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Each of three pigeons was studied first under a standard fixed‐interval schedule. With the fixed interval held constant, the schedule was changed to a second‐order schedule in which the response unit was the behavior on a small fixed‐ratio schedule (first a fixed‐ratio 10 and then a fixed‐ratio 20 schedule). That is, every completion of the fixed‐ratio schedule produced a 0.7‐sec darkening of the key and reset the response count to zero for the next ratio. The first fixed‐ratio completed after the fixed‐interval schedule elapsed produced the 0.7‐sec blackout followed immediately by food. These manipulations were carried out under two different fixed‐interval durations for each bird ranging from 3 min to 12 min. The standard fixed‐interval schedules produced the typical pause after reinforcement followed by responding at a moderate rate until the next reinforcement. The second‐order schedules also engendered a pause after reinforcement, but responding occurred in bursts separated by brief pauses after each blackout. For a particular fixed‐interval duration, post‐reinforcement pauses increased slightly as the number of pecks in the response unit increased despite large differences in the rate and pattern of key pecking. Post‐reinforcement pause increased with the fixed‐interval duration under all response units. These data confirm that the allocation of time between pausing and responding is relatively independent of the rate and topography of responding after the pause.

Bar‐pressing (Experiment I) or key‐pressing (Experiments II and III) responses of monkeys were reinforced according to a fixed‐interval schedule of negative reinforcement: the first response after a fixed interval of time terminated regularly spaced shocks for a fixed time designated as the reinforcement period. During extinction, shocks continued during the reinforcement period. That there were two types of responding generated by shock alone was indicated by (1) the level of responding maintained during extinction relative to conditions without shock, (2) the stability of two between‐shock response patterns across reinforcement and extinction conditions, and (3) the development of these two between‐shock patterns without a history of reinforcement. Subjects developed either a pre‐shock or a post‐shock response pattern when only the bar was available. However, when both a bite tube, an operandum requiring an aggressive topography, and a recessed key, an operandum that did not require an aggressive topography, were provided, the post‐shock pattern was observed in tube biting and the pre‐shock pattern was observed in key pressing. Removal of the bite tube produced post‐shock key responding similar to that observed when only the bar was available. The displacement of post‐shock, aggression‐motivated responding confirmed the confounding effect of shock‐generated responding in negative reinforcement procedures, and suggests that the use of concurrent response alternatives would reduce such confounding.

In Experiment 1, matching of relative response rates to relative rates of reinforcement was obtained in concurrent variable‐interval schedules when the absolute values of the two concurrent variable‐interval schedules varied from 6 sec and 12 sec to 600 sec and 1200 sec. Increases in the duration of the changeover delay, however, produced decreases in the relative response rates and, consequently, some deviation from matching. In Experiment 2, matching of relative response rates to the relative duration of the reinforcer failed to occur when the equal variable‐interval schedules arranging access to the two different reinforcer durations (1.5 and 6 sec) were varied in size from concurrent variable‐interval 10‐sec schedules to concurrent variable‐interval 600‐sec schedules.

Pigeons were trained on a two‐key choice procedure in which a pair of equal and concurrently available variable‐interval schedules (initial links) arranged entry into one or the other of two mutually exclusive schedules (terminal links) that ended in primary reinforcement. The terminal links were two‐component chained or tandem schedules. Responses during the initial links were distributed equally on the two keys whenever the terminal links were associated with the same sets of interreinforcement intervals. Whether or not the terminal‐link interreinforcement intervals were the same on the two keys, initial‐link responding was affected by neither the presence nor relative durations of differentially signalled components within a terminal‐link schedule. The simplest interpretation of these results is that initial‐link responding is maintained directly by delayed primary reinforcement, rather than conditioned reinforcement afforded by the stimuli correlated with the terminal‐link schedule components. This finding suggests that aspects of chained schedule performance usually attributed to conditioned reinforcement might best be reinterpreted in terms of delayed primary reinforcement and various discriminative functions served by the component‐correlated stimuli.