Definition and clinical meaning #
A hallucination is a sensory experience without an adequate corresponding stimulus. It has a perceptual quality rather than being merely a belief, memory or ordinary voluntary image. The person may experience a voice, figure, smell, taste, bodily sensation or another sensory event.
Hallucinations occur in several psychiatric, neurological, medical and sensory contexts. They may also be associated with substances, transitions into or out of sleep, or bereavement. Establish onset, associated symptoms and functional effect rather than assuming that the experience proves schizophrenia. Insight may be retained, partial or absent. An experience perceived inside the head is not automatically ordinary thought or clinically trivial.
Describe the modality and form #
- Auditory: simple sounds, music or voices. For voices, describe number, identity, intelligibility, person of address, emotional tone, commentary, conversation or instructions.
- Visual: elementary flashes or shapes versus formed objects, figures or scenes. Establish vision, lighting, eyes-open/closed context and associated cognitive or neurological changes.
- Olfactory or gustatory: unexplained smells or tastes; distinguish a sensory event from a belief that one smells unpleasant or that food is poisoned.
- Tactile and bodily: touch, movement or other sensations apparently occurring without an adequate stimulus; evaluate relevant physical symptoms.
- Hypnagogic and hypnopompic: experiences around falling asleep or awakening. Their timing matters; they do not by themselves establish a psychotic disorder.
- Functional: an additional hallucinated experience accompanies a real stimulus in the same modality. Reflex: a stimulus in one modality is associated with a hallucinated experience in another.
Content, complexity, location and timing are descriptive dimensions. None provides a reliable diagnosis in isolation.
Clarifying neighbouring experiences #
| Experience | What to establish |
|---|---|
| Illusion | An actual stimulus is misidentified rather than an additional perception occurring. |
| Intrusive imagery | The event is experienced as a mental image, although it may be vivid and unwanted. |
| Thought or inner speech | Clarify audibility, ownership, agency and perceptual quality; do not classify by location alone. |
| Delusion | The person believes something is occurring without necessarily hearing or seeing it. |
| Sensory distortion | An actual perception changes in size, shape, intensity or another quality. |
“Pseudohallucination” has been used inconsistently for internal-space experiences or experiences with insight. A precise description is more informative than an unexplained label.
A systematic enquiry #
- “Can you describe exactly what you experience?”
- “When did this begin, how often does it happen, and how long does it last?”
- “Does it seem like a sound you hear, a thought, or something different?”
- “Where does it seem to come from? Can you bring it on or stop it?”
- “What do you think causes it? Could there be another explanation?”
- “What does it make you feel or do? Has it affected sleep, work or relationships?”
For instructions or threats, explore the words used, perceived authority, distress, ability to resist, previous responses and current intentions. Do not infer either danger or safety simply from the presence or absence of command content. Assess the person and context, including physical illness and support needs.
Synthetic example #
Interpretation errors #
- Auditory does not mean psychiatric, and visual does not invariably mean neurological.
- Preserved insight does not exclude a hallucination.
- Do not treat all grief- or sleep-associated experiences as disorder.
- Ask what was experienced before supplying explanatory labels.
- New perceptual changes with fluctuating attention, fever, neurological symptoms or intoxication require prompt clinical assessment.