Dube W V, McIlvane W J
Behavioral Sciences Division, E. K. Shriver Center, Waltham, Massachusetts 02254, USA.
J Exp Anal Behav. 1997 Nov;68(3):303-16. doi: 10.1901/jeab.1997.68-303.
Stimulus control was evaluated in 3 individuals with moderate to severe mental retardation by delayed identity matching-to-sample procedures that presented either one or two discrete forms as sample stimuli on each trial. On pretests, accuracy scores on one-sample trials were uniformly high. On two-sample trials, the correct stimulus (i.e., the one that subsequently appeared in the comparison array) varied unpredictably, and accuracy scores were substantially lower, suggesting that both sample stimuli did not exert stimulus control on every trial. Subjects were then given training sessions with the one-sample task and with a new set of four stimuli. For two of the stimuli, correct matching responses were followed by reinforcers on a variable-ratio schedule that led to a high reinforcer rate. For the other two stimuli, correct responses were followed by reinforcers on a variable-ratio schedule that led to a substantially lower reinforcer rate. Results on two-sample tests that followed showed that (a) on trials in which comparison arrays consisted of one high reinforcer-rate and one low reinforcer-rate stimulus, subjects most often selected the high-rate stimulus; and (b) on trials in which the comparison arrays were either two high reinforcer-rate stimuli or two low reinforcer-rate stimuli and the samples were one high reinforcer- and one low reinforcer-rate stimulus, accuracy was higher on trials with the high-rate comparisons. These results indicate that the frequency of stimulus control by high reinforcer-rate samples was greater than that by low reinforcer-rate samples. Following more training with the one-sample task and reversed reinforcement schedules for all stimuli, the differences in stimulus control frequencies on two-sample tests also reversed. These results demonstrate experimental control by reinforcement contingencies of which of two sample stimuli controlled selections in the two-sample task. The procedures and results may prove to be relevant for understanding restricted stimulus control and stimulus overselectivity.
通过延迟的样本匹配识别程序，对3名中度至重度智力障碍患者的刺激控制进行了评估，该程序在每次试验中呈现一个或两个离散形式作为样本刺激。在预测试中，单样本试验的准确率得分一直很高。在双样本试验中，正确的刺激（即随后出现在比较阵列中的刺激）变化不可预测，准确率得分显著较低，这表明并非每次试验中两个样本刺激都能施加刺激控制。然后，让受试者进行单样本任务和一组新的四种刺激的训练。对于其中两种刺激，正确的匹配反应之后按照可变比率时间表给予强化物，这导致了高强化率。对于另外两种刺激，正确反应之后按照可变比率时间表给予强化物，这导致了显著较低的强化率。随后的双样本测试结果表明：（a）在比较阵列由一个高强化率刺激和一个低强化率刺激组成的试验中，受试者最常选择高强化率刺激；（b）在比较阵列是两个高强化率刺激或两个低强化率刺激且样本是一个高强化率和一个低强化率刺激的试验中，高强化率比较的试验准确率更高。这些结果表明，高强化率样本的刺激控制频率大于低强化率样本的刺激控制频率。在对单样本任务进行更多训练并对所有刺激采用反向强化时间表后，双样本测试中刺激控制频率的差异也发生了逆转。这些结果证明了强化偶然性对双样本任务中两个样本刺激中的哪一个控制选择的实验控制。这些程序和结果可能被证明与理解受限的刺激控制和刺激过度选择性相关。
