Inhibition, working memory, and time sense in children with attention deficit hyperactivity disorder

This study examined a prediction of Barkley's (1997) hybrid model that children with attention deficit hyperactivity disorder (ADHD) have impairments in two executive functions—inhibition and working memory—that affect their sense of time. To test this idea, children with ADHD ( n = 28) and children without ADHD (n = 28), matched for age and sex, were compared on measures of inhibition (Vigilance task of the Gordon Diagnostic System, Gordon, 1983, and Stroop Color and Word Test, Golden, 1978), nonverbal working memory (Hand Movements, Word Order, and Spatial Memory subtests of the Kaufman Assessment Battery for Children, Kaufman & Kaufman, 1983) and sense of time. Sense of time was conceptualized in this study as a multi-dimensional construct, consisting of three components—conventional (i.e., ability to read a clock), experiential (i.e., ability to estimate accurately the passage of time), and adaptive (i.e., ability to manage the time-related demands of daily life). Conventional time was measured by the Clock Knowledge Test, a measure developed for this study; experiential time by a computer-based time reproduction task, the Time Test (University of Massachusetts, 1998) and a retrospective verbal estimation task; and adaptive time by the Time and Punctuality scale of the Scales of Independent Behavior-Revised (Bruininks, et al., 1996) and a parent questionnaire, “It's About Time” (Barkley, 1998). Results showed that, with IQ and SES controlled, the ADHD group performed significantly worse than the comparison group on one measure of inhibition, three measures of time reproduction, and both measures of adaptive time, but not on measures of working memory, conventional time, or time estimation. Inhibition (r = .65) and working memory (r = .45) correlated significantly with time sense, but when both variables were entered together in a multiple regression analysis, inhibition was a significant predictor of time sense and working memory was not. The results of this study provide qualified support for Barkley's hybrid model.