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The disruptive behavior of a 9‐yr‐old boy was eliminated by the illumination of a light on the subject's desk, which represented the loss of free time later in the day. Instructions alone failed to reduce the frequency of disruptive behavior. When the light was removed and disruptive behavior no longer resulted in a loss of free time, disruptive behavior returned to its previous level.

After training to press a lever on a variable‐interval 30‐sec schedule, one group of rats was shifted to a differential‐reinforcement‐of‐other‐behavior 10‐sec schedule, while a second group was shifted to a noncontingent yoked‐control schedule that provided the same frequency and distribution of reinforcement. Then, both groups were extensively retrained on the variable‐interval schedule, after which the first group was shifted to a series of differential‐reinforcement‐of‐other‐behavior 30‐sec sessions alternating daily with variable‐interval 30‐sec sessions, while the second group was treated like the first on variable‐interval days and yoked with the first as before on differential‐reinforcement‐of‐other‐behavior days. In both phases, response‐decrement was more rapid and more marked in the differential‐reinforcement‐of‐other‐behavior animals than in the controls. The difference was due, at least in large measure, to sustainment of response in the control animals by adventitious reinforcement. All the differential‐reinforcement‐of‐other‐behavior animals developed “other” behavior—the same distinctive pattern of waiting at the foodcup—but there was no direct evidence that it contributed in any way to the decrement in lever pressing.

Two groups of four rats each were trained to bar press on a variable‐interval 2‐min schedule. During training, either 3, 5, or 9 auditory stimuli of various intensities were randomly presented. A direct relationship between stimulus intensity and rate of responding was obtained, but it was more consistent in the group trained initially with three stimuli than for the group that started with nine stimuli. The results are related to the concept of stimulus intensity dynamism and the necessary conditions for the acquisition of stimulus control.

Four pigeons were exposed to a discrete‐trial schedule in which only responses spaced by at least 6 sec were reinforced. After 45, fifty‐trial sessions, they failed to meet the spacing requirement in over 90% of the trials. When an alternative, non‐contingent key (pecks on which had no consequence) was illuminated concurrently with the first key, the spacing performance of the three pigeons that pecked the non‐contingent key improved so that they were obtaining 75% of the possible reinforcers. These data demonstrated the importance of collateral behavior in mediating spaced performance. It was suggested that pigeons may successfully refrain from responding on the spacing procedure only when another stimulus correlated with reinforcement is available for pecking, and that the form that collateral behavior takes may, in general, be non‐arbitrary, and species dependent.

Pigeons learned a free operant, go/no‐go discrimination between stimuli produced by rapid alternation of different features on the response key. The 0° –B compound consisted of a vertical black line on a white background (the 0° feature) alternated with a blank white field (the B feature), with successive 0.75‐sec feature on periods separated by 0.20‐sec dark periods. Pecks at the alternating 0° and B features were recorded separately. When pecks at the 0°–B compound were reinforced and pecks at the B—B stimulus (repeated brief presentations of the B feature) were extinguished, the birds pecked more at the 0° feature than at the B feature in the 0°–B compound; subsequently, decremental line‐tilt generalization gradients were obtained. When pecks at B—B were reinforced and pecks at 0°–B were extinguished, the rate of pecking at the 0° feature decreased to a low level much more rapidly than did the rate of pecking at the B feature in the 0°–B compound; incremental line‐tilt gradients were obtained. Following training with pecks at 0°–B reinforced and pecks at 0°–0° extinguished, incremental line‐tilt gradients were obtained, whereas the gradients were decremental following training with 0°–0° reinforced and 0°–B extinguished.

In Exp. 1, four rats were trained on a two‐component multiple schedule with tone and light each associated with different variable‐interval schedules. Extinction in light‐out no‐tone, common to previous studies reporting additive summation to compounded discriminative stimuli, was omitted from training. In testing, the simultaneous presentation of tone and light controlled a response rate intermediate between that controlled by these stimuli presented singly. In Exp. 2, animals were trained on three‐ply multiple schedules. While tone and light were each associated with variable‐interval schedules for both groups, light‐out no‐tone signalled extinction for one and differential‐reinforcement‐of‐behavior‐other‐than‐bar‐pressing for the other. This permitted response reduction during light‐out no‐tone to be viewed independently of non‐reinforcement. Responding of both groups showed summation to tone plus light in testing, with the effect clearly larger for extinction‐trained subjects. These experiments indicate that: (1) discrimination training afforded by extinction has been integral to additive summation previously reported, (2) response differentiation and non‐reinforcement consequences of extinction training contribute to the magnitude of summation, and (3) summation and peak shift might be functionally related phenomena.

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Experiment 1 demonstrated that delayed matching‐to‐sample in the capuchin monkey was superior when the delay interval was spent in darkness rather than in moderate illumination. In contrast with previous studies in which the delayed‐matching ability of primates appeared limited to 60 sec or less, in the dark condition all subjects showed above‐chance matching at a 120‐sec delay interval. Experiment 2 verified that darkness during the delay interval can facilitate delayed matching and provided evidence that the effective variable was the illumination level of the delay interval rather than change in illumination, which in Exp. 1 was confounded with illumination level.

Eight groups of pigeons were trained to discriminate between two stimulus displays that could be differentiated only by a single distinctive feature on one of the displays. For half of the pigeons, responses to displays containing the distinctive feature were reinforced (feature‐positive), and for the remaining pigeons responses to displays without the distinctive feature were reinforced (feature‐negative). The pigeons were further grouped so that half were presented displays in which the distinctive feature was in close proximity to other features (compact displays) and half were presented displays in which the features were not close together (distributed displays). Pigeons in the feature‐positive groups localized responses on the distinctive feature of the displays and seldom responded to displays without the distinctive feature. Pigeons in the distributed feature‐negative groups localized responses on features common to the two displays and did not learn the discrimination. Compacting the displays facilitated discrimination performance for the subjects in the feature‐negative condition. Tests carried out in extinction indicated that responding in the compact feature‐negative group was largely controlled by pattern rather than by the individual elements on the display.