The effects of methylphenidate on levels of processing and laterality in children with attention deficit disorder.

Effects of stimulant medication (methylphenidate) on levels (feature, name, semantic) of word processing by the left and right hemisphere were assessed in 31 attention-deficit-disordered children. In a double-blind procedure, same-different decisions were made to tachistoscopically presented word pairs under medication and placebo. Analysis of manual response times failed to show any negative effects of medication. Feature decisions were faster than name decisions, which were faster than semantic decisions. Methylphenidate induced a right visual field advantage (left hemisphere) for the name decision, which was interpreted as a normalization effect. The results suggest that (1) methylphenidate may selectively improve the phonological level of word processing and (2) methylphenidate's favorable therapeutic effect is produced through inhibition of excessive right hemisphere activity in response to task demands that engage the left hemisphere.