In this book, edited by Akira Miyake and Priti Shah, ten contemporary ‘theories’ of working memory (WM) are outlined. I say ‘theories’ because there are a great number of overlaps between the presented chapters, and so whilst each presents a view in its own right, a number are based upon the same principles. The ten chapters cover the following theories/models (with a very brief synopsis of each):
- Baddeley’s tripartite model of working memory: WM as a functionally and structurally separable memory system from long-term memory. The well known phonological loop and visuospatial sketchpad slave systems controlled by the attentional controller, the central executive. More recently, this model has been appended with the episodic buffer – invoked to help explain the growing evidence of more than just cooperation between the working and long-term memory systems.
- Nelson Cowan’s embedded processes model of working memory: inspired by the Craik and Lockhart levels of processing information processing architecture, this theory states that WM is simply that region of long-term memory which is in an activated state. Furthermore, a focus of attention is a subset of this, and contains the contents of conscious awareness at any given time. Again, a central executive is used as an attention controlling mechanism, among other things.
- Engle et al’s individual differences model of working memory: very closely related to both Cowan and Baddeley’s models, it views WM as long-term memory plus attention. As the name suggests though, it emphasises the differences in capacity between individuals.
- Lovett et al’s working memory in ACT-R: the ACT-R cognitive architecture is essentially made up declarative memory (networked nodes, each representing a piece of knowledge, and each having an activation level – this level representing attention), and procedural memory (symbolic, of the type condition->action). Given a current goal, working memory would consist of all those production rules (from procedural memory) and those declarative nodes activated by those rules which are relevant to the current goal. It is a computation model, with development tools freely available on the internet.
- Kieras et al’s working memory in the EPIC architecture: a symbolic computational architecture with a well developed interface with perceptual and motor processes. Though not explicitly a model of WM, as with ACT-R and SOAR, it does nevertheless operate in certain domains in a way functionally analogous to WM.
- Young et al’s working memory in SOAR: SOAR is a purely symbolic computation model of human cognition. Its working memory space contains the current goal (broken down into subgoals if necessary), and those pieces of information relevant to it/them. Production rules relevant to the goal at the top of the ‘goal stack’ all fire at once, and new rules may be created if no relevant rules are found. Processing, as with ACT-R, is thus goal directed.
- Ericsson and Delaney’s long term working memory: This theory of working memory distinguishes between the oft-discussed short-term working memory discussed by most other theories, and long-term working memory which is made up of those knowledge structures which enable the fast recall from nonactivated long-term memory. These structures are studied by examination of ‘memory experts’, for example people who can remember long series of numbers, which theoretically exceed the limits of standard ‘short-term’ working memory.
- Barnard’s working memory in ICS: The interacting cognitive systems model is another general cognitive architecture, however, it began life as a model of Baddeley’s phonological loop. Baddeley’s tripartite structure maps very well on top of it, although each system is described as the interaction of a number of other, more fundamental, modality specific systems.
- Schneider’s working memory in CAP2: The control and automatic processing model is a connectionist model that started life as specifically a model of working memory, but became a general cognitive architecture. In this architecture, a central executive is presented as a hierarchically structured series of neural networks.
- O’Reilly et al’s biologically based computational model of working memory: This model is based on the assumption that the effect of working memory is an emergent property of the interaction of three specialised brain systems; the prefrontal cortex, the hippocampus, and the perceptual and motor cortices. I cannot do justice to the theory here; would like to review it in a later post. On a quick note: it forms the basis of a computational model of the prefrontal cortex, which has been successfully implemented in robotic setups (presented at COGRIC recently). I also intend to post on this subject in the near future.
When I first approached the subject of WM for my research, Baddeley and Hitch’s tripartite model seemed by far the most influential. This is indeed the case – however, a multitude of models were always present even if just at the fringes. One thing I found most disconcerting was the lack of a standard definition of working memory: it seemed to be used to cover a wide range of things. More recently, however, this prevalence of Baddeley’s model seems to be declining, in favour of what may be described as more functionally general and neurally more explicit models. This book I found extremely useful as a starting point in trying to resolve the issue of definitions in particular, and to provide an overview of the majority of contemporary working memory theories. I highly recommend it. It even provided me with a brief introduction to the cognitive architectures of ACT-R and SOAR. Partly as a result of reading this book, and in conjunction with other research, I settled on a general definition of working memory upon which my current research is aimed: working memory is the interface between cognition on the one hand, and memory on the other.
REF: A. Miyake and P. Shah, "Models of Working Memory: mechanisms of active maintenance and executive control." Cambridge: Cambridge University Press. 1999.