Yes, it's important to note the measure of distance (metric) used. Quoting from the paper: Humans are not good at judging questions of the type “How big is

Yes, it's important to note the measure of distance (metric) used. Quoting from the paper: Humans are not good at judging questions of the type “How big is the difference?” that form the basis for many large difference experiments. Instead, the authors use data from decisions of "which color step is larger". They find that as the steps get larger, you need a higher difference in color steps to reach the same certainty. This is not that surprising, since people generally get worse at noticing small differences as the absolute quantities get larger. Unfortunately, the model of perception uncertainty used in the paper (Thurstone’s theory of Gaussian perceptual process) does not take this effect into account.