Reflecting the complex nature of working memory (WM) and its relation to higher order cognitive behaviors, this edited book provides varied theoretical and empirical explanations of models of WM and variation in WM capacity, illustrating recent theoretical developments in this domain of human cognition. This collection of contemporary theories and models of WM will draw attention from researchers in cognitive psychology and neuroscience. Additionally, this book will benefit SLA researchers interested in investigating how WM variation affects L2 learning.

The introductory chapter offers a brief historical overview. Similar to Miyake and Shah's (Reference Miyake and Shah1999) influential book on models of WM, each subsequent chapter is structured around four thematic questions of theoretical significance. Each contributing research group discusses (a) an overarching theory of WM that guides their research paradigm and their theoretical proposal on WM variation, (b) critical sources of WM variation according to their proposal, (c) their viewpoints on other sources of WM variation supported by the other research groups in the book, and (d) what contributions their own proposal makes to WM theory in general.

The first three chapters delineate WM variation in terms of domain-general executive attention (chapter 2), multiple temporary bindings (chapter 3), and dual mechanisms of cognitive control: proactive and reactive control (chapter 4). Interestingly enough, chapter 3 calls into question the generally assumed special relationship between WM capacity and executive attention because of insignificant findings obtained through such measures as task-set switching; in chapter 2, however, it is contended that most task-switching tasks are not valid enough to measure executive control. Chapter 5 maintains that children's performance on WM tasks is determined by the temporal dynamics of WM span; that is, the time spent processing affects the maintenance/loss of temporary information. Individual and developmental variation in WM is further discussed in a multifaceted framework that incorporates processing and storage as well as the executive ability to coordinate/combine the two demands (chapter 6) and in terms of the two complementary processes of active maintenance and information updating (chapter 7). Chapter 8 points to mental processing speed as an important source of developmental variation in WM. In chapter 9, inhibitory control that varies with age is argued to be the main source of variation in WM performance. It is claimed in chapter 10 that executive processing is involved not only in WM tasks but also in short-term memory or storage-only tasks. Particularly relevant to SLA research is the suggestion that there may be (a) a specialized system in the central executive solely dedicated to online syntactic processing, (b) a separate WM system, and (c) a system not represented by general verbal WM as measured by standard WM tests (chapter 11).

Whereas a strength of the book is the diverse theoretical perspectives presented in terms of WM and the many ways it may vary, a clearer picture of extant WM research would emerge had one or two integrative chapters been included in the book to compare, contrast, and evaluate the theories and models in detail in terms of the thematic questions provided by each contributing research group, as was the case in Miyake and Shah (Reference Miyake and Shah1999). Additionally, a chapter designed to focus exclusively on issues of validity and reliability of tests and tasks utilized in WM research would have been helpful, and this is particularly the case for researchers interested in adopting or adapting existing measures of WM span and developing new WM tasks.

Nevertheless, this work should generate a high degree of interest for SLA researchers who work on WM-related projects because it offers a comprehensive review of established and still hotly debated issues in WM research. Obviously, one potential problem for SLA researchers is the model(s) to be used, because the validity and reliability of WM span measures differs depending on the underlying assumptions of different models (e.g., with respect to domain-specificity, processing speed, executive control). By presenting differing models and interpretations of WM variation, however, this book provides an array of important issues for SLA researchers to consider in the process of designing and implementing WM-related studies. Taking into account the theories, models, and related issues presented and incorporating them into SLA research will likely lead to theoretically more valid and methodologically more reliable outcomes.