In this highly thought-provoking book, Cowan advances the hypothesis that the central limit in the working system is a capacity limited focus of attention that is needed in host of activities in and out of the laboratory. As usual, Cowan draws on a wide array of empirical findings to make a very compelling argument for a capacity limited focus of attention within a broader working memory system. There is much to like about this timely and very up to date book. In particular, the notion of a flexible focus of attention that can zoom in or zoom out depending on the requirements of the task is appealing. Furthermore, the book is written in a fairly convincing and engaging manner which should be suitable not only to experts in the field of working memory, but it should also be accessible to experts in other fields as well as undergraduate and graduate students taking advanced seminars in working memory.

In the book, Cowan argues that a capacity limited focus of attention is the central limitation of the working memory system. Before detailing his view of the focus of attention and its role in cognition, Cowan first places the idea of capacity limits in a more historical context. He notes that many early investigations were concerned with the idea that there are basic limits in cognition and that psychology, in some sense, is a search for those limits. Additionally, Cowan provides a brief review of the notion of capacity limits as well as a brief review of the history of working memory in general (Chapter 1). Cowan also introduces his own embedded process model in which the focus of attention is one component and contrasts this view with other views of working memory (Baddeley) as well as the more traditional modal model (Chapters 1 and 2). These sections provide a nice review of Cowan's model and how it relates to other working memory models. Near the end of Chapter 2, Cowan provides a more detailed view of the focus of attention and its role in the broader working memory system. In short, the focus of attention is the set of highly activated long-term representations that are currently needed for ongoing processing. The focus is capacity limited and can be directed externally to incoming sensory information or internally to relevant long-term memory representations. The main bulk of the book is centered on a number of key issues:

For each of these key points, Cowan does an excellent job of marshalling evidence for his view, while at the same time admitting that there are alternative theoretical interpretations of some of the evidence. Cowan acknowledges that there are numerous other views of capacity limits, each of which can handle some of the data he has presented in support of his view (Chapter 5). For instance, Cowan discusses ten alternate views of capacity limits, noting strengths and weaknesses of each. One problem with this section, and the book in general, is that it only discusses capacity in one way: Namely, the amount that the focus of attention can hold. However, there is also another basic definition of capacity that sometimes gets overlooked; the ability to perform or produce. Thus, working memory capacity can be viewed as the upper limit of the focus of attention (amount), or the ability to effectively use the working memory system. The latter view suggests that the capacity of working memory lies in the ability to use the system as whole in order to control cognition. That is, there may be limitations in the ability to use the focus of attention (zoom in or zoom out), but there may also be limitations in the ability to set up temporary bindings in working memory, limitations in the ability to use cues to retrieve information for long-term memory, as well as the ability to use domain specific buffers. Thus, here the capacity of working memory is not how much the focus can maintain (3-4 chunks), but the capacity is the ability to use working memory in a number of situations. This is akin to the distinction that Cowan makes between the capacity of the focus of attention and the control of attention. However, particularly in Chapter 5, it would have been nice to see a discussion on alternate views of capacity limits that do not rely on the idea of amount.

Another concern not directly spelled out in the book is how the focus of attention is used in a number of higher-order tasks where the capacity limit is shown to be related to task performance. For instance, in Cowan et al. (in press-a; now 2005) it is shown that measures of the focus attention when it is presumably zoomed out correlate quite well with measures of verbal and nonverbal IQ. However, what seems to be left unspecified is how the focus of attention is needed/used in each of these tasks. For instance, how is the focus of attention used (in its zoomed out state) in matrix reasoning tasks like Ravens and why is a zoomed out focus better in this task than a zoomed in focus? Although clearly difficult questions to answer at this time, it would be nice to see some speculation of how the focus is used in these tasks rather than simply stating that it correlates performance some how.

These minor quibbles aside, I found the book to be an excellent read. Both the last chapter and the epilogue are particularly enjoyable. In the last chapter Cowan discusses some of the reasons for a capacity limit and discusses what brain areas are likely involved in its functioning. As noted previously, according to Cowan the control of attention relies on frontal areas, whereas the focus of attention itself relies on parietal areas. Cowan provides evidence for both of these notions as well as some additional evidence linking their shared variance to intellectual functioning. It is clear from reading this chapter that there are a number of exciting possible avenues for future research. Finally, in the epilogue Cowan gives a particularly succinct discussion of why we should care about limitations in working memory outside of the laboratory. Cowan briefly discusses some very real world problems that seem to come about because of limitations in working memory. This provides a fitting end to this very engaging book by pointing out that our ultimate goal as cognitive scientists is to understand the role of cognition in the real world behavior and not just in laboratory tasks.