Adjustment of percussive movements to match the energetic requirements of the task serves as an index of skill in stone-knapping and nut-cracking. In this study, we compared strike-by-strike adjustment of percussive movements in expert bearded capuchin monkeys (Sapajus libidinosus) and (novice and expert) humans cracking palm nuts (Astrocaryum spp.) using stone hammers of varying mass. The monkeys regulated each strike's amplitude and hammer's velocity at impact to a small degree based on the propagation of a fracture in the nut's shell but overall struck a nut with consistent kinetic energy for a given hammer. They showed the smallest movement variability across strikes among all groups. Novice humans took the most strikes to crack a nut among all groups. Expert humans took the fewest strikes among all groups while showing the largest variation in hammer's kinetic energy at impact and largest movement variability across strikes. Overall, our findings confirm that expert humans can adjust their strikes more precisely to meet variable task demands and are more efficient than monkeys or novice humans in cracking nuts, but the findings also show a surprising advantage for expert monkeys over novice humans. The monkeys' strategy of striking with consistent amplitude and velocity is advantageous when hammer mass is adequate to generate sufficient kinetic energy at impact and crack open a nut in few strikes without requiring fine adjustments, explaining why the monkeys are particularly attentive to a stone's mass when choosing it as a hammer. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

中文翻译：

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敲击工具在人类（智人）和野生胡子卷尾猴（Sapajus libidinosus）中的明显感知运动特征。

调整打击乐动作以适应任务的精力充沛，是打石头和敲坚果的技能指标。在这项研究中，我们比较了使用不同质量的石锤敲打专家级胡须的卷尾猴（Sapajus libidinosus）和（新手和专家）人类敲击棕榈坚果（Astrocaryum spp。）时敲击动作的逐击调整。猴子会根据螺母外壳破裂的传播程度，在一定程度上调节每次撞击的幅度和锤击时的速度，但是对于给定的锤子，整体上会以一致的动能撞击螺母。他们显示了所有组中跨罢工的最小运动变异性。在所有组中，新手都采取了最多的行动来破坏坚果。专家级的人在所有组中进行的打击最少，而锤击时的动能变化最大，并且整个打击过程中的运动变化最大。总体而言，我们的发现证实，专家猴子可以更精确地调整其打击效果，以满足可变的任务需求，并且在裂开坚果方面比猴子或新手更有效率，但发现也显示出专家猴子比新手具有令人惊讶的优势。当锤的质量足以在撞击时产生足够的动能并在不需微调的情况下敲击几次即可使螺母裂开，因此猴子的振幅和速度保持一致的策略是有利的，这说明了为什么猴子特别注意石头的质量选择它作为锤子。（PsycINFO数据库记录（c）2019 APA，