ABSTRACT
This chapter deals with reading disability, which is often referred to as dyslexia, especially in the medical and neuropsychological literature. Most of the developmental research from a biological perspective has focused on reading rather than on writing and on disabled reading rather than on normal or exceptionally good reading. A perennial problem complicating interpretation of findings across studies is that researchers have not reached a consensus on how to define learning disability in general or reading and writing disability in particular. Reading disability has been defined in different ways by various investigators, and reading disability may be confounded with writing disability and/or attentional deficit in many studies. Extragenetic factors, such as developmental history of interactions with the environment, have important implications for both basic research and educational practice. Heritability studies provide information on the degree to which genetic factors influence a particular behavior, trait, or disorder in the population, but they provide no information about individuals.
