AO1
Baddeley & Hitch (1974) replaced the idea of a unitary STM. It is an explanation that sees short term memory as an active store holding several pieces of information simultaneously.
The central executive (CE) is at the top of the WMM and has a supervisory function that acts as a filter, determining which information is attended to. It can process information in all sensory forms, directs information to other slave systems and collects responses. It has a limited capacity and deal s with only one piece of information at a time. It therefore selectively attends to particular types of information, attaining a balance between tasks when attention needs to be divided between them, eg talking while driving. It also permits us to switch attention between different inputs of information.
One of the slave systems is the phonological loop which is a temporary storage system for holding auditory information in a speech based form. It has two parts, the primary acoustic store (PAS) or the inner ear which stores recently heard words, and the articulatory process (AP) or inner voice that keeps information in the PL through sub vocal repetition of information and is linked to speech production.
The second slave system is the visuo-spatial sketchpad (VSS). It is the component of the WMM that deals with visual information and the physical relationship of items (visual and spatial information). It is comprised of two parts, the visual cache (VC) stores visual data about form and colour, and the inner scribe which records the arrangement of objects in the visual field, and rehearses and transfers information in the visual cache to the central executive.
The third slave system is the episodic buffer added by Baddeley (2000) which acts as a temporary store for information which communicates with both long term memory and the slave system components of the WMM. The PL and VSS deal with the processing and temporary storage of specific types of information, but have limited capacity, and the CE has no storage capacity so cannot contain items relating to visual and acoustic properties. Therefore, the EB was introduced to explain how it is possible to temporarily store information combined together from the CE, the PL, the VSS and LTM.