Hallucinations and Illusions

National Institute of Mental Health

Hallucinations and illusions are disturbances of perception that are common in people suffering from schizophrenia. Hallucinations are perceptions that occur without connection to an appropriate source. Although hallucinations can occur in any sensory form—auditory (sound), visual (sight), tactile (touch), gustatory (taste), and olfactory (smell)—hearing voices that other people do not hear is the most common type of hallucination in schizophrenia. Voices may describe the patient’s activities, carry on a conversation, warn of impending dangers, or even issue orders to the individual. Illusions, on the other hand, occur when a sensory stimulus is present but is incorrectly interpreted by the individual.