Leppänen, P. H. T.
Department of Psychology, University of Jyväskylä, Finland
Speech perception problems as a risk factor for dyslexia
The role of dysfunctional neurocognitive processes for dyslexia and their interaction with phonological problems, one of the major underlying factors for dyslexia, still remain unclear. Several behavioral and brain response studies suggest that a link could be atypical speech perception. Event-related potential (ERP) findings from two large scale longitudinal studies (Jyväskylä Longitudinal Study of Dyslexia, JLD, Finland, and Dutch Dyslexia Programme) show that infant brain responses to speech sounds are related to familial risk for dyslexia and also predict later reading skills at school-age. For example, dyslexic children participating in JLD, who were diagnosed at school-age and had a familial risk background, had atypical processing of various sound features already at birth and at the age of six months. Infant brain responses also correlated to childhood language and pre-school age reading related skills, and reading and writing skills at school age. Atypical brain activation also persisted in development until pre-school and school age. Speech perception at the behavioral level also continued to differ between dyslexic and typical readers. Further, long term phonemic representations, as measured by the mismatch negativity (MMN) brain response, appear to be atypical in school-aged children for a native speech sounds in a large scale European cross-linguistic ERP-study (a part of Neurodys). Such findings, overall, suggest that speech perception may have cascading effects on later linguistic and phonological skills and consequently on dyslexia. However, evidence also shows that not all individuals with dyslexia have problems with speech perception or atypical responses to native speech sounds. This suggests that problems in speech perception are not likely alone a sufficient reason for developmental dyslexia, but rather one endophenotype /risk factor.