Textbook of Usability

Also known as: LTM

Long-term memory (LTM) is the cognitive system that stores knowledge, experiences, and skills over extended periods — from minutes to a lifetime. Unlike working memory, long-term memory has no known capacity limit.

Long-term memory is typically divided into:

• Declarative (explicit) memory: facts and events, further split into semantic memory (general knowledge) and episodic memory (personal experiences)
• Procedural (implicit) memory: motor skills and learned procedures that operate without conscious recall (riding a bicycle, touch typing)

Information transfers from working memory to long-term memory through encoding. Craik and Lockhart's levels-of-processing framework (1972) shows that deeper, more meaningful processing produces stronger memory traces. Features learned through exploration and problem-solving are better remembered than those learned by rote.

For interface design, long-term memory supports two crucial retrieval modes: recognition (identifying a previously encountered item when re-presented) and recall (producing information without cues). Recognition is dramatically easier than recall, which is why Nielsen's heuristic advocates "recognition rather than recall."

Long-term memory is also the foundation of mental models — users' internal representations of how systems work, which guide expectations and anticipate system behaviour.