Psychosis: Altered Perception

Perception is the process of interpreting sensory information into meaningful experiences. During psychosis, a person may hear, see or feel something without a corresponding external stimulus. These experiences are called hallucinations. Perceptual changes can also involve ordinary sounds or sights feeling unusually vivid, personally significant or difficult to distinguish from internally generated experiences.

Psychosis is a description of particular experiences and difficulties with reality testing. It can occur in several psychiatric, substance-related and medical conditions. The meaning of an experience depends on its context, associated symptoms and development over time, including the person’s cultural background.

Scientists study interactions between sensory processing, attention, memory and expectations to understand these changes. No single mechanism explains every hallucination. A voice can be experienced inside or outside the head, and its location does not determine whether it is distressing or clinically important. Assessment asks what is perceived, how often it happens and what effect it has. Sleep-related experiences, hearing impairment, migraine, substances and neurological disorders can also alter perception. Describing the experience carefully helps distinguish these possibilities and avoids assuming that every unusual sensation is caused by schizophrenia or requires the same treatment.

A useful sensory distinction is between hallucination, illusion and imagery. An illusion misinterprets an existing stimulus, such as seeing a face in a shadow. Imagery is usually experienced as imagined. Hallucinations have a perceptual quality without the matching stimulus. These categories can be difficult to separate in practice, so careful description is more informative than an immediate label.

Further reading: National Institute of Mental Health.