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Attack behavior was elicited from squirrel monkeys by externally applied electric shock. The shock elicited attack toward other monkeys, rats, and mice, as well as toward inanimate objects, such as a stuffed doll, and even a round ball. A method of quantifying the attack behavior was devised on the basis of the attack against inanimate objects. This method revealed that the duration and probability of attack was a direct function of the shock intensity.

Four studies were conducted to investigate the source of reinforcement of Sidman avoidance. First it was found that the acquisition of avoidance was seriously impaired if there was no immediate stimulus consequence of responding, i.e., proprioceptive and auditory feedback. The second study showed that if the shock‐shock interval was split so that only responses occurring in one half of the interval were effective in postponing shock, then learning was impaired. It made little difference which half of the interval was used. The third study demonstrated that Ss learn Sidman avoidance more quickly with a variable shock‐shock interval than with the usual fixed‐interval procedure. The results of the second and third experiments argue against the view that avoidance is reinforced by the decrease in conditioned aversiveness that occurs at long post‐shock times. The final experiment indicated that Ss do not learn Sidman avoidance if the response‐produced delay of shock is preceded by a shock, hence it seems unlikely that the crucial source of reinforcement is merely an overall reduction in shock density. All of the findings are consistent with the hypothesis that the avoidance response is reinforced by the decrease in conditioned aversiveness of stimuli at short post‐response times. This seems to be the case even at the beginning of acquisition.

Acquisition performance of 22 rats in a straight alley runway was examined. The animals were subjected to partial reinforcement when the alley was black (B±) and continuous reinforcement when it was white (W+). The results indicated (a) higher terminal performance, for partial as against continuous reinforcement conditions, for starting‐time and running‐time measures, and (b) lower terminal performance under partial conditions for a goal‐entry‐time measure. These results confirm within subjects an effect previously demonstrated, in the runway, only in between‐groups tests, where one group is run under partial reinforcement and a separate group is run under continuous reinforcement in the presence of the same external stimuli. Differences between the runway situation, employing a discrete‐trial procedure and performance measures at three points in the response chain, and the Skinner box situation, used in its free‐operant mode with a single performance measure, are discussed in relation to the present findings.

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Four rats were trained to bar press on FR 9 TO 30 sec. They were reinforced with a large or small amount of water according to whether their final IRT was long or short respectively. Four control rats always received the small amount of reinforcement. The control animals produced the high rates of responding typical of fixed‐ratio performance. The experimental animals, with one exception, developed superstitious behavior and maintained slow responding throughout the ratio. However, some features of the results pointed to a persistent influence of the factors which favor short IRTs.

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Operant responses of human subjects were conditioned according to a variable‐interval schedule of positive reinforcement. A brief noise was delivered as punishment for each of the responses. The noise suppressed the punished responses more when an alternative unpunished response was concurrently available than when only a single punished response was available. This finding extends the generality of a previous study that had used a period of extinction rather than the brief noise as the punishing stimulus.

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