Dzhafarov [(2002). Multidimensional Fechnerian scaling: Pairwise comparisons, regular minimality, and nonconstant self-similarity. Journal of Mathematical Psychology, 46, 583–608] claims that Regular Minimality (RM) is a fundamental property of “same–different” discrimination probabilities and supports his claim with some empirical evidence. The key feature of RM is that the mapping, h, between two observation areas based on minimum discrimination probability is invertible. Dzhafarov [(2003a). Thurstonian-type representations for “same–different” discriminations: Deterministic decisions and independent images. Journal of Mathematical Psychology, 47, 184–204; (2003b). Thurstonian-type representations for “same–different” discriminations: Probabilistic decisions and interdependent images. Journal of Mathematical Psychology, 47, 229–243] also demonstrates that well-behaved Thurstonian models of “same–different” judgments are incompatible with RM and Nonconstant Self-Similarity (NCSS). There is extensive empirical support for the latter. Stimulus and neural sources of perceptual noise are discussed and two points are made:Point 1: Models that require discrimination probabilities for noisy stimuli to possess the property that h is invertible would be too restrictive.Point 2: In the absence of stimulus noise, violations of RM may be so subtle that their detection would be unlikely.