Models of memory
1. (a) The multi-store model, including the concepts of encoding, capacity and duration.
(b) Strengths and weaknesses of the model.
2. The working memory model, including its strengths and weaknesses
3. Memory in everyday life:
(a) Eyewitness testimony (EWT) and factors affecting the accuracy of EWT, including anxiety, age of witness
(b) Misleading information and the use of the cognitive interview
(c) Strategies for memory improvement
Try this interactive memory test first.
Now work through the following powerpoint slides, kindly provided by Sabah Bandoui
The Basic Structure of Memory
Memory is generally thought to be made up of three parts:
1. Sensory Register (your senses).
2. Short-term memory.
3. Long-term memory.
Both short-term memory (STM) and Long-term memory (LTM) are studied in terms of their ability to encode (make sense of) information, capacity (how much information) and duration (how long information can be stored).
By way of a short introduction to this topic take a look at the following BBC video resources from the One Show.
Click on the following resource for access to BBC Radio 4’s In our Time series podcast.
Encoding in short term memory
Conrad (1964) suggested that short-term memory codes all information acoustically, that is, according to sound. Visual information is encoded (transformed) to its acoustic (sound/language) codes.
Participants were presented with a list of consonants.
For example: P J N R Z D for about 3⁄4 of a second.
Participants were then asked to recall what they had seen.
Conrad found that errors of recall were linked to letters which had a similar sound.
Bs were mistaken for Ps 62 times, Vs were mistaken for Ps 83 times but Ss were mistaken for Ps only 2 times. This suggests that visually presented information is encoded according to acoustics/sounds. Conrad referred to these errors as acoustic confusion or substitution errors
Shulman (1970) disagreed and thought that short-term memory also coded information visually and according to semantics (meaning).
This research suggests that Conrad was incorrect in proposing that all encoding in short term memory was acoustic.
Shulman presented participants visually with lists of 10 words. Recall was then tested using cue or probe words which were one of three types.
Firstly, some of the probe words used were homonyms (words which sound the same but have different meanings, for example: ball and bawl).
Secondly, some probe words were synonyms (different words with same/similar meaning, for example: talk and speak).
Thirdly some of the probe words used were identical to the ones on the original stimulus list.
Similar numbers of errors of recall from the stimulus list was made for homonym and synonym probes. This suggests that the semantic encoding (meaning) as well as acoustic encoding occurs in the short term memory.
Heyer and Barrett (1974) suggested that visual images that are difficult to acoustically code may also be stored briefly in short term memory.
Both the Conrad and Shulman research were laboratory experiments. They therefore lack ecological validity due to controlled artificial environments. Participants were undergraduate students and therefore unrepresentative of the general population. They may have exhibited demand characteristics and experimenter bias may have occurred as the experiment did not employ blind conditions.
The results may also have been influenced by individual differences or participant variables. The research has good reliability.
Capacity of short term memory
Capacity refers to the amount of information that can be stored in the short-term memory.
Miller (1956) suggested that most people store about seven independent or discrete items in short term memory. These items may be numbers, letters or words etc. Miller referred to each of these items as chunks.
For example: 7 6 5 4 3 2 1 = Seven discrete chunks
Miller further suggested that the capacity of the short term memory may be enlarged by grouping items together by associations/links they have with each other.
Eg; 1+1 2+2 3+3 4+4 5+5 6+6 7+7 = Seven discrete chunks but combined according to same numbers therefore increasing capacity of short term memory. Items are chunked according to the meanings they have in long-term memory.
Miller therefore suggested that about seven chunks of information may be stored in short term memory whether in single or combined forms give or take one or two chunks, “The magical number seven plus or minus two”____________ 7 +/- 2.
Research into capacity in short term memory Miller (1956)
Participants were given ‘sentences’ of varying lengths that approximated ‘true’ English. They were asked to recall words in the correct order given in the sentence.
The more sense the sentence made, in terms of grammar, the better the recall. This suggests that the semantic (meaning) and grammatical structure, which is probably stored in LTM, is used to help increase amount of information stored in STM by combining items to create larger chunks. Participants still recalled about seven pieces of information.
Criticisms of this laboratory experiment include ecological validity, demand characteristics, experimenter bias, participant variables/individual differences. The experiment has good reliability, but the research is dated.
Research into capacity in short term memory Bower & Springton (1970)
Participants were presented with one of two letter sequences. The first sequence was made up of well-known groups of letters for example; mfi, plc, aeb. The second sequence contained the same letters but not in the well known order: imf, lcp, eba. The first sequence was better recalled suggesting that chunking according to meaning increases the capacity of the short-term memory.
Criticisms of this laboratory experiment are as above for Miller’s research.
Duration of short term memory
Brown & Peterson & Peterson (1959) devised a technique that prevents information from being continually repeated in the STM in order to test how long information will be retained. This continual repetition of information in order to hold on to it is referred to as Maintenance Rehearsal. Brown & Peterson suggested that the short-term memory can store information for approximately 15 to 30 seconds if maintenance rehearsal is prevented.
Reitman (1974) suggested that this short duration is due to displacement; as new information is coming into the short-term memory it is kicking out the previous information due to its limited capacity (7 +/- 2 chunks).
Peterson & Peterson suggest that information decays (fades away) rapidly in short term memory unless rehearsal of that information occurs.
Research into Duration in STM: The Brown-Peterson Technique (1959)
This illustrates what Brown & Peterson referred to as a Distractor Task or Interpolated Task and should have prevented you from rehearsing the information – the trigrams.
This experiment shows that in the absence of rehearsal the short-term memory can only hold on to information for about 15 to 30 seconds.
Brown & Peterson suggested that where information is continually rehearsed it can be stored in the short-term memory indefinitely but is lost as soon as interference blocks rehearsal.
Ever been given a telephone number and had to keep repeating it avoiding all distractions until you wrote it down to prevent forgetting it? Then you were experiencing Maintenance Rehearsal.
Brown & Peterson employed a laboratory experiment and therefore may be subject to the criticisms above.
Capacity in long term memory
Capacity (amount of information which may be stored) of the long-term memory is unknown. It is impossible to measure and may be limitless. The brains ability to store information is greater than the world’s most powerful computer memory.
Duration in long term memory
Information is thought to be stored permanently – for your entire lifetime. It is now thought possible that some memories may be genetically inherited and therefore last longer than a lifetime.
The issue with duration in long-term memory relates to recall and forgetting.
Encoding in LTM
Two types of encoding are thought to operate in LTM.
Research into semantic encoding in long term memory Baddeley (1966). Baddeley presented participants with four lists to remember:
List 1: man map can cap
List 2: try pig hut pen
List 3: great big huge wide
List 4: run easy tug end
Participants had to recall as many words as possible immediately after presentation of lists and then try again 20 minutes later
Baddeley found that the immediate recall was better for list 2 than for list 1 and with little difference in recall between lists 3 and 4.
List 1 contains similar sounding words and list 2 contains non-similar sounding words. When participants were then asked to recall words after twenty minutes they recalled list 4 better than list 3, list 4 contains words with non-similar meaning words and list 3 contains words with similar meanings.
There was little difference in recall for lists 1 and 2. This shows that the short-term memory tends to store information according to sounds rather than meaning and that the long-term memory tends to store information according to semantics (meaning) rather than simply sound.
Baddeley used a laboratory experiment and can therefore be criticised in terms of ecological validity, demand characteristics, participant variables/individual differences, experimenter bias and representativeness (Baddeley used undergraduate students as participants). Although it has good reliability.
The following table is a summary of what you have learnt about encoding, duration and capacity in the STM and LTM.
7 +/- 2 Chunks
The magical number seven plus or minus two
|Brown & Peterson suggest 15 to 30 seconds||Conrad suggested only acoustic process. Shulman suggested also visual and semantic processes.|
|Unknown and impossible to measure. Maybe limitless.||Relatively permanent. Relates to theories of recall and forgetting.||Declarative and/or Procedural. Declarative may be Semantic and/or Episodic (Tulving). Baddeley showed process was largely semantic.
Models of Memory
Akinson and Shiffrin suggested that memory was comprised of three separate stores, the Sensory Memory Store, the short-term memory and the long-term memory. Each store had a specific and relatively inflexible function.
Information is simply rehearsed in the STM and if rehearsed sufficiently is transferred to LTM. Information to be recalled from LTM passes back through STM producing the associated response. This model is represented below as a diagram.
The Multi-store Model
Evidence for Multi-store model:
1. Primacy-Recency Effect – Atkinson (1970). When presented with lists to remember we recall first and last items best. First items rehearsed into LTM and last items recalled from STM. Ones in middle less likely to be recalled. This is evidence for existence of several stores.
2. Brown –Peterson Technique suggests that if rehearsal of items is prevented then information does not enter LTM.
3. Amnesiacs caused by Korsakoffs Syndrome brought on by chronic alcoholism display sound STM functioning but impaired LTM. This suggests separate and distinct memory stores.
4. Shallice and Warrington (1970). Case study of K.F. who suffered brain damage because of motorbike accident. STM impaired but LTM intact.
Evidence against Multi-store Model:
1. De Groot (1966) showed how expert chess players had phenomenal STM for chess positions as long as they fitted in with known rules. When pieces were randomly arranged their recall was no better than non-chess players therefore STM and LTM may not be so separate and distinct.
2. The working memory model suggests that the short term store is active, dynamic and complex, rather than simple, passive and unitary.
Multi-store model is basic and limited in explaining such a complex phenomena as memory.
Working Memory – Baddeley & Hitch (1974)
An alternative to the Multi-store Model. Emphasises workings of STM. It is a far more complex explanation of STM.
Rather than the STM being a single inflexible store, Baddeley and Hitch suggested that the STM was made up of several subsystems, each having a specialised function.
They suggested that these subsystems were involved in complex cognitions/thought processes, including analysis and judgements about information input.
Baddeley and Hitch (1974) provide evidence for this by people being able to carry out more than one task at once where both tasks involve STM functions.
Therefore the STM is more complex and may have several subsystems that can operate simultaneously.
Baddeley & Hitch suggested the existence of several subsystems in STM but they studied the possibility of two in particular which were governed by a central controlling mechanism which they termed the Central Executive .
This fat controller is the boss and supervises and coordinates the other subsidiary systems. The central executive decides which information is attended to and which parts of the working memory to send that information to be dealt with.
The two subsystems studied were named the Visuo-spatial Sketchpad and the Phonological/Articulatory Loop.
The Visuo-spatial Sketchpad deals with what information looks like and how it is laid out – it deals with visual and spatial information.
The Phonological Loop holds spoken information for about 1.5 to 2 seconds. Written words must be converted to spoken words to enter phonological loop. The Articulatory loop rehearses the spoken/acoustic information from the phonological store and also converts written material to acoustic material so that the phonological loop can deal with it.
There is little empirical evidence to support the Working memory Model but the recognition of the complexity of the STM makes sound theoretical sense. However some brain damaged patients appear to suffer impairment to some functions of STM and not others (Shallice & Warrington, 1974) therefore suggesting existence of several specialised systems within STM.
Forgetting in Short-Term Memory
Decay in STM
Trace decay theory in STM relates to theories of Duration in STM. The theory suggests STM can only hold information for between 15 and 30 seconds unless it is rehearsed Brown & Peterson (1959). After this time the information Decays (fades away). Waugh & Norman (1965) used the Serial Probe Technique to test the theory.
Displacement in STM
The idea of displacement in STM causing forgetting relates to the Capacity of STM as proposed by Miller (1956). It simply suggests that if the capacity of STM is limited to 7 plus or minus 2 items or chunks of information then STM is full then some of that information must be kicked out or displaced in order for new information to enter.
Retrieval Failure in LTM
This theory suggests that all information received is stored in LTM but that some information is difficult or impossible to access.
This idea is characterised by the Tip-of-the-Tongue Effect (TOT) where we know something but just cannot recall it. Retrieval of such information is thought to be dependent on three factors:
1. Firstly Context-Dependent Retrieval which suggests that recall of information depends on replicating the situation or context in which that information was originally encoded.
Godden & Baddeley (1975) provided evidence for this by asking participants to learn a list of words either on land or 15 ft underwater. They were better able to recall words if asked to do so in the setting in which they originally learnt them.
2. Secondly, State-Dependent Retrieval suggests that recall is improved if the individual is in the same physical and/or psychological state as when they first learnt the information.
Godwin (1969) investigated the effect of alcohol on recall and found individuals were better able to recall information learnt when drunk if they were drunk. Other drugs seem to affect memory similarly. Bower (1981) however found that the same principle applied to mood did not have such a convincing effect but only a tendency to produce State-Dependent Retrieval.
3. Thirdly, recall may be by the presence of cues or probes, clues or associations. This is referred to as Cue-Dependent Retrieval, Tulving & Pearlstone (1966).
Interference in LTM
This idea suggests that information in LTM may become confused or combined with other information during encoding thus distorting or disrupting memories.
Interference in LTM is thought to be either proactive where old memories disrupt new memories or retroactive where new memories disrupt old memories. Both Proactive and Retroactive Interference is thought to be more likely to occur where the memories are similar, for example: confusing old and new telephone numbers.
McGeoch (1932) tested these ideas using laboratory experiments involving lists of single words or binary associations. The findings therefore can be criticised for their ecological validity including demand characteristics and representativeness thus making generalisations impossible.
Flashbulb memories involve the vivid recall of what individuals were doing when a major event occurred. This event may be a public or a private occurrence.
Is the memory vivid and distinct in time?
Brown & Kulik (1977) asked people a series of questions about 10 major events. Participants remembered where they were, what they were doing and the emotional impact it had. These memories may be seen as ‘special’ and are thought to involve special brain mechanisms.
Rubin & Kozin (1984) showed that flashbulb memories are particularly powerful for personal events, such as love at first sight.
McCloskey (1988) suggested that flashbulb memories are as prone to forgetting as ordinary memories. Bohannon (1988) suggested that flashbulb memories are not prone to forgetting when the event produced strong emotional reactions.