Sensitivity to interference and response contingencies in attention-deficit/hyperactivity disorder.

BACKGROUND: Current theories on ADHD suggest executive and motivational deficits, but it remains unclear whether these are separate deficits or a unitary deficit.
METHOD: ADHD children and matched controls performed on a hybrid disjunctive-choice reaction time task in which target stimuli could be surrounded by flankers signaling either the appropriate response, the competing response, or response inhibition. The task was performed under three conditions; reward only, reward and occasional punishment, and equal probability of reward and punishment. Heart rate and skin conductance measures were taken during task performance.
RESULTS: Contrary to control children, ADHD children slowed their responses when flankers cueing the appropriate response surrounded the stimulus. Flankers cueing incorrect responses further slowed ADHD children relative to control children. ADHD children also responded less accurately under the threat of punishment. Phasic heart rate did not differ between groups, but immediate reward feedback induced greater heart rate responses in control than in ADHD children. Contrary to expectations, groups did not differ in skin conductance responses.
CONCLUSIONS: ADHD children appear deficient in approach tendencies in the presence of imminent reward, rather than unresponsive to punishment or negative feedback. Executive inhibition and motivational inhibition seemed to exert separate effects on behavior of children with ADHD.