Defining Dyslexia

Terminological issues

This book is devoted to a developmental cognitive disorder, more precisely, to a specific learning difficulty in reading and spelling – developmental dyslexia. To begin with it is important to ensure terminological and definitional clarity, which would be most helpful for appropriate understanding of the described phenomena. Reading disorders are quite intensively studied and several terms have been proposed in different countries to denote reading deficits of various kinds, in children and adults alike. Apparently, such a situation is a consequence of the complex nature of the skill in question as well as the diverse causes and multiple types of reading and spelling disorders.

Let us focus first on the distinction between acquired and developmental disorders. Acquired reading and spelling deficits result from brain injury or disease and connote either total or partial loss of the already possessed ability to read or spell. The intensity of symptoms largely depends on the size and location of the lesion as well as the age of the person. Acquired alexia and acquired agraphia are spelled out as a total loss of the faculty of reading and spelling, respectively, while acquired dyslexia denotes only a partial disappearance of reading competence, and dysgraphia is a partial loss of spelling ability. To stress again, acquired reading and spelling disorders are connected with deficits in qualifications that a given person, be it an adult or a child, had already possessed prior to brain injury (Bogdanowicz, 1989, 1999; Krasowicz, 1997).

Acquired reading disabilities in adult patients are often taken as a model for interpreting and achieving further understanding of the neurological concept of developmental reading impairments (Borkowska, 1997). However, such an approach is rejected by Hulme and Snowling (2009), who advocate investigating developmental reading disorders in children by relating them to patterns of typical reading development in children. Much as adult models usefully specify what normally constitutes a result of development, they do not describe the development itself.