title: Jitter Reduces Response-Time Variability in ADHD: An Ex-Gaussian Analysis.
abstract: OBJECTIVE
  "Jitter" involves randomization of intervals between stimulus events. Compared with controls, individuals with ADHD demonstrate greater intrasubject variability (ISV) performing tasks with fixed interstimulus intervals (ISIs). Because Gaussian curves mask the effect of extremely slow or fast response times (RTs), ex-Gaussian approaches have been applied to study ISV.
  
  
  METHODS
  This study applied ex-Gaussian analysis to examine the effects of jitter on RT variability in children with and without ADHD. A total of 75 children, aged 9 to 14 years (44 ADHD, 31 controls), completed a go/no-go test with two conditions: fixed ISI and jittered ISI.
  
  
  RESULTS
  ADHD children showed greater variability, driven by elevations in exponential (tau), but not normal (sigma) components of the RT distribution. Jitter decreased tau in ADHD to levels not statistically different than controls, reducing lapses in performance characteristic of impaired response control.
  
  
  CONCLUSIONS
  Jitter may provide a nonpharmacologic mechanism to facilitate readiness to respond and reduce lapses from sustained (controlled) performance.
authors.affiliation: Kennedy Krieger Institute, Baltimore, MD, USA.
authors.forename: Ryan W Y
authors.initials: RW
authors.lastname: Lee
authors.affiliation: Kennedy Krieger Institute, Baltimore, MD, USA Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Jacobson
authors.affiliation: Kennedy Krieger Institute, Baltimore, MD, USA Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Alison E
authors.initials: AE
authors.lastname: Pritchard
authors.affiliation: Kennedy Krieger Institute, Baltimore, MD, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Ryan
authors.affiliation: Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Qilu
authors.initials: Q
authors.lastname: Yu
authors.affiliation: Kennedy Krieger Institute, Baltimore, MD, USA Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Martha B
authors.initials: MB
authors.lastname: Denckla
authors.affiliation: Kennedy Krieger Institute, Baltimore, MD, USA Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Stewart
authors.initials: S
authors.lastname: Mostofsky
authors.affiliation: Kennedy Krieger Institute, Baltimore, MD, USA Johns Hopkins University, Baltimore, MD, USA mahone@kennedykrieger.org.
authors.forename: E Mark
authors.initials: EM
authors.lastname: Mahone
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000503:physiopathology / Q000523:psychology*; D016022:Case-Control Studies; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*