The relationship between momentary response probabilities and momentary reinforcement effects

Premack’s probability hypothesis provides a simple empirical rule for predicting reinforcement effects, but has always been applied to response probabilities estimated by averaging over entire sessions. If the rule is robust, it should also predict momentary (e.g., within-sessions) changes in reinforcement from parallel momentary probability changes. It seems to do so. Six rats received noncontingent water (base), then leverpressed for water (contingency), each for 15 sessions. All sessions were divided into six subsessions. Average leverpressing for individual rats was a simple monotonie, usually linear, function of the probability of drinking—estimated from that subsession ’s counterpart during base. Similar results were obtained from a second study even though different instrumental and contingent events were used. With some generality, then, it is possible to apply the probability hypothesis to momentary reinforcement effects.