Perceptual separability and spatial models

Highly analyzable two-dimensional color stimuli were generated using stimulus cards such that one part of each card varied only on the first dimension and the other part varied only on the second. Subjects were required to make judgments of similarity between pairs of these analyzable stimuli, between pairs of relatively unanalyzable color stimuli, and between pairs of geometric stimuli. The results support previous findings that the Euclidean combining rule is appropriate for judgments of single color patches but indicate that the city block combining rule may be appropriate for simple stimuli that vary on perceptually distinct dimensions.