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Key‐pecking behavior in the pigeon was maintained under second‐order schedules in which food was presented after a variable number of 2‐min fixed‐interval components were completed. When either the same stimulus (Exp. I) or different stimuli (Exp. II) appeared on the key during consecutive components, and a stimulus that was occasionally paired with food was presented briefly at completion of each component, (1) patterns of positively accelerated responding were maintained during the components, and, (2) mean response rates were generally as high during the initial components of a sequence as during the later components. In both experiments, when the food‐paired stimulus was omitted and either no stimulus or a stimulus never paired with food was presented at completion of each component, mean rates of responding increased, but patterns of positively accelerated responding were not maintained during individual components. When a food‐paired stimulus was not presented at completion of the components, mean response rates in Exp. I were low during the initial components of a sequence and gradually increased during subsequent components; in Exp. II mean response rates were variable, and pauses and abrupt changes in response rates were typical.

Two experiments studied the effects of reinforcement schedules on generalization gradients. In Exp. 1, after pigeons' responding to a vertical line was reinforced, the pigeons were tested with 10 lines differing in orientation. Reconditioning and the redetermination of generalization gradients were repeated from 8 to 11 times with the schedule of reinforcement varied in the reconditioning phase. Stable gradients could not be observed because the successive re‐conditionings and tests steepened the gradients and reduced responding. Experiment 2 overcame these effects by first training the birds to respond to all of the stimuli. Then, brief periods of reinforced responding to the stimulus correlated with reinforcement alternated with the presentation of the 10 lines in extinction. The development of stimulus control was studied eight times with each bird, twice with each of four schedules of reinforcement. Gradients were similar each time a schedule was imposed; the degree of control by the stimulus correlated with reinforcement varied with particular schedules. Behavioral contrast occurred when periods of reinforcement and extinction alternated and was more durable with fixed‐interval, variable‐interval, and variable‐ratio schedules than with fixed‐ratio or differential‐reinforcement‐of‐low‐rate schedules.

Key‐pressing responses in the cat were maintained under conditions in which brief electric shock was first postponed by responses (avoidance), then periodically presented independently of responses, and finally produced by responses on a fixed‐interval schedule of 15 min (FI 15‐min). A steady rate of responding occurred under shock avoidance and under response‐independent shock; positively accelerated responding was engendered by the FI 15‐min schedule. A second experiment studied responding under second‐order schedules composed of three FI 5‐min components. Responding was suppressed when a stimulus was presented briefly at completion of each FI 5‐min component and a shock followed the brief stimulus at completion of the third component. Responding was maintained when each of the first two components was completed either with or without presentation of a brief stimulus and a shock alone was presented at completion of the third FI 5‐min component.

Pigeons were exposed to two equal, concurrent variable‐interval schedules of reinforcement on two response keys. One key was continuously illuminated. Pecking on that key produced reinforcements of constant duration. The other key was normally dark, except that availability of reinforcement was signalled by illuminating the key. The duration of access to a grain reinforcer was varied on the key that signalled reinforcement. Rate of response on the first key, the one that did not signal reinforcement, was found to vary inversely with duration of signalled reinforcement on the other key. The latency between the signal and the peck that produced signalled reinforcement remained about constant. These results show that responding on one key in concurrent variable‐interval schedules depends on the reinforcement delivered by both schedules and is independent of responding on the other key.

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In the first of two experiments, running‐wheel activity and unsignaled (Sidman) avoidance were studied in gerbils and albino rats. All gerbils ran at higher rates than any of the four rats studied. Under the avoidance procedure, four rats developed effective responding; the other two performed much less successfully. While avoidance developed more slowly in the gerbils, all showed asymptotic performance as effective as the four superior rats. The rats showed a consistent warm‐up effect, receiving 60% to 80% of the total shocks in the initial third of the session. The gerbils displayed no warm‐up, with shocks being evenly distributed over the session. Warm‐up in the rats was not related to either response rate or to how effectively the animal was avoiding. When shock was removed, extinction occurred more rapidly in the rats than the gerbils. In the second experiment, which involved two‐way shuttle avoidance, gerbils and albino mice quickly acquired the response. All animals met a criterion of 90% avoidance over 80 trials.

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Responding was studied under various schedules of electric shock postponement and presentatation in the squirrel monkey. Under an interlocking shock‐postponement schedule, successive responses decreased the time by which a response postponed the next scheduled shock until a shock immediately followed the nth response. Some parameters of this schedule, which can be formally related to fixed‐interval schedules, engendered a pattern of positively accelerated responding between shocks. This pattern did not occur under comparable parameter values of an alternative fixed‐ratio, avoidance schedule under which each response postponed shock by a fixed duration and every nth response produced shock. Subsequently, performances were studied under schedules of shock presentation. Responding was never maintained under fixed‐ratio schedules of shock presentation, but was maintained with a pattern of positive acceleration under an alternative fixed‐ratio, fixed‐interval schedule and under a fixed‐interval schedule.

Four rhesus monkeys learned both a color and tilt discrimination. The stimuli were combined to produce incompatible behavior. The behavior controlled by one set of stimuli was reinforced until “errors” virtually disappeared. The stimuli were tested separately again. Sixteen replications of the entire procedure indicated that the stimuli producing “errors” were ignored.