Interference control and resource allocation in adults with Attention-Deficit/Hyperactivity Disorder : an evaluation of response variability and error compensation

Thesis (Ph. D.)--University of Rochester. Dept. of Clinical and Social Sciences in Psychology, 2012.This research investigated intrasubject variability in reaction time, interference control, and error compensation during a flanker task in 37 adults with Attention-Deficit/Hyperactivity Disorder (ADHD; 20 Combined subtype, 17 Predominantly Inattentive subtype) and 26 healthy controls. I hypothesized that, similar to children with ADHD, adults with the disorder would demonstrate: (a) greater interference control deficits than control subjects, as reflected in greater effects of incongruent flankers on accuracy, reaction time, and intrasubject variability; and (b) less post-error slowing than controls, indicating difficulties with error compensation associated with resource allocation deficits. Intrasubject variability was assessed using the ex-Gaussian distributional model and the deviation from the mode method. Across task conditions, similar to pediatric samples, adults with ADHD demonstrated greater intrasubject variability involving greater sigma, reflecting relatively faster reaction times in the normal portion of the curve, and greater tau, indicating greater variability in the positive skew of the distribution. These results suggest that the portion of the RT distribution affected in patients with ADHD is consistent across the lifespan. Variability in child and adult ADHD may be explained by the default-mode hypothesis, which emphasizes the role of attentional lapses in performance. In contrast to prediction, performance measures did not implicate a specific deficit in interference control among adults with ADHD. In fact, controls were more adversely affected by incongruent arrays with respect to the proportion of correct responses, directional errors, and nonresponses to targets. Only for false alarms was there a greater interference effect among adults with ADHD. However, whereas previous studies have not found an elevated flanker effect on intrasubject variability of patients with ADHD, the present results indicated that adults with ADHD exhibited increased variability with greater demands for interference control. Intrasubject variability in adults with ADHD involved greater sigma during flanker incongruent compared to congruent trials, reflecting increased variability in the normal portion of the RT distribution. In addition, adults with ADHD exhibited diminished post-error slowing, a result consistent with previous findings for children with the disorder. This deficit in executive functioning is present in individuals with ADHD throughout development and can be explained by the resource allocation hypothesis