Influence of visual conditioned stimulus characteristics on the form of Pavlovian appetitive conditioned responding in rats.

The influence of visual stimulus characteristics on the form of Pavlovian appetitive conditioned responding in rats was examined in three experiments. In Experiment 1, localized conditioned stimuli (CSs evoked behaviors mostly directed toward the CS source, and more diffuse CSs) evoked behaviors mostly directed toward the delivery site of the food unconditioned stimulus (US). In Experiment 2, localized CSs nearer the US delivery site evoked more CS-directed but less US site-directed behaviors than localized CSs farther from the US delivery site. In Experiment 3, the extent to which rats contacted CS sources depended on variation in a number of CS features casually described as affecting the feasibility of contact with those CSs. In all three experiments, some differences in behavior evoked by the various CSs were noted prior to conditioning; these differences were enhanced by conditioning and further magnified by discrimination training. These results are related to a hypothesis in which orienting responses play an important role in determining the character of Pavlovian conditioned responding.