Inhibition and mental effort in attention deficit hyperactivity disorder

The efficiency of cognitive inhibition was contrasted in children diagnosed with ADHD and a control group of age- and IQ-matched average children. Two tasks were used to measure inhibitory ability: the negative-prime Stroop task and a directed-forgetting memory task. Based on contemporary theoretical perspectives that postulate deficits in inhibitory function in the ADHD population, it was predicted that ADHD children would be significantly less efficient inhibitors than the average children. Contrary to predictions, however, ADHD children showed no deficits in inhibitory abilities compared to controls. Average children were faster on the second administration of the Stroop task, whereas ADHD children were slower. These results were interpreted within the framework of the inhibition models. It was proposed that differences in inhibitory abilities, such as the ones tapped here, may appear earlier than age 8, and that the engaging aspects of tasks may have optimized the ADHD children's performance. The slower performance of the ADHD group on the second administration of the Stroop task is consistent with the hypothesis that although ADHD children can inhibit, they find it more effortful to do so than do average children.