Non-Gaussian Distributional Analyses of Reaction Times (RT): Improvements that Increase Efficacy of RT Tasks for Describing Cognitive Processes.

This didactic aims of this review are to demonstrate the advantages of examining the entire reaction time (RT) distribution to better realize the efficacy of mental speed assessment in clinical neuropsychology. RT distributions are typically non-normal, requiring consideration of a host of statistical issues. Specifically, the appropriate model of the mental speed task's distribution (e.g., ex-Gaussian, Weibull, Normal-Gaussian, etc.) must be determined to know what parameters can be used to characterize test performance. While RT mean and standard deviation are typically used to characterize clinical performance, these parameters are usually inappropriate because RT performance rarely conforms to a normal-Gaussian distribution. For illustrative purposes, a tutorial for examining the entire RT distribution is provided that demonstrates differences between an Attention Deficit/Hyperactivity and a neurotypical group of college students. While such analyses are descriptive, it is important to characterize test performance in the context of a theoretical model of RT performance. Therefore, the tutorial includes interpretation that uses the Diffusion model (Ratcliff Psychological Review, 85, 59-108, 1978), which assumes an ex-Gaussian distribution. It is concluded that current results conform to a large literature demonstrating a more nuanced understanding of cognition afforded by non-Gaussian analysis of RT. This literature is compelling neuropsychology to enlarge assessment technology beyond the limitations of paper-and-pencil instruments.