RESPONSE ACQUISITION UNDER TARGETED PERCENTILE SCHEDULES - A CONTINUING QUANDARY FOR MOLAR MODELS OF OPERANT-BEHAVIOR

The number of responses rats made in a ''run'' of consecutive left-lev er presses, prior to a trial-ending right-lever press, was differentia ted using a targeted percentile procedure. Under the nondifferential b aseline, reinforcement was provided with a probability of .33 at the e nd of a trial, irrespective of the run on that trial. Most of the 30 s ubjects made short runs under these conditions, with the mean for the group around three. A targeted percentile schedule was next used to di fferentiate run length around the target value of 12. The current run was reinforced if it was nearer the target than 67% of those runs in t he last 24 trials that were on the same side of the target as the curr ent run. Programming reinforcement in this way held overall reinforcem ent probability per trial constant at. 33 while providing reinforcemen t differentially with respect to runs more closely approximating the t arget of 12. The mean run for the group under this procedure increased to approximately 10. Runs approaching the target length were acquired even though differentiated responding produced the same probability o f reinforcement per trial, decreased the probability of reinforcement per response, did not increase overall reinforcement rate, and general ly substantially reduced it (i.e., in only a few instances did respons e rate increase sufficiently to compensate for the increase in the num ber of responses per trial). Models of behavior predicated solely on m olar reinforcement contingencies all predict that runs should remain s hort throughout this experiment, because such runs promote both the mo st frequent reinforcement and the greatest reinforcement per press. To the contrary, 29 of 30 subjects emitted runs in the vicinity of the t arget, driving down reinforcement rate while greatly increasing the nu mber of presses per pellet. These results illustrate the powerful effe cts of local reinforcement contingencies in changing behavior, and in doing so underscore a need for more dynamic quantitative formulations of operant behavior to supplement or supplant the currently prevalent static ones.