Galbicka G, Kautz M A, Jagers T
Department of Medical Neurosciences, WRAIR, Washington, DC 20307-5100.
J Exp Anal Behav. 1993 Jul;60(1):171-84. doi: 10.1901/jeab.1993.60-171.
The number of responses rats made in a "run" of consecutive left-lever presses, prior to a trial-ending right-lever press, was differentiated using a targeted percentile procedure. Under the nondifferential baseline, reinforcement was provided with a probability of .33 at the end of a trial, irrespective of the run on that trial. Most of the 30 subjects made short runs under these conditions, with the mean for the group around three. A targeted percentile schedule was next used to differentiate 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 the last 24 trials that were on the same side of the target as the current run. Programming reinforcement in this way held overall reinforcement probability per trial constant at .33 while providing reinforcement differentially with respect to runs more closely approximating the target 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 of reinforcement per trial, decreased the probability of reinforcement per response, did not increase overall reinforcement rate, and generally substantially reduced it (i.e., in only a few instances did response rate increase sufficiently to compensate for the increase in the number of responses per trial). Models of behavior predicated solely on molar reinforcement contingencies all predict that runs should remain short throughout this experiment, because such runs promote both the most frequent reinforcement and the greatest reinforcement per press. To the contrary, 29 of 30 subjects emitted runs in the vicinity of the target, driving down reinforcement rate while greatly increasing the number of presses per pellet. These results illustrate the powerful effects 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.
在每次试验结束前进行右杠杆按压之前，大鼠连续进行左杠杆按压的“一轮”中的反应次数，通过目标百分位数程序进行区分。在无差异基线条件下，无论该试验中的轮次如何，在试验结束时给予强化的概率为0.33。30只受试大鼠中的大多数在这些条件下进行的轮次较短，该组的平均值约为3次。接下来使用目标百分位数程序来区分接近目标值12的轮次长度。如果当前轮次比过去24次试验中与当前轮次在目标同一侧的那些轮次的67%更接近目标，则对当前轮次给予强化。以这种方式设置强化程序，使每次试验的总体强化概率保持在0.33不变，同时对于更接近目标值12的轮次给予差异化强化。在该程序下，该组的平均轮次增加到约10次。即使差异化反应导致每次试验的强化概率相同、每次反应的强化概率降低、总体强化率没有增加且通常大幅降低（即，只有少数情况下反应率增加足以补偿每次试验反应次数的增加），接近目标长度的轮次仍被习得。仅基于总体强化偶然性的行为模型都预测，在整个实验过程中轮次应该保持较短，因为这样的轮次既能促进最频繁的强化，又能促进每次按压获得的最大强化。相反，30只受试大鼠中有29只在目标值附近发出轮次，降低了强化率，同时大大增加了每获得一粒食丸的按压次数。这些结果说明了局部强化偶然性在改变行为方面的强大作用，并且在这样做的过程中强调了需要更动态的操作性行为定量公式来补充或取代当前流行的静态公式。
