Some individuals with a severe mental health disorder or significant psychological disturbance experience a break with reality, often referred to as psychosis. Characteristic symptoms of psychosis include hallucinations, delusions, and disorganized thinking and speech. The focus of this entry is on hallucinations. Hallucinations are defined as false sensory or perceptual experiences that have a compelling sense of reality. Indeed, hallucinations can be experienced in each of the five human senses, and these are defined and described next.

Auditory hallucinations involve the (false) perception of sound, most typically involving voice. Auditory hallucinations are the most common type of hallucinations. The hallucinatory experience may be of a single voice or of many voices. In some cases, the voices are of a distinctly negative or unpleasant nature, for example, ...