Duration vs capacity: time vs amount
Statement 2.1.2 names two features that must be kept apart. Duration is how long information stays in a store before it is lost, measured in time — seconds for STM, years for LTM. Capacity is how much a store can hold at once, measured as an amount — items for STM, no known limit for LTM. Quick test: a sentence ending in a unit of time is about duration; one ending in a number of items is about capacity. Name the feature, give the figure, say which store.
Short-term memory: ~7 items, 18-30 seconds
Short-term memory holds what you are consciously working with now. Its capacity is about 7 items, plus or minus 2 (roughly 5 to 9); once full, new information displaces what is there. Its duration is up to about 18 to 30 seconds when the information is not rehearsed — the clause is part of the fact, because repeating information keeps it in the store. Chunking raises the effective capacity: grouping a number into three chunks fills three slots, not eleven.
Long-term memory: unlimited, a lifetime
Long-term memory holds everything you are not currently thinking about. Its capacity is potentially unlimited — no upper limit has ever been found. Use "potentially": it cannot be shown directly, only that no ceiling is reached. Its duration is potentially a lifetime. LTM beats STM on both features, best shown comparatively: STM holds about 7 items for up to 30 seconds without rehearsal, whereas LTM is potentially unlimited and lasts a lifetime.
Drawn from real examiner reports.
Duration and capacity swapped
A common error is swapping the two features. Writing that the capacity of STM is "about 30 seconds", or its duration is "about 7 items", pairs a feature with the wrong unit — and the unit gives it away: seconds are duration, items are capacity. Answer to the pattern "the [feature] of [store] is [figure]", which forces you to name the feature and commit to a store.
Tautological definitions score zero
Examiners record memory terms defined using the term itself, which earns nothing: "duration is how long the duration is." Each definition needs two elements — what is measured, and what it is measured about: duration is how long information stays in a store before it is lost. And "state one feature" wants a feature and its figure, not a full definition of the store.
Tautological definitions of a memory term earn no credit (Nov 2020 P1 Q6); a state-one-feature item answered by defining the term is at June 2023 P1 Q6.
Attach the evidence to the right feature
Match the evidence to the feature. The duration of STM is supported by Peterson and Peterson (1959), whose participants could not rehearse; examiners record it muddled with Baddeley, Miller or Murdock, so keep to one researcher, one feature. Be specific — "up to about 18 to 30 seconds without rehearsal" beats "it does not last long".
The mark needed specific figures, and weak answers muddled Peterson and Peterson with Baddeley, Miller or Murdock (June 2019 P1 Q5a).
A figure with no feature named
Writing "short-term memory is 7 plus or minus 2" gives a number without saying what it measures, so the examiner cannot tell capacity from duration. Name the feature: "the capacity of STM is about 7 items, plus or minus 2." The same precision earns the mark on duration — "up to about 18 to 30 seconds without rehearsal", not "a short time".
Answers that scored used short-term memory capacity or rehearsal into long-term memory precisely (Nov 2020 P1 Q7a; June 2024 P1 Q10).
Attach the figure to the right store
An easy mark is thrown away by attaching a feature to the wrong store — giving STM an unlimited capacity, or LTM a duration of seconds. Fix the four values: STM about 7 items and up to 18 to 30 seconds without rehearsal; LTM potentially unlimited and potentially a lifetime. Check which store the question names before writing the figure.
STM duration needs the not-rehearsed clause
"Short-term memory lasts 30 seconds" is incomplete: the figure of up to about 18 to 30 seconds applies only when the information is not rehearsed. Repeating it keeps it in the store for as long as the repetition continues. Always give the clause — up to about 18 to 30 seconds if it is not rehearsed.
STM is no timer; unlimited is not forever
STM does not wipe at exactly 30 seconds: about 18 to 30 seconds is its duration when information is not rehearsed, an average not a timer. An unlimited LTM capacity does not mean nothing is forgotten — it means no known limit on how much is stored, not whether a memory can be retrieved (2.1.1). Capacity counts items, not detail, so chunking helps.
Feature, figure, store in one line
The safe pattern is "the [feature] of [store] is [figure]", which forces all three into one sentence: the capacity of STM is about 7 items, plus or minus 2. Answering this way stops a bare number, the wrong store, or a confused feature.
Define features in relation to the scenario
Duration and capacity must be defined in relation to the scenario; naming the character or copying the stimulus does not count. Tie the figure to the detail — eleven digits in one go exceed the capacity of about 7 items. AO3 needs AO2, so apply before you evaluate.
Difference needs a connective
STM against LTM is often examined as a difference. Two definitions side by side earn one mark; the second needs a connective such as whereas: "STM holds about 7 items, whereas LTM is unlimited." A 2-mark describe needs two unique points; prose, not bullets.
The 9-mark Assess needs AO3 and balance
On the 9-mark Assess (AO1 3, AO2 3, AO3 3), the top band is lost through weak AO3 and balance. Argue both sides with named lenses — reliability, validity (nonsense syllables are unlike everyday memory) and generalisability — then conclude by weighing them.
Duration - how long information stays in a memory store before it is lost. Measured in units of time.
Capacity - how much information a memory store can hold at any one time. Measured as an amount, usually a number of items.
Short-term memory (STM) - the temporary store holding the information a person is consciously working with at that moment.
Long-term memory (LTM) - the lasting store holding everything a person is not currently thinking about.
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