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A 15‐sec stimulus followed by unavoidable monetary loss was presented to human subjects who were avoiding loss on a free‐operant schedule. As has been observed in studies where shock is the aversive event, initial reactions to the pre‐loss stimulus were transient increases in overall and stimulus rates. Unlike shock studies, continued training produced decreased rates, in the presence of the 15‐sec stimulus, which were maintained in two of three subjects. Subsequent observations indicated that lowered rates were a function of the subject's rate of avoidance responding, the duration of the stimulus, and the scheduling of avoidable losses. Increasing the duration of the stimulus eliminated lowered rates in the presence of the stimulus and subsequent exposures to conditions which previously produced lowered rates did not result in recovery of the phenomenon. Introduction of the pre‐loss stimulus on an extinction baseline (avoidable losses were omitted), however, reinstituted lowered rates. It is proposed that the pre‐loss stimulus assumed discriminative control over low rates because responding in the presence of the stimulus was ineffective in avoiding the unavoidable loss. Recovery from lowered rates is attributed to the occurrence of avoidable losses during the stimulus period, and maintenance of lowered rates on the extinction schedule to the omission of such avoidable losses.

A discrimination reversal task followed by a conditional discrimination problem was administered to children (age range 36 to 107 months). A fading procedure was used during the discrimination reversal training of some subjects and other subjects were trained by a traditional procedure. More subjects trained by the fading procedure performed without errors during training and more subjects in the traditional group solved the conditional discrimination problem.

Two illustrations of single‐case research are described in which an isolated therapeutic variable was sequentially introduced, withdrawn, and reintroduced while changes in a clinically relevant behavior were measured. A claustrophobic patient and a knife‐phobic patient received graduated practice in facing their phobic stimuli; length of time the claustrophobic patient stayed in a small dark room per trial, and length of time the knife‐phobic patient kept knife exposed per trial were measured. In both experiments, when feedback of these time scores was withdrawn, ongoing progress was retarded. Reinstatement of feedback led to renewed improvement. In Experiment 2, adding and removing contingent verbal praise against a constant background of precise feedback did not significantly alter rate of progress.

After response‐dependent reinforcement established key‐pecking as the predominant response, pigeons received schedules in which reinforcements occurred without reference to responding. These response‐independent schedules involved either a reinforcement every 5 min, or reinforcements at irregular intervals that averaged 5 min. The response‐independent schedules generated characteristic patterns of responding. The fixed schedule produced positively accelerated responding between reinforcements, and the variable schedule produced either steady rates, erratic, or negatively accelerated patterns. The pat/terns developed independent of the distribution of responses existing when the schedule was first imposed. The rate of responding varied for the three birds, but, for all, response‐independent schedules decreased the rates below the level maintained by response‐dependent reinforcement. Although the rate of responding was affected primarily by the events contiguous with reinforcement, the pattern of responding appeared to be determined mainly by the presentation of reinforcements in relation to time.

The average rate of bar‐pressing maintained by a variable‐interval schedule of milk reinforcement in 33 rats was found to be a decreasing function of intensity of concurrent punishment and, over a wide range of shock intensities, was inversely related to punishment frequency. Cumulative records were, however, negatively accelerated during 30‐min punishment sessions with complete suppression occurring earlier and earlier (after fewer and fewer shocks) as intensity increased. In addition, acceleration was often observed between successive fixed‐interval shock presentations and, at low and moderate intensities, bursts of responding occurred after each shock. The time to recover between punishment sessions (post‐punishment recovery) was an increasing monotonic function of punishment intensity.

Pigeons' responding was maintained by two concurrently available variable‐interval reinforcement schedules. A fixed‐ratio punishment schedule of timeout periods from the concurrent reinforcement schedules was arranged for responding during one of the variable‐interval schedules. The greater the probability of a timeout after a response on the punished variable‐interval schedule (the smaller the fixed ratio that produced timeout), the greater the decline in the relative punished response rates. Relative reinforcement rates remained invariant when relative response rates declined. Both behavioral contrast and induction effects were observed on the unpunished variable‐interval schedule as a function of timeout punishment of the other schedule.

Pigeons' pecks were conditioned with food reinforcement. Subjects were exposed to sessions of no‐reinforcement and of fixed‐ratio reinforcement. The pigeons attacked a target animal during the fixed‐ratio reinforcement conditions. The attack occurred primarily during the post‐reinforcement pause and occurred after almost every instance of reinforcement. Little or no aggressive behavior was demonstrated during periods of no‐reinforcement except on the initial days of these conditions. The results indicated that a fixed‐ratio schedule of reinforcement has certain characteristics capable of producing aggression.

The five pigeons in Group 1 were given successive intradimensional discrimination training in which responses to a line of 49° were reinforced on a variable‐interval schedule and responses to a line of 33° were not reinforced. Subsequent generalization testing with other line orientations revealed a peak shift from the positive stimulus in the direction away from the negative stimulus in all subjects. The four pigeons in Group 2 received successive discrimination training with the 49° value on the key during both stimuli. During the negative stimulus, however, the floor was tilted 16° counterclockwise. When tested (with the floor flat) these subjects showed peak shifts similar to those observed with Group 1. A third group of three pigeons, given successive interdimensional discrimination training with the 49° line as the positive stimulus and the absence of the line as the negative, showed no peak shift in a subsequent generalization test. It was concluded that tilting the floor on which the pigeon stood systematically distorted the bird's visual perception of the orientation of the line in a manner consistent with the results of other studies in this laboratory.

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