Event-related potentials to visual and language stimuli in normal and dyslexic children.

Event-related potentials (ERPs) were recorded in 31 normal and 21 dyslexic children, the latter with visual processing impairment, in three visual reading-related tasks: a nonalphabetic, an alphabetic, and a lexical decision task (two levels of difficulty in each). ERPs were recorded from fifteen active electrodes for 1.5 s following stimulus presentation; analyses were done on difference waves. N2 and P3 components were usually longer in latency and P3 was lower in amplitude in the dyslexic than in the normal children. The P3 had a flatter, broader distribution in the dyslexics than in the controls, which was very similar to the effect of difficulty in the two easier tasks. The lack of Group X Age interactions is inconsistent with either a maturational lag between the groups of children, or with the dyslexic children catching up to normals in terms of their speed of processing. Thus, the dyslexic children required more time to process the visual information across tasks (with only their letter classification being equal to that of the normal controls) and approved to have a different developmental pattern in their ERPs from that of the normal children.