Sensitivity to molar contingencies of food presentation

Twelve rats were exposed to two variable-time schedules that differed in their rates of food delivery. The imposed schedule was normally in effect, but lever pressing occasionally switched to the alternate schedule for periods averaging 30 s. Increases in food frequency afforded by switching to the alternate schedule were manipulated across conditions. All rats were exposed to the same absolute food frequency increases, but the programming of these increases was varied among the rats by holding particular food delivery rates constant across conditions. For half of the rats, the schedules were signaled. In general, response rates were directly related to the size of the food-frequency increase, although the effect was more robust when the schedules were signaled. Response rates were undifferentiated when imposed schedule food delivery rates were held constant. The results lend limited support to the molar account that behavior is sensitive to changes in rates of stimulus events