Revisiting inhibitory control across the life span: insights from the ex-Gaussian distribution.

Changes in inhibitory control occur across the life span and have been associated with alterations in prefrontal function. In this study, ex-Gaussian analysis was used to reexamine data from an inhibitory control task. Participants (ages 6 to 82 years) composed three groups: children, young adults, and older adults. In fitting the ex-Gaussian distribution to reaction time data, estimates of three parameters were obtained: mu (mu), reflecting average performance; sigma (sigma), reflecting variability in performance; and tau (tau), reflecting extremes in performance. Older adults differed from young adults in terms of mu, sigma, and tau. For children, mu and tau values were comparable to those of young adults; sigma, however, was different. Thus, inhibitory changes in older adults were due to slower, more variable, and more extreme responding. Inhibitory changes in children were due only to more variable responding. These findings suggest that different mechanisms underlie age-related changes in inhibitory control during different epochs of the life span. This study demonstrates that the ex-Gaussian approach provides a finer level of analysis than data analytic approaches typically used in neuropsychological research.