Response variability in Attention Deficit Hyperactivity Disorder: Evidence for neuropsychological heterogeneity

Katherine Johnson, S.P. Kelly, M.A. Bellgrove, E. Barry, M. Cox, M. Gill, I.H. Robertson

Research output: Contribution to journalArticlepeer-review

199 Citations (Scopus)


Response time (RT) variability is a common finding in ADHD research. RT variability may reflect frontal cortex function and may be related to deficits in sustained attention. The existence of a sustained attention deficit in ADHD has been debated, largely because of inconsistent evidence of time-on-task effects. A fixed-sequence Sustained Attention to Response Task (SART) was given to 29 control, 39 unimpaired and 24 impaired-ADHD children (impairment defined by the number of commission errors). The response time data were analysed using the Fast Fourier Transform, to define the fast-frequency and slow-frequency contributions to overall response variability. The impaired-ADHD group progressively slowed in RT over the course of the 5.5 min task, as reflected in this group's greater slow-frequency variability. The fast-frequency trial-to-trial variability was also significantly greater, but did not differentially worsen over the course of the task. The higher error rates of the impaired-ADHD group did not become differentially greater over the length of the task. The progressive slowing in mean RT over the course of the task may relate to a deficit in arousal in the impaired-ADHD group. The consistently poor performance in fast-frequency variability and error rates may be due to difficulties in sustained attention that fluctuate on a trial-to-trial basis. (c) 2006 Elsevier Ltd. All rights reserved.
Original languageEnglish
Pages (from-to)630-638
Number of pages9
Issue number4
Publication statusPublished - 2007

ASJC Scopus subject areas

  • Behavioral Neuroscience
  • Neuropsychology and Physiological Psychology


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