Four groups of rats were traiaed to bar press in the presence of either of two stimuli (Si or 82) on a fixed-interval (FI) 30-sec. schedule. In a second phase, one group had the discriminative stimuli correlated with reinforced and nonreinforced intervals, and for a second group the FI responding was reinforced 50% of the time to both stimuli. The other two groups were reinforced for responding to both stimuli following every interval, one matched to the experimental groups for number of intervals per day, the other matched for number of reinforcements per day. Positive behavioral contrast was observed in the discrimination group, and the partially reinforced group showed a comparable increase in response rate. Further analysis showed that the increased rate in both groups occurred only in intervals following nonreinforced intervals.

Experiments in the double runway and its analogs are reviewed and evaluated in terms of several theories that have been applied to this situation. Because of the complexity of the situation, a simple correspondence between the frustration effect (FE) and a hypothetical frustration response has not been convincingly demonstrated. Rather, a theoretical account of the FE must include possible effects of secondary reward, competing responses, generalization decrements, demotivation, and differential conditioning. Frustration theory is not clearly supported by the FE, but neither are there clear grounds for denying the role of frustration in producing it.

Pigeons were exposed to multiple schedules in which a key was lit in one component and a bar was present in the other. Ten subjects were trained to peck the key and to press the bar with their feet, and four subjects were trained to peck both the bar and the key. After a period of exposure to variable-interval reinforcement in both components, subjects were exposed to extinction in one component. Only one of the 10 pigeons in the key-peck:barpress condition showed an increase in rate in the other component, while seven of them showed a decrease. In the key-peck:bar-peck condition, three of the four subjects showed positive contrast. The data suggest that a condition for contrast to occur is that topographically similar behaviors be required in both components of the multiple schedule.

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Four groups of domestic chicks received imprinting, imprinting•shock, shock, or control treatment in the first week of life, and later learned a hunger-motivated running response in a runway under either continuous-or partial-reward conditions. When the running response was extinguished, a partial reinforcement effect (PRE) was shown in all four treatment groups. In the imprinting-shock treatment, persistence was enhanced following both partialand continuous-reward acquisition training. Implications for counterconditioning views of persistence are discussed.