1 UNESCOG (Unité de recherche en Neurosciences Cognitives), Université Libre de Bruxelles (ULB), Belgium
2 CNRS, Laboratoire de Psychologie de la Perception, Université Paris Descartes
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.