The goal of the proposed research is to understand the bases of various forms of dyslexia resulting from damage to the early stages of visual work recognition. Of particular interest is neglect dyslexia--those impairments of reading which disproportionately affect the side of words contralateral to the side of brain damage (either the right or the left hemisphere). The principal aims of the research are 1) to characterize the various forms of neglect and other peripheral dyslexias in terms of damage to the perceptual, attentional and cognitive/linguistic mechanisms that underlie visual word recognition and reading and 2) to specify neuroanatomical correlates of the different forms of the deficit. As part of this effort we will evaluate a set of hypotheses about the representation and processing of spatial structure by the normal visual word recognition system, and how selective damage to parts of this complex process can result in the observed forms of neglect and other peripheral dyslexias. To address these issues, we propose to carry out a two-phase program of research. Phase I will consist in the administration of an extensive battery of tests to brain-damaged patients with clinical signs of unilateral visual neglect in reading or other tasks (e.g. line cancellation) and patients with other forms of peripheral dyslexia; Phase II will consist in the highly detailed investigation of individual patients who present with relatively selective deficits of the various levels of processing in the early stages of visual word recognition. Phase I will serve as the basis for an initial """"""""classification """""""" of patients into subtypes corresponding to the forms of neglect dyslexia or other peripheral dyslexias predicted by the multi-stage model of visual word recognition. Phase II will serve as the basis for testing specific hypotheses regarding the attentional, perceptual, and cognitive/linguistic components operating at different levels of representation. The results of both phases will be used to explore hypotheses about the neuroanatomical correlates of the different subtypes of neglect dyslexia and of the processing mechanisms that are implicated in these forms of neglect. In short, the proposed investigation should provide important evidence for our understanding of: 1) the clinical manifestations of various forms of neglect and other peripheral dyslexias; 2) the nature and organization of perceptual, attentional and cognitive/linguistic processes in normal reading; 3) the possible neuroanatomical correlates for the hypothesized components of the visual word recognition system; and 4) the relationship between various forms of neglect dyslexia and the more general disorder of unilateral spatial neglect.
