Types of developmental dyslexia

To the best of our knowledge, the first person to suggest that there are different types of developmental dyslexia was the educational psychologist Helmer Myklebust. In Myklebust (1965), he suggested that some dyslexic children have difficulty in learning to read because they “could not acquire the auditory equivalents of the appearances of the letters” (p. 30: Myklebust referred to this condition as “auditory dyslexia”), whilst for other dyslexic children the problem is “the inability to mentally visualize letters and sounds” (p. 23: Johnson and Myklebust, 1967, referred to this condition as “visual dyslexia”). These ideas were taken up by the pediatric neurologist Elena Boder (see for example Boder, 1968, 1969, 1970, 1971, 1973). She developed a diagnostic screening test based on the distinction between auditory and visual dyslexia and this allowed her to characterize these two subtypes in a little more detail. She proposed (see e.g. Boder, 1973) that some dyslexic children, when attempting to read aloud words that are not in their sight vocabularies, are typically unable to do so because they are “unable to sound out and blend the component letters and syllables of a word” (p. 688). This is Myklebust’s auditory dyslexia. Boder referred to it as “dysphonetic dyslexia”. These days the form of developmental dyslexia in which there is a specific difficulty in reading aloud unfamiliar letter strings is called “developmental phonological dyslexia”. A second group identified by Boder (1973) were those dyslexic children who are “analytic readers” and read “by ear”, “through a process of phonetic analysis and synthesis, sounding out familiar as well as unfamiliar combinations of letters, rather than by whole-word gestalts. . . [they] can often read the word list by phonetic analysis up to or near [their] grade level, missing out only words that cannot be decoded phonetically” (that is, irregular words). This is Myklebust’s visual dyslexia. Boder referred to it as “dyseidetic dyslexia”. These days the form of developmental dyslexia in which there is a specific difficulty in reading irregular words aloud is called “developmental surface dyslexia”. Developmental dyslexias 2