Orthographic dependency in the neural correlates of reading: evidence from audiovisual integration in English readers

Reading skills are indispensible in modern technological societies. In transparent alphabetic orthographies, such as Dutch, reading skills build on associations between letters and speech sounds (LS pairs). Previously, we showed that the superior temporal cortex (STC) of Dutch readers is sensitive to the congruency of LS pairs. Here, we used functional magnetic resonance imaging to investigate whether a similar congruency sensitivity exists in STC of readers of the more opaque English orthography, where the relation among LS pairs is less reliable. Eighteen subjects passively perceived congruent and incongruent audiovisual pairs of different levels of transparency in English: letters and speech sounds (LS; irregular), letters and letter names (LN; fairly transparent), and numerals and number names (NN; transparent). In STC, we found congruency effects for NN and LN, but no effects in the predicted direction (congruent > incongruent) for LS pairs. These findings contrast with previous results obtained from Dutch readers. These data indicate that, through education, the STC becomes tuned to the congruency of transparent audiovisual pairs, but suggests a different neural processing of irregular mappings. The orthographic dependency of LS integration underscores cross-linguistic differences in the neural basis of reading and potentially has important implications for dyslexia interventions across languages.