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Six male White Carneaux pigeons were trained to peck at one of two keys to obtain food on several fixed‐ratio schedules of reinforcement. Concurrently, the first response on a second key could, I—change the conditions of visual stimulation and remove the food reinforcement contingency, II—change the conditions of stimulation and have no effect upon the reinforcement contingency, or III—do nothing. The second response on the stimulus change key always restored baseline conditions. When second‐key responses produced a stimulus change, the number of such responses was a function of the ratio value on the first key. Typically, second‐key responses occurred before the start of fixed‐ratio runs. The duration of stimulus change periods was an exponential function of the number of responses required for reinforcement when the possibility for reinforcement was not disturbed by periods of stimulus change (Condition II).

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To analyze bar‐holding behavior during escape conditioning three rats were trained to escape from shock by pressing a bar, and three were trained to escape by releasing a bar. Bar holding behavior was stronger and more stable under the release condition. These effects were related to the relative shock duration of onbar versus offbar shocks.

It was possible to distinguish three closely‐related psychomotor stimulants, caffeine, methamphetamine, and methylphenidate, by means of two operant behavior procedures, fixed interval and fixed number. Under the fixed interval procedure, the percentage change in the number of RBs per reinforcement was significantly smaller with caffeine than with methamphetamine or methylphenidate (p < .001). Under the fixed number procedure, the percentage change was significantly smaller with methamphetamine than with caffeine or methylphenidate (p < .001). Thus, methylphenidate had a methamphetamine‐like effect under fixed interval and a caffeine‐like effect under fixed number.

Four pigeons were trained on a multiple reinforcement schedule consisting of two limited‐hold schedules, one in which a discriminative stimulus (SD) accompanied the periodic reinforcement contingency, and one in which the discriminative stimulus was omitted. The duration of the limited‐hold in each component of the multiple schedule was reduced in parallel steps. It was shown that behavioral differences between the two schedules were attenuated by this manipulation of temporal parameters. When SD was reduced in duration, three out of four pigeons responded with extremely high SΔ rates, despite the regular pairing of SD with the reinforcement contingency. These high rates qualitatively resembled the rapid rates emitted on the analogous no‐SD component.