Is instrumental variability abnormally high in children exhibiting ADHD and aggressive behavior?

To test whether instrumental behavior of some children with attention deficit hyperactivity disorder (ADHD) is more variable than control subjects, the sequences of responses by three groups of children were compared: (i) those diagnosed with ADHD who lived in a residential treatment facility for children demonstrating aggressive behavior; (ii) age-matched children from the same facility who did not have an ADHD diagnosis but who had also demonstrated abnormal levels of aggression; and (iii) normal children from a local school. The experiment consisted of rewarding children for responding in a computer 'game' on two keys of a keyboard during each of three phases. In phase 1, rewards were provided independently of sequence variability (IND). In phase 2, rewards depended upon highly variable sequences of left and right responses. Phase 3 was a return to the IND contingencies. The results showed that sequence variability was higher in the sequence variability (VARY) phase than in the preceding IND phase, but remained high when the contingencies returned to IND, thus replicating previous findings. In none of the phases did the ADHD children respond more variably than the controls. However, ADHD subjects made more off-task responses than did controls. Thus, although the present research showed differences between ADHD and control subjects, there was no evidence to support higher behavioral variability in the ADHD subjects.