Home > Encyclopedia of Neurological Disorders > Hallucination

Definitions

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...