Pavlovian processes in the motivational control of instrumental performance

Hungry rats were rewarded for pressing a lever on a multiple schedule. During one component the reward was a sucrose solution, whereas food pellets acted as the reward during another component. Lever pressing was never rewarded during the third component. When the drive state was switched from hunger to thirst and the animals tested in extinction, they pressed more in the presence of the component stimulus that had been associated with the sucrose reward during training. A similar effect was observed during the extinction test of a second study in which the component stimuli had signalled non-contingent presentations of either the sucrose or pellet rewards in the absence of the lever. This suggests that the instrumental irrelevant incentive effect observed in the first experiment was due, at least in part, to the Pavlovian relationship between the component stimuli and the reinforcers during training. In fact, when the size of the effects controlled by purely Pavlovian and supposedly instrumental contingencies was compared directly in the final study, no difference could be detected.