Research on fluent adult readers has shown that these brain areas seem to be (at least partially) recruited even in processing arbitrary associations between letters and speech sounds, indicating a certain degree of plasticity in audiovisual brain areas during reading acquisition ( Amedi et al., 2005 Blomert & Froyen, 2010 Hocking & Price, 2008). The effects of audiovisual integration (i.e., the absolute difference between bimodal and unimodal presentations) and audiovisual congruency (i.e., the absolute difference between matching and mismatching bimodal presentations) have mainly been localized in the auditory cortex and the superior temporal cortex ( Amedi, von Kriegstein, van Atteveldt, Beauchamp, & Naumer, 2005 Hocking & Price 2008), with possible left lateralization ( Calvert, 2001 Calvert, Brammer, & Iversen, 1998). The processing of natural audiovisual associations (e.g., the correspondence between speech and lip movements) has been widely explored in the literature. We hypothesized that during reading acquisition pre-existing brain circuits for audiovisual processing should become progressively tuned to the arbitrary relationships between letters and speech sounds ( Blomert, 2011). The present MEG study focused on these audiovisual processes, testing how they changed as a function of developing reading abilities. Efficient reading skills crucially depend on the ability to compare and connect visual and auditory representations of letters ( Blomert, 2011). However, the core of reading acquisition lies in the interaction between these two modalities. A considerable amount of research on reading-related brain changes has examined this plasticity in either visual and auditory brain circuits ( Dehaene et al., 2010, 2015 Goswami & Ziegler, 2006 Ziegler & Muneaux, 2007). Learning this life-changing skill thus requires considerable modulation of pre-existing brain networks, such as the visual object recognition and spoken language networks ( Carreiras et al., 2009 Dehaene, Cohen, Morais, & Kolinsky, 2015). Literacy is a relatively recent cognitive achievement in human evolution for which there are no specialized neural circuits already in place. ![]() This reading-specific brain plasticity implies (partial) recruitment of pre-existing brain circuits for audiovisual analysis. These findings suggest that children progressively change the way they treat audiovisual syllables as a function of their reading experience. Both studies showed that during the first years of reading instruction children gradually set up audiovisual correspondences between letters and speech sounds, which can be detected within the first 400 ms of a bimodal presentation and recruit the superior portions of the left temporal cortex. To address these questions, the present longitudinal and cross-sectional MEG studies characterize the temporal and spatial neural correlates of audiovisual syllable congruency in children (4-9 years old, 22 males and 20 females) learning to read. Understanding the neural adjustments required for acquisition of these arbitrary audiovisual associations can shed light on fundamental reading mechanisms and help reveal how literacy builds on pre-existing brain circuits. ![]() The ability to establish associations between visual objects and speech sounds is essential for human reading.
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