Effects of hemisphere-specific stimulation on brain activity and reading in dyslexics

Dyslexic readers, classified as L-types or P-types, received direct or indirect stimulation of the right (L-types) or left (P-types) hemisphere. Direct stimulation was produced by presenting words in the left (L-types) or right (P-types) visual field. Indirect stimulation took place through the presentation of visual-perceptual (L-types) or phonetic (P-types) demanding texts. Analyses of event-related potentials (ERP), elicited by centrally presented words, revealed the component reflecting P250 activity to be asymmetrically affected by experimental vs. control treatments. Treatment effects on scholastic achievement were shown in L-type dyslexics who had received direct stimulation of their right hemisphere and in P-type dyslexics whose left hemisphere had been indirectly stimulated. Training-induced electrical changes in brain asymmetry correlated with changes in measures of reading accuracy and speed. The set of findings replicated most of the results of a previous study (Bakker, Moerland, & Goekoop-Hoefkens, 1981).