The working memory model (WMM)
Replacing the single STM of the MSM (see page 24), the working memory model (WMM) proposes a 4-component working memory based on the form of processing each carries out.
The limited-capacity central executive (CE) acts as a filter, dealing with all sensory information and determining which information is attended to, and then allocating this to ’slave systems’, temporary stores dealing with different types of sensory information.
The phonological loop (PL) is a slave system dealing with auditory information. It is similar to the rehearsal system of the MSM, with a limited capacity determined by the amount of information spoken in about 2 seconds. It divides into the primary acoustic store (PAS), which stores words in the order they were heard, and the articulatory process (AP), which permits sub-vocal repetition of information stored in the PL.
Another slave system is the visuo-spatial sketchpad (VSS), a temporary store for visual and spatial items and the relationships between them. It divides into the visual cache (VC), which stores visual material concerning form and colour, and the inner scribe (IS), which stores information about spatial relationships (where objects are in relationships to each other).
A slave system added to the model later on is the episodic buffer (EB), which is a temporary store of integrated information from the CE, PL, VSS and LTM.
Fig 2.2 The working memory model
Alkhalifa (2009) examined the existence of the EB, by presenting 48 students with numerical information on a screen, either in sequential fashion (e.g. 1, 2, 3, 4) or in parallel fashion (where information was presented in different parts of the screen simultaneously). The numbers used were of sufficient complexity to override the capacities of both the PL and the VSS. Participants were set problem-solving questions based on the numbers presented. Those using sequentially presented material were superior. This suggests a limitation exists on information passing from perception to learning, as parallel processing was a hindrance to learning. As sequential processing was superior, it indicates that the capacity of the working memory (WM) is larger than that determined by the capacity of the PL and the VSS, implying the existence of a limited-capacity EB, which acts as a temporary ’general store’ of integrated material.
• Trojani & Grossi (1995) reported the case study of ’SC’, who had brain damage affecting the functioning of his PL, but not his VSS. This suggests the PL and VSS are separate systems associated with different brain areas.
• Gathercole & Baddeley (1993) found that participants had difficulty simultaneously tracking a moving point of light and describing the angles on a hollow letter ’F’, as both tasks involved using the VSS. However, they had little difficulty tracking the light and performing a simultaneous verbal task, as those tasks used the VSS and the PL, indicating the VSS and PL to be separate systems.
• Alkhalifa (2009) reported a case study of a patient with severely impaired LTM, who had a STM capacity of 25 prose items, far exceeding the capacity of both the VSS and the PL. This supports the idea of an EB, which holds items in working memory until they are recalled.
PET scans show different brain areas are activated when individuals perform verbal and visual tasks. This supports the idea of the PL and the VSS being separate systems based within the biology of the brain.
The PL is associated with the evolution of human vocal language, as the development of the PL produced an increase in the short-term ability to remember vocalisations. This helped the learning of more complex language abilities, like grammar (the rules of language) and semantics (the meanings of things).
The WMM is a superior explanation of STM to the MSM, as it explains STM as having several storage systems and so is better able to explain how STM actually operates.
Studies of the PL and VSS often use a dual task technique (doing 2 tasks at once), but the tasks performed are often ones that do not relate to everyday life (like tracking a moving dot of light) and so are artificial and thus lacking in external validity.
Although the CE is seen as the most important component of the WMM (as it oversees the operation of working memory), little is known about how it works — for example, how it decides what we pay attention to.
Children with attention deficit hyperactivity disorder (ADHD) often have impairments in working memory. Alloway (2006) recommends: using brief, simple instructions (so they are not forgotten); giving instructions as individual, frequently repeated steps; and getting children to periodically repeat instructions so that they stay focused.