The working memory model

Baddeley and Hitcg (1974) used the term 'working memory' to refer to the part of memory you use when doing a complex task which requires you to store information as you go along. 

There are 4 components in the working memory model. 1. Central executive. 2. Phonological loop. 3. Visuo-Spatial sketchpad. 4. Episodic buffer. 

Central executive
The function of the central executive is to direct attention to particular tasks. The central executive sends information from its store to the 3 slave systems it controls. It has very limited capacity, so it can't attend to too many things at one time. 

Phonological loop.
The phonological loop is a slave system of the central executive which encodes speech sounds in working memory, it usually involves maintenance rehearsal. It also has limited capacity. There are 2 parts to the phonological loop, the phonological store and the articulatory process. The store holds words you hear like an inner ear, and the articulatory process is used for words you heard or seen like an inner voice.

Visuo-spatial sketchpad
The visuo-spatial sketchpad encodes visual information in terms of seperate objects as well as the arrangement in one's visual field. Visual and/or spatial information is temporarily stored in here. Visual information is what things look like. Spatial information is the relationship between things. It can be divided into a visual cache (store) and inner scribe which deals with spatial relations.

Episodic buffer
The episodic buffer is the general store. It recieves input from many sources, temporatily stores this infomrtion and then intergrates it in order to construct a mental episode of what is being experienced right now. The phonlogical loop and visuo-spatial sketchpad deal with processing and temporart storage of specific kinds of information. The central executive has no storage capacity. The episodic buffer is an extra storage system.

The episodic bufffer intergrates information from the cetnral executive, the phonological loop, the visuo-spatial sketchpad and also forms long term memory. 

Evidence from brain-damaged patients.
The case study of KF showed that the STM works independently of LTM, as he had no problem with long-term learning but some aspects of his immediate memory were impaired. His short-term forgetting of auditory information was much greaer than that of visual stiumuli, and his auditory oribkems were limited in respect of verbal material such as letters and digits but not meaningful sounds. Therefore showing that his brain damage seemed to be restricting to the phonological loop.

Evidence for the cenral executive
Bunge et al (2000) used fMRI to see which parts of the brain were most active when participants were doing 2 tasks. The same brain arease were active in either dual- or single- task conditions but there was significantly more activation in dual-task condition indicating that increased attential demands were refelected in brain activity.  

Making comparisons with the multi-store model
The WMM offers a better acount than the STM component of the MSN. This is because it moves from describing imediate memory as a unitary store to one with a number of components. 

In comparision with the MSM, the WMM includes verbal maintenance as rehearsal as an optional process rather than the only means by which information is kept in immediate memory. The WMM also emphasises process more than MSN, which emphasised structure, 

The WMM suggests that immediate memory holds the most recently activated portion of long-term memorym rather than portrating short-term memory as a way station on the way to and from long-term memory. WM moves the activated elements in and out of brief, temporary storage. 

The central executive
Some psychologists feel that the explaination of the central executive "Directs attention and allocates information to slave system" is too vague and doesn't explain anything. Critics also feel that the notion of a single central executive is wrong and that there are probably several components.
Patient EVR had a cerebal tumour removed. He performed well on tests requiring reasoning which suggested that his central executive was intact, however he had poor decision-making which suggest his central executive was not wholly intact. 
In summary the account offered of the central executive is un satisfactory and because it is probably more complex than currently represented.

Evidence from brain-damaged patients
Most of the key evidence for the WMM are from case studies of people who suffered brain damage. Using this evidence will not allow comparisions of 'before' and 'after', so it isn't clear whether changes in behaviour are caused by the damage.