Florkiewicz Brittany N, Lazebnik Teddy
Department of Psychology, Lyon College, Batesville, AR, USA.
Department of Mathematics, Ariel University, Ariel, Israel.
Anim Cogn. 2025 Apr 30;28(1):34. doi: 10.1007/s10071-025-01955-0.
There have been shifts toward more systematic and standardized methods for studying non-human primate facial signals, thanks to advancements like animalFACS. Additionally, there have been calls to better integrate the study of both facial and gestural communication in terms of theory and methodology. However, few studies have taken this important integrative step. By doing so, researchers could gain greater insight into how the physical flexibility of facial signals affects social flexibility. Our study combines both approaches to examine the relationship between the flexibility of physical form and the social function of chimpanzee facial "gestures". We used chimpFACS along with established gestural ethograms that provide insights into four key gesture properties and their associated variables documented in chimpanzee gestures. We specifically investigated how the combinatorics (i.e., the different combinations of facial muscle movements) and complexity (measured by the number of discrete facial muscle movements) of chimpanzee facial signals varied based on: (1) how many gesture variables they exhibit; (2) the presence of a specific goal; and (3) the context in which they were produced. Our findings indicate that facial signals produced with vocalizations exhibit fewer gesture variables, rarely align with specific goals, and exhibit reduced contextual flexibility. Furthermore, facial signals that include additional visual movements (such as those of the head) and other visual signals (like manual gestures) exhibit more gestural variables, are frequently aligned with specific goals, and exhibit greater contextual flexibility. Finally, we discovered that facial signals become more morphologically complex when they exhibit a greater number of gesture variables. Our findings indicate that facial "gesturing" significantly enhanced the facial signaling repertoire of chimpanzees, offering insights into the evolution of complex communication systems like human language.
由于诸如动物面部动作编码系统（animalFACS）等技术的进步，对于非人类灵长类动物面部信号的研究已转向更系统、标准化的方法。此外，也有人呼吁在理论和方法上更好地整合面部和手势交流的研究。然而，很少有研究迈出这一重要的整合步骤。通过这样做，研究人员可以更深入地了解面部信号的身体灵活性如何影响社交灵活性。我们的研究结合了这两种方法，以检验黑猩猩面部“手势”的形式灵活性与社会功能之间的关系。我们使用了黑猩猩面部动作编码系统（chimpFACS）以及已建立的手势行为图谱，这些图谱能深入了解记录在黑猩猩手势中的四个关键手势属性及其相关变量。我们具体研究了黑猩猩面部信号的组合方式（即面部肌肉运动的不同组合）和复杂性（通过离散面部肌肉运动的数量来衡量）如何基于以下因素而变化：（1）它们表现出多少手势变量；（2）是否存在特定目标；（3）产生这些信号的背景。我们的研究结果表明，与发声同时产生的面部信号表现出较少的手势变量，很少与特定目标一致，并且表现出较低的情境灵活性。此外，包括额外视觉动作（如头部动作）和其他视觉信号（如手势）的面部信号表现出更多的手势变量，经常与特定目标一致，并且表现出更大的情境灵活性。最后，我们发现，当面部信号表现出更多的手势变量时，其形态会变得更加复杂。我们的研究结果表明，面部“手势”显著丰富了黑猩猩的面部信号库，为人类语言等复杂通信系统的进化提供了见解。
