This study was mainly concerned with the effects of reinforcement upon the behaviour that immediately follows its occurrence . Rats' responding on a variable-ratio schedule and on three kinds of variable-interval schedule,
namely, arithmetic variable-interval, constant probability variable-interval and arithmetic variable-interval with added short intervals, were investigated.
On the variable-interval schedules, the duration of the post-reinforcement pause was an increasing function of the magnitude of reinforcement. When some of the
reinforcements were omitted, and a 'neutral' stimulus presented in place of them, the pause following the stimulus was shorter than the post-reinforcement pauses.
The local changes in the probability of reinforcement, with respect to the time-since-previous-reinforcement, on the schedules also affected the duration of the post-reinforcement pause. Changing the magnitude of the reinforcer or omitting the reinforcer did not systematically affect the rate and pattern of responding. The response rate was related, however, to the time that had elapsed
since the preceding reinforcement. These relationships were also observed in the variable-ratio schedules. In the latter case the schedule parameter also affected the duration of the post-reinforcement pause . These results were discussed with reference to two hypotheses, viz. Amsel's frustration hypothesis and Staddon's discriminative control hypothesis .