Differences Between ADHD Inattentive and Combined Types on the CPT

Two samples of school-age boys with attention-deficit/hyperactivity disorder (ADHD-Combined and ADHD-Inattentive Types) and a non-ADHD control group were administered an AX version of the continuous performance task (CPT) to examine specific sustained attention deficits. Three levels of time-on-task were included to study performance declines, and 3 interstimulus intervals were included to examine vigilance deficits. As predicted by R. A. Barkley's and H. C. Quay's behavior inhibition deficit models (R. A. Barkley, 1997; H. C. Quay, 1997), the performance of the ADHD-Combined Type (ADHD-C) participants deteriorated more quickly than the other samples. No significant evidence of vigilance deficits among the inattentive (ADHD-IA) sample was found. These findings suggest that distinct criteria for the two ADHD subtypes may be warranted when the CPT is used for diagnostic assessment, and sustained attention-related declines in performance may be typical of the ADHD-C Type only.