Fourteen children with attention-deficit hyperactivity
disorder (ADHD) and 14 normal control children were compared
with respect to stimulus- and response-related processes.
Subjects with ADHD took part in two additional sessions
under methylphenidate or placebo. In both experiments,
performance and electrophysiological measures such as the
P2, N2, and P3 components of event-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 neutral stimuli (response interference),
which were again slower than RTs to target-alone stimuli
(perceptual interference). Children with ADHD made more
errors to incongruent stimuli and showed more response
interference. For correct 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 specifically reduce interference from the flanking
stimuli. Methylphenidate had no effects on RT, N2 and P2
latency, P3 amplitude or latency, or EMG activity. The
conclusion that methylphenidate did not influence response
processes contrasts sharply with findings reported by authors
using the Sternberg memory search task.