Similarity index of ex-Gaussian reaction time signatures

In psychology and cognitive neuroscience, reaction time (RT) series and their ex-Gaussian distributions are commonly used to explore the time course of cognitive processes. This study investigated the hypothesis that successive triads of ex-Gaussian mu, sigma, and tau parameters of reaction-time variability across time can be used to construct a geometrical object we termed ex-Gaussian RT-signature, which could help characterize interindividual differences between congruent and incongruent stimuli. To test this hypothesis, we calculated the similarity index of these geometrical objects in young adult participants without detectable neurological disorders. Our findings show that each participant displayed distinct ex-Gaussian RT-signatures in a Cartesian 3D plot, thus exhibiting distinct psychophysical fingerprints. Furthermore, our results revealed that the ex-Gaussian RT-signatures for incongruent stimuli demonstrated a significantly higher similarity index across participants than congruent stimuli (p<0.001; Cohen d=0.4). We suggest that visualizing this psychophysical signature could serve as a valuable tool in characterizing differences in cognitive functioning between individuals, thus providing insights into the development of personalized medicine.