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The effect of reinforcement dependent on the social responses of two severely retarded withdrawn children was investigated. During 30 training sessions (30 min each) food and praise were administered dependent upon the children's mutual participation in a ball‐rolling and block‐passing task. Both children showed a progressive increase in social interaction in a non‐training situation during this reinforcement period. After the reinforcement procedures were removed, social behavior decreased markedly. Response generalization to children not involved in training occurred.

Rats were trained to press one of two keys when a standard intensity value of a 4.0‐kHz sine tone (70 or 100 db re 2 × 10−4 microbar) was presented from a centrally located loudspeaker. Pressing the other key was reinforced when comparison intensity values (as much as 30 db less than the standard value) were presented. The animals initiated tone presentations by breaking a light beam at the rear of the chamber. Correct choices produced brain‐stimulation reinforcement, and errors produced a timeout. A procedure designed by Jenkins was used to partial out choice data under potential control of sequential cues in the stimulus series. When the standard‐comparison intensity difference was varied, the rats showed similar psychometric functions despite wide differences in response bias (relative position preference). A signal detection analysis showed that response biases for individual animals remained fairly consistent during psychophysical testing. The trend of decreasing choice accuracy at small intensity differences was described by the cumulative normal probability function. The similarity of psychometric functions obtained with 70‐ and 100‐db standards supported Weber's law. There was some evidence that response latencies were controlled by intensity differences even when choice behavior was undifferentiated.

Three dogs were exposed to a DRL‐escape procedure that required them to endure a minimum duration of electric shock without responding in order for a response to terminate that shock. When this minimum duration increased from 0 to either 2.25 or 7.00 sec, response latencies increased proportionately. With the minimum duration held constant at 2.25 sec, a gradual increase in shock intensity to 5.0 ma had no systematic effect upon latencies. Even under the highest shock intensity, 5.0 ma, latency and interresponse‐time distributions were unimodal with very few latencies and interresponse times less than the minimum duration. Three additional dogs were exposed to an escape procedure in which every response was immediately reinforced. For these subjects, the same increase in shock intensity to 5.0 ma was accompanied by a decrease in latencies. The precise temporal spacing of responses obtained with the DRL‐escape procedure may in part be due to the fact that every response latency and interresponse time that did not meet the minimum duration was not only extinguished but was also punished.

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Five different reinforcement durations occurred randomly within each session on fixed interval 60‐sec. Postreinforcement pause was directly related (and “running” rate inversely related) to the duration of reinforcement initiating each fixed interval.

Three pigeons were trained to perform a two‐key sequential match‐to‐sample task. During baseline conditions, food reinforcement was contingent upon the first match response to occur following 8‐min periods, and orange illumination of both keys preceded the delivery of food by 0.5 sec. The baseline schedule of food reinforcement was in effect throughout the study. In some conditions, a 0.5‐sec flash of orange keylight alone was presented contingent upon mismatch responses that followed variable time periods averaging 1 min. Rate of mismatch responses increased and accuracy of matching performances decreased as compared with baseline conditions. The ability of the 0.5‐sec orange flash to reinforce mismatch responses was markedly reduced when it no longer immediately preceded the delivery of food.

Rats were exposed to a situation in which a response on lever B was followed by reinforcement if a preceding response on lever A had been made at least 5, 10, or 15 sec before. The effects of signalled unavoidable shock were studied on the behavior maintained by this procedure. All rats made fewer A‐to‐B sequences during the periods of pre‐shock stimulus. In addition, when the A‐to‐B delay was 10 or 15 sec, the distribution of A‐to‐B times changed, there being more shorter intervals. However, for animals where the A‐to‐B delay was 5 sec, the distribution of A‐to‐B times was not changed during the pre‐shock stimulus. In all cases, there was an increased proportion of inappropriate B responses (i.e., with no preceding A response) during the pre‐shock stimulus; this was most marked with animals exposed to a 15‐sec A‐to‐B delay.

Chlorpromazine was studied for its effects on responding under a second‐order schedule in which food was presented following a sequence of 20 one‐minute fixed‐interval components. A brief visual stimulus occurred at the completion of each fixed interval including the one that terminated with food presentation. Chlorpromazine showed rate‐dependent effects in that it increased low rates in the early components of the second‐order schedule and, to a lesser extent, decreased high rates in the later components. Chlorpromazine also increased rates in the early quarters within the 1‐min fixed‐internal components and to a smaller extent decreased rates in the final quarter. The alteration in the patterns of responding within 1‐min fixed‐interval components terminating in a brief stimulus presentation was substantially less than that which occurred throughout the succession of 1‐min fixed‐interval components terminating in food presentation, thus suggesting that the presentation of the brief stimulus exerted more control over responding within components than did food presentation over the sequence of components. This result and others suggest that studies using drugs may be useful in elucidating the factors controlling patterns of responding in second‐order schedules.