Working Memory Model
The working memory model championed by Alan Baddeley, was developed initially to counter the view that short-term memory Opens in new window is a unitary storage system: a single place, or store, where complex forms of cognitive processing (e.g., reasoning or language comprehension) occur concurrently with temporary storage.
Baddeley and Hitch (1974) argued instead for a multicomponent system with separate subsystems designed to handle particular kinds of processing, such as the temporary storage of visual versus phonological information.
The working memory model maintains a strong distinction between short-term and long-term memory, but it fractionates short-term memory into separate parts.
Baddeley and Hitch (1974) noted, for example, that remembering a span-length list of items produces little disruption of a concurrent reasoning or problem-solving task. If both temporary storage and on-line cognitive processing are controlled by the same processing machinery—the same processing store—then significant interference Opens in new window should have occurred between the two.
The fact that little interference is found suggests that temporary storage and attention-based central processing may be controlled by separate mechanisms.
Data from the study of brain-damaged patients proved troubling as well: It was discovered, for example, that patients with severely impaired short-term memory can show relatively intact long-term memory (e.g., Shallice & Warrington, 1970); a view proposing that both temporary storage and long-term learning are controlled by the same system has trouble accounting for this pattern.
The working memory model has undergone significant changes since its inception, but its core architecture still consists of three basic components:
- the central executive,
- the phonological loop, and
- the visuo-spatial sketchpad.
The central executive, as the name suggests, controls and coordinates the actions of the remaining subsystems. It is assumed to be a limited-capacity attentional system that directs the focusing and switching of attention, and it may play a role in activating structures in long-term memory as well (Baddeley, 1996).
According to the working memory model, the key component of working memory Opens in new window is the central executive. The phonological loop Opens in new window and the visuo-spatial sketchpad Opens in new window are slave systems used by the central executive for specific purposes.
The phonological loop preserves the order in which words are presented, and the visuo-spatial sketchpad is used for the storage and manipulation of spatial and visual information. All three components have limited capacity, and are relatively independent of the other components.
In effect, Baddeley’s model is hierarchical, with the central executive as the top-level, domain-free factor that controls all the subcomponents. The central executive plays no role in storage per se, except as the controller of the loop and the sketchpad.
Apparently, Baddeley views the central executive as the essence of working memory; he usually refers to the two subsidiary systems as short-term memory components.
Recently, Baddeley (2000) added another subcomponent—the episodic buffer, which is a temporary storage system that can hold and integrate information from the phonological loop, the visuo-spatial sketchpad, and long-term memory. As with the other components, this too, is controlled by the central executive.