Pigeons responded in a two-key situation. Responses on the right key (food key) were reinforced with food presentation on a response-initiated fixed-interval schedule, (i.e., first response after a fixed period of time was reinforced); responses on the left key (target key) were reinforced on a fixed-ratio schedule (i.e., every nth response was reinforced) with the presentation of a target bird that could be attacked. When the interval value of the food reinforcement schedule was varied from 1 min to 5 min, both the rate of attack responding on the target bird and the rate of responding on the target key were a function of the interval value. Responding on the target key was not maintained by the stimulus change associated with target availability, and was successively extinguished and reconditioned by removing and returning the target bird to the restraining box. When food was delivered independently of behavior, responding on the target key either remained unchanged or decreased, but was not eliminated. Responding on the target key was not maintained in the absence of an intermittent schedule of food presentation.

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Four experiments are reported in which the amount of CRF training prior to extinction is examined as it effects transient changes in response frequency and duration immediately following extinction onset. The first two experiments, using albino rats as subjects and water reinforcement, revealed a reliable relationship between length of time on CRF and the tendency to increase response frequency, duration, and the variability of response frequency and duration. Two comparative experiments were conducted using 53-to-69-month old children as subjects, and recorded music as reinforcement. The results of the first child study failed to conform with those obtained in the rat experiments. However, manipulation of the reinforcer in a subsequent study reproduced the rat extinction -effect. Despite the differences in the rat and child experiments, the qualitative similarity of the results of the four studies suggests a basic underlying comparability of the relationship between the amount of training and transient changes in response frequency.The experiments reported here are part of a comparative research program designed to examine a variety of response topographical changes in extinction and the variables effecting these changes. Previous research by one of the authors has dealt with the effects of pharmacological agents on the increased frequency of emission of a lever-pressing response following extinction onset in press). A number of other investigators have reported changes in response frequency, duration and force during extinction (Amsel and Roussel, 1952;Hurwitz, 1954;Margulies, 1961;Millenson and Hurwitz, 1961;Notterman, 1959). However, there is little information relating specific topographical extinction changes to antecedent behavioral manipulations. The present series of studies examines the significance of the amount of training prior to the extinction test session using albino rats and children as subjects.

Retention of a conditioned emotional response (CER) was tested after 14 electroconvulsive shock treatments (ECS), after chlor-

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