A perception that occurs when there is no external stimulus. Auditory hallucinations (the hearing of voices) are a major symptom of schizophrenia but may also be caused by manic–depressive illness and certain brain disorders. Visual hallucinations are most often found in states of delirium brought on by a physical illness (such as pneumonia) or alcohol withdrawal ( delirium tremens). Hallucinogenic drugs are another common cause of visual hallucinations. Hallucinations of smell are associated with temporal lobe epilepsy. Those of touch and taste are rare, however, and occur mainly in people with schizophrenia. People subjected to sensory deprivation or overwhelming physical stress sometimes suffer from temporary hallucinations.


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