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When a variable‐interval schedule of reinforcement was segmented into small fixed‐interval components, with reinforcements following some components and brief blackouts following the others, rate of responding doubled and a positively accelerated pattern within each component was obtained. Presented according to this percentage reinforcement paradigm, the blackouts approximated the functions of a food reinforcer. These effects occurred only when the behavior sequence required to produce reinforcement was identical to that required to produce blackout. The quasi‐reinforcing effects of these blackout stimuli suggest that a neutral stimulus need not occasion or accompany a primary reinforcer to acquire reinforcing properties.

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When a pigeon's choices between two keys are probabilistically reinforced, as in discrete trial probability learning procedures and in concurrent variable‐interval schedules, the bird tends to maximize, or to choose the alternative with the higher probability of reinforcement. In concurrent variable‐interval schedules, steady‐state matching, which is an approximate equality between the relative frequency of a response and the relative frequency of reinforcement of that response, has previously been obtained only as a consequence of maximizing. In the present experiment, maximizing was impossible. A choice of one of two keys was reinforced only if it formed, together with the three preceding choices, the sequence of four successive choices that had occurred least often. This sequence was determined by a Bernoulli‐trials process with parameter p. Each of three pigeons matched when p was 1/2 or 1/4. Therefore, steady‐state matching by individual birds is not always a consequence of maximizing. Choice probability varied between successive reinforcements, and sequential statistics revealed dependencies which were adequately described by a Bernoulli‐trials process with p depending on the time since the preceding reinforcement.

Nine rats were trained to bar press in the presence of a clicking sound of 6.67 cps (SD) for 1‐min variable‐interval food reinforcement randomly alternated with a clicking sound of 20 cps (SΔ) signifying extinction. After a criterion of 90% of total responses in the presence of the SD was obtained, a generalization test was administered, including values of 6.67, 10.00, 13.33, and 20.00 cps, with responses in the presence of the SD continuing to be reinforced during testing. The test yielded a gradient of response strength with rate highest in the presence of the SD and decreasing with increasing distance from this value. An inter‐response time (IRT) analysis of responding during generalization testing revealed no systematic differences in modal IRT category or in median IRT to the different test stimuli. Mean IRT was lowest in the presence of the SD and increased systematically with increasing distance from this value, supporting the hypothesis that the generalization gradient of response rate is primarily the result of an increasing proportion of “long” IRT responses to stimuli increasingly distant from the SD.

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The presence or absence of pulses of low intensity electric shock was used as a discriminative stimulus to control responding under fixed ratio reinforcement in the squirrel monkey. Initially brief periods of non‐reinforcement were lengthened only when discriminative control was evident. Discriminative control was studied by (1) varying the duration of non‐reinforcement periods; (2) reversing the stimulus conditions correlated with reinforcement and non‐reinforcement periods; and (3) determining the minimum shock intensity necessary to maintain discriminative control. Stimulus control was not reliably affected by d‐amphetamine, chlorpromazine, or morphine. The discriminative control by pulses of low intensity electric shock was similar to that by other discriminative stimuli, except that the control developed slowly and was better when the pulsing shock was correlated with reinforcement than when correlated with non‐reinforcement.

Three keys were available for monkeys to press. The objective was to teach the animals to press the keys in sequences up to 10 members in length. With fading procedures, a light that cued the correct key at a given serial member of the sequence faded out slightly each time the animal selected it, and became slightly brighter after the animal made an error at that sequence member. The correct keys were faded out, starting from the end of the sequence and proceeding toward the beginning. With control procedures, the cue lights were turned off suddenly, rather than being faded gradually. In almost every instance, the animals learned a longer series of unlighted key positions with the fading procedures than they did when each key‐light was turned off suddenly. Also, requiring the animals to press a series of keys cued by lights before they could reach the sequence members they were to learn hampered them in learning the later serial members. By using several different sequences, it was possible to replicate these findings within the individual animal.

Key‐pecking responses of a pigeon were maintained by a variable‐interval schedule of food reinforcement. The responses were suppressed during the occasional presentation of a warning stimulus paired with electric shock. The presence of a second pigeon emitting the same response for food reinforcement reduced the suppression that otherwise occurred during the warning stimulus when the second pigeon was absent. These results reveal that the social facilitation phenomenon can be used to restore behavior that is suppressed by a conditioned aversive stimulus.