Food reinforcement for nonhungry nonthirsty rats: Conditioned reinforcement or manipulatory behavior?

Two studies were done to test the assertion that food is rewarding for satiated rats because of food’s manipulatory value rather than its secondary reinforcing value. In Experiment I, satiated Ss ran faster to food pellets in a goal box than to either wood replicas of food pellets or an empty goal box. In Experiment II, satiated Ss ran faster to familiar food than to either an unfamiliar food or an empty goal box, but the differences were not statistically significant. It was concluded that the results favored a secondary reinforcement interpretation rather than a manipulatory one.