ABSTRACT

Psychologists researching the mechanisms and processes underlying normal cognitive functions have become increasingly interested in the study of how these may break-down in patients with acquired neurological damage. In this chapter, I shall give an introduction to how cognitive psychologists have interpreted the varieties of disorders of reading and spelling that follow brain damage and which are often concomitant features of aphasia. Such disorders are acquired dyslexias and dysgraphias, because they occur as a result of neurological damage in adults in whom reading and spelling were premorbidly normal. As such, they are to be distinguished from developmental disorders of literacy (to which the blanket term dyslexia is commonly applied). This chapter will review a number of the major varieties of these acquired disorders of literacy. My approach throughout the chapter will be a cognitive neuropsychological one (see Ch. 1). Although not to the taste of all neuropsychologists, this has been the approach within which much of the recent detailed empirical characterization of acquired dyslexia and dysgraphia has taken place. Cognitive neuropsychology entails a reciprocal relationship between theories of normal cognitive processes and investigations of acquired disorders of those processes. On the one hand, data from neurological patients are used to illuminate theories of normal processing. On the other hand, patterns of specific impaired and preserved abilities of particular neurological patients are interpreted within models of normal processing: the performance observed is presumed to reflect selective breakdown of (or functional dissociation between) separable, normal processing systems. In this chapter I will focus on this second, interpretative aim of cognitive neuropsychology and so, before my descriptive account of reading and spelling disorders, I will need to discuss briefly the general theoretical framework within which one may attempt to understand normal visual word recognition and production. I shall first consider reading. I shall discuss the construction of a model of the oral reading of single words (and nonwords such as MANT) and show how predictions concerning acquired disorders of reading may be derived from it. These hypothetical disorders will be used to structure a discussion and evaluation of different varieties of acquired dyslexia. Varieties of acquired dysgraphia will 179then be described and interpreted within a structurally similar model of spelling production. It will then be necessary to consider the heterogeneity within these varieties of reading and spelling disorders and to consider the utility of analyses based upon clinical syndromes. Finally, I shall offer a brief discussion of the relationship between reading and spelling disorders.