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What Is Hallucination?

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Updated February 25, 2012

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Definition:

A hallucination is something you see, hear, feel, smell or taste that isn't really there. Hallucinations can happen through any of the five senses, but the most common types are visual and auditory (hearing). Hallucinations can happen under the influence of drugs, especially hallucinogenic drugs, such as LSD, or they can be a symptom of psychosis. They can also happen to almost anyone when they are subjected to extreme physical or mental stress, or when they are extremely sleep deprived.

Visual Hallucinations

Visual hallucinations can include mild distortions of what you see around you - colors appearing more vivid; seeing things differently in your peripheral vision; seeing faces as looking artificial or made of plastic, clay or some other inanimate substance; seeing walls "breathing;" and noticing patterns that had not been apparent before. They may also include seeing entire objects or people who are not really there.

Visual hallucinations are a hallmark effect of hallucinogenic drugs, such as LSD, although the extent to which people experience hallucinations while under the influence of these drugs varies. Visual hallucinations can be pleasant or unpleasant, and can quickly shift from one to the other, causing rapid shifts in mood.

Auditory Hallucinations

Auditory hallucinations can range from mild distortions in what you hear, to hearing voices when nobody is speaking. The voices may be quiet or loud, friendly or intimidating. Auditory hallucinations are the most common type of hallucination experienced by people suffering from schizophrenia.

Tactile Hallucinations

Tactile hallucinations are physical sensations of something that is not there. Mild tactile hallucinations are common in people high on psychoactive drugs. However, they are not always pleasurable or mild, and all drugs are unpredictable and vary in effect from one person to another.

Crystal meth is notorious for producing unpleasant tactile hallucinations, often felt as bugs crawling over or underneath the skin. These tactile hallucinations can feel so real to a meth user that they scratch or pick holes in their skin while trying to remove the bug. This can lead to sores, scabs, scars and infections.

Olfactory and Taste Hallucinations

Olfactory hallucinations - smelling something that is not there - and taste hallucinations (quite rare) may also be experienced, although these have not been the subject of much interest. Like other hallucinations, olfactory and taste hallucinations can be troubling to the person experiencing them, especially if they overlap with delusions. For example, in a person who has a delusion that he or she is being poisoned, a taste hallucination would be extremely distressing. The person might perceive it as proof that the delusion is true.

Pronunciation: hal-oo-sin-A-shun
Also Known As:

Visual Hallucinations -- visuals, visual disturbances, visual distortions, seeing things

Auditory Hallucinations -- hearing voices, hearing things

Tactile Hallucinations -- bugs

Common Misspellings: hellucination, hullucination, helucination, helusination, hallusination, hellusination
Examples:
Gary experienced visual hallucinations while he was on LSD.
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