Discrimination by pigeons of mixture and uniformity in arrays of stimulus elements.

In 5 experiments, pigeons learned to discriminate uniform arrays of colored elements from mixed arrays containing 2 colors in various proportions. When only the uniform arrays were positive, mixture-negative gradients were obtained. When only the arrays containing equal numbers of red and blue elements were positive, mixture-positive gradients were obtained. When elements of different colors from 2 independent mixture-negative discriminations were recombined, mixture-negative gradients were obtained with the transfer patterns. When elements from a mixture-negative discrimination were combined with a new set of positive elements, responding was not suppressed. Appropriate combinations of the elements in mixture discriminations reduce responding, but the elements themselves do not acquire inhibitory properties.