Differential effects of orthographic transparency on dyslexia: word reading difficulty for common English words.

Orthographic transparency is increasingly being recognised as an important factor in determining the manifestation of dyslexic tendencies in individuals. Recent evidence has shown that normal English-speaking children have reading deficits in the range associated with same age dyslexic German-speaking children for less frequently used words, and English orthography has been identified as a contributing factor. Spencer (Reading (1999) 33(2), 72-77; Journal of Research in Reading (1999) 22(3), 283-292) has proposed a predictive model for English children's reading and spelling deficits, based on orthographic features. Two main factors have been identified: consistency of sound representation and inclusion of redundant letters in English words. Using new data for reading, a unified model will be discussed which incorporates measures of depth of orthographic transparency and relates these to recent positron emission tomography (PET) research. Implications for the relative frequency and severity of dyslexia in both deep and shallow orthographies is considered in the light of such studies.