Same/different abstract-concept learning experiments were conducted with two primate species and three avian species by progressively increasing the size of the training stimulus set of distinctly different pictures from eight to 1,024 pictures. These same/different learning experiments were trained with two pictures presented simultaneously. Transfer tests of same and different learning employed interspersed trials of novel pictures to assess the level of correct performance on the very first time of subjects had seen those pictures. All of the species eventually performed these tests with high accuracy, contradicting the long-accepted notion that nonhuman animals are unable to learn the concept of same/different. Capuchin and rhesus monkeys learned the concept more readily than did pigeons. Clark’s nutcrackers and black-billed magpies learned as readily as monkeys, and even showed a slight advantage with the smallest training stimulus sets. Those tests of same/different learning were followed by delay procedures, such that a delay was introduced after the subjects responded to the sample picture and before the test picture. In the sequential same/different task, accuracy was shown to diminish when the stimulus on a previous trial matched the test picture previously shown on a different trial. This effect is known as proactive interference. The pigeons’ proactive interference was greater at 10-s delays than 1-s delays, revealing time-based interference. By contrast, time delays had little or no effect on rhesus monkeys’ proactive interference, suggesting that rhesus monkeys have better explicit memory of where and when they saw the potential interfering picture, revealing better event-based memory.

通过将明显不同的图片的训练刺激集的大小从8张逐渐增加到1,024张，对两个灵长类和三个禽类进行了相同/不同的抽象概念学习实验。这些相同/不同的学习实验是通过同时呈现的两张图片进行训练的。相同和不同的转移测试学习使用散布的新颖图片试验来评估受试者第一次看到这些图片时正确表现的水平。所有这些物种最终都以高精度进行了这些测试，这与长期以来公认的非人类动物无法学习相同/不同概念的观点相矛盾。卷尾猴和恒河猴比鸽子更容易理解这一概念。克拉克的胡桃夹子和黑嘴喜像猴子一样容易学习，甚至在最小的训练刺激下也显示出一点优势。那些相同/不同的测试学习之后是延迟程序，这样在对象对样本图片做出响应之后以及测试图片之前就引入了延迟。在顺序相同/不同的任务中，当先前试验的刺激与先前在不同试验中显示的试验图相匹配时，显示准确性降低。这种效应称为主动干扰。鸽子的主动干扰在延迟10秒时要大于延迟1秒，这表明了基于时间的干扰。相比之下，时间延迟对恒河猴的主动干扰几乎没有影响，甚至没有影响，这表明恒河猴对何时何地看到潜在干扰图片有更好的显式记忆，从而揭示了更好的基于事件的记忆。