Income maximizing on ratio-interval schedules of reinforcement

In Experiment 1, three pigeons earned their daily food ration by choosing in 30-minute sessions between concurrent variable-ratio 30 variable-interval 40-second schedules. Access to the grain hopper was 2 or 12 seconds, depending upon the condition. Relative variable-ratio response rate was inversely related to hopper duration. In Experiment 2, four pigeons received their daily feeding by responding on the same schedule pair as in Experiment 1 for 4 seconds of access to grain in sessions that varied from 10 to 30 minutes, depending on the condition. The length of a vertical slit projected on a response key increased as time passed. This stimulus was used to ensure that "passage of time" was discriminable. As session duration decreased, relative variable-ratio response rate increased. In Experiment 3, four pigeons chose between two variable-interval 40-second schedules in which one schedule operated without regard to the schedule selected while the other operated only when the subject responded in its presence (dependent). Although these schedules have the same feedback function, preference for the dependent variable interval increased as session duration decreased from 30 to 10 minutes. The results of these experiments demonstrate that pigeons choose so as to maximize their food intake, a finding called income maximizing (Sakagami, Hursh, Christensen & Silberberg, in press).