Harris Justin A, Gharaei Saba, Pincham Hannah L
School of Psychology, University of Sydney, NSW, Australia.
J Exp Psychol Anim Behav Process. 2011 Jul;37(3):277-86. doi: 10.1037/a0023079.
When conditioning involves a consistent temporal relationship between the conditioned stimulus (CS) and unconditioned stimulus (US), the expression of conditioned responses within a trial peaks at the usual time of the US relative to the CS. Here we examine the temporal profile of responses during conditioning with variable CS-US intervals. We conditioned stimuli with either uniformly distributed or exponentially distributed random CS-US intervals. In the former case, the frequency of each CS-US interval within a specified range is uniform but the momentary probability of the US (the hazard function) increases as time elapses during the trial; with the latter distribution, short CS-US intervals are more frequent than longer intervals, but the momentary probability of the US is constant across time within the trial. We report that, in a magazine approach paradigm, rats' response rates remained stable as time elapses during the CS when the CS-US intervals were uniformly distributed, whereas their response rates declined when the CS-US intervals were exponentially distributed. In other words, the profile of responding during the CS matched the frequency distribution of the US times, not the momentary probability of the US during the CS. These results are inconsistent with real-time associative models, which predict that associative strength tracks the momentary probability of the US, but may provide support for timing models of conditioning in which conditioned responding is tied to remembered times of reinforcement.
当条件作用涉及条件刺激（CS）与非条件刺激（US）之间一致的时间关系时，在一次试验中条件反应的表达会在相对于CS的US通常出现时间达到峰值。在此，我们研究了在条件刺激与非条件刺激间隔可变的条件作用过程中反应的时间特征。我们用均匀分布或指数分布的随机条件刺激与非条件刺激间隔对刺激进行条件作用。在前一种情况下，指定范围内每个条件刺激与非条件刺激间隔的频率是均匀的，但在试验过程中，非条件刺激的瞬时概率（风险函数）会随着时间的推移而增加；在后一种分布中，短的条件刺激与非条件刺激间隔比长的间隔更频繁，但在试验过程中，非条件刺激的瞬时概率在整个时间内是恒定的。我们报告称，在一种接近食盒的范式中，当条件刺激与非条件刺激间隔均匀分布时，随着条件刺激过程中时间的推移，大鼠的反应率保持稳定，而当条件刺激与非条件刺激间隔呈指数分布时，它们的反应率会下降。换句话说，在条件刺激期间的反应特征与非条件刺激出现时间的频率分布相匹配，而不是与条件刺激期间非条件刺激的瞬时概率相匹配。这些结果与实时联想模型不一致，实时联想模型预测联想强度会追踪非条件刺激的瞬时概率，但可能为条件作用的时间模型提供支持，在该模型中，条件反应与记忆中的强化时间相关联。
