Pup retrieving as a reinforcer in nulliparous mice.

Six nulliparous female mice were trained to bar press with bar pressing reinforced by the opportunity to retrieve pups to the nest. Then, responses on one bar produced the opportunity to retrieve pups, while responses on a second bar produced sensory contact with non-retrievable pups, presented behind a screen door. All subjects emitted more responses on the bar yielding retrievable pups. When the bar-pup contingency was reversed, five subjects learned to press the opposite bar for retrievable pups. The sixth subject showed extinction of responding on the bar that had previously yielded retrievable pups, but failed to press the other bar. A major portion of the reinforcing value of pup presentation resulted from the opportunity to perform the behavior of pup retrieving. This finding supports theoretical formulations which state that the performance of species-typical consummatory behaviors should have reinforcing properties.