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Florida Learning Disabilities Research Center



Dyslexia: It’s complicated

By: Mia Daucourt

Dyslexia is one of the most common learning difficulties that children experience, but we are still trying to understand the specific weaknesses that cause its development. The term “dyslexia” refers to children who, despite having average levels of intelligence and receiving quality instruction, persistently struggle to accurately and fluently read words. The most common explanation for dyslexia is weak phonological awareness, or a “phonological deficit.” Phonological deficit refers to a problem with associating letters and letter combinations with the sounds of language. However, there is a fundamental problem with this phonological deficit explanation for dyslexia: many children who have phonological deficits do not go on to develop dyslexia. So what else is going on? The most likely explanation is that dyslexia develops because of multiple deficits, not just one. It may be that children with a phonological deficit, along with additional reading-related deficits, are the ones who go on to develop dyslexia.

A recent study by Catts and colleagues (2017) tested this multiple deficit theory of dyslexia in children from kindergarten to second grade. Specifically, they tested whether children’s phonological awareness, oral language, and rapid automatized naming (RAN) skills helped explain children’s development of dyslexia in second grade. Oral language refers to spoken language skills, and RAN refers to the ability to rapidly name letters, numbers, colors, or objects.

Their results supported both the multiple deficit theory and phonological deficit theory of dyslexia. In support of the multiple deficit theory, they found that children with a combination of deficits in phonological awareness, oral language, and RAN were the most likely to develop dyslexia. The remainder of their findings showed that although multiple deficits matter, a phonological deficit is a core deficit in dyslexia, and problems in oral language and RAN may serve as additive factors, but only when phonological deficits are also present. In fact, kindergarten children with a phonological deficit alone were found to be five times more likely to have dyslexia in second grade than children without such a deficit. On the other hand, children with no phonological deficits and problems in oral language only, RAN only, or both oral language and RAN were the least likely to develop dyslexia. Finally, in the other direction, dyslexic children were found to have the most severe phonological deficits.

In conclusion, phonological deficits appear to be a causal weakness in dyslexia, but they’re not all that matters. It’s important for researchers, practitioners, and instructors to be aware of children’s performance in multiple reading-related skills in order to properly identify children at risk for developing reading problems. Catts and colleagues’ (2017) work is an important step forward in better understanding the nature of dyslexia.

Catts, H. W., McIlraith, A., Bridges, M. S., & Nielsen, D. C. (2017). Viewing a phonological deficit within a multifactorial model of dyslexia. Reading & Writing, 30, 613-629.