title: Response variability in attention deficit hyperactivity disorder: evidence for neuropsychological heterogeneity.
abstract: 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 5.5min 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.
authors.affiliation: Schools of Psychiatry and Genetics and Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin 2, Ireland. johnsoka@tcd.ie
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Johnson
authors.forename: Simon P
authors.initials: SP
authors.lastname: Kelly
authors.forename: Mark A
authors.initials: MA
authors.lastname: Bellgrove
authors.forename: Edwina
authors.initials: E
authors.lastname: Barry
authors.forename: Marie
authors.initials: M
authors.lastname: Cox
authors.forename: Michael
authors.initials: M
authors.lastname: Gill
authors.forename: Ian H
authors.initials: IH
authors.lastname: Robertson
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D001288:Attention; D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis* / Q000523:psychology; D002648:Child; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D016014:Linear Models; D008297:Male; D009483:Neuropsychological Tests / Q000706:statistics & numerical data*; D010364:Pattern Recognition, Visual; D011594:Psychometrics / Q000706:statistics & numerical data; D011597:Psychomotor Performance; D011930:Reaction Time; D012016:Reference Values