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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