Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
Anim Cogn. 2011 Nov;14(6):775-86. doi: 10.1007/s10071-011-0410-9. Epub 2011 May 6.
Wild capuchin monkeys select stone tools to crack open nuts on the basis of their weight and friability, two non-visual functional properties. Here, we investigated whether they would select new stick-like tools on the basis of their rigidity. In Experiment 1, subjects faced an out-of-reach reward and a choice of three unfamiliar tools differing in color, diameter, material, and rigidity. In order to retrieve the reward, capuchins needed to select the rigid tool exemplar. Capuchins gathered information regarding tools' pliability either by (1) manipulating the tools themselves (manipulation condition), (2) observing a human demonstrator repeatedly bending the tools (observation condition), or (3) seeing the tools placed on a platform without any manipulation taking place (visual static condition). Subjects selected the rigid tool above chance levels in both the manipulation and observation conditions, but not in the visual static condition. In Experiment 2, subjects needed to select and use a flexible tool to access a liquid reward (as opposed to the rigid tool, as in previous experiment). Again, capuchins selected above chance levels the appropriate tool (i.e., flexible), thus demonstrating a good appreciation of the relation between the tool properties and the task requirements.
野生卷尾猴会根据坚果的重量和易碎性这两个非视觉功能特性来选择用来砸开坚果的石器。在这里，我们研究了它们是否会根据石器的硬度来选择新的棍棒状工具。在实验 1 中，被试面对的是一个够不着的奖励，以及三种不同颜色、直径、材料和硬度的陌生工具可供选择。为了获得奖励，卷尾猴需要选择硬度较大的工具。卷尾猴可以通过以下方式了解工具的柔韧性：（1）自己操作工具（操作条件），（2）观察人类演示者反复弯曲工具（观察条件），或（3）看到工具放在没有任何操作的平台上（视觉静态条件）。在操作和观察条件下，被试选择的工具都超过了随机水平，但在视觉静态条件下则不然。在实验 2 中，被试需要选择并使用灵活的工具来获取液体奖励（与之前的实验中使用的坚硬工具相反）。再次，卷尾猴选择了合适的工具（即灵活的工具），这表明它们很好地理解了工具特性和任务要求之间的关系。
