Two stores with very different limits
- Short-term memory holds only a little information, and only for a short time.
- Long-term memory holds far more, and it can keep hold of it for years.
- The two stores are compared on two features, duration and capacity.
Key Idea
- Duration means how long a store holds information.
- Capacity means how much a store can hold at once.
- Picture short-term memory as a small whiteboard you keep wiping clean, and long-term memory as a library that just keeps adding shelves.
Short-term memory
Definition
Short-term memory
The store that briefly holds the small amount of information you are working with now, for around 15 to 30 seconds unless you rehearse it.
- Its duration is short, roughly 15 to 30 seconds, unless you keep the information alive by rehearsing it.
- Rehearsal is the only reason anything stays there longer, so an interruption wipes it.
- Its capacity is limited to about seven items, give or take two, which Miller (1956) put at 5 to 9 units.
- An item can be a digit, a letter or a word, so a longer list pushes earlier items out.
Long-term memory
Definition
Long-term memory
The store that holds information over long periods, from hours to potentially a lifetime, with no known limit on how much it can hold.
- Its duration is said to be very long, running from hours to potentially a lifetime.
- Nothing has to be rehearsed continuously to stay there, which is the sharpest contrast with short-term memory.
- Its capacity is thought to be potentially unlimited, with no known ceiling on how much it can hold.
Example
- Glancing at the live departure time on a bus-stop screen and holding it just long enough to decide whether to run uses short-term memory.
- Still knowing your childhood postcode years later uses long-term memory.
Mistakes that cost marks
Common Mistake
- Do not give a single exact number for short-term capacity, because it is about seven items, plus or minus two.
- Do not claim long-term memory lasts forever as a proven fact, because the safe wording is potentially unlimited and potentially lifelong.
- Do not blur duration and capacity together, because each store has to be described on both features separately.
Turning this into marks
- Give the figures rather than vague words, so about 15 to 30 seconds for the duration of short-term memory and about seven items, plus or minus two, or 5 to 9 units, for its capacity.
- For long-term memory say the duration is said to run from hours to potentially a lifetime and the capacity is potentially unlimited.
- The mark most often lost is answering a comparison with a difference only, so add the similarity that both stores are described by the same two features.
Self review
- State the duration and the capacity of short-term memory, with a figure for each.
- State the duration and the capacity of long-term memory.
- Write a comparison of the two stores that contains one similarity and one difference.
