Key features of the multi-store model
- Proposed by Atkinson and Shiffrin in 1968.
- It arose from information being processed where memory is characterised as a flow of information through a system - the system is divided into stages.
- There are capacity and duration limitations at each stage.
- Transfer of information between stages may need re-coding.
- External stimuli first enter the sensory memory where they register for brief periods of time before decaying or being passed onto the short term store.
- STM contains a small amount of info. that is stored at any one time - usually encoded acoustically.
- Memory's in STM are fragile and can be lost within 30 seconds through displacement or decay, unless they are rehearsed.
- Info. that's been rehearsed will pass into LTM, where it can remain for a lifetime - altough loss can be from decay, retrieval failure or interference.
- Coding in LTM is assumed to be in terms of meaning i.e. semantic.
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- Holds memory in relatively unprocessed forms for fractions of a second after physical stimulus is no longer available.
- Baddeley - 1988 suggested: a function of SM is to allow information from successive eye-fixations to last for a long enough time to be integrated.
- Example:- when watching a film your conscious experience is of a continuous visual scene in which all action appears to be running smoothly.
- The film is being presented as rapid series of frozen images interspersed by fletting moments of darkness.
- To makes sense of it your sensory store holds the information from one frame of film to the next is presented.
- We are capable of storing visual images for brief periods - it is assumed that we have separate sensory stores for all the senses - including an echoic store for auditary info. - but it is the visual sensory store - iconic memory - which has been researched most.
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- Stores information for brief periods of time
- Atkinson and Shiffrin - 1968 see STM as a temporary storage depot for incoming information
- Baddeley - 1986 prefers to use 'working memory' as a term to indicate its dynamic, flexible aspects.
- Capacity - the amount of information that can be stored in STM at any one time.
- Duration - the length of time that information can be held in STM.
- Encoding - the way that sensory input is represented in STM - as images or sounds.
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Capacity of short-term memory
- STM has limited capacity - we can only hold a small number of items at any one time.
- One way of assessing capapcity of STM is by finding out how many digits you can repeat in correct order immediately affter hearing them - immediate digit span.
- A technique used by reading out a list of random digits and requiring the pts. to repeat them back in the correct order.
- They usually start in a list of three digits and steadily increase in length unitl they are impossible to recall in serial order.
- The sequence length at which the pts. is correct 50% of the time is defined as their digit span.
- Miller - 1956 most people have a digit span of 7±2 (Millers' magic number seven).
- 7±2 can hold for lists of digits, letters, words or larger 'chunks' of information.
- Chunking occurs when we combine individual letters or numbers into a larger meaningful unit.
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Baddeley et al. for Capacity of STM
- To see if people could remember more short words than long words in a serial recall test and so demonstrate that pronounciation time, rather than the number of items to be recalled, determines the capacity of short term memory.
- Reading speed of pts. measured, pts. presented with set of five words on a screen, words taken from one or two sets: a set of one syllable words or polysyballic words, pts. asked to write down five words in serial order immediately after presentation, recalled several lists of both short and long words.
- Pts. could recall more short words than long words, they could recall as many words as they could articulate in 2 seconds, there was a strong positive correlation between reading speed and memory span.
- Immediate memory span represents the number of items of whatever length can be articulated in approximately 2 seceonds.
- Short words easier to recall than long words, importance of pronounciation over familiarity, Miller not able to account for memory span of nature of stimulus.
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Factors affecting the capacity of STM
- Influence of long-term memory - difficulties in using immediate digit span as a measure of STM capacity. It is difficult to exclude influence from LTM.
- Bower and Winzenz - 1969 digit strings are repeated withing a series of immediate memory span trials become progressively easier for pts. to recall.
- Information stored in LTM is helping to increase STM capacity temporarily.
- Reading aloud - if pts. read digits aloud before attempting to recall them, performance is better than when they simply read them without speaking - subvocally - to themselves.
- Rhythmic grouping - performance improves if the numbers are grouped together rhythmically. This is why we divide telephone numbers into rhythmic clusters.
- Pronounciation time - Schweikert and Boruff - 1986 tested immediate span for a number of different types of stimulus, letters, colours, shapes and nonsense words.
- They found people consistently remembered as many items as they were able to pronounce in 1.5-2 seconds.
- Naveh-Benjamin and Ayres -1986 tested memory span for speakers around the world, they found digit span for native English speakers is greater than Arabic speakers.
- This might be due to Arabic numbers taking longer to pronouce than English numbers.
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Peterson and Peterson for duration of STM
- STM has a brief duration due to its nature of capacity, as it is a temporary store longer term memorys are transferred to LTM. The Brown-Peterson technique is used by Peterson and Peterson - 1959:-
- To test how long STM lasts when rehearsal is prevented.
- Pts. briefly shown consonant trigram, asked to count backwards in threes from specified number to stop rehearsal of letters, after intervals of 3, 6, 9, 12, 15 or 18 seconds, pts. asked to recall original trigram, procedure repeated several times with different trigrams.
- Pts. able to recall 80% of trigrams after 3 second interval, progressively fewer trigrams were recalled as time intervals lengthened, after 18 seconds fewer than 10% of trigrams were recalled correctly.
- Fewer trigrams correctly recalled as the interval between learning and recall increased.
- Trigrams are artificial things to remember and may not reflect everyday memory, interference from earlier trigrams caused poor recall, experimental method allows us to see the effect of time passing on recall.
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Strengths of the multi-store model
- It can distinguish between short-term and long-term stores of capacity, duration and encoding.
- Evidence in support of the distinction between STM and LTM comes from case studies of people with brain damage that has given rise to memory impairment
- Brain damage and memory - Milner 1965
- Studied a young man left with sever memory impairment after brain surgery. Able to talk normally and recall acurrately events and people from his life before surgery and his digit span within normal limits. He was unable to retain new information and could not lay down new memory's in LTM. This lends to support the multi-store model by pointing out a clear distinction between STM and LTM.
- Evidence for existence of separate stores comes from laboratory experiments which investigated primacy and recency effects.
- Demonstrated when people are presented with a list of 20 words, one at a time, and asked to immediately recall the words in any order.
- Words at the beginning are easily recalled - Primacy.
- Words at the end are also recalled - Recency.
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Weaknesses of the multi-store model
- It is too simplistic and inflexible to explain entire memory system. It fails to take account of factors such as strategies people employ to remember things - it puts emphasis on the amount of information that can be processed rather than its nature. Some things are easier to remember than others.
- It is criticized for focusing on structure of memory system at expense of adequately explaining the processes involved.
- Visual stimuli registering in sensory memory must be changed to an acoustic code for STM. In order to translate letter 'M' into sound 'em' individual needs access to knowledge about letter shapes and sounds - stored in LTM. This means info must flow backwards through system to re-coding stage prior to STM. Suggesting flow of inforomation through system is interactive rather than sequential.
- Suggestion of route rehearsal is only means of transfer from STM to LTM has been crtiticised - rehearsal may be important for storing some information in LTM but people acquire new knowledge continually without need for rehearsal.
- The Working Memory Model casts doubt on assumption of Atkinson and Shiffrin that STM is a unitary store with limited capacity.
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Evidence in support of the multi-store model
- Conducted by Glanzer and Cunitz in 1966 to see if they could find evidence for the existence of separate short-term and long-term memory stores.
- Pts. presented with list of words, one at a time, asked to recall words in any order (free recall) - divided into two groups:- Immediate recall group and Delayed recall group.
- Immediate recall group remembered first and last words best, delayed recall group (recalled words after 30 second count) remembered words from beginning of the list best. Both groups had difficulty in remembering words in the middle of the list.
- Both groups easily remembered words at beginning of list as they were stored in LTM, words at end of list still in STM. When recall was delayed pts. unable to rehearse words in STM consequently they were not maintained in STM or passed into LTM so were forgotten. These findings support separate memory stores by showing delayed recall interfered with STM store and caused recency effect to disappear but had no effect on LTM store and left primacy effect almost unaltered.
- Crowder - 1993 interpreted this differently - recency effects occur because most recent items are most distinctive not because they're held in a separate STM store.
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Factors affecting the duration of STM
- Maintenance rehearsal - Items only disappear from STM when rehearsal is prevented. New items can can take their place if existing items move on - either to LTM or decay. If we want to remember something for a short period we repeat it to ourselves - repetition serves as a method of continually reinserting the info. into STM there-by strengthening the memory.
- Deliberate intention to recall - Sebrechts - 1989 briefly presented pts. with a list of three common English nouns and gave them an unexpected test where they recalled the words in correct order. Correct recall of the items fell to 1% after 4 seconds - this demonstrates that info. can vanish from STM in a matter of seconds if people do not make a conscious effort to retain it.
- Amount of info. to be retained - Murdock - 1961 presented pts. with either a three letter words or three unrelated words, he then followed the Brown-Peterson technique, forgetting three unrelated words was the same as the consonant trigrams in Peterson and Peterson - the three letter word was resistant to forgetting and accurate recall level was still 90% after 18 seconds. Millers digit span with the important factor is the number of chunks to be remembered rather than the individual items.
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