Five observers made color-difference judgments by the method of triads. A triad (S: A,B) consisted of a standard stimulus S and two comparison stimuli, A and B. The observer reported which color difference appeared smaller, that between A and S or that between B and S. Triads were composed of monochromatic stimuli, adjusted to constant brightness for each observer. They contained both small color differences and ones that are markedly supraliminal. For any triad (S: A,B) it was assumed that the choice probability is an index of the relative sizes of the subjective differences (A,S) and (B,S). Estimated choice probabilities were converted to estimated distance measures by means of a scaling model based on assumptions about the observers’ judgmental task.
The obtained distance estimates were compared with standard wavelength-discrimination data, with Wright’s data on slightly supraliminal color differences, and with the large-difference predictions of the Hurvich–Jameson HBS color specification system. While the present data cannot be regarded as providing definitive color-difference measures (even for the limited range of conditions employed) they nevertheless contribute to the development of a metric space representation combining discriminability and supraliminal similarity.
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