be critical or positive. In mental disorders such as schizophrenia, however, the content of what the voices say is usually unpleasant and negative. In schizophrenia, a common symptom is to hear voices conversing and/or commenting. When someone hears voices conversing, they hear two or more voices speaking to each other (usually about the person who is hallucinating). In voices commenting, the person hears a voice making comments about his or her behavior or thoughts, typically in the third person (such as, "isn't he silly"). Sometimes the voices consist of hearing a "running commentary" on the person's behavior as it occurs ("she is showering"). Other times, the voices may tell the person to do something (commonly referred to as "command hallucinations").
- Gustatory: A false perception of taste. Usually, the experience is unpleasant. For instance, an individual may complain of a persistent taste of metal. This type of hallucination is more commonly seen in some medical disorders (such as epilepsy) than in mental disorders.
- Olfactory hallucination: A false perception of odor or smell. Typically, the experience is very unpleasant. For example, the person may smell decaying fish, dead bodies, or burning rubber. Sometimes, those experiencing olfactory hallucinations believe the odor emanates from them. Olfactory hallucinations are more typical of medical disorders than mental disorders.
- Somatic/tactile hallucination: A false perception or sensation of touch or something happening in or on the body. A common tactile hallucination is feeling like something is crawling under or on the skin (also known as formication). Other examples include feeling electricity through one's body and feeling like someone is touching one's body but no one is there. Actual physical sensations stemming from medical disorders (perhaps not yet diagnosed) and hypochondriacal preoccupations with normal physical sensations, are not thought of as somatic hallucinations.
- Visual hallucination: A false perception of sight. The content of the hallucination may be anything (such as shapes, colors, and flashes of light) but are typically people or human-like figures. For example, one may perceive a person standing before them when no one is there. Sometimes an individual may experience the false perception of religious figure (such as the devil, or Christ). Perceptions that would be considered normal for an individual's religion or culture are not considered hallucinations.
- Mood-congruent hallucination: Any hallucination whose content is consistent with either the depressive or manic state the person may be in at the time. Depressive themes include guilt, death, disease, personal inadequacy, and deserved punishment. Manic themes include inflated self-worth, power, knowledge, skills, and identity and a special relationship with a famous person or deity. For example, a depressed person may hear voices saying that he or she is a horrible person, whereas a manic person may hear voices saying that he or she is an incredibly important person.
- Mood-incongruent hallucination: Any hallucination whose content is not consistent with either the depressed or manic state the person is in at the time, or is mood-neutral. For example, a depressed person may experience hallucinations without any themes of guilt, death, disease, personal inadequacy, or deserved punishment. Similarly, a manic person may experience hallucinations without any themes of inflated self-worth, power, knowledge, skills, or identity or a special relationship to a famous person or deity.
See also Alcohol and related disorders; Major depressive disorder; Substance abuse and related disorders; Substance-induced psychotic disorders
American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th edition, text revised. Washington, DC: American Psychiatric Association, 2000.
Jennifer Hahn, Ph.D.
Compelling perceptual experiences which may be visual, tactile, olfactory, or auditory, but which lack a physical stimulus.
Although hallucinations are false perceptions, they carry the force of reality and are a definitive sign of mental illness . Hallucinations may be caused by organic deterioration or functional disorders, and can occur in normal people while asleep or awake, or as a result of sensory deprivation . Generally not positive experiences, hallucinations are often described as frightening and distressing. A person under a hallucinatory state may be either alert and intelligent or incoherent, depending on the type and degree of the disturbance.
One psychological condition commonly characterized by hallucinations is schizophrenia . In schizophrenia, the hallucinations are usually auditory, involving one or more voices. The voices may issue commands, comment on or seem to narrate the person's actions, or sound like an overheard conversation, and can be analyzed for greater insight into the patient's emotional state. Auditory hallucinations can also occur in severe depression and mania ; seriously depressed persons may hear voices making derogatory remarks about them or threatening them with bodily harm. Visual hallucinations, on the other hand, are more likely to characterize organic neurological disturbances, such as epilepsy , and may occur prior to an epileptic seizure. Hallucinations involving the senses of smell and touch are less frequent than visual or auditory ones; however, tactile hallucinations have proven useful in the study and diagnosis of schizophrenia. Together with fearfulness and agitation, hallucinations are also a component of delirium tremens, which can afflict persons suffering from alcohol dependence.
Hallucinations can also be induced by ingesting drugs that alter the chemistry of the brain . (The technical name used for drug-induced hallucinations is hallucinosis.) The most widely known hallucinogens , or mind-altering drugs, are LSD, psilocybin, peyote, and mescaline, which act on the brain to produce perceptual, sensory, and cognitive experiences that are not occurring in reality. Effects vary from user to user and also individually from one experience to the next. Hallucinations produced by LSD are usually visual in nature. On an LSD "trip," for example, hallucinations can last eight to ten hours while those produced by mescaline average six to eight hours. Two illegal drugs manufactured to produce psychoactive effects, PCP (phencyclidine) and MDMA (Ecstasy), are not true hallucinogens, but both produce hallucinations of body image as well as psychoses. A person may also experience hallucinations while attempting to withdraw from a drug, such as "pink elephants" and other visual hallucinations from alcohol withdrawal. Withdrawal symptoms from cocaine are associated with the hallucinatory tactile sensation of something crawling under one's skin, often termed "the cocaine bug."
Other causes of hallucinations are hypnosis , lack of sleep , stress , illness, and fatigue, which can produce a rare and unique hallucination known as "the doppelganger." A person who has this experience sees his or her mirror image facing him or her three or four feet away, appearing as a transparent projection on a glassy surface. The hypnagogic hallucinations that occur in the zone between sleep and waking are both visual and auditory, and are strikingly detailed to those who can remember them. Sensory deprivation in subjects of laboratory experiments over a period of time has also been shown to produce hallucinations, as has electrical stimulation of the brain. Experiences called pseudohallucinations involve the perception of vivid images without the sense that they are actually located in external space—the perceiver recognizes that they are not real. Associated with isolation and emotional distress, they include such examples as shipwrecked sailors visualizing rescue boats or travelers stranded in the desert visualizing an oasis. Pseudo-hallucinations do not have the same psychiatric significance as true hallucinations.
People suffering from hallucinations may try to conceal them from others because of their negative connotations, and may receive more drastic forms of treatment or inadequate prognoses because of them. In contrast to mainstream cultural opinion, however, users of hallucinogens in the United States view hallucinations as positive and potentially enlightening, and in other cultures they are regarded for their healing faculties. In the Moche culture of coastal Peru, for example, traditional healers may ingest mescaline as part of a healing ritual in the belief that the hallucinations produced by it offer insight into the patient's condition and thus aid in the healing process.
Andrews, Barbara. Dreams and Waking Visions: A Journal. New York: St. Martin's Press, 1989.
Guiley, Rosemary. The Encyclopedia of Dreams: Symbols and Interpretations. New York: Crossroad, 1993.
hal·lu·ci·nate / həˈloōsənˌāt/ • v. [intr.] experience a seemingly real perception of something not actually present, typically as a result of a mental disorder or of taking drugs: people sense themselves going mad and hallucinate about spiders. ∎ [tr.] experience a hallucination of (something): I don't care if they're hallucinating purple snakes. DERIVATIVES: hal·lu·ci·nant / -sənənt/ adj. & n. hal·lu·ci·na·tor / -ˌātər/ n.