Alan Baddeley on the Development of the Working Memory Model

Working memory is the ability to actively hold information in the mind needed to do complex tasks such as reasoning, comprehension and learning. Working memory tasks are those that require the goal-oriented active monitoring or manipulation of information or behaviors in the face of interfering processes and distractions. The cognitive processes involved include the executive and attention control of short-term memory which provide for the interim integration, processing, disposal, and retrieval of information. Working memory is a theoretical concept central both to cognitive psychology and neuroscience.

Theories exist both regarding the theoretical structure of working memory and the role of specific parts of the brain involved in working memory. Research identifies the frontal cortex, parietal cortex, anterior cingulate, and parts of the basal ganglia as crucial. The neural basis of working memory has been derived from lesion experiments in animals and functional imaging upon humans.

The term “working memory” was coined by Miller, Galanter, and Pribram, and was used in the 1960s in the context of theories that likened the mind to a computer. Atkinson and Shiffrin (1968) also used this term, “working memory” (p. 92) to describe their “short-term store.” What we now call working memory was referred to as a “short-term store” or short-term memory, primary memory, immediate memory, operant memory, or provisional memory. Short-term memory is the ability to remember information over a brief period of time (in the order of seconds). Most theorists today use the concept of working memory to replace or include the older concept of short-term memory, thereby marking a stronger emphasis on the notion of manipulation of information instead of passive maintenance.

The earliest mention of experiments on the neural basis of working memory can be traced back to over 100 years ago, when Hitzig and Ferrier described ablation experiments of the prefrontal cortex (PFC), they concluded that the frontal cortex was important for cognitive rather than sensory processes. In 1935 and 1936, Carlyle Jacobsen and colleagues were the first to show the deleterious effect of prefrontal ablation on delayed response.

There have been numerous models proposed regarding how working memory functions, both anatomically and cognitively. Of those, three that are well known are summarized below.

Baddeley and Hitch
Baddeley and Hitch (1974) introduced and made popular the multicomponent model of working memory. This theory proposes that two “slave systems” are responsible for short-term maintenance of information, and a “central executive” is responsible for the supervision of information integration and for coordinating the slave systems. One slave system, the phonological loop (PL), stores phonological information (i.e., the sound of language) and prevents its decay by continuously articulating its contents, thereby refreshing the information in a rehearsal loop. It can, for example, maintain a seven-digit telephone number for as long as one repeats the number to oneself again and again. The other slave system, the visuo-spatial sketch pad(VSSP), stores visual and spatial information. It can be used, for example, for constructing and manipulating visual images, and for the representation of mental maps. The sketch pad can be further broken down into a visual subsystem (dealing with, for instance, shape, colour, and texture), and a spatial subsystem (dealing with location). The central executive (see executive system) is, among other things, responsible for directing attention to relevant information, suppressing irrelevant information and inappropriate actions, and for coordinating cognitive processes when more than one task must be done at the same time.

Baddeley (2000) extended the model by adding a fourth component, the episodic buffer, which holds representations that integrate phonological, visual, and spatial information, and possibly information not covered by the slave systems (e.g., semantic information, musical information). The component is episodic because it is assumed to bind information into a unitary episodic representation. The episodic buffer resembles Tulving’s concept of episodic memory, but it differs in that the episodic buffer is a temporary store.

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