The proposed project will provide a direct comparison of two experimental methods commonly used to study choice behavior: concurrent procedures and concurrent-chains procedures. Data derived from these two procedures have fostered numerous theoretical models of choice behavior that attempt to account for choice in both procedures. However, preliminary research by the principal investigator indicates that choice under these two procedures may be controlled by different variables, a finding that greatly restricts the generality of theoretical models of choice based on a single controlling variable. The proposed project includes two experiments designed to extend these previous findings, evaluate their generality, and further elucidate the variables that control choice behavior under concurrent and concurrent-chains procedures. Experiment 1 will assess the effects of "forced choices," which will force a subject to complete the requirements for reinforcement imposed by the unpreferred alternative whenever a specified number of consecutive reinforcements have been obtained from the preferred alternative. Forced choices will ensure that subjects remain in contact with the requirements for reinforcement imposed by both choice alternatives. The frequency of forced choices will be varied over experimental conditions, and their effects on choice behavior under concurrent and concurrent-chains procedures will be compared. Experiment 2 will examine the effects of various fixed-ratio response requirements for reinforcement on choice between fixed and variable response requirements under concurrent and concurrent-chains procedures. This experiment will provide a comparison of how large the fixed-ratio response requirement must be before preference shifts from the fixed to the variable response requirement under each of these two procedures. Results of this study will permit a more thorough and quantitative analysis of the differences in choice behavior generated by concurrent and concurrent-chains procedures. Taken together, the two experiments of the proposed project will help to elucidate the factors that control choice behavior under these two experimental procedures, and provide important tests of the generality of theoretical models of choice behavior.