Ordinal properties of subjective ratios and differences: Comment on Veit.

Because nonmetric analyses of judged ratios and differences in sensory magnitude have yielded similar scales, some investigators have concluded that a single perceived relation underlies both judgment tasks. Issues rasied by this interpretation are considered in this article. Simulated data based on the assumption that subjects evaluate both perceived relations were computed for stimulus values used by Veit to investigate judgments of ratios and differences in grayness. A nonmetric analysis of both sets of simulated data in terms of a difference model yielded a solution such that each set of data was a weak monotonic transformation of the model's values, and the scale values were approximately linear with those obtained by Veit from empirical data. This result leaves open the question of whether one or two perceived relations underly the data. Ordinal properties of ratios and differences for a finite set are discussed together with their relation to systematic biases in psychophysical judgment tasks.