Abstract
Three pigeons were studied under two-key concurrent variable-interval schedules with food as the reinforcer on one key and ectostriatal brain stimulation as the reinforcer on the other. Brain-stimulation parameters were kept constant while the rate of food reinforcement availability was varied. The results showed that qualitatively different reinforcers could be handled in the same theoretical framework that applies when choice is between different rates, immediacies, and amounts of a single reinforcer.