Differences in Ex-Gaussian Parameters from Response Time Distributions Between Individuals with and Without Attention Deficit/Hyperactivity Disorder: A Meta-analysis

Abstract

Attention Deficit Hyperactivity Disorder (ADHD) is one of the most prevalent neurodevelopmental disorders in childhood and adolescence. Differences in reaction times (RT) in cognitive tasks have been consistently observed between ADHD and typical participants. Instead of estimating means and standard deviations, fitting non-symmetrical distributions like the ex-Gaussian, characterized by three parameters (µ, σ, and τ), account for the whole RT distributions. A meta-analysis is performed with all the available literature using ex-Gaussian distributions for comparisons between individuals with ADHD and controls. Results show that τ and σ are generally greater for ADHD samples, while µ tends to be larger for typical groups but only for younger ages. Differences in τ are also moderated by ADHD subtypes. τ and σ show, respectively, quadratic and linear relationships with inter-stimulus intervals from Continuous Performance Test and Go/No Go tasks. Furthermore, tasks and cognitive domains influence the three parameters. Interpretations of ex-Gaussian parameters and clinical implications of these findings are also discussed. Fitting ex-Gaussian distributions to RT data is a useful way to explore differences between individuals with ADHD and healthy controls.

We don't know what you did last summer. On the importance of transparent reporting of reaction time data pre-processing

“…The most widely used theoretical distribution in ADHD research is the ex-Gaussian distribution." (Bella-Fernández et al, 2023)…”

Assessment of ADHD Subtypes Using Motion Tracking Recognition Based on Stroop Color–Word Tests

“…Although individuals with ADHD and typical controls exhibit noticeable differences in performance in numerous tests, there is still considerable controversy surrounding the outcomes of these tests [ 11 , 16 , 17 , 18 , 19 , 20 , 21 ]. Some studies suggest that inhibition and variation in reaction times are core features of ADHD, although others question this view [ 16 , 17 , 19 ].…”

ADHD Adults Show Lower Interindividual Similarity in Ex-Gaussian Reaction Time Vectors for Congruent Stimuli Compared to Control Peers

“…Intraindividual variability can be manifested as inconsistent or erratic RTs, where an individual may respond quickly on some trials and much more slowly on others, even when the stimuli and task demands remain constant. This measurement has been correlated to cognitive control deficits in people with ADHD (Bella-Fernández et al, 2023; Einziger et al, 2023; Kofler et al, 2013). On the other hand, we define that the interindividual variability in RT highlights the differences in RT performance between different individuals with ADHD, thus illustrating the heterogeneity of the disorder in a group of individuals with ADHD.…”

“…The intraindividual variability in individuals with ADHD has been widely analyzed with or without the ex-Gaussian distributions of RT (Hohle, 1965; Ratcliff, 1979), which has proven to be a valuable tool in characterizing differences in RT between individuals with ADHD and controls (Bella-Fernández et al, 2023; Bluschke et al, 2021; Buzy et al, 2009; Castellanos et al, 2009; Flehmig et al, 2007; Fredriksen et al, 2021; Galloway-Long et al, 2022; Gmehlin et al, 2014; Gu et al, 2013; Guo et al, 2022; Hervey et al, 2006; Horowitz et al, 2020; Kofler et al, 2013; Kuntsi & Klein, 2012; Lin et al, 2015; Leth-Steensen et al, 2000; Schmid et al, 2020; Schulz-Zhecheva et al, 2023; Vainieri et al, 2022; Vaurio et al, 2009). Computational models using ex-Gaussian distributions used in conjunction with clinical assessments refine our understanding of cognitive concepts as: slow processing speed, and inhibition failures, which are commonly found in Individuals with ADHD (Ging-Jehli et al, 2021; Nikolas et al, 2019).…”

“…Computational models using ex-Gaussian distributions used in conjunction with clinical assessments refine our understanding of cognitive concepts as: slow processing speed, and inhibition failures, which are commonly found in Individuals with ADHD (Ging-Jehli et al, 2021; Nikolas et al, 2019). In addition, many studies suggest that the tau parameter of these ex-Gaussian distributions is greater in ADHD than in control patients, thus meaning that a larger tau in individuals with ADHD reflects lapses of attention (Bella-Fernández et al, 2023; Gmehlin et al, 2016; Gu et al, 2013; Hwang-Gu et al, 2019; Kóbor et al, 2015; Leth-Steensen et al, 2000; Machida et al, 2022; Thomson et al, 2020).…”