The Multi-Store Model of Memory
The Multi-Store Model
Where does a memory go after you first encounter it? The multi-store model of memory proposes that information travels through three distinct stores: the sensory register, short-term memory, and long-term memory. Each store differs in how it codes information, how much it can hold (capacity), and how long it retains information (duration).
The multi-store model has three stores: the sensory register (large capacity, very brief duration), short-term memory (limited capacity of about 7 items, up to about 30 seconds), and long-term memory (potentially unlimited capacity, potentially permanent duration).
The Sensory Register
The sensory register receives information from all your senses simultaneously. It has a very large capacity — it can hold a huge amount of incoming sensory data — but its duration is extremely brief, lasting only fractions of a second. Most information in the sensory register is never processed further and simply fades away. Only information that is attended to moves on to short-term memory.
The coding in the sensory register matches the sense that detected it: visual information is coded visually (iconic memory), and auditory information is coded acoustically (echoic memory). Think of the brief afterimage you see when someone takes a flash photograph — that flicker of visual information is your iconic sensory register in action.
Short-Term Memory
Short-term memory (STM) holds information that is currently in use — for example, a phone number you have just read or the words in the sentence you are reading right now. STM has a limited capacity: research suggests around 7 items, plus or minus 2. Its duration is also limited — without rehearsal, information in STM lasts only around 15 to 30 seconds before it fades. The coding in STM is primarily acoustic — we tend to hold information as sounds in our head, even when we read written words silently.
Peterson & Peterson (1959) is the AQA named study for STM duration. Aim — to investigate the duration of STM without rehearsal. Method — participants were given a consonant trigram (e.g. CHJ) and immediately required to count backwards in threes from a given number to prevent rehearsal; recall was tested after intervals of 3, 6, 9, 12, 15 or 18 seconds. Results — recall fell sharply with time; after 18 seconds, recall dropped to approximately 5% of items. Conclusion — without rehearsal, STM duration is approximately 18–30 seconds.
Rehearsal is the key mechanism for transferring information from STM to long-term memory. By repeating or thinking about information, you keep it active in STM and eventually strengthen it enough to be stored long-term. Without rehearsal, information in STM decays and is lost. This is why repeating a phone number to yourself works — until you stop rehearsing, it stays available.
Long-Term Memory
Long-term memory (LTM) is the relatively permanent store for information that has passed through STM. Its capacity is thought to be essentially unlimited — there is no known upper bound on how much LTM can hold. Duration can be extremely long; people retain memories for their entire lifetime. The coding in LTM is primarily semantic — information is stored in terms of its meaning rather than its sound or appearance.
STM codes mainly acoustically, holds about 7 items (±2), and lasts up to around 30 seconds without rehearsal. LTM codes mainly semantically, has potentially unlimited capacity, and can last a lifetime.
A strength of the multi-store model is that it is supported by research. For example, Murdock’s serial position curve study (covered in the next lesson) provides evidence for the distinction between STM (recency effect) and LTM (primacy effect). The model also generates clear, testable predictions about coding, capacity and duration.
A weakness is that the model may be oversimplified. It treats STM and LTM as single, unitary stores, but later research suggests both are more complex. For instance, long-term memory is divided into episodic, semantic and procedural memory (as you saw in Lesson 1). The model also suggests rehearsal is the only route to LTM, but we know that emotionally significant events can enter LTM even without deliberate rehearsal.
How Information Moves Between Stores
Understanding the flow of information through the multi-store model is as important as knowing the features of each store. Information first reaches the sensory register automatically and simultaneously from all active sense organs. At any given moment, your sensory register holds a vast amount of information — every sound in the room, every patch of colour in your visual field, every sensation on your skin. Nearly all of this is never consciously attended to and fades within fractions of a second.
The gateway between the sensory register and STM is attention. When you selectively attend to a piece of incoming sensory information — for example, you hear your name mentioned in a noisy room — it is transferred into STM and becomes available for conscious processing. Everything else in the sensory register is lost without ever being consciously registered.
Once information is in STM, rehearsal determines whether it passes into LTM. Maintenance rehearsal — simply repeating information — keeps it circulating in STM. With sufficient repetition, the trace is strengthened enough to be stored in LTM as a more permanent memory. Without rehearsal, STM traces decay within about 30 seconds and are gone. This explains why you can forget a phone number almost immediately if you are interrupted before you dial it.
Not all information enters LTM only through deliberate rehearsal. Elaborative rehearsal — thinking deeply about meaning and linking new information to what you already know — is more effective than simple repetition. Emotionally significant events can also bypass ordinary rehearsal and enter LTM rapidly, which is why flashbulb memories (such as exactly where you were when you heard dramatic news) can be so vivid and lasting even without conscious rehearsal.