hallucination, false perception characterized by a distortion of real sensory stimuli. Common types of hallucination are auditory, i.e., hearing voices or noises and visual, i.e., seeing people that are not actually present. Hallucinations play a prominent role in schizophrenia and in the mania stage of bipolar disorder (see depression). They are also significant during withdrawal from various drugs, particularly depressants such as barbiturates, heroin, and alcohol (see delirium tremens), and under the influence of hallucinogenic drugs such as LSD, mescaline, and psylocybin. Hallucinations may occur in normal people under conditions of sensory deprivation, emotional stress, religious exaltation, or great fatigue.

Perception of objects, sounds, or sensations having no demonstrable reality, usually arising from a disorder of the nervous system or in response to certain drugs (see hallucinogen). Hallucinations are in many ways similar to dreams: they derive their content from perceptions known to memory, though these can be greatly transformed. Hallucinations can result when attention collapses from intense arousal due to extreme anxiety, fatigue, excitement, or other causes. They figure prominently in the diagnosis of schizophrenia.

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