Electrophysiological indices of spatial attention during global/local processing in good and poor phonological decoders.

Previous research suggests a relationship between spatial attention and phonological decoding in developmental dyslexia. The aim of this study was to examine differences between good and poor phonological decoders in the allocation of spatial attention to global and local levels of hierarchical stimuli. A further aim was to investigate the relationship between global/local processing and electrophysiological indices (N1, N2) of spatial attention in these groups. Good (n=18) and poor (n=16) phonological decoders were selected on the basis of non-word reading ability. Participants responded to either the global or local level of hierarchical stimuli presented in the left or right visual field in a sustained attention task. Poor phonological decoders showed slower RT relative to good phonological decoders regardless of whether attention was directed to either global or local processing levels. This was accompanied by a lack of task-related modulation of the posterior N1 and N2 Event-Related Potential (ERP) components, suggesting differences in the early allocation of spatial attention and later perceptual processing respectively. Poor decoders also showed greater N2 amplitude overall, suggestive of compensatory processing at later perceptual stages. There was preliminary evidence for sex differences in hemispheric lateralisation, with a reversal of hemispheric lateralisation observed among male and female poor phonological decoders. These findings have important implications for the understanding of the relationship between spatial attention and phonological decoding in developmental dyslexia.