The working memory model

Shallice and Warrington carried out a case study of patient KF who had brain damage. He had poor STM ability for verbal information but could process visual information normally (difficulty with sounds but could recall letters/digit.)

So his phonological loop had been damaged but other areas of memory were intact. This suggests there are separate visual and acoustic stores.

However, evidence from brain-damaged patients may be unreliable because it concerns unique cases of patients who have had traumatic experiences.

Baddeley et al found pariticipants had more difficulty doing two visual tasks (tracking a light and describing the letter F) than doing a visual and verbal task at the same time. 

The greater difficulty is because both visual tasks compete for the same limited resources. When doing a verbal and visual task simultaneously, there is no competition.

Therefore dual task performance activity provides evidence for the existence of the visuo-spatial sketchpad. The MSM can't explain this. 

Cognitive psychologists suggest that the CE is unsatisfactory and doesn't really explain anything.

The CE should be more clearly specified than just being simply 'attention'. Some psychologists believe it may consist of spearate components.

This means that the WMM hasn't been fully explained. 

Baddeley et al. found people have more difficutly remebering a list of long words (e.g. 'association') than short words. This is the word length effect.

This is because there is limited space for rehearsal in the articulatory process (probably about two seconds).

Word length effect disappears if a person is given a repetitive task tying up the articulatory process, demonstrating the process at work. 

Braver et al's. participants did tasks involving the CE while they were having a brain scan. Activity seen in an area known as the prefrontal cortex.

Activity in this area increased as the task became harder. This makes sense in terms of the WMM: as demands on the CE increase, it has to work harder to fulfil its function.

So this study provides evidence that the CE may have a physical reality in the brain.