Developmental dyslexia is characterised by poor reading and spelling skills affecting up to twenty percent of English children and adults (Habib, 2000). Phonological deficits have been proposed to be a core feature of dyslexia (Snowling, 2000). Here we used event-related potentials (ERPs) to examine neurophysiological correlates of phonological processing in dyslexic adults. We found that, unlike controls, dyslexic adults engaged in a lexical decision task fail to shift their attention to phonological variations within a stream of alliterated words. However, when phonological deviants are made task-relevant, no differences between dyslexic adults and controls are found, even for minimal pairs (e.g., /b/ - /p/). The first result is consistent with a phonological deficit in developmental dyslexia, but the latter suggests an important role of attention. Therefore, we subsequently used a phoneme deletion task in which
phonological deviants remained task-relevant but attentional demands were increased. In such conditions, the phonological deficit, characterized by significantly reduced P3 ERP amplitudes, reappeared in dyslexic adults. To test the verbal specificity of this effect, we then compared phoneme and pure tone deletion: In both tasks dyslexic participants showed a P3b amplitude reduction, which correlated with reading and spelling performance. Finally, we tested whether the attentional deficit generalizes to the visual modality using a nonverbal oddball paradigm in which participants had to detect targets differing from the standards in one dimension (pitch or volume for tones; form or contrast for shape) or two dimensions simultaneously. Contrary to our
predictions, we found reduced P3b amplitudes in dyslexic adults for stimulus changes in one but not two dimensions. The findings are discussed in relation to compensation strategies and ADHD co-morbidity. Overall, our results suggest the existence of an attention capacity deficit in developmental dyslexia, which may interact with phonological processing but is not specific to verbal material.