Leppänen, P. H. T. 1 & Serniclaes, W. 2, 3
1 Department of Psychology, University of Jyväskylä, Finland
2 UNESCOG (Unité de recherche en Neurosciences Cognitives), Université Libre de Bruxelles (ULB), Belgium
3 CNRS, Laboratoire de Psychologie de la Perception, Université Paris Descartes
Speech perception problems as a risk factor for dyslexia, Paavo H.T. Leppänen.
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.
Allophonic theory of dyslexia : Recent developments and perspectives,
Evidence from a wide range of studies indicates that individuals with dyslexia have a phonological deficit. The phonological problems experienced by dyslexics have initially been related to the access to phonemic representations but they are now more and more frequently attributed to the perceptual processing of phonemes. However, the very nature of the phonemic deficit in dyslexia remains debated. One of the questions raised is whether dyslexics have merely a lower acuity in phoneme perception or, more radically, whether they do not use phonemes for perceiving speech. This last possibility has been formalized in the framework of allophonic theory. Normally, the universal predispositions for perceiving speech are adapted to the phonemes of the environmental language during the first year of life. According to allophonic theory, dyslexic people do not adapt these predispositions to their native language. Consequently, they segment speech sounds into universal ?allophonic? segments that do not correspond to language-specific phonemes. In support to this theory, behavioral and brain studies conducted in different languages (French, Dutch, Spanish) suggest that dyslexics present an over-discrimination of allophonic features, different from the language-specific phonemic features. Also, convergent evidence from behavioral and brain data indicates that dyslexics have a better acuity in the perception of subphonemic segments than typical readers, that might be related to an oversampling at some cortical time scales. Finally, intervention studies conducted in different laboratories point to possible impact of remediation of allophonic perception on reading performances. However, several questions remain. For example, over-discrimination of allophonic features by dyslexic people has not been found in all behavioral studies. However, other studies consistently found that when the dyslexics? allophonic sensitivity was absent from their behavioral responses it was still present at the neural level. This raises different questions about alternative neural pathways for accessing to phoneme perception and their possible exploitation in remediation assays.