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The Multi-Store Model (MSM), proposed by Atkinson and Shiffrin (1968), was the first comprehensive model of how memory works. It describes memory as a linear flow of information through three distinct stores — the sensory register, short-term memory (STM) and long-term memory (LTM) — connected by processes such as attention, rehearsal and retrieval. Each store differs in its capacity, duration and coding, and these three properties, together with the supporting studies, form the examinable core of this topic. Despite well-documented limitations, the MSM remains foundational and is the structural reference point against which later models (the Working Memory Model; the types of LTM) are understood.
Key Definition: The Multi-Store Model is a representation of memory in terms of three stores (sensory register, STM, LTM) and the processes that move information between them (attention, rehearsal, retrieval).
This lesson covers the AQA Paper 1 Memory content on the multi-store model: the sensory register, short-term memory and long-term memory, with the coding, capacity and duration of each store. It also introduces the supporting and challenging research that the specification requires for evaluation — Sperling, Miller, Jacobs, Peterson and Peterson, Baddeley and Bahrick et al. — and links forward to the Working Memory Model and the types of LTM, which arose as critiques of the MSM. You should be able to describe the three stores and their features (AO1), apply the model to everyday memory examples (AO2), and evaluate it through controlled research, case studies and competing models (AO3).
The diagram below shows the full architecture of the MSM: the three stores, the processes that transfer information between them (attention, maintenance and elaborative rehearsal, retrieval), the rehearsal loop within STM, and the routes by which information is forgotten at each stage.
flowchart LR
INPUT["Environmental<br/>stimulus"] --> SR["Sensory Register<br/>(iconic, echoic)"]
SR -->|Attention| STM["Short-Term Memory<br/>STM"]
STM -->|Maintenance rehearsal<br/>(rehearsal loop)| STM
STM -->|Prolonged / elaborative rehearsal| LTM["Long-Term Memory<br/>LTM"]
LTM -->|Retrieval| STM
SR -.->|Not attended to:<br/>decay| LOST1["Forgotten"]
STM -.->|Not rehearsed:<br/>decay / displacement| LOST2["Forgotten"]
LTM -.->|Retrieval failure /<br/>interference| LOST3["Cannot be recalled"]
The sensory register is the first store; all incoming sensory information enters here automatically.
| Feature | Detail |
|---|---|
| Duration | Very brief — under half a second for visual (iconic) memory and around 2–4 seconds for auditory (echoic) memory |
| Capacity | Very large — it receives the full inflow of sensory input across all senses simultaneously |
| Coding | Modality-specific — information is held in the raw form in which it arrived (visual, acoustic, haptic, etc.) |
STM is the second store, holding a small amount of information temporarily for immediate use.
| Feature | Detail | Key Research |
|---|---|---|
| Capacity | Approximately 7 ± 2 items | Miller (1956), "The Magical Number Seven, Plus or Minus Two", reviewed evidence that STM holds about 5–9 items, and showed that chunking raises the effective capacity by grouping items into meaningful units. |
| Capacity (digit span) | Around 7 letters; slightly more for digits | Jacobs (1887) used the serial digit-span technique and found a mean span of about 9.3 digits and 7.3 letters — digits being easier because there are only ten of them (0–9). |
| Duration | About 18–30 seconds without rehearsal | Peterson and Peterson (1959) gave participants a consonant trigram (e.g., BKG) and had them count backwards in threes (an interference task preventing rehearsal). Recall was around 80% after 3 seconds but only about 3% after 18 seconds, showing STM fades rapidly without maintenance rehearsal. |
| Coding | Primarily acoustic (sound-based) | Baddeley (1966) found that immediate recall of acoustically similar words (cat, cab, can) was significantly worse than acoustically dissimilar words, indicating STM codes acoustically. |
Key Definition: Maintenance rehearsal is repeating information to keep it active in STM. In the MSM, sufficient maintenance rehearsal transfers information into LTM.
LTM is the third store, capable of holding information for very long periods, potentially permanently.
| Feature | Detail | Key Research |
|---|---|---|
| Capacity | Potentially unlimited | No study has identified an upper bound to LTM capacity. |
| Duration | Up to a lifetime | Bahrick et al. (1975) tested recall of high-school classmates. Using yearbook photographs, recognition was about 90% even 15 years after graduation and around 70% after 48 years; free recall was poorer (around 60% at 15 years, 30% at 48 years), but the findings still demonstrate extremely durable storage. |
| Coding | Primarily semantic (meaning-based) | Baddeley (1966) found that recall of semantically similar words (big, large, great) after a delay was significantly worse than semantically dissimilar words, indicating LTM codes semantically. |
A defining feature of the MSM is that it treats memory as a linear, largely unidirectional flow: information must pass through each store in sequence — sensory register, then STM, then LTM — and the only major backward step is retrieval (bringing material from LTM into STM for conscious use). This sequential structure is what makes the model so testable, because it generates clear predictions: information that is never attended to cannot reach STM; information that is never rehearsed cannot reach LTM; and damage to the transfer process between STM and LTM should leave a person able to hold information briefly yet unable to store anything new permanently — precisely the pattern seen in patient HM. The model's clarity is therefore also the source of its vulnerability, since each of these strong predictions becomes a point at which contrary evidence (such as the dual-task and levels-of-processing findings discussed below) can challenge it.
| Process | Description |
|---|---|
| Attention | Moves information from the sensory register into STM; without it, information decays |
| Maintenance rehearsal | Repetition that keeps information in STM (the rehearsal loop) and, if prolonged, transfers it to LTM |
| Retrieval | Brings information back from LTM into STM for conscious use |
Key Definition: Chunking is combining individual items into larger, meaningful units to increase the effective capacity of STM.
Miller (1956) observed that although STM holds about 7 items, the size of each item can vary. The string "F-B-I-C-I-A-B-B-C" is 9 separate letters (beyond STM capacity) but can be recoded into three familiar chunks — "FBI", "CIA", "BBC" — which sit comfortably within capacity. Chunking draws on existing knowledge in LTM to form meaningful groups, which is why experts recall far more domain-specific material than novices: a chess master encodes a board position as a few meaningful patterns rather than dozens of individual pieces. This has an interesting theoretical implication that complicates the MSM's neat linear flow: if chunking in STM depends on knowledge retrieved from LTM, then information must be travelling backwards from LTM to STM at the very moment it is first being encoded — which sits awkwardly with the model's largely unidirectional architecture, and hints at the more interactive relationship between the stores that later models would emphasise.
A strength of the MSM is that Baddeley's (1966) coding research supports its claim that STM and LTM are qualitatively distinct stores. Recall errors in immediate (STM) tasks were dominated by acoustic confusions, whereas errors in delayed (LTM) tasks were dominated by semantic confusions — exactly the dissociation the MSM predicts if the two stores code information differently. This matters because it provides controlled experimental evidence that STM and LTM are not simply the same memory at different time points but different systems. The implication is that the model's most basic structural claim — separate short- and long-term stores — rests on solid empirical ground, not merely intuition.
The model is further supported by case studies of patients with brain damage that selectively impairs one store. HM (Henry Molaison), after surgical removal of much of his hippocampus to treat epilepsy, retained a functioning STM and largely intact old long-term memories but could no longer transfer new information into LTM — a striking double dissociation that supports the existence of separate STM and LTM stores with distinct neural bases. Clive Wearing, following viral encephalitis, shows the same pattern: a few-seconds STM yet devastated long-term episodic memory. This matters because such selective impairments are difficult to explain unless STM and LTM are genuinely separate stores. The implication is that the model's architecture is corroborated by neuropsychological as well as experimental evidence — though, as noted below, case-study evidence carries its own caveats.
Further support for two separate stores comes from the serial position effect. When people are given a list of words to recall in any order, they typically remember the first few words well (the primacy effect) and the last few words well (the recency effect), but words in the middle poorly. The MSM explains this elegantly: the early words have been rehearsed and transferred into LTM (primacy), while the final words are still active in STM at the moment of recall (recency). Critically, Glanzer and Cunitz (1966) found that introducing a brief distractor task between presentation and recall — which would displace items still held in STM — abolished the recency effect but left the primacy effect intact, exactly as the model predicts if recency depends on a fragile short-term store and primacy on a durable long-term store. This matters because it is difficult to explain such a clean dissociation between the start and end of a list unless two functionally distinct stores are operating. The implication is that the serial position curve, and especially the selective destruction of recency by a distractor, provides experimental behavioural evidence (complementing the coding and case-study evidence) for the MSM's central claim of separate STM and LTM.
A major limitation is that the MSM treats STM as a single, unitary store, whereas evidence shows it has separable components. Dual-task studies demonstrate that people can perform a visual task and a verbal task simultaneously with little interference, which is impossible if a single store handles both. This finding led Baddeley and Hitch (1974) to replace the MSM's STM with the multi-component Working Memory Model (a phonological loop and a visuo-spatial sketchpad under a central executive). This matters because it shows the MSM is not merely incomplete but structurally wrong about STM. The implication is that, while the MSM correctly identifies a short-term store, its characterisation of that store as unitary has been superseded by a better-evidenced model.
Similarly, the MSM treats LTM as a single undifferentiated store, but research indicates several distinct types. Tulving (1985) proposed that LTM comprises episodic (personal events), semantic (general knowledge) and procedural (skills) memory, each with different properties and brain locations — supported by patients like Clive Wearing, whose procedural memory (playing the piano) survives even as episodic memory collapses. This matters because the MSM cannot explain how one "long-term store" can be selectively damaged in this way. The implication is that the MSM's LTM, like its STM, is an oversimplification that later, more differentiated accounts have had to correct.
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