The working memory model, devised by Baddeley and Hitch in 1974, proposes that short-term memory (STM) is a collection of multiple stores which actively process different types of STM. According to the 1974 model, it consists of 3 components; the central executive, the phonological loop and the visuo-spatial sketchpad. The central executive is an attentional control system which processes all types of STM and coordinates the other slave systems. The second part of the model is the phonological loop which processes auditory information. This slave system is often referred to as ‘the inner ear’. The final system, known as the visuo-spatial sketchpad, processes visual and spatial information. This slave system is often referred to as ‘the inner eye’. All three of these components are temporary storage systems of STM with a limited capacity. In 2000, Baddeley added a fourth component which he named the episodic buffer. He proposed that this store is responsible for integrating information from the other slave systems and works as a link between working memory and long-term memory.