Individual differences and visuo-spatial working memory

VISUO-SPATIALWORKING MEMORYAND INDIVIDUAL DIFFERENCES. C. Cornoldi andT. Vecchi. Psychology Press, Hove, UK, 2003. No. of pages 169. ISBN 1-84169-216-6. Price £29.95(hardback).

The ability of the brain to retain and manipulate visual and spatial information plays a crucialrole during higher cognitive functions such as mental representation, creative thinking, andthe planning of complex actions. However, despite this importance in everyday cognition thetopic of visuo-spatial working memory has been comparatively neglected by cognitive psychologyover the last 50 years. The majority of models of working memory are based on empiricalevidence gathered from studying the retention and processing of verbal and linguistic materialrather than information originating in the visuo-spatial domain (see Miyake & Shah, 1999, for acomprehensive review). Although during the 1980s several key influential studies into visuo-spatial working memory were carried out, the main focus of research remained resolutely onverbal working memory processes. In the last ten years, however, this situation has alteredmarkedly, with a considerable increase in the amount of research that focuses on visuo-spatialworking memory. As a result there have been considerable theoretical and methodological gains inthis area.

This timely book by Cesare Cornoldi and Tomaso Vecchi provides an excellent review of thesedevelopments and their implications for theories of visuo-spatial ability. The book forms part ofthe ‘Essays in Cognitive Psychology’ series published by Psychology Press, which aims toproduce brief volumes in cognitive psychology that provide an overview of the authors’ ownresearch, as well as outlining current trends in the area. Cornoldi and Vecchi are both highlyexperienced researchers in the field of visuo-spatial ability who have conducted a wide range ofstudies on mental imagery and working memory, and this book summarizes the key findingsfrom that research. They approach the topic of visuo-spatial working memory from an indivi-dual differences perspective, arguing that understanding why different groups of peoplesignificantly differ on measures of visuo-spatial performance provides an essential step in forminggeneral theories of psychological functioning. In light of this, the book is structured by chaptersthat focus on individual differences in specific populations, including differences linked togender, age, and congenital blindness, as well as genetic syndromes such as Down’s, Williams,and Fragile-X.

Although the title of the book refers to visuo-spatial working memory, the authors admit in theirintroductory section that this is not a tightly defined concept, and can be related to a wide range ofresearch areas, including mental representation, mental imagery, visual and spatial short-termmemory, and many general aspects of visuo-spatial cognition. The book therefore tends to focus onindividual differences in visuo-spatial ability per se, taking a broader view of visuo-spatial workingmemory than has typically been presented in the literature. In the introductory section the authorsargue that mental imagery and visuo-spatial processes should be considered as part of workingmemory functions, namely a system that is devoted to the storage and manipulation of information.Although there is undoubted value in such a definition, a potential danger in such a broadclassification is that important functional differences between visuo-spatial abilities may becomeglossed over. For example, mental imagery is associated with many unique processes, bothfunctional and phenomenological, that do not necessarily occur in other forms of visuo-spatialprocessing (Pearson, 2001).

Cornoldi and Vecchi approach the problem of interpreting different cognitive functions byfocusing both on the nature of the information involved and the characteristics of the underlyingprocesses. They are guided in this by a theoretical framework they term a ‘continuity approach’, adetailed description of which forms the final chapter in the book. Their continuity model consists of avertical and horizontal dimension. The vertical continuum represents the amount of activity orcontrol required by a specific cognitive process or task, while the horizontal continuum representsthe specific material used in the task (e.g. visual, spatial, verbal etc.) This framework allows specificcognitive processes and tasks to be defined relative to their positions on both of these dimensions.Cornoldi and Vecchi draw a major distinction between ‘passive’ tasks that require only thatrepresentations be maintained, and ‘active’ tasks that require that representations be manipulated

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and transformed. They argue that individual differences in visuo-spatial performance associated withspecific populations, such as the congenitally blind or the elderly, can be understood better using thisactive-passive distinction.

This is an elegant and well-described framework that works very well in characterizing theindividual differences between groups described by Cornoldi and Vecchi, although I am lessconvinced how well it holds up as a general cognitive model of visuo-spatial working memory. Theauthors acknowledge that the existence of continuum vs. discrete dimensions in their frameworkremains a source of theoretical debate, and the definitions of exactly what constitutes a ‘passive’ or‘active’ task could be more tightly specified. On one level, the continuum model can be seen asoffering an alternative approach to that adopted by multi-component models of working memorysuch as those proffered by Baddeley (1986) and Logie (1995), which stress the interaction of discretecognitive subsystems rather than locating processes and tasks across continuous dimensions.Cornoldi and Vecchi make reference to my own work on visuo-spatial working memory, in whichI have argued for a pivotal role for central executive resources in the generation and maintenance ofvisual mental images (Pearson, 2001; Pearson, Logie, & Gilhooly, 1999). They argue that such aposition goes against a long-standing research tradition showing specific analogical properties ofmental images, but this is something I feel is far from the case! A task can place a high load ongeneral processing resources and still involve modality-specific representations and processes(Pearson, De Beni, & Cornoldi, 2001; Pearson, Logie, & Green, 1996; Salway & Logie, 1995),and attentional control has formed a key feature in influential models of imagery such as thecomputational approach proposed by Stephen Kosslyn (1980, 1994). In fact, this situation isperfectly compatible with the continuum framework outlined by Cornoldi and Vecchi, particularlyif their horizontal dimension is mapped on to type of modality-specific subsystem involved, and theirvertical dimension is mapped on to the extent to which a task or process needs to draw on additionalexecutive resources. From this perspective, therefore, the continuum model could be seen to offer adifferent but still compatible view on visuo-spatial working memory than that provided by multi-component models. I feel its strength lies in the fact that it may provide more flexibility in terms ofhow cognitive processes can be defined. Traditionally it has been common to label a task as beingpredominantly associated with only one component of working memory (e.g. digit span is classifiedas a verbal task, random number generation as an executive task etc.), without recognizing that many(if not all) tasks will require an interaction between several components, even if one is utilized to agreater extent than another.

I found this to be an enjoyable and stimulating book, which does an excellent job of reviewingkey concepts and theories in the area in a clear and authoritative manner. The fact that the book isstructured in terms of chapters that focus on individual differences in specific populations isparticularly welcome, as this will make it easily accessible to researchers who may be interestedonly in these specific populations, rather than issues connected with visuo-spatial workingmemory in general. I would strongly recommend this book to researchers or postgraduate stu-dents working in the area of visuo-spatial cognition, as well as those interested in seeing whatcontribution an individual differences approach can make to our understanding of psychologicalfunctioning.

REFERENCES

Baddeley, A. D. (1986). Working memory. Oxford: Oxford University Press.Kosslyn, S. M. (1980). Image and mind. Cambridge, MA: Harvard University Press.Kosslyn, S. M. (1994). Image and brain: The resolution of the imagery debate. Cambridge, MA:

MIT Press.Logie, R. H. (1995). Visuo-spatial working memory. Hove: LEA.Miyake, A., & Shah, P. (1999).Models of working memory: Mechanisms of active maintenance and

executive control. Cambridge: Cambridge University Press.Pearson, D. G. (2001). Imagery and the visuo-spatial sketchpad. In J. Andrade (Ed.), Working

memory in perspective. Hove, UK: The Psychology Press.Pearson, D. G., De Beni, R., & Cornoldi, C. (2001). The generation, maintenance, and transfor-

mation of visuo-spatial mental images. In M. Denis, R. H. Logie, C. Cornoldi, M. De Vega,

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& J. Engelkamp (Eds.), Imagery, language, and visuo-spatial thinking. Hove: The PsychologyPress.

Pearson, D. G., Logie, R. H., & Gilhooly, K. (1999). Verbal representations and spatial manipulationduring mental synthesis. European Journal of Cognitive Psychology, 11(3), 295–314.

Pearson, D. G., Logie, R. H., & Green, C. (1996). Mental manipulation, visual working memory,and executive processes. Psychologische Beitrage, 38, 324–342.

Salway, A. F. S., & Logie, R. H. (1995). Visuo-spatial working memory, movement control,and executive demands. British Journal of Psychology, 86, 253–269.

DAVID PEARSONUniversity of Aberdeen

Published online in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/acp.1008

Rethinking vision and attention

ACTIVE VISION: THE PSYCHOLOGY OF LOOKING AND SEEING. J. M. Findlay and I. D.Gilchrist. Oxford University Press, New York, 2003. ISBN 0-13-398876-7. £24.95 (paperback).

In keeping with the Oxford Psychology Series, Findlay and Gilchrist have put forward a novelapproach to a common research area. The central tenet of Active Vision is that the contribution eyemovement makes to visual attention is greater than the emphasis vision researchers have tradition-ally given it. They argue that saccades, rather than being downplayed, should be considered centralto theories of visual perception and cognition. Specifically, Findlay and Gilchrist suggest that theorientation of the eyes in order to project a stimulus of interest onto the high acuity region of theretina is the instrumental process of attention.

After laying down their central thesis in the first chapter, Chapter 2 describes some fundamentalphysiology of the visual system. However, rather than simply relating the usual biological basics(e.g. rods, cones, Lateral Geniculate Nucleus (LGN), magno and parvocellular pathways) the authorsnicely place these within the active vision framework. Thus we are told for example of how variousaspects of the oculomotor system work and physiological pathways of saccadic eye movement.Chapter 3 covers visual selective attention, including the relationship between covert and overtattention and the ‘early’ versus ‘late’ selection issue. In Chapter 4 we learn of work from gazeorienting studies whilst Chapter 5 provides an excellent review of work assessing eye movementduring reading. Chapter 6 reviews work from visual search, again placing this within the activevision framework by emphasizing the role saccades make to such tasks. In Chapter 7 the scanning ofnatural scenes is covered whilst Chapter 8 reviews clinical disorders of vision. In the final chapter,the book attempts to use active vision to better conceive the problem of ‘trans-saccadic integration’.That is, how we experience a stable and coherent visual world despite the frequent, rapid, andirregular sampling process performed by the eyes.

Findlay and Gilchrist’s starting point for their active vision account is to note the inadequacies ofwhat they call passive vision. Although the authors don’t state what is meant by this term, insteadassuming readers will ‘recognise this account’, they highlight some fundamental limitations of theapproach. The most serious of these, the authors argue, is the commonly held assumption thatinformation from the retinal image results in a ‘processed’ internal mental representation. At worst,this leads to the notion of the ‘picture in the head’, which, the authors argue, still pervades ourconception of vision. Another concern is the lack of emphasis placed on the inhomogeneity of theretina and its visual projections. The authors suggest that difficulties arise as a consequence of this.For instance, the number of neurons and connections needed to process all the information from eachretinal position would be vast. The main principles of active vision are then introduced. Central is therole of the fovea. Rather than being co-incidental, Findlay and Gilchrist argue that the fovea-basedorganization of the visual system is a fundamental feature. It is therefore surprising to find littlereference in the literature to differences in acuity across the retina.

Their thesis leads the authors to challenge one of the oldest tenets of visual attention theory; thenotion of a covert attentional system. This idea is most commonly expressed with reference to the

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