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

What this dot point is asking

AQA wants you to describe the working memory model (WMM) and its components, including their coding and capacity, with evaluation. The exam skill is to describe all four components with their sub-parts, to use dual-task and case study evidence, and to note that the WMM explains only short-term (working) memory.

The components

The working memory model was developed because the multi-store model's single short-term store was too simple to explain how we can carry out two tasks at once. Baddeley and Hitch proposed that working memory is an active processor with several components. The central executive is the most important: it is the attentional control system that decides what we attend to and allocates resources to the other components, which act as its slave systems. It has a very limited capacity and, crucially, does no storage itself. The phonological loop deals with auditory and verbal information and has two parts: the phonological store (the "inner ear") that holds spoken words, and the articulatory process (the "inner voice") that allows maintenance rehearsal. The visuo-spatial sketchpad handles visual and spatial information and likewise splits into a visual cache (storing visual data) and an inner scribe (recording the arrangement of objects in space). The episodic buffer was added by Baddeley in 2000 to fill a gap in the original model: it is a temporary store that integrates information from the other components into a single sequence and links working memory to long-term memory.

Coding and capacity

Each component codes information in a specific format, and this difference in coding is what allows two tasks to be done simultaneously if they use different components. The phonological loop codes acoustically and is limited to roughly two seconds of speech, which is why a longer list of words is harder to rehearse (the word-length effect). The visuo-spatial sketchpad codes visually and spatially, with a limited capacity of around three to four objects. The episodic buffer also has a limited capacity, around four chunks, but unlike the other slave systems it can code across formats, integrating visual, spatial and verbal information into a unified episode. The central executive itself has no storage and a very limited capacity.

Evidence

Dual-task studies show two tasks using the same component (e.g. two visual tasks) interfere, but tasks using different components do not, supporting separate stores. The patient KF had poor verbal STM but intact visual STM, supporting separate sub-systems.

The evidence for separate components is strong. Dual-task studies show that participants struggle to do two tasks that draw on the same slave system (two visual tasks, or two verbal tasks) because they compete for the same limited resource, but they can do one visual and one verbal task together with little loss, exactly as the model predicts. Clinical evidence comes from the patient KF, who after brain damage had a very poor verbal short-term memory but an intact visual short-term memory, which a single unitary STM cannot explain but the separate phonological loop and visuo-spatial sketchpad can. The model is therefore widely regarded as a better account of short-term memory than the multi-store model. Its main limitations are that the central executive is the least understood component, vaguely defined and probably itself more than one system, and that the WMM explains only working (short-term) memory, not long-term memory, so it is a model of one part of memory rather than the whole.