Stanton M, Lobaugh N, Amsel A
J Exp Psychol Anim Behav Process. 1984 Jul;10(3):376-89.
Simultaneous (SimNC) and successive negative contrast (SNC), two paradoxical effects that are related to shifts in reward magnitude, were studied in rats from 11 to 17 days of age. Experiments 1 and 2 looked at the emergence of SimNC at 11, 14, and 17 days. At all of these ages, rats were able to discriminate between the large (milk suckling) and small (dry suckling) reward odor cues as measured by attachment latencies, but only the 14- and 17-day-olds showed SimNC. At none of the three ages was a discrimination formed to the differential odor cues in the alley in terms of runway speeds. Experiment 3 was designed as a further test of the absence of SimNC at 11 days. In this experiment, the pups were placed directly on the dam's ventrum to facilitate attachment. As in the earlier experiment, the 11-day-old pups discriminated between the odors signaling the two reward conditions but did not show the SimNC effect. In Experiment 4, SNC was measured in pups 14 and 17 days of age. SNC was shown at 17 days but not at 14 days in the attachment latency measure and at neither age in the run measure. These four experiments extend our earlier findings that the paradoxical effects that emerge out of intermittent schedules of reward magnitude occur earlier than those associated with single abrupt shifts in reward magnitude.
同时性负对比（SimNC）和相继性负对比（SNC）是与奖励大小变化相关的两种自相矛盾的效应，在11至17日龄的大鼠中进行了研究。实验1和实验2观察了SimNC在11日龄、14日龄和17日龄时的出现情况。在所有这些年龄段，通过依恋潜伏期测量发现，大鼠能够区分大（哺乳）和小（干吸）奖励气味线索，但只有14日龄和17日龄的大鼠表现出SimNC。在这三个年龄段中，就跑道速度而言，在小巷中均未形成对不同气味线索的辨别。实验3旨在进一步测试11日龄时是否不存在SimNC。在该实验中，将幼崽直接放在母鼠的腹部以促进依恋。与早期实验一样，11日龄的幼崽能够区分表示两种奖励条件的气味，但未表现出SimNC效应。在实验4中，对14日龄和17日龄的幼崽进行了SNC测量。在依恋潜伏期测量中，17日龄时表现出SNC，而14日龄时未表现出；在跑道测量中，两个年龄段均未表现出。这四个实验扩展了我们早期的研究结果，即奖励大小间歇性变化产生的自相矛盾效应比与奖励大小单次突然变化相关的效应出现得更早。
