This hungry pigeon, on the other hand, pecks the biggest circle because it has received a food pellet in the past for doing so. This is relational responding. In this case, the relative characteristics of the circles control the pigeon’s response. This pigeon must attend to the relation of size among the circles to make the response that is likely to be reinforced. Just pecking the same circle each time won’t work.
The pigeon’s response and the condition for obtaining reinforcement are based on a relation among the circles. They are not based on the absolute characteristics of a single circle. With sufficient training, most organisms can learn to respond to the relative, rather than absolute, physical properties of stimuli like this.