[Effects of variable-interval punishment on lever pressing maintained by variable-ratio reinforcement in the rat]

The effects of reinforcement and punishment on response suppression under variable-ratio reinforcement and variable-interval punishment schedules were investigated. In the baseline period, lever pressing in rats was maintained by a variable-ratio food reinforcement schedule. In the punishment condition, responding was punished by a grid shock under a variable-interval schedule. Baseline and punishment conditions alternated, and were continued until the response stabilized. Three rats were given five or six punishment rates with a fixed reinforcement rate and another three rats were given four or five reinforcement rates with a fixed punishment rate. The results indicated that the responses were either completely suppressed or not suppressed at all. When the punishment rate increased or the reinforcement rate decreased, the response was suppressed completely. Whereas when the punishment rate decreased or the reinforcement rate increased, the responses were not suppressed. These results agree with the predictions of the molar theory.