“Are thou not, fatal vision, sensible to feeling as to sight? Or art thou a dagger of the mind, a false creation, proceeding from the heat-oppressed brain?” — Macbeth, Shakespeare
A hallucination is the perception of a noise, smell, or sight that is not physically present. It is sensation without stimulus. The origin of the word "hallucination" contains two elements—to dream and to be distraught. It is derived from the Latin alucinari, meaning “to wander in mind." Hallucinations are highly idiosyncratic, and many are transient, unreal and bewildering. They may be culture-specific and sometimes are accepted as signs of being blessed by special spirits. There are various types of hallucinations and multiple theories about their cause.
Sensory hallucinations may include:
- hearing voices of long dead or mythical people;
- the sensation of insects crawling on or under the skin;
- the sight of angels or fairies dancing in bright lights; or
- perceiving a freshwater lake when thirsty in the desert.
Hallucinations should never be confused with illusions and delusions:
- An illusion is a real reaction to a real sensation with a mis-attributed cause. Some have a fascination with artistic, visual illusions, or "illusion artists" who appear to do impossible things like saw people in half.
- A delusion is a real reaction to a real sensation, but which is given an unreal, impossible, bizarre or overly significant cause.
Hallucinations are associated with many things, including:
- sleep (particularly deprivation)
- certain drug use (such as hallucinogens)
- mental illness (particularly psychosis)
- very specific neurological illnesses. Some are mild and common, like "hypnagogic" hallucinations (which occur while falling asleep) or the opposite, "hypnopompic" hallucinations (which occur while awake).
Often through the use of very specific drugs, people can have the oddest hallucinations. "Chromatopsia," for example, involves seeing everybody and everything as the same color. "Lilliputian" hallucinations see imaginary people in miniature, often with pleasant accompanying feelings. On the other hand, "Brobdingnagian" hallucinations see everyone as giants.
Pseudo-hallucinations occur when a person vividly experiences a hallucination but knowsit to be such—that is, it has no external foundations. Hallucinatory episodes may follow a pattern: First, something like a particular memory or sound sparks off the hallucination. The person then tests if it’s real and begins to believe it is. The fantasy, distortion, and unreality continues and grows and gets confused with actual perception.
Hearing voices is perhaps one of the most well known "signs of madness." Hallucinations often occur in schizophrenic episodes and are described in psychiatric manuals as “a running commentary on the person, and two or more voices conversing with each other." People hear voices of specific or unidentifiable people when others present cannot hear them. Some who experience these hallucinations appear to be straining to listen to these voices, while others talk to themselves, sometimes pausing as if they are in conversations. They may shout at people not physically present.
Hearing voices occurs less when a person is in conversation with a real person present. People hear voices most often when they are alone. Other forms of auditory hallucinations may involve hearing music—often very familiar music that has powerful emotional associations. This can occur when listening to very loud music for very long periods of time.
People have reported seeing animals, innate objects and people not present. They may see ‘ghosts’ or ‘angels,’ and some involve quite complicated scenes or bizarre situations. Some visual hallucinations are silent, although in some there are people speaking, often directly to the individual experiencing the hallucination, giving them specific commands.
There are a whole range of highly specific visual illusions with appropriate diagnostic labels. "Dysmegalopsia" is seeing objects misshaped or with odd/unusual forms; micro and "macropsia" is seeing objects as either much small or bigger than they really are. "Allesthesia" changes the place where objects actually are while "Palinopsia" is the sensation that an object that should be visually present has been removed from sight.
There are various causes for experiencing persistent, often distressing hallucinations. When people are deprived of their senses in deserts or jailed in bare cells for “brainwashing,” they often hear and see hallucinated objects. People deprived of sleep or who are completing long, monotonous tasks, such as long-distance driving, can also have hallucinations. It is also possible to “induce” hallucinations. Here are 5 of the most common reasons people experience hallucinations:
- Drugs, including alcohol and marijuana, cocaine, crack, heroin, and LSD. Some cultures and cults cultivate crops to provide the material to induce hallucinations.
- High fever, especially in young or old people.
- Disability. Those with very specific sensory problems like blindness or deafness often experience hallucinations. People who go deaf often say they hear voices. Similarly, those who have had limbs amputated experience "phantom limbs" with all the movement, even pain, experienced.
- Severe physical illness, such as brain cancer, or kidney or liver failure, or later-life dementia, or alcohol-related delirium tremens.
- Severe psychotic disorder, such as post-traumatic stress disorder (PTSD) and schizophrenia. Those who have experienced PTSD often experience flashbacks. When they hear certain sounds or detect certain smells, they are instantly transformed back to times of trauma—war or accidents, for example—and may have powerful flashback hallucinations of particular events. In times of great stress and mourning, some people hear reassuring voices that calm their senses.
Brain scientists know that stimulating specific parts of the brain may lead to hallucinations of numbness, tingling, heat, or running water. Further, patients with brain damage or degenerative issues may experience olfactory hallucinations (nearly always unpleasant) or aural gustatory (taste) hallucinations which may be pleasant or unpleasant. Similarly, certain neurological problems, from the relatively common epilepsy to the rare Ménière's disease, have been associated with very specific, often bizarre, hallucinations.
Diagnosticians go through a structured and systematic medical history interview to try to determine the primary cause of hallucinations. They would first inquire about the specific nature of the hallucinations—what was it like, when it first occurred, when does it typically occur, how long have they been present, etc. Next, they ask questions about alcohol, drugs, and other medication. They inquire about traumatic and emotional events as well as evidence of physical concomitants of agitation, confusion, fever, headaches, and vomiting.
The clinical management starts with attempting to specify possible medical or neurological causes or reactions to particular drugs “within the context of culturally valid phenomena" (i.e., a religious festival or concerts). Any serious psychiatric diagnosis should only occur after a very close inspection of the nature of the hallucinations and the symptoms that might flow from them.
There are traditionally several varied psychological explanations for the occurrence of hallucinations:
- Freudians see the hallucinations as projections of unconscious wishes or wants. What the person experiences as real may be something they feel but cannot express because of its subconscious nature.
- Cognitive psychologists point to problems in cognition processing, particular metacognition—your understanding of others' understanding of events. They posit that hallucinations are misinterpretations of others’ behavior.
- Biological psychologists are most clear about the causes. They posit that hallucinations are the result of deficits in brain states due to damage or chemical imbalance. They have located brain regions and identified pharmaceutical processes that lead to hallucinations. However, explaining why a particular individual has a specific hallucination remains something of a mystery.