Thus, essentially, the findings from Vervliet et al. showed that participants became less certain of the outcome occurrence with progressively dissimilar test stimuli. In the present study, on the other hand, outcome-expectancy ratings were already centered near 5/10, in line with the actual contingency between S+ and the outcome (67%). It thus seems possible that the contingency schedule already induced an amount of uncertainty about the S+ that was indistinguishable from the uncertainty elicited by the stimulus dissimilarity at test. Nevertheless, the finding of differential rates of extinction clearly shows that these “uncertainty” ratings covered different amounts of (generalized) excitatory strength. Arguably, the uncertainty rating on the first generalization test trial may reflect underlying cognitive judgments made about perceptual events. This is the first time that participants are confronted with a circle of a differing size, and the rated “uncertainty” may reflect a stage in the discrimination process.