Orthographic specific visual processes during word recognition in developmental dyslexia: an event-related potential study
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There is accumulating evidence from Event-Related Potential (ERP) studies with adult populations of a visual system specialization for orthographic information, which is thought to develop during childhood with increased exposure to text. However, few ERP studies of word reading in children have focused on orthographic specific visual processes involved single word reading. The current examination of electrophysiological activity during word recognition in children was an investigational one to further the current understanding of normal development of brain systems involved in reading. A comparison of brain activity between normally developing readers and children with dyslexia provided opportunity to look for impairment at a basic level of visual processing. The relationship between ERP activity and reading and language skills was also examined. ERP data were obtained from children aged 9-15 in a group of children with dyslexic (n = 12) and a group of normally developing readers (n = 11) to examine activity during an implicit word recognition task. ERPs elicited by orthographic (words, pseudowords, consonant strings) and visual (false fonts, symbol strings) word-type stimuli were recorded at sites over the posterior scalp. In order to examine the relationship between ERP activity and language processes, these children completed measures of phonological, orthographic, and naming processes. Grand averaged ERP waveform for both groups showed a negative going component between 170-270ms with a peak around 230 for all word-type stimuli. ANOVA results found the N230 amplitude elicited by orthographic stimuli significantly larger than the ERPs elicited by visual stimuli in the control but not dyslexic group. The robust orthographic effect in the control group is consistent with the developmental hypothesis that visual word expertise increases with age and reading exposure and supports the understanding of the N1 as an index of reading related visual specialization. Regression analyses found measures of phonological, not orthographic, processes to significantly predict variance in ERP amplitude.