Working memory is a system or systems that allow(s) you do concurrently hold and process information in tasks like reasoning, comprehension and learning. It is also known as ‘memory at work’, and it is important in complex cognitive abilities, like learning a language, reasoning, comprehension, and cognitive control.
The two primary functions of working memory are temporary storage of information, and information manipulation.
Working memory capacity changes with age, brain damage, disease, and intelligence. It is different from short term memory in that it relies more on executive attention. It also depends on long-term memory. For example, you remember a phone number much better in your own language (long term phonological memory is important to short term verbal memory).
Central Executive: The central executive resides primarily in the dorsolateral prefrontal cortex. However, it also has components in parietal, premotor, cingulate, occipital and cerebellar regions.
Episodic Buffer: The episodic buffer was thought to reside in the hippocampus, but this was disproved when examining people who lacked a hippocampus. It was found that they could still perform tasks that used the episodic buffer, such as taks switching. It is now thought that a number of brain regions work together to fulfill the function of the episodic buffer.
Visuospatial Sketchpad: The visuospatial sketchpad is in the occipital lobe, where visual processing occurs, as well as in the parietal lobe, where spatial transformations occur.
Models of Memory
The current model of working memory is a product of an evolution of models of memory that took place over the course of the 20th century. Initially, memory was regarded as a single unitary system. The unitary view of memory was challenged by the finding that some people with brain damage had no long term memory but could still complete tasks that required short term memory. And conversely, some people who appeared to have a limited short term memory store, still showed normal long term memory learning. This led to two component models such as the Atkinson and Shiffrin model.
The Atkinson & Shiffrin Model
The Atkinson and Shiffrin model is a two component model. In other words, it characterizes short term memory as distinct from long term memory and vice versa. But inherent to their model is the belief that the short term memory system also acts as the working memory system. Therefore, this model suggests that one unitary system was considered responsible for short term memory storage, cognitive performance, learning and long term memory retrieval. But Baddeley found some major issues with this construct, leading him to suggest a new model entirely.
When Baddeley came on the scene about 6 years after Atkinson and Shiffrin first published their model, he showed that when short term capacity is reached, people are still able to do cognitive reasoning tasks. As you can see in this graph, reasoning time takes longer as you load short term memory store, but only by a very small percentage. We see about a 20% rise in in reasoning time on cognitive tasks when the short term memory is heavily loaded. If a single unitary short term memory system were responsible for cognition as well, we’d expect a way bigger effect.
Baddeley’s model is composed of four parts: the central executive, the visuospatial sketchpad, the phonological loop and the episodic buffer.
The central executive is an attentional controlling system that coordinates the two slave systems: the visuospatial sketchpad and the phonological loop. The visuospatial sketchpad manipulates visual images while the phonological loop stores and rehearses speech-based information. The episodic buffer is a limited capacity system that provides temporary storage of information held in multimodal code, which is capable of binding information from the slave systems, and from long-term memory, into a unitary episodic representation. Imagine in your mind your current house or apartment, and try to determine how many windows there are. Most people visualize themselves walking through their living space, counting windows as they go. In this scenario, the central executive is responsible for generating the strategy you use to solve the problem, the visuospatial sketchpad is responsible for generating the image of your home as you walk through it, and the phonological loop does the counting. The information you need from long term memory is delivered to these systems via the episodic buffer.
View the video below to hear Dr. Susan Gathercole, a colleague of Baddeley’s, describe another common task that captures the function of working memory.