Abstract：
Prior research with terrestrial toads (Rhinella arenarum) in a water-reinforced instrumental situation indicated a direct relationship between acquisition rate and reward magnitude. However, a reward downshift produced a gradual adjustment of instrumental performance and a rapid adjustment of consummatory performance, rather than the abrupt and transient deterioration of behavior typical of a successive negative contrast effect. In Experiment 1, using a two-chamber box, a downshift from deionized water (which supports maximal rehydration) to 250-mM sodium chloride solution (which supports a lower rehydration), also yielded a gradual adjustment of instrumental behavior. In this experiment, animals received one trial per day and were allowed 300 s of access to the reward in the goal box. Experiment 2 used the same procedure, except that animals were allowed access to the solution in the goal box for 600 s. Under these conditions, reward downshift led to longer latencies (instrumental) and lower rehydration levels (consummatory) than those of unshifted controls, providing evidence for successive negative contrast. Unlike in similar experiments with mammals, the effect was not transient, but persisted relatively unmodified over twelve daily postshift trials. In this case, the possibility of adaptation of the peripheral mechanisms for water uptake is considered. The comparative relevance of these results is discussed in terms of habit formation versus expectancy-guided behavior in vertebrate learning.
摘要：
先前在水增强的仪器情况下对陆地蟾蜍（Rhinellaarenarum）的研究表明，获取率与奖励幅度之间存在直接关系。然而,奖励降档产生了工具性能的逐步调整和完善性能的快速调整，而不是一个连续的负反差效应典型的行为的突然和瞬时恶化。在实验1中，使用两腔盒，从去离子水（支持最大复水）到250-mM氯化钠溶液（支持较低的复水）的下移，也产生了工具行为的逐步调整。在这个实验中,动物每天接受一次试验，并被允许获得目标框中的奖励300秒。实验2使用了相同的程序，除了允许动物接触目标框中的溶液600秒。在这些条件下，与未转移的控制相比，奖励降档导致更长的延迟（工具性）和更低的补液水平（完成性），为连续阴性对比提供证据。与哺乳动物的类似实验不同，效果不是短暂的，但在12个每日轮班后试验中相对未修改地持续存在。在这种情况下,考虑了适应吸收水分的外围机制的可能性。从脊椎动物学习中的习惯形成与预期指导行为方面讨论了这些结果的比较相关性。
