The peak procedure was used to characterize response timing during acquisition and maintenance of conditioned responding in goldfish. Subjects received light-shock pairings with a 5- or 15-s interstimulus interval. On interspersed peak trials, the conditioned stimulus light was presented for 45 s and no shock was delivered. Peaks in the conditioned response, general activity, occurred at about the time of the expected unconditioned stimulus, and variability in the activity distribution was scalar. Modeling of the changes in the activity distributions over sessions revealed that the temporal features of the conditioned response changed very little during acquisition. The data suggest that times are learned early in training, and, contrary to I. P. Pavlov's (1927/1960) concept of "inhibition of delay," that timing is learning when to respond rather than learning when not to respond.

As an alternative to a symbolic interpretation of transitivity in the discriminative performance of pigeons, a modified reinforcement theory (value transfer theory) was proposed by Fersen, Wynne, Delius, and Staddon (1991). Its novel assumption was that the value of the negative member of a pair of stimuli with which an animal is trained is enhanced by the value of the positive member of the pair. In this article, that assumption is shown to be unnecessary. All of the transitivity data for pigeons can be simulated with a simple conditioning model developed for honeybees that retains the conventional independence assumption.

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Data are presented on extinction in free-flying honeybees previously reinforced for landing on distinctively colored and scented targets. A variety of phenomena familiar from the study of vertebrate learning, such as the overlearning-extinction effect, the partial reinforcement effect, overshadowing, summation, and conditioned inhibition, are described, and their significance is considered.

Free-flying honeybees were extinguished in choice tests after reinforcement for response to distinctively colored and scented targets. In an overshadowing experiment of conventional 2X2 design, color was overshadowed by odor, but odor was potentiated by color. These results, together with those for other groups studied concurrently, are interpreted in terms of compound uniqueness and within-compound association, both of which were demonstrated in subsequent experiments.