Varying required effort during interference control in children with AD/HD: task performance and ERPs.

Prominent models of attention-deficit/hyperactivity disorder (AD/HD) contend that disinhibition is the core deficit, or that any inhibition deficits that exist are secondary to dysfunctional energetic regulation (i.e. effort and arousal). This study tested these models by investigating the influence of task-directed effort, as manipulated by stimulus degradation, on interference control deficits in children with AD/HD. Twenty children with AD/HD aged between 7 and 14years were matched in age to 20 controls and performed a modified visual Eriksen flanker task, while EEG and skin conductance level (SCL) were recorded. Participants completed the task under three conditions varying in stimulus degradation: none, 30% or 60%. Results revealed a quadratic effect with improved task performance in the 30% degradation condition, relative to the other conditions. Overall, children with AD/HD showed a tendency towards increased errors and more variable responding, although this did not differ between conditions. Importantly, children with AD/HD showed no deficits in interference control at a behavioural level. SCL revealed reduced activity in the AD/HD group during the non-degraded condition which normalised to control levels in the highest degradation condition. ERPs revealed two functionally distinct N2 components, one of which, along with the P3, was larger to incongruent stimuli, consistent with previous studies linking this component to inhibitory processing. Atypical activation of these components was evident in children with AD/HD and occurred as a function of degradation condition. Taken together these findings suggest the role of other factors such as state regulation as underlying deficits in AD/HD.