Working Memory Model

Working memory Opens in new window has been described as the temporary storage of information that is being processed in a wide range of cognitive tasks. Baddeley and Hitch (1974) proposed a tripartite system of working memory, composed of:

1. the Central Executive, which is a control mechanism helped by two slave systems,
2. the Phonological Loop (originally called Articulatory Loop) and
3. the Visuo-Spatial Sketchpad (VSSP).

The two slave systems function independently from each other, as demonstrated by the use of dual task paradigms.

1. Phonological Loop

The Phonological Loop is the most studied part of the system; its role is to hold and manipulate verbal material. It consists of two components:

• a phonological store, which is relatively passive and to which verbal material presented auditorily has obligatory access; and
• a rehearsal mechanism which helps to maintain stored items as well as recoding verbal material presented visually.

The phonological loop is temporally limited: It contains as many items as can be rehearsed in approximately 1.5 to 2 seconds. It is therefore closely linked to articulation rate. The functioning of this subsystem accounts for phenomena repeatedly observed in verbal short-term memory studies, such as word length, articulatory suppression, and phonological similarity effects.

2. Visuo-Spatial Sketchpad

The visuo-spatial sketchpad (VSSP) is responsible for the holding and manipulation of visual and/or spatial information.

Experimental studies are less numerous, although their number has greatly increases in the last decade, and results are sometimes difficult to interpret. In particular, the rehearsal mechanism and the limits of the system remain largely unknown. Recent work (Baddeley, 1988; Logie & Baddeley, 1990) tends to show that it consists of two distinct, a visual and a spatial one.

3. Central Executive

The central executive (CE) is an attentional system, with a limited capacity, which can use either slave system in order to free up some of its own resources. It has been relatively little studied, and remains some kind of a “conceptual black box” (e.g. Van der Linden, 1989).

Recently, however, experimental studies have directly addressed the CE. For instance, Baddeley (1992) considers that the greater difficulty Alzheimer’s patients have in co-ordinating two simple tasks, one calling for the phonological loop system and the other one for the VSSP system, is due to a deficit of the CE.

A task of generating random numbers is considered to directly tap the central executive (CE); it probably requires the active rehearsal of instructions and the inhibition of automatic routines. Thus, the CE is mainly viewed as a mechanism for monitoring and co-ordinating the processing of information Opens in new window.

Baddeley’s model has generated numerous studies. From a developmental perspective, most studies up to now have attempted to determine whether similar effects are found in children.

For instance, Hitch et al. (1989c) have shown that the phonological system grows in importance with age, although the ages at which rehearsal has been observed vary with situations. With auditory presentation of verbal stimuli, word length effects are found as early as 4 years of age. By contrast, with visual presentation (drawings of objects), word length effects do not appear before 7 or 8 years of age.

Older children (at least from 8 years onwards) spontaneously use articulatory rehearsal, whether presentation is auditory or visual. Incidentally, it is interesting to note that such results converge with Flavell’s (e.g. Flavell & Wellman, 1977) and other researchers’ work on spontaneous rehearsal in memory tasks. In their recent work, Hitch et al. also suggest that verbal coding does not merely replace visual coding, but that development consists in a multiplication of the number of possible coding systems.