Learning disability subtypes and the effects of auditory and visual priming on event-related potentials.

A control group of normal readers and three subtypes of learning disability (LD) were compared in their visual event-related potentials (ERPs) to primed and unprimed words. The LD subtypes are characterized by deficient performance on tests of arithmetic skill (Group A), reading and spelling skills (Group RS), or both (Group RSA). The primed words were preceded by pictures or spoken words having a related meaning, while unprimed words were preceded by pictures or spoken words having a non-associated meaning. For normal readers, N400 amplitude was greater to unprimed words than to words primed by pictures and spoken words. For Group A, parietal N400 was reduced by spoken word primes, but not by picture primes. For Group RS and Group RSA, neither picture nor spoken word primes reduced N400 amplitude. These groups were differentiated by the amplitude of parietal N400. The normal readers displayed a greater left than right hemisphere frontal N400 amplitude to unprimed words. This asymmetry was absent in the ERPs of all the LD subtypes. The pattern of ERP results supports an LD typology that characterizes subtypes on the basis of difficulty with arithmetic or reading and spelling, or with a combination of both. The hemispheric asymmetry results suggest that left hemisphere dominance is associated with skilled reading