Discriminability and the contrafreeloading phenomenon.

According to previous reports of the "contrafreeloading phenomenon," animals will work for a reward, and sometimes work quite hard, in the presence of the same reward available freely. With rats as the subjects two experiments are presented which suggest that the contrafreeloading data are explainable with a basic learning principle, discriminability and its accompanying response decrement. For some animals the change in stimulus conditions with introduction of free water was made more highly discriminable by a change in earned reinforcement conditions. The other animals remained on the same earned reinforcement conditions under which all the animals had been trained. The results demonstrated that the discriminability between the conditions of working and freeloading is a most important factor contributing to the continued responding in the presence of free rewards.