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Industry: Email Alert RSS FeedTime perception: modality and duration effects in attention-deficit/hyperactivity disorder
Journal of Abnormal Child Psychology, Oct, 2005 by Maggie E. Toplak, Rosemary Tannock
What is also novel in this study is the pattern of associations obtained in the ADHD and control samples. That visual-spatial span was a significant predictor of visual duration discrimination performance at the 1000 ms interval in the ADHD, but not in the control group, suggests that participants with ADHD activate different processes because they may need to recruit additional resources on some cognitive tasks that are not necessary for control participants. Then, our dissociation in predictors of auditory duration discrimination at the 1000 ms interval (visual-spatial memory in the ADHD group and auditory-verbal working memory in the control group), adds an additional conceptualization of understanding cognitive performance in participants with ADHD. Specifically, not only is it likely that individuals with ADHD need to recruit additional cognitive resources, but they may also recruit different resources than controls on the same task. These results therefore suggest that inefficiencies in basic processing, like duration discrimination, may have cascading effects on other cognitive mechanisms, resulting in a general inefficiency in the system and giving rise to the deficits we observe in ADHD. If this is the case, then these findings are consistent with some recent functional magnetic resonance imaging research that has reported that children with ADHD do not activate frontostriatal regions in the same manner as normally developing children, but rather rely on a more diffuse network of regions (Durston et al., 2003). This pattern has also been reported in samples of adults with ADHD (Schweitzer et al., 2003). One of the key questions is whether the pattern of associations and dissociations we observed are specific to the mechanisms of timing and memory that were examined in the present study, or whether these patterns reflect only a sample of the types of inefficiency that occur in the cognitive processes in individuals with ADHD. This line of work needs further examination.
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Implications for Neuroimaging Research
Based on the current findings, one important question that emerges is whether time perception, as measured in this study, is related specifically to basic timing or to other functions, such as working memory. Although adolescents with ADHD were consistently worse in duration discrimination, the largest difference seemed to occur in the visual modality at the longer 1000 ms interval. Some research has reported cerebellar activation with visual tasks (Penhune, Zatorre, & Evans, 1998; Schubotz, Friederici, & von Cramon, 2000), and duration discrimination tasks have been found to be sensitive to cerebellar dysfunction (Hetherington et al., 2000; Ivry, 1997; Ivry & Keele, 1989). While the cerebellum has traditionally been viewed as the key part of the motor system, recent investigations have implicated the cerebellum in the internal control of timing (Casini & Ivry, 1999; Ivry, 1996; Ivry & Fiez, 2000; Mangels, Ivry, & Shimizu, 1998). We also know that, based on the largest prospective, longitudinal neuroimaging study to date of children and adolescents with ADHD, Castellanos et al. (2001) reported that participants with ADHD had significantly smaller cerebral volumes and smaller cerebellar volumes than controls. While group differences were observed on all of the duration discrimination tasks, the largest effect size was at 1000 ms in the visual modality, and not the 200 ms duration. This raises questions about the extent of cerebellar involvement, as sensory events greater than 1 s have been hypothesized to place greater demands on frontal functions, such as working memory (Mangels & Ivry, 2001). In addition, the pattern of correlations between the discrimination tasks and the visual working memory tasks in the adolescents with ADHD suggest an important role for working memory in timing functions.
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