Serial Position and Murdock's Study
Serial Position and Recall
If someone reads you a list of twenty words and asks you to recall them in any order, the position of each word in the list affects how likely you are to remember it. This is called the serial position effect. Psychologists have found two consistent patterns in this effect: you tend to remember words at the beginning of the list (the primacy effect) and words at the end of the list (the recency effect) better than words in the middle.
The primacy effect refers to better recall of items at the start of a list; the recency effect refers to better recall of items at the end. The primacy effect is explained by transfer to long-term memory via rehearsal; the recency effect is explained by items still being active in short-term memory.
The Primacy Effect
The primacy effect occurs because the first few items on a list receive the most rehearsal. When you hear the first word, there is nothing else competing for your attention in short-term memory, so you repeat it several times. By the time the list is over, those early words have been rehearsed enough to be transferred into long-term memory, where they can be retrieved later. Words in the middle of the list receive less rehearsal because STM is quickly filled by new incoming items.
The Recency Effect
The recency effect occurs because the last few words on the list are the most recently heard and are still being held in short-term memory at the time of recall. They have not had time to fade. However, the recency effect is fragile: if there is a delay before recall, or if participants are asked to do a distracting task between hearing the list and recalling it, the recency effect disappears because STM trace has faded. The primacy effect remains because those early words are safely in LTM.
When psychologists plot the probability of recall against the position of each word in a list, the result is a U-shaped graph called the serial position curve. Recall is high for the first few words (primacy), drops in the middle, and rises again for the last few words (recency). This characteristic shape appears consistently across many free recall studies.
Murdock’s Serial Position Curve Study
The most important study in this area is Murdock’s (1962) investigation of the serial position effect. It is a named study you need to know in detail: aim, method, results, and conclusion.
Murdock (1962): Aim — to investigate the serial position effect in free recall. Method — participants heard lists of words (typically 20 words, presented at a rate of one word per second) and were asked to recall them in any order immediately afterwards. Results — words at the start (primacy) and end (recency) were recalled better than words in the middle; a U-shaped serial position curve was produced. Conclusion — the pattern supports the idea of separate STM and LTM stores.
A strength of Murdock’s study is that it used a controlled laboratory method, which allows replication and high internal validity — extraneous variables such as word length and presentation rate were carefully controlled. The study produced consistent, replicable results that have been repeated many times, supporting its reliability.
A weakness is that the task was artificial: memorising lists of unrelated words has little resemblance to everyday memory tasks. This reduces ecological validity — results may not reflect how memory works in real life. The study also used participants in a restricted setting, which may limit how far findings generalise to all people and all types of memory task.
Link to the Multi-Store Model
The serial position curve provides evidence for the multi-store model of memory. The primacy effect demonstrates that rehearsal can transfer information into long-term memory — early items are recalled from LTM. The recency effect demonstrates the existence of a separate, limited short-term store — end items are recalled directly from STM. When a delay is introduced before recall, the recency effect disappears but the primacy effect remains, which is exactly what the multi-store model would predict: STM traces fade quickly while LTM traces persist.
Why Middle Items Are Recalled Poorly
It is worth understanding precisely why items in the middle of a list are the hardest to recall. When you hear the first few words, your STM is relatively empty and you can rehearse them repeatedly. But as more words arrive, your STM fills to its limited capacity of around seven items. New words displace older ones before those older words have had enough rehearsal to reach LTM. At the same time, the middle items are not the most recent, so they are no longer active in STM at the point of recall. The result is that they fall through the gap between the two stores and are lost.
This competition between new and old items in a limited-capacity store is sometimes called displacement. Each new item in a full STM pushes out the item that has been there longest without sufficient rehearsal to move it to LTM. Middle items receive neither the rehearsal advantage of early items nor the recency advantage of final items, which is why the serial position curve dips in the middle.
The displacement account is consistent with the multi-store model’s claim that STM has a fixed capacity of around seven items (plus or minus two). If STM had unlimited capacity, every item would have as much opportunity for rehearsal as the first item, and there would be no primacy advantage — the serial position curve would be flat, not U-shaped.