ABSTRACT
By definition, dyslexic children and adults have abnormally low reading skills in spite of normal educational opportunity and general intelligence (Critchley, 1970). Over the past several years, we have been studying the unexpected reading failures of dyslexic children to better understand their expression and etiology. We have examined a wide variety of component skills in reading and related cognitive processes to see which of these are uniquely deficient, and to see if the pattern of deficits varies significantly among dyslexic children (Olson, Kliegl, Davidson, & Foltz, 1985). We have explored the genetic and environmental etiology of deficits in component reading and cognitive skills by comparing the degree of similarity for identical and fraternal twins (Olson, Wise, Conners, Rack, & Fulker, 1989). For reasons that will become apparent in this chapter, most of our research has focused on deficits in word recognition and its component processes, some of which are uniquely deficient and significantly heritable in our sample of dyslexic children.
