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When either a timeout period (darkening the response key) or a blackout period (darkening both chamber and response key) was alternated with a stimulus associated with variable‐interval reinforcement, behavioral contrast was obtained. Either peak contrast or maintained contrast occurred, depending on whether or not responding was evidenced during the negative condition. These results are contrary to recent accounts emphasizing the role of non‐reinforced responding in the production of contrast, but are consistent with interpretations emphasizing the aversiveness of the negative condition.

Two pigeons were exposed to factorial combinations of two values of line tilt and two frequencies of houselight flashes. During each of four baseline stages, key pecking in the presence of all four combinations was reinforced according to a variable‐interval schedule. The baseline phases were followed by four different conditional discrimination training procedures in which reinforcement availability for pecking in the presence of the line tilts depended upon the houselight frequency. The subjects acquired each conditional discrimination. Behavioral contrast occurred during the acquisition and abolition of the discriminations. Generalization tests, given after each conditional discrimination, revealed that both the line tilt and houselight frequency dimensions controlled pecking only after conditional discriminations in which reinforcement availability depended upon the value of both dimensions.

Squirrel monkeys were restrained in a centrifuge capsule and trained to escape and avoid increases in artificial gravity. During escape‐avoidance, lever responses reduced centrifugally simulated gravity or postponed scheduled increases. The effect of variation in the interval of postponement (equal to the duration of decrease produced by escape responses) was studied under a multiple schedule of four components. Three components were gravity escape‐avoidance with postponement times of 20, 40, and 60 sec. The fourth component was extinction. Each component was associated with a different auditory stimulus. Rate of responding decreased with increasing postponement time and higher mean g‐levels occurred at shorter intervals of postponement. Effects of the schedule parameter on response rate and mean g‐level were similar to effects of the schedule on free‐operant avoidance and on titration behavior maintained by shock.

Techniques of behavioral self‐control were employed in a class where a high level of on‐task behavior had been established with externally administered reinforcement procedures. The behavioral self‐control techniques maintained behavior at its ongoing high level both immediately following the externally administered reinforcement treatments and during follow‐up treatments after five and seven weeks. Variability in on‐task behavior was reduced during the behavioral self‐control phases of the study.

The interaction between the arousal to action of environmental stimuli and recovery from that activity was presumed to generate biorhythms in the activity level of children. The level of environmental stimuli was manipulated by varying the play‐group size and the apparatus, and higher environmental complexity was expected to produce more pronounced rhythms. The heart rates of 16 subjects playing in monad, dyad, and tetrad group sizes, in two playroom configurations, were monitored and spectral analysis used to locate significant biorhythms. There was a tendency toward 40‐min (slow frequency) and 15‐min (fast frequency) biorhythms. The group size manipulation produced the strongest biorhythmic behavior in the dyadic groups. Apparatus differences were not significant but the configuration containing a minimum quantity of play apparatus produced more variable activity than the configuration containing a large amount of play apparatus.

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