“…The results of various clinical studies of ADHD, however, are mixed, with some demonstrating no difference in vigilance performance between diagnosed and control groups (Breen, 1989;Corkum & Siegel, 1993;Schachar, Logan, Wachsmuth, & Chajczyk, 1988) or normal performance in a large proportion of diagnosed groups (Halperin et al, 1990). Other studies show little difference in CPT performance between children diagnosed with ADHD and children with other psychiatric or learning disorders (Dienske, deJonge, & Sanders-Woudstra, 1985;Robins, 1992), and still others show a high rate of poor CPT performance even among non-diagnosed normal controls (Trommer et al, 1988). Heterogeneity of ADHD-diagnosed groups is often problematic, and patterns of CPT performance may depend in part on the presence or absence of such features as hyperactivity (Barkley et al, 1992;Goodyear & Hynd, 1992), anxiety (Pliszka, 1992), learning disabilities (Tarnowski, Prinz, & Nay, 1986), conduct disorder Halperin et al, 1990;O'Brien et al, 1992), and other comorbid psychiatric disorders (Halperin et al, 1993).…”