Is there a thing called dyslexia?

A controversy whether developmental dyslexia is qualitatively different from other forms of reading disability has existed among reading specialists for many years because poor readers, regardless of the labels attached to them, resemble each other symptomatically (i.e., in reading achievement). For this reason, it is difficult to establish a priori criteria based on symptoms to identify dyslexia and compare it with other forms of reading disability. One possible solution to this impasse is to see if poor readers differ in the etiology of their reading disability and, if they do, then to see whether one group of poor readers fits the traditional definition of dyslexia. This strategy was adopted in the present study. In this paper, it was hypothesized that the etiology of dyslexia is different from that of other forms of reading disability because there is a difference in the components that malfunction in dyslexia and other forms of reading disability. Studies have shown that the two components that account for a large proportion of variance in reading are decoding and comprehension. Previous studies also indicate that dyslexic children are deficient in decoding skills but not necessarily in comprehension. In this study, reading-disabled children were divided into two groups on the basis of their listening comprehension. Children whose listening comprehension was at or above grade level were placed in one group; poor readers with below-grade-level listening comprehension were placed in the second group. Both groups, however, were matched for reading comprehension. The two groups and a control group of normal readers were administered a number of tasks that were designed to assess the efficiency of the components of reading. It was found that poor readers with normal listening comprehension were deficient in tasks that involved grapheme-phoneme conversion (Component I, decoding). When tested on tasks that minimized decoding requirements, their reading comprehension was comparable to that of normal readers. In contrast, the group with sub-average listening comprehension was poor in measures of reading comprehension, even when decoding requirements were minimal. With the exception of very few children, this group also had adequate decoding skills. Because poor readers with normal listening comprehension had average or above average IQ, they conform to the traditional definition of dyslexia. Poor readers with below average listening comprehension had below average IQ and could be considered as "general reading backward." It was, therefore, concluded that the etiology of developmental dyslexia is different from that of general reading backwardness.