Visuo-spatial Working Memory as a Limited Resource of Cognitive Processing

Working memory is considered a cognitive component that mainly serves two functions. It temporarily maintains information that was either perceived but is no longer present in the environment, or that was internally generated, and it supplies a work space for transforming and manipulating elements of perception and thinking. Both functions are relevant for a successful interaction with the environment and it is therefore not surprising that WM is a central topic of research in the field of general psychology. This interest is further increased by the fact that WM is seen as a limited resource that constrains cognitive performances. Understanding working memory capacity (WMC) therefore promises gainful training methods to surmount these capacity limitations. In this chapter, we want to discuss aspects of WM that are relevant when we are talking about WM as a limited resource of cognitive processing. Our focus will be on VSWM although many principles can be applied also to other types of inputs. Historically, WM research has its origin in research on short-term memory (STM). In 1887 already, Jacobs [47] introduced the so-called digit span to measure the capacity of STM. He presented a random series of digits and participants were required to repeat them in their correct serial order. The longest sequence that was correctly repeated was defined as digit span. It is usually limited to six or seven items and this figure was therefore given as the capacity of STM [76]. Until today, span measures remain the gold standard for estimating WM capacity [18], although nowadays different types of spans are distinguished and a limit of four items is discussed as we will show later. The reason for this differentiation was the observation that STM is not a unitary compartment. Patients with a verbal STM deficit, for example, have a digit span as short as two items, but they have a normal visuo-spatial span [120].