Working memory refers to the active maintenance of information while the same or other information is simultaneously processed (e.g., Baddeley & Logie, 1999; Engle, Tuholski, Laughlin, & Conway, 1999; Just & Carpenter, 1992) and is an important aspect of cognitive development. This is demonstrated by the fact that performance on measures of working memory is an excellent predictor of educational attainment (Bayliss, Jarrold, Gunn, & Baddeley, 2003; Daneman & Merikle, 1996; Hitch, Towse & Hutton, 2001). Moreover, studies have consistently shown that working memory capacity is strongly related to intelligence – so-called psychometric g. Indeed, some researchers have argued that working memory is almost synonymous with g (Colom, Rebollo, Palacios, Juan-Espinosa, & Kyllonen, 2004; Kyllonen & Christal, 1990; see also Conway, Kane, & Engle, 2003; although see Ackerman, Beier, & Boyle, 2005 for a meta-analysis and critique of this field). For example, Süß, Oberauer, Wittman, Wilhelm, and Schulze (2002) have suggested that: “at present, working memory capacity is the best predictor for intelligence that has yet been derived from theories and research on human cognition” (p. 284). It is unsurprising, therefore, that researchers should focus on working memory as a possible underlying cause of many different forms of learning disability.
Much of the research into working memory deficits associated with intellectual disability has been guided by Baddeley’s (1986) model. According to Baddeley, working memory involves the combined functioning of a central control system, the central executive, and two peripheral short- term memory systems, the phonological loop and the visuo-spatial sketch pad, that are specialized for the maintenance of verbal and visuo-spatial information respectively. Researchers have typically been interested in whether these different components of the model can be impaired selectively or differentially in particular developmental disorders (see Alloway & Gathercole, 2006). However, our focus in this chapter is less on specific disorders (although examples from specific syndromes will be covered where relevant); rather, our aim is to provide an overview of the range of working memory impairments associated with learning disability, and the possible consequences of such deficits. In doing this we ask a number of questions, notably: are there aspects of short-term or working memory that are particularly vulnerable to intellectual disability; are there any syndrome- specific patterns of working memory impairments; and how might these relate to educational outcomes and other aspects of cognitive and linguistic development? In order to properly interpret findings from studies involving individuals with intellectual disability, we begin by raising a number of general methodological points about the assessment of working memory, and by emphasising the theoretical distinction between working memory and short-term memory.