A developmental perspective on dyslexic subtypes

In this paper we apply a developmental model of reading to the question of dyslexic subtypes. Groups of normal readers (n=40) and dyslexic children (n=50), matched on reading level and IQ, were given a comprehensive test battery measuring level of development of visual, phonological, and orthographic skills. As a group, dyslexics deviated from normal readers of equivalent reading achievement primarily in phonological skills (spelling-to-sound translation and phonemic analysis), although limited differences in knowledge of word-specific spellings were also observed. Dyslexics were superior to the younger normal readers in visual processing of print. Analysis of individual data by reference to the reading level control group revealed three major subgroups: a group with a specific deficit in phonological processing of print (52 percent), a group with deficits in processing both the phonological and orthographic features of printed words (24 percent), and a group with phonological deficits in language (8 percent). The remainder of the sample (16 percent) had specific deficits in visual or orthographic processing of print, in spelling, or did not differ from the control group. The data support the view that most developmental dyslexics have a specific language disorder involving some aspect of phonological processing. However, small subgroups with very different configurations of reading and nonreading difficulties may exist as well.