Wednesday, February 18, 2015

Phonological deficits in specific language impairment and developmental dyslexia: Towards a multidimensional mode

Ramus, F., Marshall, C.R., Rosen, S., & van der Lely, H.K.J. (2013). Phonological deficits in specific language impairment and developmental dyslexia: Towards a multidimensional model. Brain, 136, 630-645.

Children with specific language impairment (SLI) have an unexpected, developmental delay in the onset or developmental of oral language. Children with developmental dyslexia fail to learn to read at the expected rate despite adequate opportunities. SLI and dyslexia often co-occur leading to questions about distinctions between these impairments. Several views exist regarding the co-existence of these disorders: (1) SLI is a more severe form of dyslexia; (2) Phonological deficits are common to both SLI and dyslexia. Children with SLI also have impairments in other aspects of language (i.e., grammar, word knowledge); (3) The phonological deficits observed in SLI and dyslexia are qualitatively different.

These researchers compared models to fit data from 127 children who had completed measures of grammatical skills, sentence processing, manipulating sounds in words, discriminating sounds in words, and others. The data were explained by 3 factors as follows: (1) nonphonological skills – that is, measures not related to the sound structures of words including grammatical skills and sentence processing, (2) phonological awareness – that is, tasks requiring some sound manipulations in words, and (3) phonological representations – that is, tasks requiring recognition of the sound structures in words. The factors were associated with the different impairment profiles in unique ways: Children with both SLI and dyslexia had low scores on all three factors. Those with SLI-only scored low on the phonological representations and nonphonological skills factor, and those with dyslexia-only on the phonological awareness factor only.

The authors argued that there might be qualitative differences in the phonological deficits that characterize SLI and dyslexia. Those with SLI may have poor phonological representations stored in long-term memory, which makes it difficult for them to complete phonological awareness tasks too. Those with dyslexia, on the other hand, may have intact phonological representations, but have difficulty accessing and manipulating this information. Deficits in nonphonological skills may be characteristic of those with SLI, but also those who struggle with comprehending what they read rather than decoding words.

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