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Stimuli of 20, 40, and 80 sec duration terminated with five non‐response‐contingent food pellets were superimposed upon lever pressing reinforced with single pellets on a DRL 30‐sec schedule. Two rhesus monkeys served as subjects. No change in response frequency was observed during the 20‐ and 40‐sec stimuli. During the 80‐sec pre‐food stimulus, overall response frequency increased to approximately 150% and 220% of pre‐stimulus levels, and the temporal distributions of interresponse times shifted toward the shorter intervals. When the 80‐sec stimulus was no longer terminated with food, the response frequency decreased and the temporal distributions of interresponse times gradually approached pre‐stimulus levels. An increased frequency of short interresponse times and an increase in response rate was again observed when the pellet termination procedure was reinstituted with the 80‐sec stimulus. No change in response frequency or interresponse times was observed in the absence of the conditioning stimulus, and performance efficiency, as reflected in the ratio of responses to reinforcements during non‐stimulus periods, remained stable throughout the experiment.

An operant conditioning technique for use with passerine birds is described. Two redwinged blackbirds were successfully conditioned to perch‐hop for food reinforcement. Continuous reinforcement and fixed‐ratio schedules involving substantial ratio requirements were used to maintain this response. The behavior of the two redwinged blackbirds was comparable to that of more conventional organisms working on similar schedules of reinforcement.

A grade of A was given in an introductory statistics course for meeting a set of contingencies that included no work outside of class (except by request), near‐perfect performance on exams following each unit of work in a programmed text, correction of all exam errors, self pacing of work, and the chance to finish the course early. A grade of incomplete was given otherwise. Correlations among performance measures failed to show any meaningful relationships between time taken to finish the course, errors made on exams, and errors made in the programmed text. Responses to a five‐part questionnaire were overwhelmingly favorable to the course, but did not vary as a function of grade point average, time taken to finish the course, or number of errors made on exams. The uniformly high level of performance, the students' lack of interest in social contact with the instructor during class, and the absence of drop‐outs are all attributed to the contingencies employed, chief among which, according to the instructor's judgment and student rankings, were self‐pacing, frequent non‐punitive exams and a guaranteed grade of A for near‐perfect work at every stage.

A subject who spoke essentially in “telegraphic” English, leaving out most articles and auxiliary verbs, was trained to use a particular sentence form that included the articles and verbs to describe a set of standardized pictures. The subject used the trained sentence form to describe the trained pictures, and in addition, use of the sentence form generalized to sets of untrained and novel stimuli. When the trained sentence form was changed, the subject used the new form to describe both training and generalization stimuli. When the original correct form of response was retrained, the subject once again used the trained sentence form to respond to both training and generalization trials.

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Two auditory stimuli, separated by a fixed intertrial interval, were alternately presented to two rats in a closed environment. The positive conditioned stimulus (CS+) terminated with the offset of a 2‐mA, 0.75‐sec shock. The negative conditioned stimulus (CS−) terminated without shock. The incidence of the “stereotyped fighting posture” was recorded during the CS+, the CS−, the intertrial interval, and shock. The results showed an increase in the percentage of conditioned responses during the CS+, and a decrease during both the CS− and the intertrial interval, when the duration of the conditioned stimuli and the intertrial interval was 16 sec. Appropriate changes in the incidence of aggression during the two stimuli were obtained following the reversal of the stimulus functions. During the acquisition and reversal phases there was a between‐session decrement and a within‐session improvement in the incidence of aggression during the CS+, defined as warm‐up: The presentation of free shocks before the conditioning sessions was effective in reducing the warm‐up only when the interval between shocks was 64 sec. These data were interpreted as demonstrating classical conditioning of shock‐elicited aggression, with little chance of non‐associative factors contributing to the measurement of the conditioned response.

Pigeons were trained to discriminate the presence of one or more human forms in displays projected on a panel above the response key. This task was mastered, although imperfectly, with successive and with simultaneous presentations of positive and negative instances. The course of acquisition of the discrimination was similar for the two training procedures. Animals were able to transfer the discrimination from the successive to the simultaneous situation. Various tests were carried out to control for artifactual cues on which the discrimination might have been based. The discrimination was maintained when new displays were presented, when reinforcement was omitted, and when displays were inverted 180°. Animals were also able to discriminate between pairs of displays that were identical, except that one member of the pair contained a human form. The research extends the techniques used by Herrnstein and Loveland (1964), and confirms their finding that pigeons can master the concept of “person‐present” in a visual display.

Drinking was studied in rats pressing a bar on a second‐order schedule in which every third completion of a 1‐min fixed interval was followed by food presentation. A brief flash of light signaled the completion of each fixed‐interval component. The rats drank not only after the food presentations but also after presentations of the light flash alone. A high rate of steady drinking followed intervals terminated by a food presentation. Drinking that followed intervals terminated by a light flash alone was of comparable rate, but characteristically interrupted by bar pressing. When 250‐mg food pellets were used instead of 45‐mg pellets, both drinking and bar‐pressing rates increased substantially.

Responding of rats was maintained on a variable‐interval schedule of food reinforcement. The same response also produced a blinking light followed by electrical brain stimulation according to a fixed‐interval schedule. This conjoint schedule produced two behavioral changes. First, instead of a steady rate of responding throughout the session, which would be characteristic of the variable interval food schedule alone, responding between occurrences of the light‐brain stimulation pairings became positively accelerated and thus was more characteristic of the fixed‐interval schedule of these pairings. Second, food responding was suppressed during the light that preceded brain stimulation. These results indicate that positive reinforcement and suppression resulted from the same occurrence of the light‐brain stimulation combination. This finding suggests that stimuli such as conditioned reinforcers that precede an unconditioned reinforcer may have a suppressive effect upon responding in their presence that is being maintained by another reinforcer.

Pigeons were trained on a two‐link concurrent chain schedule in which responding on either of two keys in the initial link occasionally produced a terminal link, signaled by a change in the color of that key and a darkening of the other. Further responding on the lighted key was reinforced with food according to a fixed‐interval schedule. For one of the keys, this fixed interval was always 20 sec, while for the other it was held at values of 5, 14, 30, or 60 sec for several weeks. In the initial link, all pigeons responded relatively more often on the key with the shorter fixed interval than was predicted by the matching hypothesis. Responding in the initial link showed a large negative recency effect: pigeons responded less frequently on the key that provided their last reinforcement than predicted from the overall response rates