"There was definitely nothing there"
A 58-year-old man on a medical ward, three days post-operatively, tells the nurse that last night he "saw a man standing in the corner of the room, just watching me." Asked to describe it further, he says: "He was as clear as you are now. I looked right at him. There was nothing there — no coat on a hook, no shadow, nothing that could have looked like a person. I know now it wasn't real, but at the time it felt completely real, like any other thing I've ever seen." He denies any visual difficulty, and the room was adequately lit at the time.
This case works through a connected sequence — each part builds on what came before, leading to an integrated picture.
Identify
What is the man describing?
Correct. He is describing a full-force perception occurring where there was, by his own account, nothing there at all.
Not quite — look again at what he says was actually in the corner of the room: nothing. That absence of any real stimulus is the detail that settles this.
Key discriminating feature: He is explicit that there was nothing in the corner that could account for the figure — no coat, no shadow, nothing physically present to be misread. A perception with no real stimulus behind it at all is a hallucination.
Discriminate
Which single detail in his account would most reliably rule out an illusion instead?
Correct. Ruling out a real stimulus is exactly how a hallucination is separated from an illusion at the bedside.
Reconsider — timing and clinical context can raise suspicion of either phenomenon, but only the presence or absence of a real stimulus actually distinguishes them.
Key discriminating feature: An illusion always has a genuine external stimulus behind it — something that can, at least in principle, be pointed to afterwards. His own account rules that out here.
Common misconception: Students sometimes assume any visual experience on a postoperative ward must be an illusion (a misread IV pole, a curtain), rather than checking directly whether the patient reports any real object being present at all.
Elicit
Which question would best clarify whether this was a hallucination or an illusion?
Correct. This question goes straight to the one fact that decides between the two phenomena.
The other questions may be useful background, but none of them establishes whether a real object was present — which is the question that actually matters here.
Clinical interviewing principle: Ask directly and concretely about the presence or absence of a real stimulus before asking about the emotional or contextual surroundings of the experience — the stimulus question is what actually separates the two phenomena.
Explain
Why is this a hallucination rather than an illusion?
Correct. That absence of any real stimulus, combined with the full sensory quality of the experience, is the defining feature of a hallucination.
Retained insight afterwards, the ward setting, and frequency don't distinguish these two phenomena — only the presence or absence of a real stimulus does.
Integrate
A second postoperative patient reports an equally vivid, equally convincing experience of "seeing a shadow move across the ceiling." Before deciding whether this is a hallucination or an illusion, what is the one piece of information from this case that is now essential to establish, and why can't vividness alone settle it?
Correct. The presence or absence of a real stimulus is the one fact that settles it, precisely because vividness — as this case demonstrated — cannot.
Fear level, assuming the two patients must match, and lighting conditions don't settle this — only checking for a real stimulus does, because conviction alone, as this case showed, cannot distinguish a hallucination from an illusion.
Summary
This case illustrates the most fundamental perceptual distinction in the phenomenology of hallucinations: an illusion always has a real stimulus at its root, while a hallucination never does. Both can carry full sensory conviction at the time, which is why the deciding question is always about the stimulus, not about how vivid or convincing the experience felt.
Finish caseReferences
- Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 3, 'Disorders of Perception'.