Two experiments investigated the perceptual generalization of acquisition and extinction in human contingency learning. In Experiment 1, the degree of perceptual similarity between the acquisition stimulus and the generalization stimulus was manipulated over five groups. This 1; the degree of perceptual perceptual e a the response to the generalization stimulus was successfully generated generalization gradient of acquisition. In the subsequent phase guished in each group: Finally, the acquisition stimulus was presented again. The response recovered differently over groups, thereby establishing the generalization, gradient of extinction: In Experiment 2;'the acquisition stimulus itself was extinguished before the: set of generalization stimuli was tested between groups. One group evidenced a response recovery at test, which suggests that the gradient of acquisition is somewhat broader than the gradient of extinction.