Development of dyslexic subgroups:

Abstract

There is a consensus that dyslexia is on a continuum with normal reading skill and that dyslexics fall at the low end of the normal range in phonological skills. However, there is still substantial variability in phonological skill among dyslexic children. Recent studies have focused on the high end of the continuum of phonological skills in dyslexics, identifying a “surface” dyslexic, or “delayed” profile in which phonological skills are not out of line with other aspects of word recognition. The present study extended this work to a longitudinal context, and explored differences among subgroups of dyslexics on a battery of component reading skills. Third grade dyslexics (n=72) were classified into two subgroups, phonological dyslexics and delayed dyslexics, based on comparisons to younger normal readers at the same reading level (RL group). The children were tested at two points (in third and fourth grade). The results revealed that the classification of dyslexics produced reliable, stable, and valid groups. About 82 percent of the children remained in the same subgroup category when retested a year later. Phonological dyslexics were lower in phoneme awareness and expressive language. Delayed dyslexics tended to be slower at processing printed letters and words but not at rapid automatic naming of letters, and relied more heavily on phonological recoding in reading for meaning than did phonological dyslexics. A subset of the delayed dyslexics with the traditional “surface dyslexic” pattern (relatively high pseudoword and low exception word reading) was also identified. The surface subgroup resembled the RL group on most measures and was not very stable over one year. The results are discussed in light of current models of dyslexia and recent subgrouping schemes, including the Double-Deficit Hypothesis.