De Villiers P A, Millenson J R
J Exp Anal Behav. 1972 Sep;18(2):287-94. doi: 10.1901/jeab.1972.18-287.
Three rats were trained to lever press on concurrent random interval 2-min random interval 2-min schedules of milk reinforcement. With a 5-sec changeover delay, relative response rate matched the relative reinforcement duration associated with each lever. A stimulus, during which unavoidable shocks occurred at random intervals, was superimposed on this concurrent baseline, and shifts in preference were found. However, data from this procedure were ambiguous, apparently confounded by shock-elicited response bursts. Termination of the shocks during the stimulus resulted in a rapid recovery of matching, which was preceded by a brief facilitation of responding on the less-preferred lever. The procedure was then changed to a conventional conditioned anxiety paradigm with a variable duration pre-shock stimulus. A marked shift in relative response rate towards the preferred lever was found in all three rats; that is, responding on the preferred lever was far less suppressed during the pre-shock stimulus than responding on the less-preferred lever.
三只大鼠被训练在同时呈现的随机间隔2分钟-随机间隔2分钟的牛奶强化程序下按压杠杆。在有5秒转换延迟的情况下，相对反应率与每个杠杆相关的相对强化持续时间相匹配。一种刺激（在此期间不可避免的电击以随机间隔出现）被叠加在这个同时呈现的基线之上，并且发现了偏好的转移。然而，这个程序的数据是模糊的，显然被电击引发的反应爆发所混淆。在刺激期间电击的终止导致匹配的迅速恢复，在此之前对较不偏好的杠杆的反应有短暂的促进。然后该程序被改为具有可变持续时间的电击前刺激的传统条件性焦虑范式。在所有三只大鼠中都发现相对反应率明显向偏好的杠杆转移；也就是说，在电击前刺激期间，对偏好杠杆的反应受到的抑制远小于对较不偏好杠杆的反应。
