Using inspection time and ex-Gaussian parameters of reaction time to predict executive functions in children with ADHD.

Slower and more variable performance in speeded reaction time tasks is a prominent cognitive signature among children with Attention Deficit Hyperactivity Disorder (ADHD), and is often also negatively associated with executive functioning ability. In the current study, we utilize a visual inspection time task and an ex-Gaussian decomposition of the reaction time data from the same task to better understand which of several cognitive subprocesses (i.e. perceptual encoding, decision-making, or fine-motor output) may be responsible for these important relationships. Consistent with previous research, children with ADHD (n = 190; 68 girls) had longer/slower SD and tau than non-ADHD peers (n = 76; 42 girls), but there were no group differences in inspection time, mu, or sigma. Smaller mu, greater sigma, longer tau, and slower inspection time together predicted worse performance on a latent executive function factor, but only tau partially mediated the relationship between ADHD symptomology and EF. These results suggest that the speed of information accumulation during the decision-making process may be an important mechanism that explains ADHD-related deficits in executive control.