Multi-Store Model (Atkinson and Shiffrin, 1968)
The multi-store model is a classic model of memory. It is sometimes called the modal model or the dual process model.
Atkinson and Shiffrin (1968) suggest that memory is made up of a series of stores (see below)
The multi-store model (Atkinson and Shiffrin 1968) describes memory in terms of information flowing through a system.
Information is detected by the sense organs and enters the sensory memory (SIS).
If attended to this information enters the short-term memory (STM).
Information from the STM is transferred to the long-term memory (LTM) only if that information is rehearsed.
If rehearsal does not occur, then information is forgotten, lost from STM through the processes of displacement or decay.
Sensory Memory (SIS)
The multi-store model states that there is a separate store for each of the sensory modalities (vision, hearing, touch etc.). Most research has concentrated on visual and auditory modalities, the iconic and echoic stores respectively.
The sensory stores act as a temporary buffer store holding information from the environment very briefly in a relatively raw, unprocessed state and is modality specific (i.e. information is held in the form in which it is received, be it visual, auditory, tactile or olfactory). Some of this information is attended to and is transferred to short term memory.
Short Term Memory (STM)
STM has three key aspects:
1. limited capacity (only about 7 items can be stored at a time)
2. limited duration (storage is very fragile and information can be lost with distraction or passage of time)
3. encoding (primarily acoustic, even translating visual information into sounds).
There are two ways in which capacity is tested, one being span, the other being recency effect.
Miller’s (1956) Magic number 7 (plus or minus two) provides evidence for the capacity of STM. Most adults can store between 5 and 9 items in their short-term memory. This idea was put forward by Miller (1956) and he called it the magic number 7. He though that short-term memory could hold 7 (plus or minus 2 items) because it only had a certain number of “slots” in which items could be stored. However, Miller didn’t specify the amount of information that can be held in each slot. Indeed, if we can “chunk” information together we can store a lot more information in our short-term memory. Miller’s theory is supported by evidence from various studies, such as Jacobs (1887). He used the digit span test with every letter in the alphabet and numbers apart from “w” and “7” because they had two syllables. He found out that people find it easier to recall numbers rather than letters. The average span for letters was 7.3 and for numbers it was 9.3.
Duration seems to be between 15 and 30 seconds, according to Atkinson and Shiffrin (1971). Items can be kept in STS by repeating them verbally (acoustic encoding), a process known as rehearsal. Using a technique called the Brown-Peterson technique which prevents the possibility of retrieval by
having participants count backwards in 3s, Brown and Peterson (1959) showed that the longer the delay, the less information is recalled. The rapid loss of information from memory when rehearsal is prevented is taken as an indication of short term memory having a limited duration.
Long Term Memory (LTM)
Theoretically, the capacity of LTM could be unlimited, the main constraint on recall being accessibility rather than availability. Duration might be a few minutes or a lifetime. Suggested encoding modes are semantic (meaning) and visual (pictorial) in the main but can be acoustic also.
Bahrick et al (1975) investigated what they called very long term memory (VLTM). Nearly 400 participants aged 17 – 74 were tested. There were various tests including: A free recall test, where participants tried to remember names of people in a graduate class. A photo recognition test, consisting of 50 pictures. A name recognition test for ex-school friends. Participants who were tested within 15 years of graduation were about 90% accurate in identifying names and faces. After 48 years they were accurate 80% for verbal and 70% visual. Free recall was worse. After 15 years it was 60% and after 48 years it was 30% accurate.
Key Characteristics of SIS
• Duration: ¼ to ½ second
• Capacity: all sensory experience (v. larger capacity)
• Encoding: sense specific (e.g. different stores for each sense)
Key Characteristics of STM
• Duration: 0-18 seconds
• Capacity: 7 +/- 2 items
• Encoding: mainly auditory
Key Characteristics of LTM
• Duration: Unlimited
• Capacity: Unlimited
• Encoding: Mainly Semantic (but can be visual and auditory)
Empirical Evidence for Separate Long and Short-Term Stores
Some of the strongest evidence for the multi-store model comes from serial position effect studies and studies of brain damaged patients.
Experiments show that when participants are presented with a list of words, they tend to remember the first few and last few words and are more likely to forget those in the middle of the list. This is known as the serial position effect (see fig.2). The tendency to recall earlier words is called the primary effect; the tendency to recall the later words is called the recency effect.
Murdock (1962) asked participants to learn a list of words that varied in length from 10 to 30 words and free recall them. Each word was presented for one to two seconds. He found that words presented either early in the list or at the end were more often recalled, but the ones in the middle were more often forgotten.
Murdock suggested that words early in the list were put into LTM (primacy effect) because the person has time to rehearse the word, and words from the end went into STM (recency effect). Words in the middle of the list had been there too long to be held in STM (due to displacement) and not long enough to be put into LTM. In a nutshell, when participants remember primary and recent information, it is thought that they are recalling information from two separate stores (STM and LTM).
