A hallucination is a sensory experience that seems real to the person having it, but occurs in the absence of any external perceptual stimulus. The word comes from the Latin verb hallucinere or allucinere, meaning to “wander in mind” or “idle talk” (Aleman & Larøi, 2008). 

Hallucinations can occur in any sensory modality (auditory, visual, olfactory, tactile, or gustatory). However, auditory hallucinations (e.g., hearing voices) are by far the most common. Hallucinations can even be induced in healthy people if they are under a lot of stress and drink a lot of caffeine.

Hallucinations often have relevance for the patient at some affective, conceptual, or behavioral level. Patients can become emotionally involved in their hallucinations, often incorporating them into their delusions. In some cases, patients may even act on their hallucinations and do what the voices tell them to do. People who consider themselves to be socially inferior tend to perceive the voices they hear as being more powerful than they are and to behave accordingly (Paulik, 2011).

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