Models of memory

Created by Atkinson and Shiffrin (1968)

The model proposes that here are three stores of memory - SR, LTM and STM, and info has to move through them to become a memory.

Info from our environment initially goes into the SR. Most of it is forgotten rapidly. However, if you pay attention to it, or think about it, the info passes into STM.

STM has a small capacity and duration. But if info is processed further then it can be transferred to LTM. 

The Primacy Effect - reseach shows that participants are able to recall the first few items of a list better than those from the middle. The MSM explains this because the earlier items will have been rehearsed better and transferred to LTM. If rehersal is prevented by an interference task, the effect dissapears.

The Recency Effect - Participants tend to remember the last few items better than those from the middle of the list. As STM has a capacity of around 7 items, the words in the middle of the list, if not rehearsed, are displaces from STM by the last few words heard. These last words are sill in STM at the end of the experiment and can be remembered.

People with Korsakoff's Syndrome provide support for the model. They can recall the last few items in a list, suggesting an unaffected STM. However, their LTM is very poor. This supports the model by showing that STM and LTM are different stores. 

Milner et al (1957) carried out a case study into a patient called HM who suffered from severe & frequent epilepsy. Siezures were based in the hippocampus. Doctors decised to remove part of the brain around this area. Operation reduced his epilepsy, but led him to memory loss. He could sill form short-term memories, but was unable to form new LTM. This supports the idea of seperate stores for STM and LTM.

In the model, info is transferred from the STM to the LTM through rehearsal. But in real life people don't always spend time rehearsing, yet they still transfer info into the LTM. Rehearsal is not always needed for info to be stored and some items can't be rehearsed.

The model is oversimplified. It assumes there is only one LTM store and one STM store. This has been disproved by evidence from brain damaged patients, suggesting several different STM stores, and other evdence suggesting different LTM stores.

Developed by Baddeley and Hitch (1974)

The model proposes that STM is an active processor which contains several differetn stores.

The centeral executive is a key compound and can be descried as attention. It has a limited capacity and controls 'slave' systems that also have limited capacity:

• The phonological loop holds speech based info - it's made up of a phonological store and an articulatory process.
• The visuo-spatial sketchpad deals with the tempoary storage of visual and spatial info.
• The episodic buffer briefly stores info from the other subsystems and intergrates it together, along with info from LTM, to make complete scenes or episodes.

Baddeley and Hitch based their models on results from studies that used 'interference tasks'

If participants are asked to perform two tasks simultaniously that use the same system, their performance will be affected - e.g. saying 'the the the' while silently reading something is hard.

According to the working model, both these tasks use the phonological loop. This has to limited capacity, so it can't cope with both tasks. Performance on one, or both tasks will be affected.

However, if the two tasks involve different systems, performance isn't affected on either task - e.g. saying 'the the the' whilst tracking a moving object.

Shallice and Warrington (1974) - Did a case study on patient KF who was brain damages and had impared STM. His problem was immediate recall of words presented verbally, but not with visual information. Suggested that he had an impared articulatory loop, but an intact visuo-spatial sketchpad, therefore providing evidence for the WMM of STM.

Gathercole and Baddeley (1993) - Participants split into two groups. All of the participants had to carry out a task where they had to follow a moving spot of light - using the visuo-spatial sketchpad (VSS). At the same time, one group of participants also had to describe the angles on a letter - using the VSS. The other group were given a second task that would use the PL - verbal task while following the light. Gathervole & Baddeley found that performance was much better in the participants doing taskings which used seperate systems.

Psychologists have criticised it because:

• They didn't think that Baddeley & Hitch's idea of a central executive is simplistic and vague.
• The model only explains how information is dealth with in the STM. It doesn't explain how it's transferred to LTM.
• Much of the research which supports it has been lab studies. Reduces ecological validity of the evidence, as highly controlled studies might not be representative of what happens in the real world.