A further study of stimulus generalization following three-stimulus discrimination training.

A group of pigeons was trained in a Skinner box to peck for VI reinforcement when the key was illuminated by a monochromatic light of 540 or 580 mmu but were non-reinforced for responding to 560 mmu. Two control groups, differing in amount of training, received only the two positive stimuli. At the completion of training all Ss received generalization tests under extinction. Both control groups produced bi-modal generalization gradients with the peaks of responding at the S+ values. The post-discrimination gradient revealed peaks displaced from the S+ values in the direction away from the S-, low responding and increased steepness in the region of S- and a general elevation of the gradient.