Interactions in multiple schedules with different responses in each of the components.
Pigeons were exposed to multiple schedules in which a key was lit in one component and a bar was present in the other. Ten subjects were trained to peck the key and to press the bar with their feet, and four subjects were trained to peck both the bar and the key. After a period of exposure to variable-interval reinforcement in both components, subjects were exposed to extinction in one component. Only one of the 10 pigeons in the key-peck:bar-press condition showed an increase in rate in the other component, while seven of them showed a decrease. In the key-peck:bar-peck condition, three of the four subjects showed positive contrast. The data suggest that a condition for contrast to occur is that topographically similar behaviors be required in both components of the multiple schedule.