Elongated Tau in an Ex-Gaussian Decomposition of Vocal Articulation Speed in Children With Attention Deficit Hyperactivity Disorder

Objective: Slower and more variable reaction time is one of the most prominent cognitive signatures in childhood attention-deficit/hyperactivity disorder (ADHD). However, standard use of tasks that involve motor responses to index “speed” potentially confounds fine-motor coordination with central cognitive processing speed. One promising alternative is a vocal articulation task, which provides a measure of speeded performance that is independent of fine-motor coordination. Method: The present study applies an ex-Gaussian decomposition to preparatory interval (the time to initiate a vocal response) and speech rate on a speeded articulation task among children aged 8–12 with and without ADHD (N = 119). Results: There was substantial evidence that the tail of the distribution, as indexed by the tau parameter (which is linked to the rate of information accumulation), was larger in children with ADHD and among children with low working memory capacity (regardless of ADHD status). Variance in tau was also greater among children with ADHD, and the greater variance was not fully explained by individual differences in working memory. Conclusions: Results highlight the importance of adopting analytic methods that can more accurately describe performance.