Illusion vs Hallucination vs Pseudohallucination
Illusion Hallucination Pseudohallucination
Overview
All three involve a perceptual experience without an accurate corresponding external reality, but they split apart on three questions: was there a real stimulus to begin with, where does the experience seem to be located, and does the person believe it is real. Getting these three questions in the right order resolves almost every confusion between the three.
| Dimension | illusion | hallucination | pseudohallucination |
|---|---|---|---|
| Is there a real external stimulus present? | Yes — a real object or sound is present but misperceived | No — there is no external stimulus at all | No — there is no external stimulus at all |
| Where is the experience located? | In external space, on the real object that was misperceived | In external, objective space, indistinguishable in location from a real perception | In inner, subjective space ("in the mind's eye"), not projected into the external world |
| Sensory quality, compared to a real perception | Full sensory vividness, since a real stimulus underlies it | Full sensory vividness and clarity, indistinguishable from a real perception | Reduced vividness and substance; typically described as less solid or less real than genuine perception |
| Does the person believe it is real? | Usually yes, until corrected, since a real stimulus is genuinely present | Usually yes — experienced with full conviction as a real perception | Usually no — the person retains insight that it is an image or experience of their own mind, not an external event |
| Typical context | Reduced attention, poor lighting, high emotional arousal, or mild sensory impairment, in a person who may otherwise be well | Psychotic illness, organic brain disease, or severe sensory deprivation | Bereavement, high emotional stress, or as a normal variant, often in someone without significant mental illness |
Common confusion
Students often assume pseudohallucination just means 'a hallucination the person doubts,' but the defining feature is not doubt — it's location. A pseudohallucination is placed in inner, subjective space from the start, not projected outward and then second-guessed. A hallucination can also be held with less than full conviction (some hallucinating patients express some doubt) without that alone making it a pseudohallucination.
Clarifying questions
- Was there actually something there that you looked at or heard, or did the experience come from nowhere?
- Does it feel like it's happening out here in the room with you, or more like it's happening in your mind's eye?
- At the time, did it feel completely real, the same as anything else you were seeing or hearing — or did some part of you know it wasn't quite real?
Provenance
Class B · tier T1 · lifecycle migrated_candidate
- Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 3, 'Disorders of Perception'.