Based on experiments demonstrating connections between LTM and STM, as well as experiments indicating that STM consists of more components, Alan Baddeleyand GrahamHitchproposed a multi-component working memory model in 1974. The new term working memory was supposed to emphasize the importance of this system in cognitive processing. Baddeley and Hitch suggested working memory is composed of three parts: the central executive, a system that controls the phonological loop (a subsystem for remembering phonological information such as language by constant refreshing through repetition in the loop), and the visuospatial sketch pad (a subsystem for storing visual information).
This model was later revised and improved by Baddeley but also contributed by other authors, which resulted in additional component of episodic buffer in year 2000 and more detailed functions and analysis of other components, as described in table below.
It is still unclear whether it is a single system or more systems working together. Central executive's functions include attention and focusing, active inhibition of stimuli, planning and decision-making,
sequencing, updating, maintenance and integration of information from phonological loop and visuospatial sketchpad. These functions also include communication with long-term memory and connections to language understanding and production centers.
Episodic buffer has the role of integrating the information from phonological loop and visuospatial sketchpad, but also from long-term memory. It serves as the storage component of central executive, or otherwise information integration wouldn't be possible.
According to Baddeley, phonological loop consists of two components: a sound storage which lasts just a few seconds and an articulatory
processor which maintains sound information in the storage by vocal or sub vocal repetition. Verbal information seems to be automatically processed by phonological loop and it also plays an important, maybe even key role in language learning and speech production. It can also help in memorizing information from the visuospatial sketchpad. (For example, repeating “A red car is on the lawn.”)
This construct according to Baddeley enables temporary storing, maintaining and manipulating of visuospatial information. It is important in spatial orientation and solving visuospatial problems. Studies have indicated that visuospatial sketchpad might actually be containing two different systems: one for spatial information and processes and the other for visual information and processes.