N300 indexes deficient integration of orthographic and phonological representations in children with dyslexia

In transparent orthographies, like German, children with developmental dyslexia (DD) are mainly characterized by a reading fluency deficit. The reading fluency deficit might be traced back to a scarce integration of orthographic and phonological representations. In order to address this question, the present study used EEG to investigate the N300, an ERP component which has been associated with the integration of orthographic and phonological representations. Twenty children without DD and 18 children with DD performed a phonological (P)-orthographic (O) matching task (P-O condition), which tapped the integration of orthographic and phonological representations. A control task was applied which did not require the integration of orthographic and phonological representations and consisted only of orthographic information (O-O condition). The O-O condition revealed a similar N300 distribution between groups with a bilateral activity over fronto-temporal electrodes. However, in the P-O condition N300 differentiated the 2 groups of children. The control group revealed greater activity over left fronto-temporal electrodes, whereas the N300 was distributed bilaterally in the group of children with DD suggesting deficient integration of orthographic and phonological representations. These findings might be related to the reading fluency deficit as it was also observed that better reading fluency was correlated with higher (r=-.36) and earlier peaking (r=-.33) N300 amplitudes in the left hemisphere and attenuated N300 amplitudes (r=.45) in the right hemisphere. Standardized low-resolution electromagnetic tomography analysis (sLORETA) revealed that children with DD rely more on right temporo-parietal brain areas compared to children without DD. Furthermore, in order to rule out that earlier deficient processes might influence the group differences found in the N300, we analyzed the N170 for group differences. We did not find significant differences between children without DD and children with DD. In conclusion the results suggest deficient integration of orthographic and phonological representations in dyslexia, as indexed by the N300, and further highlight how this activity is relevant for fluent reading.