short term memory

Meaning: In the Atkinson-Shiffrin model, information moves from sensory memory to short-term memory when it is attended to, and from there to long-term memory through encoding. Short-term memory is limited. Miller estimated its capacity at about 7 ± 2 items, and without rehearsal its contents fade in roughly 20–30 seconds. Maintenance rehearsal (simple repetition) keeps items active, while elaborative rehearsal (linking items to meaning) favors transfer to long-term memory. A second account, Baddeley's working memory, stresses that the system also manipulates information, using a central executive and subsystems such as the phonological loop.

On the MCAT: The serial position effect is the classic setup. In free recall of a word list, the recency effect (good recall of the last items) reflects items still in short-term memory, and the primacy effect (good recall of the first items) reflects items rehearsed into long-term memory. A delay filled with a distractor task usually weakens recency but leaves primacy largely intact. Passages also use digit span and chunking.

Common confusion: Capacity is counted in chunks, not single digits. Chunking (grouping 1-9-4-5 as one year) does not add slots; it packs more information into each slot. Also, short-term memory and working memory are related but not identical terms: the first emphasizes storage, the second emphasizes active processing.