The state regulation model postulates that ADHD performance difficulties result from failures to regulate activation states in response to changing environmental conditions – producing poor performance under sub-optimal conditions. Behavioral and electrophysiological studies involving the manipulation of event rate (ER) lend support to this idea.

In this preliminary study, we extended this investigation by comparing pupil dilation, an established marker of cognitive effort allocation, in individuals with ADHD, and controls, in response to varying ERs on a simple cognitive task.

Nineteen children with ADHD (age range: 8–14 years) and 21 controls (age range: 10–16 years) completed a target detection task under three different ERs (1300, 4000, and 8000 msec). Pupil dilation was monitored using an eye-tracker.

Our results show that for controls, pupil dilation to targets varied as a function of ER according to a “U” function – with fast and slow ERs inducing greater phasic dilation than the moderate ER. However, for children with ADHD the relationship was linear with dilation increasing as ER decreased.

The results provide the first pupillary evidence suggestive of effort allocation dysregulation in ADHD especially under fast event rate conditions. Future studies should explore interventions to overcome effort allocation problems.

The authors have not supplied their declaration of competing interest.