Cognitive control processes in attention-deficit hyperactivity disorder : behavioural and cardiovascular measures

Specific strategic control (executive) processes were investigated in 17 boys with ADHD and 18 normal control boys, ages 9--13 years, using a paradigm combining the Warned Reaction Time and Stimulus-Response Compatibility tasks. The length and constancy of the preparatory interval (PI) were manipulated in order to study preparatory processes associated with prediction and temporal adjustment. Compared to control boys, boys with ADHD had particular difficulty with long, fixed, and short, variable preparatory intervals, suggesting problems with the strategic control of response preparation and adaptation to temporal changes. Heart rate deceleratory patterns recorded during the PI indicated that impaired active, accurate, prediction played a major role in the preparatory deficit. The study also manipulated compatibility and predictability of response demands in order to assess inhibitory processes and the ability to shift flexibly between changing response demands. Boys with ADHD had particular difficulty shifting flexibly between compatible and incompatible responding, indicating a problem with strategic response adjustment. Findings also suggested possible difficulties with the allocation of consistent, effortful attention and the inhibition of inappropriate responding. In addition, interactions were also observed in the ADHD group between the strategic and inhibitory measures. Overall, the findings supported Douglas's (1988; 1999) conceptualization of ADHD as involving a self-regulatory deficiency consisting of interacting strategic, effortful, and inhibitory components. The study also addressed the question of whether Sanders' (1983) cognitive-energetic model, which has been used widely in studies of ADHD, can deal adequately with the cognitive difficulties associated with ADHD. The findings indicated that the model has not been developed adequately to deal with the kinds of higher level processing deficits that were identified in the ADHD group. In addition, i