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Killeen and Hall (2001) showed that a common factor called strength underlies the key dependent variables of response probability, latency, and rate, and that overall response rate is a good predictor of strength. In a search for the mechanisms that underlie those correlations, this article shows that (a) the probability of responding on a trial is a two-state Markov process; (b) latency and rate of responding can be described in terms of the probability and period of stochastic machines called clocked Bernoulli modules, and (c) one such machine, the refractory Poisson process, provides a functional relation between the probability of observing a response during any epoch and the rate of responding. This relation is one of proportionality at low rates and curvilinearity at higher rates.

This study examined whether preference for a drug (diazepam or placebo) could be switched using conditioning procedures. During the first 4 sessions of Phase 1, 6 participants received 5 mg of diazepam or placebo under double-blind conditions. During the remaining 5 sessions of Phase 1, participants selected the drug they wished to receive. The first 4 sessions of Phase 2 were a replication of Phase 1, except that following ingestion of the drug, participants completed a computer task for which they could earn money. Payment for the computer task was lowest following ingestion of the drug they preferred in Phase I and highest following the drug they had avoided. Preference was reassessed during the last 5 sessions of Phase 2. Five of the participants preferred placebo in Phase 1 but diazepam in Phase 2. Subjective responses to the drugs also changed across the 2 phases.

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