Developmental dissociations between lexical reading and comprehension: evidence from two cases of hyperlexia

We report two cases of developmental hyperlexia - JY and AD - who performed at normal levels or above in converting print into speech, but who were very impaired in spoken and written word comprehension. Our investigations focussed on whether these cases displayed evidence for normal acquisition of lexical reading skills, as indexed by unimpaired performance for age in reading aloud a set of irregular words, despite poor acquisition of semantic knowledge of the same words. In both cases, this dissociation was evident. The pattern of results was also demonstrated at an item level: the two cases showed no significant differences in reading accuracy for irregular words which they could define than for those which they could not. The results provide further evidence for the existence of a direct-lexical route from orthography to phonology, which is not necessarily mediated by semantic knowledge.