Subtypes of developmental dyslexia: The influence of definitional variables

The purpose of this study was to investigate the hypothesis that the manner in which a reading disability is defined will influence the conclusions that are made about the characteristics of the disability. To test this hypothesis, learning disabled and normally achieving children, aged 6 to 14, were administered tasks measuring grammatical, shortterm memory, phonological, reading, and visual-spatial skills. The poor readers were divided into groups of poor readers withinadequate phonics skills,inadequate word recognition skills,adequate word recognition skills but low reading comprehension scores, andadequate word recognition scores but a slow reading speed.These children were compared with children who had normal reading scores. Children with deficits in phonics and/or word recognition scored significantly below normal on all the cognitive tests, except some of the visual-spatial tasks. Reading comprehension difficulties were characterized by average phonics, word recognition, and language skills but below average scores on some memory tasks. Slow readers had cognitive profiles similar to the normal children. The presence of a deficit in phonics and/or word recognition constituted the basis of the most serious impairment of language and memory functioning. Reading disabled children, defined in this manner, appear to be reasonably homogeneous in regard to the presence of language and memory problem. There does not appear to be evidence for a distinctive non-language impaired subtype within this type of reading disability. Children with low comprehension scores and/or slow readers did not have language problems. The definition of a reading disability appears to determine the subtypes and characteristics of reading disability that will emerge.