Moderate variability in stimulus presentation improves motor response control.

To examine the impact of interstimulus "jitter" (i.e., randomization of the interval between successive stimulus events) on response control during continuous task performance, 41 healthy adults completed four go/no-go tasks that were identical except for interstimulus interval (ISI) jitter: a 0% jitter task with a fixed (1,000-ms) ISI, a 10% jitter task with an ISI range of 900-1,100 ms, a 30% jitter task with an ISI range of 700-1,300 ms, and a 50% jitter task with an ISI range of 500-1,500 ms. Repeated measures analysis of variance (ANOVA) revealed a quadratic effect of jitter on commissions across the group and on intrasubject reaction time variability in men; in both cases, performance was best for the 10% jitter condition. A linear effect of jitter was observed for reaction time (RT) with high levels of jitter (50%) resulting in longer RT. Findings suggest that response selection, including inhibition, is optimized by moderate increases in ISI jitter. More deliberate and controlled responding observed with increasing jitter may have important treatment implications for disorders (e.g., attention-deficit/hyperactivity disorder, ADHD), associated with impaired response control.