Perceptual and response interference in children with attention-deficit hyperactivity disorder, and the effects of methylphenidate

Fourteen children with attention-deficit hyperactivity disorder (ADHD) and 14 normal control children were compared with respect to stimulus- and resp onse-related processes. Subjects with ADHD took part in two additional sess ions under methylphenidate or placebo. In both experiments, performance and electrophysiological measures such as the P2, N2, and P3 components of eve nt-related potential and electromyogram (EMG) activity were measured during an Eriksen flanker task. In both groups of children, reaction times (RTs) to arrow stimuli incongruent with the target were longer than those to neut ral stimuli (response interference), which were again slower than RTs to ta rget-alone stimuli (perceptual interference). Children with ADHD made more errors to incongruent stimuli and showed more response interference. For co rrect responses, no differences between the groups in response interference effects on reaction time, P2, N2, and P3 latency, or EMG onset were found. Methylphenidate had a general enhancing effect on accuracy but did not spe cifically reduce interference from the flanking stimuli. Methylphenidate ha d no effects on RT,N2 and P2 latency, P3 amplitude or latency, or EMG activ ity. The conclusion that methylphenidate did not influence response process es contrasts sharply with findings reported by authors using the Sternberg memory search task.