Timeperceptionde¢citsinattention-de¢cit/ hyperactivitydisorderand comorbid reading di/culties in child and adolescent samples M.E. Toplak, 1 J.J. Rucklidge, 2 R. Hetherington, 1 S.C.F. John, 3 and R. Tannock 1 1 Brain and Behaviour Research Programme, Research Institute of The Hospital for Sick Children, Toronto, Canada; 2 University of Canterbury, Christchurch, New Zealand; 3 Ontario Institute for Studies in Education of The University of Toronto and with the Brain and Behaviour Research Programme, Toronto, Canada Background: Our objective was to investigate time perception in Attention-Deficit/Hyperactivity Dis- order (ADHD) with and without comorbid reading difficulties (RD) in child and adolescent partici- pants. Method: In study 1, 50 children with ADHD (31 ADHD, 19 ADHD+RD) and age-matched healthy controls (n ¼ 50) completed three psychophysical tasks: duration discrimination (target dur- ation of 400 ms versus a foil duration), frequency discrimination (a control condition to evaluate general perceptual ability), and a duration estimation task using the method of reproduction for intervals of 400 ms, 2000 ms, and 6000 ms. Study 2 used the same tasks with an adolescent sample (35 ADHD, 24 ADHD+RD, 39 controls). Results: In both studies, children and adolescents with ADHD and ADHD+RD displayed some impairments in duration discrimination and the precision with which they reproduced the intervals on the estimation task, particularly the shorter 400 ms interval. The most severe impairments tended to occur in the comorbid ADHD+RD group. No impairments were found on the frequency discrimination task. ADHD participants also displayed significant intra-individual vari- ability in their performance on the estimation task. Finally, short-term and working memory, estimated full-scale IQ, and teacher report of hyperactivity/impulsivity were found to differentially predict per- formance on the time perception measures in the adolescent clinical sample. Conclusions: Deficits in duration discrimination, duration estimation, and intra-individual performance variability may have cascaded effects on the temporal organisation of behaviour in children and adolescents with ADHD and ADHD+RD. Keywords: Time perception, working memory, attention-deficit/hyperactivity disorder, reading difficulties, teacher report, behaviour ratings. Time perception is an adaptive function that facili- tates the ability to predict, anticipate, and respond efficiently to coming events. For example, the pre- paration of fast responses benefits from the ability to predict precisely the point in time when an impend- ing event requires a response. Also, precise repre- sentation of temporal information is required for the ability to organise and plan sequences of actions, particularly when sequences of novel or unskilled movements are required (Gibbon, Malapani, Dale, & Gallistel, 1997; Hazeltine, Helmut, & Ivry, 1998; Ivry, 1997). Time perception is a complex cognitive ability and comprises multiple component processes that engage multiple brain regions, including the neocerebellum, basal ganglia and prefrontal cortex (e.g., Casini & Ivry, 1999; Mostofsky, Kunze, Cutting, Lederman, & Denckla, 2000; Gibbon et al., 1997; Harrington, Haaland, & Hermanowicz, 1998a; Harrington, Haaland, & Knight, 1998b; Ivry & Keele, 1989; Ivry & Hazeltine, 1995; Jueptner et al., 1995; Jueptner, Flerlch, Weiller, Mueller, & Diener, 1996; Mangels, Ivry, & Shimizu, 1998; Meck, 1996; Nichelli, Always, & Grafman, 1996a; Nichelli, 1996b; Rubia et al., 1999a; Rubia, Taylor, Taylor, & Sergeant, 1999b). Recent work suggests that the neocerebellar cortex and prefrontal cortex (particu- larly, the dorsolateral prefrontal cortex) participate in a working memory system, which is involved in discrimination of intervals ranging from a few milliseconds to several seconds. Moreover, the neocerebellum may subserve a central timing mechanism, whereas the prefrontal cortex subserves supplementary functions implicated in the acquisi- tion, maintenance and organisation of temporal representation in working memory (Casini & Ivry, 1999; Mangels et al., 1998). Time perception is postulated to be impaired in Attention Deficit Hyperactivity Disorder, according to current models of ADHD and impulsivity (e.g., Barkley, 1997a, b, c; Barkley, Koplowitz, Anderson, & McMurray, 1997; Barkley, Murphy, & Bush, 2001; Barratt & Patton, 1983; Gerbing, Ahadi, & Patton, 1987; Stanford & Barratt, 1996). For example, one recent theoretical model of ADHD proposes that four executive neuropsychological functions are compro- mised by an underlying impairment in behavioural inhibition, which is believed to be the fundamental deficit in ADHD (Barkley, 1997a). One of these ex- ecutive functions is working memory, which sup- ports some components of time perception. Impaired time perception in ADHD is also predicted in- dependently by models of impulsivity, which propose a link between time perception and impulsive beha- viour – the latter being a core feature of ADHD (e.g., Journal of Child Psychology and Psychiatry 44:6 (2003), pp 888–903 Ó Association for Child Psychology and Psychiatry, 2003. Published by Blackwell Publishing, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA