The working memory model: central executive, phonological loop, visuo-spatial sketchpad and episodic buffer. Features of the model: coding and capacity.

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Baddeley and Hitch (1974) constructed the Working Memory Model to explain short-term memory in greater detail. They agreed with Atkinson and Shiffrin that we have STM and LTM, but saw STM as being much more complex. Working memory is still viewed as having limited capacity, but it has multiple, inter-connected components:

  • The central executive
  • The phonological (or articulatory) loop
  • The visuospatial sketchpad (or scratchpad)
  • The episodic buffer (added in 2000)

The Central Executive

The main role of the central executive is to decide how to allocate its resources – in effect, how to share out and direct attention to incoming information:

  • It has limited capacity
  • It can accept information from any sensory modality
  • It is flexible in how it allocates its limited resources. It can do more than one thing at a time or attend to one thing whilst inhibiting attention to another

The central executive deploys the following resources, collectively called slave systems, which can operate at the same time.

The Phonological (Articulatory) Loop

The articulatory loop can be thought of as a maintenance rehearsal mechanism for retaining mainly acoustic, verbal information. It has a limited capacity and consists of:

  • The phonological store (the inner ear), which briefly holds acoustically coded information, chiefly speech.
  • The articulatory control process (the inner voice), which allows for subvocal rehearsal of items in the phonological store, e.g. words we are about to say.

The Visuospatial Sketchpad (Scratchpad)

The visuospatial sketchpad (the inner eye) is responsible for briefly storing visual and spatial information, which can be maintained for rehearsal. It too has a limited capacity.

  • It codes information for images
  • It is involved in pattern and movement perception
  • It can create and manipulate visual and spatial images, e.g. a choice of routes you want to take.

To illustrate how the visuospatial sketchpad works, Baddeley (1997) suggested mentally counting the number of windows in your home. Most of us would take a ‘mental’ walk around our home while conjuring up images as we go. If you were to also attempt to imagine your route home from school simultaneously you would struggle, as this salve system has a limited capacity for resources.

Evaluation

  • Active process: It sees memory as an active process and not merely a passive store.
  • Explanatory power: A strength is that it has better explanatory power than the MSM. It can explain how it is possible to carry out more than one task at a time but that if tasks both require the same system, ability is impaired.
  • Rehearsal: It only considers rehearsal to be important in the phonological loop.  It is widely considered that the multi-store model does place too great an emphasis on rehearsal in transferring information to STM.
  • Research Support: PET scans (Positron Emission Tomography), show that different parts of the brain are active when different parts of the system are in use.  This provides further evidence for distinct components or slave systems.  The central executive seems to reside in the frontal cortex and the visuospatial sketchpad in the right side of the occipital lobe, known to be associated with vision.
  • Amnesiac case studies: A single component STM is unable to explain the case of KF, who, following a motorbike accident suffered impairment of his STM.  Shallice & Warrington (1974) showed that although his memory for verbal material was poor his memory for visual information was unaffected.  The working memory model can explain that it was damage to the articulatory loop with the sketchpad remaining intact.
  • Supporting Research: Baddeley (1973) found that participants struggled to track a moving spot of light using a pointer, whilst simultaneously asked to picture a block capital letter ‘F’ and, starting at the bottom left hand corner, mentally follow its border saying ‘yes’ if a corner was joined to the top or bottom horizontal part, or ‘no’ if it wasn’t. This supports the idea of a limited capacity for the visuospatial sketchpad. On other dual-task studies Baddeley found that performance on two tasks was no inhibited when they each required the use of a separate slave system, suggesting that verbal and visual/spatial information are processed independently in different parts of the brain

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Extension Resources