multi-store model of memory and types of long term memory

Duration of STM

About 18 seconds

Duration of LTM

A few minutes to a lifetime

Capacity of STM

7 ± 2 chunks

Capacity of LTM

Limitless

Type of coding for STM

Acoustic (sound)

Type of coding for LTM

Semantic (meaning)How do we know STM is acoustic

How do we know STM is acoustic

Conrad (1964) demonstrated that STM uses acoustic coding by finding that rhyming letters were harder to remember than non rhyming letters. Similar effects with rhyming and non rhyming words.

What test was used to work out STM capacity

Immediate digit span test

Immediate digit span test

List of random digits is read out to participants and they have to repeat them straight back in the correct order. The sequence length at which they are correct 50% of the time is the digit span. Miller (1956) claimed this was 7±2 items for lists of digits, letters, words or larger chunks of information.

Chunking

Occurs web we combine individual letters etc into a larger meaningful unit. This means more information can be remembered, but the amount of chunks remembered is still 7±2.

What test was used to work out STM duration

Consonant trigram experiment

Consonant trigram experiment

Peterson and Peterson (1959) carried out the consonant trigram experiment. They asked participants to remember a single nonsense syllable of 3 consonants. Participants were then given an interference task to stop them rehearsing the trigram (counting back in 3s from a random number). Participants to were asked to recall the trigrams after different times (3,6,9,12,15 or 18 seconds). While recall was good after 3 seconds (about 80%) only 10% were remembered after 18 seconds.How do we know LTM acoustic

How do we know LTM acoustic

Barely (1966) gave participants a list of words to remember and found that when recall was tested after 20 minutes, the recall of lists containing words of similar meanings were more difficult to recall than words of non-similar meanings. These semantic confusing errors suggest that coding in LTM is by meaning

Capacity of LTM

Enormous but impossible to measure

American yearbook study

Bahrick (1975). An opportunity sample of 392 American ex-high school students aged rom 17-74 years was used. They were tested in a number of ways:

• Free recall of the names of as many of their former classmates as possible

• A photo recognition test where they were asked to identify former classmates in a set of 50 photos, only some of which were their classmates

• A name recognition test

• A name and photo match test

Participants accuracy was assessed by comparing responses with high school yearbooks

Findings of the American yearbook study

90%accuracy in face and name recognition was found, even in the participants who has left high school 34 years previously. After 48 years this declined to 80% for name recognition and 40% for face recognition. Free recall was less accurate: 60% accurate after 15 years and only 30% accurate after 48 years

Conclusion of the American yearbook study

Classmates are rarely forgotten when recognition clues are given therefore LTM cab have a very long duration

Sensory memory duration

Less than ½ a second

Sensory memory capacity

Very large as the sensory register receives information form all senses

Sensory register

External information from the environment first enters the sensory register where it can be stored very briefly before decaying or being passed to the STM. There are different sensory memory stores for different senses. visual information enters iconic memory and sound based information enters echoing memory. Although the capacity of the sensory register is very large, information can only be held in it for about ½ a second

Multi-store model: STM

If a persons attention is focused on one of the sensory stores, then the information will be transferred to STM which only contains the information that is actively active at any one time. Information is STM is stored via acoustic code. STM has very limited capacity (7±2). Therefore, information can be lost very easily due to being pushed out by new information. Memory traces in STM are fragile and can be lost within about 30 seconds if they’re not rehearsed

Multi-store model: LTM

Material that is rehearsed is passed onto the LTM where its stored semantically and it can remain there for a lifetime. Capacity of the LTM is impossible to measure, however the loss of information is possible through the process of forgetting.

multistore model evaluation summary

• free recall experiments

• primary and recency effects can be manipulated independently

• supporting evidence

• use artificial tasks

• HM case study

• KF case study

• rehearsal

multistore model evaluation - free recall experiments

Participants are given 20 words in succession to remember and are asked to recall them in any order. The results fall into a pattern known as the serial position curve - shows the existence of 2 separate memory stores

primacy effect - Participants tend to recall first words in the list indicating that these words entered STM and had time to be rehearsed and passed to LTM. This effect therefore reflects recall from LTM

asymptote - middle portion of the list is remembered poorly. The increasing number of words fill STM and therefore the words in the middle of the list can no longer be rehearsed

recency effect - participants recall the last items on the list which are still stored in STM. If recall of the list is immediate, these words have not had time to be forgotten

the primary and recency effects show the existence of 2 separate memory stores as the model suggests

multistore model evaluation - primary and recency effects can be manipulated independently

Further evidence for the two stores comes from the fact that the primacy and recency effect can be manipulated independently:

Presenting the words more slowly improves primacy effect (as there is more time to rehearse each word before the next one is presented)

The recency effect disappears if the last words of the list are not recalled straight away e.g. by giving an interference task lasting at least 30 secs. This is because too much time has passed for the words still to be in STM. This further evidence strengthens support for the MSM

multistore model evaluation - supporting evidence

Another strength of the MSM is that much of the supporting evidence comes from lab experiments such as the immediate digit span test (capacity of STM) or the Trigram study (duration of STM). These experiments enabled high control of extraneous variables e.g. having an interference task to stop rehearsal, therefore allowing cause and effect to be inferred. This means that the studies provide valid support for the MSM.

multistore model evaluation - artificial tasks

However, a problem with the lab experiments used to support the MSM is that they use very artificial tasks such as asking Ps to remember a string of letters This is not reflective of how we use our memory in real life meaning that the studies lack ecological validity and results will not generalise to real life situations. Therefore, if there are issues with the supporting studies they may not be valid supporting evidence for the MSM.

multistore model evaluation - HM case study

Case of HM: Milner showed that HM had normal STM but greatly impaired LTM suggesting that the memory stores are separate as the MSM claims.

However, although HM cannot learn any new facts or events, research shows that he is capable of learning new skills e.g. mirror drawing (see later info on types of LTM). This suggests LTM is not just one store, instead there are different types of LTM, for example memory for skills (procedural memory) and memory for events & facts (episodic memory). The model does not consider that LTM may not be a single store, therefore the MSM oversimplifies the MSM memory.

multistore model evaluation - KF case study

Case study of KF: Shallice & Warrington (1970) reported that KF had a greatly impaired immediate digit span of only 2 items (shows very small capacity of

STM) but his LTM was normal. This again suggests that the memory stores are separate as the MSM claims.

However, upon further inspection KF does not support the model because his case study does not explain how information can be passed onto LTM if there are problems with his STM. (The model clearly states that the flow of direction must be through STM to LTM).

multistore model evaluation - rehearsal

Another weakness of the MSM is that the idea of rehearsal being the mechanism of transferring information from STM to LTM has been criticised. This is because we do not repeat everything that gets transferred into LTM (e.g. what we ate for breakfast) or transfer everything we repeat (e.g. revision notes). The model therefore does not explain why some things are remembered and others things are forgotten and rote rehearsal cannot be the only way information is passed to LTM.

In contrast, Craik & Lockhart developed the levels of processing model (LOP) which can explain this. They argued that info that is processed more deeply is remembered better. So if we process something in terms of its meaning (deep processing) then we remember it better than information that has only been processed in terms of its physical features (shallow processing). Therefore, it is the type of processing that affects our memory, not simply rehearsal.

Episodic memory

Explicit memory

an event or group of events. Memories of personal experiences. Have three elements:

• details of the event

• context

  • emotion

semantic memory

Explicit memory

Information about the world that is linked to particular personal events; it is shared memories for facts and knowledge. - social customs, mathematic events etc. May start off as episodic memories because we acquire knowledge based on personal experiences but the memory may slowly lose its association to particular events and become a semantic memory.

Procedural memory

Implicit memory

Skilled based memory - knowing how to ride a bike, hoe to tie a shoelace, how to read. About remembering how to do something; they are usually acquired through repetition and practice. Different from episodic and semantic memories in that they are implicit'; we are less aware of these memories because they have become more automatic

Explicit memory

fact-based memory which can be consciously retrived

Implicit memory

Memories we are not consciously aware of

types of long term memory evaluation summary

• brain scans

• HM case study

• Clive Wearing case study

• research method

• supporting evidence

types of long term memory evaluation - brain scans

Research shows that different areas of the brain are active when the different kinds of LTM are used. Brain scans studies get participants to perform various memory tasks while their brains are scanned. These studies show that episodic memory is associated with the hippocampus and temporal lobe, semantic memory uses the temporal lobe, and procedural memory uses the cerebellum and motor cortex (as both of these are associated with motor skills). Therefore, as there is a difference in where each type of LTM is stored in the brain this supports that there are different types of LTM.

types of long term memory evaluation - HM case study

HM had an operation to reduce his epileptic fits which removed the hippocampus from both sides of the brain; this also destroyed part of his temporal lobes. HM could not form episodic or semantic memories because his hippocampus and temporal lobes had been removed. But he could still form procedural memories,

Milner (1962) found HM could learn new procedural skills (but he didn't know he had learnt them) e.g. mirror drawing - Milner found error and time scores on the mirror drawing task decreased over 3 days of

training. First day, first attempt = 30 errors but 3rd day, first attempt

= 1 error.

types of long term memory evaluation - Clive Wearing case study

CW suffered from an infection which damaged the hippocampus and temporal lobe region of the brain. After this he was unable to remember episodes in his life, for example if his wife left the room and re-entered he would greet her as if he hadn't seen her. However, CW can still play the piano, a procedural memory. as his cerebellum was intact.

types of long term memory evaluation - research method

Each individual case study has unique characteristics; therefore, it may not be possible to generalise the conclusions from a single case study like HMs/CWs to the rest of the population.

types of long term memory evaluation - supporting evidence

Researchers have found that some patients with Alzheimer's disease have the ability to form new semantic memories but not episodic memories. Therefore, suggesting these two types of explicit memory are separate. However, others have argued that this is not sufficient evidence that the two are distinct types of memory. Instead it could be that they are stored together in one LTM store, but episodic memories place greater demands on mental processing which is why they are more affected by brain damage.