serial position effect

Meaning: When people try to recall a list, they tend to remember the first and last items better than the middle ones, so a graph of percent recalled against list position is U-shaped. The primacy effect (better recall of early items) is usually explained by extra rehearsal, which helps early items be encoded into long-term memory. The recency effect (better recall of final items) is usually explained by those items still being held in short-term (working) memory when recall begins.

On the MCAT: A passage describes free recall of a word list, often with a graph of percent recalled versus serial position. You are asked what happens to the curve when the procedure changes. A delay filled with a distractor task, such as counting backward, typically lowers the recency portion because the last items leave short-term memory, while primacy is largely unchanged. Presenting items faster, or preventing rehearsal, typically lowers primacy. Questions may also ask which part of the curve reflects long-term memory and which reflects short-term memory.

Common confusion: Students treat primacy and recency as one effect, or assume middle items are never recalled. They are two separate effects with different proposed memory stores. The fact that settles it is the distractor test: a delay hurts recency far more than primacy. The effect is a tendency, and middle items are still recalled at a lower rate.