Discrimination and Generalization of Complex Visual Shape Variations in Pigeons

Three experiments investigated stimulus control of key pecking in pigeons by varying the distance of vertices movement for a six-point complex visual shape. Ease of discrimination learning was monotonically related to the distance of vertices movement when the directions of vertices movement were held constant. As suggested by selective attention theory, steep generalization gradients were obtained following intradimensional differential training but not following nondifferential training or interdimensional differential training. These results indicate that, unlike the dimension of angular orientation or tilt, distance of vertices movement provides a consistent functional representation of complex shape similarity.