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Techniques are described for conditioning key‐pecking reinforced with food and for recording cheeping in newly hatched chickens. A mirror in the test box is essential when conditioning isolated chickens up to five or more days old. Conditioning proceeds more rapidly when frequently pecked objects and materials that move when scratched are not present. Stimulus control over key‐pecking is present in the three‐day‐old chicken and multiple fixed‐ratio, fixed‐interval schedule control develops in succeeding days. In young chickens, pecking and cheeping are inversely related. The newly hatched chicken is useful for pharmacological studies and appears to offer other advantages for behavioral studies.

Six naive male subjects were reinforced for responses in the 20–30 microvolt range, and two each for those in 10–20 and 30–40 microvolt ranges. Records were taken of 15 min of “settling down,” 15 min of initial operant level responding, 30 min of conditioning, and 45 min of extinction, 30 min with light present and 15 min without. The results were: (1) small‐scale muscle potentials from the thenar eminence, in the 10–20, 20–30, and 30–40 microvolt ranges, were conditioned, using pointer movement as the reinforcement; (2) the response rate in adjacent ranges of greater and lesser amplitude also increased during such conditioning and decreased during the subsequent extinction; (3) during conditioning the frequency of response distribution shifted toward the reinforced range; (4) subjects were unaware of the reinforced response; (5) observing a noncontingent moving pointer increased the response rate in the 20–30 microvolt range, but did not lead to conditioning.

Eight alligators were trained to escape heat by traversing an 8‐ft runway containing right or left approaches to a water tank. All subjects were run until they had satisfied three criteria of stable response time, after which the predominant escape path was blocked, requiring discrimination reversal. Seven subjects again met the criteria; three also met them in a second reversal.

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A single principle, “momentary maximizing”, may account for much of a pigeon's steady‐state behavior in both probability learning and concurrent variable interval experiments. The principle states that a pigeon tends to choose the alternative that momentarily has the higher probability of reinforcement. A successive discrimination procedure, which produced matching in an earlier experiment, produced here a tendency to maximize if training were adequately extended. Maximizing was produced also by other procedures, in which no reinforcing event was presented on some trials: one procedure did and two did not provide a bird with information about the availability of reinforcement on a key after an unreinforced response on the other key. The latter two procedures were analogous to concurrent variable interval schedules in two respects: the reinforcement probability on one key increased while a bird responded on the other key; and they produced matching. But sequential statistics suggested that matching resulted from momentary maximizing. Depending on the procedure, the tendency to maximize produced different relative frequencies of pecking a key for a fixed relative frequency of reinforcement. Computer simulation of maximizing behavior in several concurrent variable interval schedules produced matching and sequential statistics similar to those produced by a real bird.

Variable interval (VI) responding was hypothesized to be a function of differential reinforcement susceptibilities of various unspecified behavior chains that mediate interresponse times (IRTs). To test this hypothesis, probabilities of reinforcement were regulated for the lengths of chains of key pecking responses of pigeons, analogous to the way that VI regulates probabilities of reinforcement for IRTs. This procedure generated a number of VI‐like effects, supporting the notion that VI behavior can be construed as a special case of an interaction between the organism's function relating reinforcement susceptibilities to chain length and the experimenter's function relating probabilities of reinforcement to chain length.

Mental hospital patients were reinforced for responding in a two‐response operant situation. When a noise was used to punish one of the responses, all subjects shifted to the unpunished one. When the noise was then paired with positive reinforcement, the subjects responded to produce the noise. Also, a novel response was reinforced by noise in the absence of other reinforcers. This study with humans extends the findings of previous studies with animals in revealing how a punishing stimulus can acquire discriminative or conditioned reinforcing properties.

Two experiments were conducted to determine the effects of punishment by time‐out from positive reinforcement on the extinction of discriminated shock‐avoidance responding. Subjects were trained initially to bar press for food on an intermittent schedule of reinforcement and, concurrently, to avoid shock at the onset of a warning signal. Experiment I compared avoidance extinction performance under no punishment and when avoidance responding resulted in a 30‐sec TO from reinforced appetitive responding. In Exp II, the contingent use of TO punishment was compared with its random, or noncontingent use. The results of both experiments showed that in the absence of punishment, avoidance extinction was characterized by short latencies and nearly 100% avoidance responding. Avoidance responding in extinction was little affected by noncontingent TO punishment. When TO was made contingent upon avoidance responding, however, avoidance latencies immediately increased and the frequency of avoidance responses subsequently decreased to zero.