Continuous performance task in ADHD: Is reaction time variability a key measure?

Objective: To compare the use of the Continuous Performance Task (CPT) reaction timevariability (intraindividual variability or standard deviation of reaction time), as a measure ofvigilance in attention-deficit hyperactivity disorder (ADHD), and stimulant medication response,utilizing a simple CPT X-task vs an A-X-task.Method: Comparative analyses of two separate X-task vs A-X-task data sets, and subgroupanalyses of performance on and off medication were conducted.Results: The CPT X-task reaction time variability had a direct relationship to ADHD clinicianseverity ratings, unlike the CPT A-X-task. Variability in X-task performance was reduced bymedication compared with the children’s unmedicated performance, but this effect did not reachsignificance. When the coefficient of variation was applied, severity measures and medicationresponse were significant for the X-task, but not for the A-X-task.Conclusion: The CPT-X-task is a useful clinical screening test for ADHD and medicationresponse. In particular, reaction time variability is related to default mode interference. TheA-X-task is less useful in this regard