The influence of intelligence and cognitive abilities on the reading ability of Japanese students with developmental disorders.

Objective: We examined the differences in reading skills between Japanese students with developmental dyslexia (DD) having developmental disorders who had borderline IQ (BIQ) and those who had normal IQ (NIQ), and the influence of cognitive factors through subscale scores of the Wechsler Intelligence Scale for Children - Fourth Edition on the reading skills of all students with DD having developmental disorders.

Methods: One-way analysis of variance revealed differences in reading scores among the four groups (DD with NIQ, DD with BIQ, as well as non-DD with NIQ and non-DD with BIQ as control groups). To examine the influence of cognitive factors, we used multiple regression analysis for all participants, and then for participants with DD.

Results: Regarding hiragana nonword fluency reading, no difference was observed between the two DD groups, and cognitive factors did not affect the performance of all participants with DD. Concerning hiragana word fluency reading, DD with NIQ group performed better than DD group with BIQ, and working memory index affected reading skills of participants with DD. Regarding kanji accuracy reading, DD with NIQ group performed better than DD with BIQ group, and processing speed index affected performance of participants with DD.

Conclusions: The results of hiragana reading suggest that the two DD groups shared similar weak sub-lexical route processing, while the acquisition of lexical route processing was hindered by lower IQ and weak phonological working memory in transparent phonographic hiragana reading. For kanji reading, lower IQ and weak visuomotor processing ability hampered the learning of visually complex logographic kanji characters.