Evaluation of the original working memory model

There are some advantages to the original model, and some evidence to support it. Dual task studies for example support the idea of having two specialised subcomponents. There is also neuropsychological and neuroimaging evidence that different brain regions are associated with the phonological loop and the visuospatial sketchpad and its subcomponents. Finally, there is strong evidence for an executive control system.

There are some difficulties with the original three component model however. Problems arise from the poor specification of interaction with the long term memory. There is evidence that the central executive is more than simply an attentional system, as an amenesiac patient with impaired long term memory was still found to have immediate memory for passages of prose that extend beyond the capacity of the PL and VSS. Another problem is that there is no system that allows for 'chunking'. Chunking allows for the information in the longterm memory to supplement immediate recall. If stimuli is a meaningful sentence then the memory span is increased. The model does not account for this however .

A further criticism of the original model is that there is no mechanism proposed for the interaction between the phonological loop and the visuospatial sketchpad, as well as no mechanism for the role of working memory in conscious awareness . The central executive was originally proposed to assist in binding this but how could it do this without a multimodal short term store to integrate the information.

Because of these criticisms and flaws with the model, Baddeley, in 2000, added in a 4th component to the model to account for the problems.

• Episodic Buffer: This hold on to and integrates diverse information
• It has limited capacity to temporarily store information
• it has a binding role and acts as a common multidimensional code.
• It has a temporary interface with the slave systems (VSS and PL)
• it is accessible to conscious awareness
• It links the working memory with the longterm memory more explicitly
• The information held in this buffer interacts with the visual semantics and language components and gets converted to the long term memory

The Visuospatial Sketchpad and Phonological/Articulatory Loop

Baddeley and Hitch 1974 & Baddeley 1986

They separated memory into two forms, which with rehearsal work into the central executive (which is modality free). The two forms are:

• The visuo-spatial sketchpad (inner eye) which is specialized for spatial and/or visual coding
• Phonological/articulatory loop (inner voice) which holds information in a speech-based form

• All three of the components have limited capacity, and are relatively independent.
• The theory has implications for dual task processing:
• If 2 tasks are performed simultaneously and use the same component, they cannot be performed successfully.
• If the two tasks are performed simultaneously using different components it should be possible to perform them equally well.
• This theory was tested by giving participants a primary task and asking them to carry out a second task simultaneously.
• To use the phonological/articulatory loop, participants carried out an articulatory rehearsal at the same time as being asked to produce irrelevant speech.
• The visuo-spatial sketchpad was used through carrying out through spatial rehearsal. Participants were simultaneously asked to generate irrelevant hand movements.

Phonological Loop

• This stores verbal information in a speech based form
• Information is maintained by articulatory rehearsal
• Information enters the phonological store through articulatory word presentation and visual word presentation.
• Henson Burgess and Frith 2000 identified the areas associated with the PL.
• Storage: left inferior parietal
• Rehearsal: left prefrontal

Phonological similarity effect

• This asks participants to serially recall a word list. When these are phonologically similar, this proves to be more difficult than when they are dissimilar. eg knee, he, lee, she, me is more difficult than odd, shy, up, bay, hoe
• This was tested by Larsen, Baddeley and Andrade in 2000. They found that similar word recall was 25% worse than dissimilar recall.

Word Length Effect

• The ability to reproduce a series of words is better with short words than long words
• Baddeley et al.. 1975: Articulatory suppression eliminates the word length effect, which suggests that word length effect depends on the phonological loop.
• Baddeley et al. 2002: There is still a word length effect when the output delay is controlled by using recognition memory rather than recall

Articulatory Suppression

• Phonological loop is disrupted if there is performance of overt or covert articulatory rehearsal of irrelevant items
• Articulatory suppression removes the word length effect and also the phonological similarity effect.
• Articulatory suppression process dominates the articulatory control process component of the phonological loop.

Evidence for the two components and the distinction between phonological store and the articulatory control process comes from brain damaged patients...

• Individuals with damage to the PS but not the ACP seem to have poor short term memory for auditory-verbal material but they still have normal speech production. These individuals have lesions in the left temporo-parietal cortex
• Individuals with the opposite; damage to the ACP but intact PS tend to have lesions to thepremotor, frotal paraventricular and anterior insula of left hemisphere

Visuospatial Sketchpad

• This area provides temporary storage and manipulation of visual and spatial information
• Info is maintained by spatial rehearsal
• Logie (1995) said that there are two components:
• The visual cache - this stores info about form and colour.
• The inner scribe - this contains spacial and movement information. It rehearses information in the visual cache.

Evidence for the visuospatial sketchpad:

• Quinn and McConnel 1996
• Participants had to learn a word list by one of 2 methods. While they did this there was visual or spatial interference tasks.
• Method 1: Method of loci. In this example, memory performance was interrupted by the visual task, but not the spatial task, suggesting that learning is dependent on visual cache.
• Method 2: Pegword. This method used a linked word with the item t aid memory. The memory performance observed was affected by both the visual and spatial interference tasks, suggesting that learning requires both visual and spatial components.

Evidence for both components from brain damaged patients:

• Unilateral presentational neglect (Beschin et al. 1997)
• Patient found it hard to describe details from the left side of scenes in visual imagery unless a visual stimulus is available
• No problems were found in perceiving the left sides of scenes so visual perception is therefore intact
• This suggests that damage to the visual cache where there are stores about form and colour

Evidence for both components of visuospatial sketchpad from imaging studies

• PET - Smith and Jonides 1997
• They found that a spatial task produced activity in the right hemisphere, particularly the prefrontal, premotor, occipital and parietal cortices.
• The visual task however produced activation in the left hemisphere, particularly the parietal and inferotemporal cortices.
• There was also further evidence for the visual 'what' pathway (ventral PFC) and the spatial 'where' pathway (dorsal PFC)
• There is support for the separation of visual cache and inner scribe components from the fact that there is no interference between visual and spatial tasks when they are performed together (Quinn and McConnell 1986)
• Brain damaged patients can also have damage to the visual but not the spatial component
• Imaging data suggests that VC and IS are associated with the activation of different brain regions
• Functions = geographical orientation and the planning of spatial tasks