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Three pigeons were trained on a chained fixed interval‐fixed ratio schedule. Avoidance behavior which postponed a return to the first chain component from the second component was maintained on a second response key concurrently with the second component. When the fixed interval length was increased, avoidance rates first increased and then decreased as a function of fixed interval length. As the fixed ratio requirement was increased for one subject, avoidance rates first declined and then increased at larger fixed ratio values. Avoidance behavior maintained by postponing the first chain component was similar to avoidance behavior maintained by postponing a time out period.

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Behavioral contrast and the peak shift, two widely observed phenomena in experiments on successive discrimination learning, were shown to disappear during extended discrimination training. This finding and an analysis of the conditions under which behavioral contrast and the peak shift occur suggested that both phenomena were by‐products of emotional responses that resulted from response suppression and that their disappearance after extended discrimination training could be attributed to the dissipation of such emotional responses.

Newly hatched ducklings were exposed to imprinting procedures and subsequently trained to peck a key by presenting the imprinting stimulus as the reinforcing (response contingent) event. It was found that the key peck was learned only when imprinting procedures were initiated during the first 6 to 8 hr after hatch. Additional studies revealed that: (1) the duckling's distress vocalizations were reduced in the presence of the imprinting stimulus and enhanced in its absence; (2) when the ducklings had constant access to the imprinted stimulus (via a key peck), pecking responses occurred in bursts and relatively few distress vocalizations occurred; (3) the initial effect of extinction procedures was an increase in key peck rate. When, however, repeated key pecks failed to produce the imprinted stimulus, distress vocalization ensued and peck rate declined; (4) both the presentation of an unfamiliar mechanical figure and delivery of electrical shock enhanced distress vocalization and key pecks; (5) for some ducklings, certain familiar objects in the environment influenced distress calls in a manner comparable to the imprinted stimulus in that distress calls increased when these objects were removed.

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