Phonemic Deficits: A Core Symptom of Developmental Dyslexia?

Abstract

The basic weakness in developmental dyslexia is lack of facility with words. Instead of searching for various behavioural, educational or social correlates of this deficiency, we analysed the critical cognitive and linguistic demands raised by the alphabetical code. Dyslexic children suffer from poor access to the phonemic units of spoken language and this lack of phonemic awareness is then a serious obstacle in the process of reading acquisition. A longitudinal study of children from preschool to the end of grade 3 clearly demonstrated that a speciflc phonemic deficiency already exsisted before starting school among 35 dyslexics. The poor reading and spelling development observed among these children was interpreted as causally related to their problems with the elusive and abstract phonemes. In a second study with dyslexic adolescents we looked for the biological basis of poorly developed phonological skills. Strong tendencies of phonological difficulties were observed in families of dyslexics. Magnetic resonance imaging examinations of the brains of dyslexics and age-matched controls revealed a significantly higher incidence of symmetric planum temporale in the former. All dyslexics with pronounced phonological problems showed abnormal symmetry of the investigated brain regions. Thus a neurological correlate of a critical symptom of dyslexia seems to have been revealed.