Glossary

Terms, in plain English

The words the research uses, in the shortest honest definitions we can write.

Acquired aphantasia: Aphantasia that appears after a specific neurological event — a head injury, stroke, seizure, or surgery — in a person who previously had intact mental imagery.
Anendophasia: The absence of inner speech — no internal monologue. Distinct from aphantasia but often discussed alongside it as another form of internal-experience atypicality.
Aphantasia: The inability, or severely reduced ability, to form voluntary mental imagery. Most often used for visual imagery but can apply to other senses.
Aphantasia subtypes: Aphantasia is heterogeneous: some people have no voluntary imagery in any sense, others lack only visual imagery, some have vivid dreams despite no waking imagery. The field is still sorting out the internal structure.
Autobiographical Interview: A structured research interview developed by Levine and colleagues in 2002 that separates episodic from semantic detail in a person’s recall of their own life. The main objective tool for documenting SDAM.
Autobiographical memory: Memory of one’s own life. A combination of episodic (re-living) and semantic (knowing-about) components.
Autonoetic consciousness: The self-aware sense of re-experiencing a past event — knowing that it is you, now, remembering something that happened to you, then. Proposed by Endel Tulving in 1985.
Binocular rivalry: An experimental method used by Keogh & Pearson (2018) to measure imagery objectively, without relying on self-report.
Confabulation: The production of false or invented memories without any intention to deceive. Unrelated to SDAM or aphantasia, but often confused with them.
Default-mode network: A coordinated set of brain regions — medial prefrontal cortex, posterior cingulate, hippocampus — most active during internally-directed thought: remembering, imagining, mind-wandering.
Episodic memory: The re-livable kind of memory — recalling a specific event in a way that feels like returning to it.
Hippocampus: A seahorse-shaped brain structure central to memory formation and retrieval, especially the binding of specific details into coherent episodic memories.
Hyperphantasia: Unusually vivid, often photograph-like mental imagery — the opposite end of the spectrum from aphantasia.
Hypnagogia: The transitional state between wakefulness and sleep, in which involuntary imagery sometimes appears — including for some people who otherwise have aphantasia.
Memory consolidation: The gradual process by which new memories become stabilised in long-term storage, usually over hours to days, heavily involving sleep.
Mental imagery: The experience of perceiving something — a picture, a sound, a smell — without the thing being physically present.
Mental rotation: The ability to imagine an object rotating in three dimensions — a classic spatial-reasoning task.
Mental time travel: The capacity to mentally project yourself into a past or future episode — closely tied to episodic memory and imagery.
Noetic consciousness: The sense of knowing something factually — knowing it is true — without re-experiencing it. The counterpart Tulving distinguished from autonoetic consciousness.
Prosopagnosia: Face blindness: an inability to recognise faces, including familiar ones. Sometimes confused with aphantasia, but a distinct condition.
SAM: Survey of Autobiographical Memory. A twenty-six-item self-report measure across four subscales, used for SDAM research.
SDAM: Severely Deficient Autobiographical Memory. A lifelong pattern of not being able to mentally re-experience past events, while still remembering facts about them.
Semantic memory: The fact-based kind of memory — knowing things about the world (and your own life) without needing to re-experience the moment you learned them.
Source memory: Memory for where or when you learned something — separable from the fact itself.
VVIQ: Vividness of Visual Imagery Questionnaire. A sixteen-item self-report measure of how vivid a person’s mental imagery is, widely used in aphantasia research.
Visual cortex: The region at the back of the brain that processes vision. In aphantasia it is structurally normal but less strongly recruited when a person tries to form a mental image.