Fanselow M S, Tighe T J
Department of Psychology, Dartmouth College, Hanover, New Hampshire 03755.
J Exp Psychol Anim Behav Process. 1988 Apr;14(2):187-99.
Rats received unsignaled shocks in an observation chamber, with different groups varying with respect to time between shocks. Twenty-four hours later the rats were returned to the observation chamber for a test of conditioning to contextual stimuli. The freezing response served as the dependent variable. In Experiment 1 we found that distributed shock trials (60 s) resulted in more context conditioning than did massed trials (3 s or 16 s). Experiment 2 replicated this intertrial interval (ITI) effect when total time in the context was equated for the massed and distributed groups. The observed beneficial effect of distributed practice for conditional stimuli arises because of decreased contextual conditioning with longer ITIs (e.g., Gibbon & Balsam, 1981; Rescorla & Wagner, 1972). Although the basic effect of enhanced performance with longer ITIs is consistent with Wagner's rehearsal model (e.g., 1978), three findings argue against such an account. First, posttrial stimulation did not reduce the benefit obtained from distributed trials (Experiment 3). Second, intertrial distractors did not improve performance of the animals subjected to massed trials (Experiment 4). And third, the ITI effect was not eliminated when conditioning was brought to its asymptote (Experiment 5). The overall pattern of data is consistent with an opponent-process account suggesting that in addition to supporting conditioning, the unconditional stimulus (US) activates a B-state capable of reducing the impact of the next US and that this B-state lasts longer than 16s but decays before 60 s.
大鼠在观察室中接受无信号电击，不同组之间电击间隔时间不同。24小时后，将大鼠放回观察室，以测试对情境刺激的条件反射。僵住反应作为因变量。在实验1中，我们发现分散电击试验（60秒）比集中试验（3秒或16秒）产生更多的情境条件反射。当集中组和分散组在情境中的总时间相等时，实验2重复了这种试验间隔（ITI）效应。观察到的分散练习对条件刺激的有益效果是由于较长的ITI导致情境条件反射减少（例如，吉本和巴尔萨姆，1981；雷斯克拉和瓦格纳，1972）。虽然较长的ITI提高表现的基本效应与瓦格纳的复述模型一致（例如，1978），但有三个发现反对这种解释。第一，试验后刺激并没有减少分散试验获得的益处（实验3）。第二，试验间隔干扰因素并没有提高接受集中试验的动物的表现（实验4）。第三，当条件反射达到渐近线时，ITI效应并未消除（实验5）。数据的总体模式与对手过程解释一致，这表明除了支持条件反射外，无条件刺激（US）还激活了一种B状态，这种状态能够降低下一个US的影响，并且这种B状态持续时间超过16秒但在60秒之前衰减。
