Developmental dyslexia: Heterogeneity without discrete subgroups.

Is the dual route model of word recognition useful in explaining individual differences in reading behaviors for most developmental dyslexics? Many past case studies of surface and phonological acquired dyslexics and a few similar studies of developmental dyslexia have suggested this might be so. The present study investigated individual differences among a group of 65 dyslexics, age 10 to 13, in reading, phonemic segmentation, and word retrieval. The dyslexics' performance was compared to that of 65 reading age controls and 17 age-matched good readers. The research questions were: (1) Are there discrete subgroups of developmental dyslexics as suggested by the case studies? (2) How do oral language measures relate to the various reading tasks? The data indicated there were no discrete subgroups within the group of dyslexics; in addition, the variability in performance on reading tasks was quite similar for the dyslexic and reading age-control groups. A few dyslexics resembled phonological dyslexics and surface dyslexics, but these subjects were still part of a continuum. We also report the relationship between phonemic segmentation and word retrieval and various reading tasks. It appears that dyslexics at extreme ends of the continuum may exhibit quite different patterns from each other in their oral language task performance as well as in their reading.