Lohvansuu, K. , Hämäläinen, J. A. & Leppänen, P. H. T.
Department of Psychology, University of Jyväskylä
The role of speech processing problems as a risk factor for dyslexia still remain unclear. Here our purpose was to study whether brain responses reflecting early stages of speech processing (obligatory event-related potentials, ERPs) would be related to phonological processing, decoding and spelling skills in children with and without dyslexia. ERPs of 9 - 11 -year-old Finnish children (50 typical and 58 dyslexic readers) were recorded to a repeated /i/-vowel presented in a cross-linguistic oddball-paradigm of a European NeuroDys study. Temporal principal component analysis (tPCA) was applied to identify the obligatory auditory responses. The ERPs at the time windows of P1 (70 ms) and N1 (110 ms) were differently associated with behavioral measures in dyslexic readers compared to typical readers. In typical readers, a larger P1 response at the right temporal areas was related to better performance in pseudoword phoneme deletion and pseudoword spelling tasks as well as faster pseudoword reading time. A larger response at the N1 time window was related to faster pseudoword decoding only. In dyslexic readers, however, a larger right hemispheric P1 was only related to pseudoword repetition. Instead, larger left hemispheric responses at the P1 and N1 time windows were related to better performance in the spelling task. In dyslexic readers, no association between obligatory ERPs and pseudoword decoding time was found. These results indicate that basic level speech processing is related to phonological processing, spelling accuracy, and decoding speed, but differently in dyslexic and typical readers. In typical readers, the associations of the responses at the right hemisphere to behavioural measures are in line with findings of right hemispheric dominance of vowel processing. Dyslexic readers show, in contrast, the opposite hemispheric pattern in the brain-behavior associations. This suggests differences in the organization of the neurocognitive processes related to reading and writing.