Anterior-posterior beta asymmetries in dyslexia during lexical decisions

High-density EEG was recorded in 12 compensated dyslexics, 6 classified as dysphonetic and 6 as dyseidetic, and in 12 matched controls while they carried out a lexical-decision task. Relative to normal controls, dysphonetics showed higher beta power in anterior relative to posterior regions, while dyseidetics showed higher beta power in posterior relative to anterior regions. Further, controls (but not dyslexics) showed a positive correlation between performance on the task and the ratios of both left-to-right and anterior-to-posterior beta asymmetry. According to the dual-route theory of reading, there are two strategies that can be used in lexical decision: A visual strategy involving visual word identification and direct access to a visual lexicon, and a phonological strategy involving grapheme-to-phoneme conversion and access to a speech output lexicon. Our results therefore suggest compensation through weakness rather than strength, with phonological dyslexics focusing on a grapheme-to-phoneme strategy and dyseidetics focusing on visual word identification.