Perception › Hallucination

Reflex Hallucination

A reflex hallucination is a hallucination that is triggered by a real stimulus in one sense, but experienced in a completely different sense. A real sound, for example, might reliably trigger a hallucinated visual image or a hallucinated bodily sensation, rather than another sound.

This has traditionally been described as related to, but distinct from, synaesthesia — the ordinary cross-sensory blending some people experience (such as associating colours with numbers) — because a reflex hallucination is a true hallucination in the second sense, not merely an association or metaphorical blending of two sensory qualities.

Recognition features

• A real stimulus in one sensory channel reliably and specifically triggers a hallucination in a different sensory channel
• The relationship between trigger and hallucination is consistent and reproducible for that person
• The hallucination in the second sense has the same full perceptual quality as any other hallucination
• Distinguishable from ordinary synaesthesia by its involuntary, unpleasant, or unbidden character in most clinical presentations

Eliciting it at interview

• Ask about any consistent trigger across senses: "Does anything you hear, see, or feel reliably bring on an experience in a different sense — for instance, does a sound ever make you see or feel something?"
• Clarify that this is a genuine perceptual experience in the second sense, not simply an association or a figure of speech
• Note how consistent and reproducible the link is, since a one-off coincidence is not the same as a true reflex hallucination

Distinguishing features

• Differs from a functional hallucination, in which the trigger and the hallucination occur in the same sense rather than two different ones
• Differs from ordinary synaesthesia, a non-clinical cross-sensory blending most people experiencing it do not find distressing or perceive as a true hallucination
• Differs from a coincidental hallucination that merely happens to occur near a particular stimulus without a reliable, reproducible link

Common misconceptions

• That reflex hallucination is simply another name for synaesthesia; the two are related in concept but differ in perceptual force and clinical context
• That this pattern is common; it is one of the rarer, more specifically named types of hallucination in descriptive psychopathology

Related phenomena

Hallucination · Functional Hallucination

Practice this

Every time a patient hears a car door slam nearby, she reliably and reproducibly experiences a full, vivid visual hallucination of a figure in the corner of the room, distressing and unbidden each time. What is this? · A patient explains that she has, for as long as she can remember, experienced a distinct colour whenever she hears music, finding the experience pleasant and unremarkable rather than distressing. Before revealing the answer: is this a reflex hallucination? · Two patients each describe a real sound reliably triggering a hallucination. Before revealing the answer, decide what single question tells a functional hallucination apart from a reflex hallucination. · A stimulus in one sense reliably triggers an experience in a different sense. Before revealing the answer, decide what distinguishes a reflex hallucination from synaesthesia. · A patient reports that certain sounds seem to bring on other perceptual experiences. Before revealing the answer, decide how you would assess whether this is a reflex hallucination. · Explain why the consistency and reproducibility of the trigger-hallucination relationship matters when identifying a reflex hallucination.

Illustration

A 38-year-old man reports that whenever a door slams nearby, he experiences a vivid, unpleasant sensation of cold water being poured down his back, every single time, without fail. He finds it deeply unsettling and has started avoiding rooms with doors that might slam.

References

• Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 3, 'Disorders of Perception'.