Chimpanzees have been found to show the inversion effect to visual stimuli of intact chimpanzee bodies, suggesting that they have a specific way of body processing. In this study, we examined how changes of body structures affect the inversion effect to reveal the properties of their body processing. We focused on two aspects of body structures: the first-order relations (i.e., body part arrangements) and body proportions. The experimental conditions had stimuli of chimpanzee bodies with scrambled first-order relations in Experiment 1 and chimpanzee bodies with distorted body proportions in Experiment 2. Both experiments had a control condition consisting of stimuli of intact chimpanzee bodies. A total of 7 chimpanzees participated in matching-to-sample tasks on touch screens. In each trial, the stimuli were chimpanzee bodies with the same kind of manipulation of body structures and were either all upright or all inverted. We compared their performances in the upright and inverted trials to examine the inversion effect. The chimpanzees did not show any inversion effect to scrambled bodies but showed the inversion effect to distorted bodies and to intact bodies. The results suggest that chimpanzees' configural body processing relies on correct first-order relations, and distorted body proportions do not interfere with configural processing. It also implies that chimpanzees may have knowledge of the arrangement of body parts, but they may be less sensitive to body proportions. This study could facilitate the understanding of the evolution of visual processing of bodies, faces, and other objects. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

中文翻译：

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黑猩猩（盘尾猿）的身体感知：身体结构变化的影响。

已经发现黑猩猩对完整的黑猩猩身体具有视觉刺激的反转作用，表明它们具有特定的身体加工方式。在这项研究中，我们研究了身体结构的变化如何影响反演效果以揭示其身体加工的特性。我们专注于身体结构的两个方面：一阶关系（即身体部位安排）和身体比例。实验条件在实验1中具有刺激的一阶关系的黑猩猩体刺激，在实验2中具有扭曲的身体比例的黑猩猩体刺激。两个实验的控制条件均由完整的黑猩猩体刺激组成。共有7只黑猩猩参加了触摸屏上的样品匹配任务。在每次审判中 刺激是黑猩猩的身体，具有与人体结构相同的操纵方式，它们要么全部直立，要么全部倒立。我们比较了他们在立式和倒置试验中的表现，以检查倒置效果。黑猩猩对扰乱的物体没有任何反转作用，但对变形的物体和完整的物体却有反转作用。结果表明，黑猩猩的体形加工依赖于正确的一阶关系，畸形体比例不会干扰体形加工。这也意味着黑猩猩可能对身体部位的安排有所了解，但对身体的比例可能不太敏感。这项研究可以促进对身体，面部和其他物体的视觉处理演变的理解。