A MultiforM ApproAch of reAding disorders Mind, Brain and Education in Reading Disorders

This book offers a tentative synthesis of different methodological approaches in the study of dyslexia. A fairly large panel of authors from various backgrounds contributed to the different chapters, which are grouped in four parts. The first part is devoted to the specification of dyslexia in an evolutionary perspective (four chapters, 60 pages), the second one to the results of brain studies (five chapters, 116 pages), the third one to the analysis of four case studies by different researchers (five chapters, 70 pages, plus an appendix of 34 pages), and the last one to the longterm trajectory for reading and learning problems (three chapters, 38 pages). In chapter 1, the editors present several guidelines for relating the different chapters, with an emphasis on the dynamic tension between plasticity and constraints in neural networks, the absence of evolutionary precedent for reading, and the difference between explanations grounded on whole language (i.e., those with all linguistic levels taken together) versus those relying on phonology, and the presence of cyclic growth circles. The evolutionary perspective leads the authors to define reading as a kludge (i.e., a system made of poorly matched components), implying that reading performances are achieved in multiple ways, based on combinations of genes, and that problems in reading acquisition possibly arise from a variety of small localized disturbances. Chapter 2, by M. H. Immordino-Yang and T. W. Deacon, deals with the evolutionary perspective on reading and reading disorders. In the absence of organic disorders and given the fairly recent arousal of writing systems in human history, the authors consider that literacy cannot be assigned to specific genes or to genes unique to humans. Rather, reading performances would be related to a coincidence of traits with diverse developmental trajectories. Possible sources of reading disorders in the brain are then reported, in visual areas, in the Wernicke area, and in the connection between hemispheres. Differences between children and adults are related to differences in neural plasticity, with changes toward more constrained processing around 6 years. Possible specific brain localizations of reading deficits are then considered, with an emphasis on the sensorimotor explanation of developmental dyslexia, especially the auditory explanation and the visual– magnocellular explanation. However, this is challenged by the view that reading is a kludge, implying variability, combination of genes, and small localized disturbances. A nested model of reading deficiencies is suggested, in which low-level disturbances are compensated by increased workload at higher levels (compensatory strategies). Chapter 2 ends with an essay, by V. S. Caviness, on individual differences in brain volume. In chapter 3, A. M. Galaburda and G. F. Sherman examine the questions raised by the genetics of dyslexia. After warning that correlations between genes and dyslexia are difficult to interpret because anatomic and behavioral phenotypes are still debated, the authors take as a guideline the functional and anatomic implications of ectopias. They remind us that although there are multiple genes for a single system, an abnormal single gene affects the whole system. Difficulties of linking genes to complex behaviors are discussed, including those arising from the role of culture and writing systems in reading acquisition. Taking phonological deficits to characterize the behavioral phenotype, genetic studies point to seven chromosomes and two different genes. The phenotype is redefined in terms of phonological and sensory or perceptual problems in spoken language processing, with an emphasis on rapid auditory processing. The link between anatomic and behavioral phenotypes is examined, with evidence from animal models showing the implications of ectopias for the thalamus anatomy and the audition of rapid changes. Interestingly, the earlier development of higher-order cortices suggests that the latter might be the cause rather than the consequence of sensory deficits. In conclusion, the authors consider the possible implications of top-down processing; they admit that causality is not proved and draw the attention to the fact that genes for ectopia are not genes for dyslexia. Chapter 4, by M. Wolf and J. Ashby, deals with rapid auditory processing, phonology, and other explanations of developmental dyslexia. The possible evidence on the rapid auditory naming performances and those related to vision, audition, phonology, and whole language, together with neurophysiological differences, are presented in a historical perspective. The main emphasis is on variability and its implications for the study of dyslexia.