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Sidman's (2000) theory regarding the origin of equivalence relations predicts that a reinforcing stimulus common to distinct equivalence classes must drop out of the equivalence relations. This prediction was tested in a study by arranging class-specific reinforcers, R1 and R2, following correct responding on the prerequisite conditional discriminations (Ax-Bx, Cx-Bx) for stimulus classes A1B1C1 and A2B2C2.

The authors discuss an experiment using pigeons to test their sensitivity to reinforcement when trained on variable-interval schedules in which two travel times between alternatives were arranged randomly.

Researchers examine pigeons' insistence in foraging for prey, and the length of foraging time spent in one area. An evaluation of the relationship between food deprivation, patch residence time, and session duration in an open economy is presented.

The responses of pigeons show an increase in time allocation over response-allocation sensitivity in concurrent exponential and arithmetic variable-interval schedules. The exponential-schedule sensitivity is also greater than arithmetic-schedule sensitivity for both measures of choice. The correlation of the shortest interval of the Hybrid 6 schedule with the mean interval, produce response and time sensitivities is lower than the changes variedly with overall reinforcer rates.

An experiment studied how pigeons responded to food reinforcement on multiple variable-interval schedules where the total food consumption was fully dictated by the pigeons' interaction with the schedules. Results found evidence of overmatching, as seen in more extreme response allocation between components than the distribution of reinforcers. There was a drop in generalized-matching sensitivity from overmatching to undermatching values in traditional multiple schedules when food deprivation was raised by cutting session duration. Sensitivity likewise increased from undermatching to overmatching when the session became longer.

Experiments involving the response of pigeons for food reinforcement on switching-key concurrent variable-interval schedules are conducted to examine whether different independent variables control choice independently. Results indicate that relative reinforcer rates and magnitude do not control concurrent choice independently.

The effects that sequences of same-key reinforcers obtained from the same response key have on local preference in concurrent variable-interval schedules with pigeons as subjects are investigated. Although there was a general tendency to stay at the just-reinforced alternative, this tendency was considerably decreased in conditions where same-key reinforcer sequences were short.

The quantification of steady-state choice in concurrent schedules is analyzed. The results extended previous research using the same basic procedure that had included only reinforcer distributions symmetrical around 1:1 and the analysis suggests that the variables controlling choice operated at a number of levels.

An experiment was conducted in which five pigeons are trained on pairs of concurrent variable-interval schedules in a switching key procedure. The results of the study that maintained an overall constant rate of reinforcement are described.

Six pigeons were experimented to find the response on pairs of concurrent variable-interval schedules with, four different arrangements of alteration between the schedules. Differences in behavior preceding the different-postswitch are exhibited in the signaled random alternation procedure.

A study revealed that, the control choice have both short-term and long-term effects and that the short-term effects increased, when the reinforcer ratios arranged were more extreme. The regular effects on preference of individual reinforces are not solely the results of rapidly changing contingencies.