Abnormal processing of irrelevant information in attention deficit hyperactivity disorder

The presence of a selective attention deficit in children with attention deficit hyperactivity disorder (ADHD) was investigated by administering a trial-by-trial version of the Stroop Color-Naming Task to children, aged 9-12, with ADHD (n = 19) and age-matched normal control children (n = 19). Performance was evaluated on both interference and facilitation components of the task. On the standard version of the task, with equal numbers of color words and neutral words, children with ADHD showed increased Stroop interference (prolongation of color-naming times by color-incongruent stimuli) but normal amounts of facilitation (speeding of color naming by color-congruent stimuli). This finding suggests that children with ADHD show increased disruption of color-naming performance by task-irrelevant information, probably secondary to decreased attentional control over the interference process. In contrast to findings of studies in adults, both groups of children failed to use an attentional strategy to reduce interference when they were administered blocks of trials that varied their expectancy for color word trials. This precluded a direct test of the diminished control hypothesis. There were no significant correlations between abnormal Stroop performance and impairment on the Continuous Performance Test or the Wisconsin Card Sorting Test or measures of IQ or reading performance. The implications of these findings for our understanding of information-processing deficits in children with ADHD and of the neurobiological underpinnings of these deficits are discussed.