Bennet Murdock (1962) ran a study that has become a textbook demonstration of two memory stores. He gave participants lists of 10–40 unrelated words, read aloud at 1 word per second, then asked them to free-recall as many as they could in any order. He plotted the probability of recall against the serial position of each word in the list.
The curve
The resulting graph is U-shaped:
- Primacy effect — words at the start of the list are recalled well.
- Recency effect — words at the end of the list are recalled best of all.
- Middle items are recalled poorly.
Why?
- The primacy effect is explained by rehearsal. The first words have more time to be rehearsed, transferring them into long-term memory. They can be retrieved at recall because they are stored.
- The recency effect is explained by the STM trace. The last words are still circulating in short-term memory at the moment recall begins, so they can be reported directly.
- Middle items suffer both: not rehearsed enough to enter LTM and pushed out of STM by the later items.
Confirmatory experiments
Glanzer & Cunitz (1966) added a counting-back task between list presentation and recall. The interference task occupied STM, so the recency words were lost — but the primacy effect was intact (those words were already in LTM). This dissociation supports the multi-store model.
Reducing presentation rate (e.g. 2 sec per word instead of 1 sec) strengthens primacy because rehearsal time increases. Adding visual distraction during the list also reduces primacy because rehearsal is disrupted.
Quick exam phrasing
"The serial position curve shows that recall depends on a word's position in a list. Words near the start (primacy) and near the end (recency) are remembered better than middle items. Primacy reflects rehearsal into LTM; recency reflects items still in STM. The two-store explanation is supported by Glanzer and Cunitz's interference experiment."
Common pitfalls
- Confusing which end is which: primacy = first, recency = last.
- Forgetting to link each end to a memory store.
- Saying the curve is "bell-shaped" — it is U-shaped (or J-shaped, depending on list length).
AI-generated · claude-opus-4-7 · v3-deep-psychology