An interval scale of saturation for the pigeon

Pigeons were required to discriminate between “identical” vs. “different” pairs of lights in a yes/no signal-detection task with a symmetrical payoff matrix. If the two lights projected on the two halves of the bipartite field constituting the center response key in a three-key chamber were identical in wavelength composition, then a single peck on the left key was reinforced with food. If the two lights differed in wavelength composition, then right-key pecks were reinforced. Each pigeon experienced all possible pairs (55) of 11 lights having the same dominant hue (630 nm) but differing in colorimetric purity. The percentage of correct responses was taken as a measure of the dissimilarity between the two lights constituting a pair. The rank-order information available in these dissimilarity measures was used to determine an interval scale of saturation in the pigeon. Saturation was found to be linearly related to colorimetric purity.