ESM raw data from Goats prefer positive human emotional facial expressions.

Domestication has shaped the physiology and the behaviour of animals to better adapt to human environments. Therefore, human facial expressions may be highly informative for animals domesticated for working closely with people, such as dogs and horses. However, it is not known whether other animals, and particularly those domesticated primarily for production, such as goats, are capable of perceiving human emotional cues. In this study, we investigated whether goats can distinguish human facial expressions when simultaneously shown two images of an unfamiliar human with different emotional valences (positive/happy or negative/angry). Both images were vertically attached to a wall on one side of a test arena, 1.3 m apart, and goats were released from the opposite side of the arena (distance of 4.0 m) and were free to explore and interact with the stimuli during the trials. Each of four test trials lasted 30 s. Overall, we found that goats preferred to interact first with happy faces, meaning that they are sensitive to human facial emotional cues. Goats interacted first, more often and for longer duration with positive faces when they were positioned on the right side. However, no preference was found when the positive faces were placed on the left side. We show that animals domesticated for production can discriminate human facial expressions with different emotional valences and prefer to interact with positive ones. Therefore, the impact of domestication on animal cognitive abilities may be more far-reaching than previously assumed.

驯化作用已重塑动物的生理与行为特征，使其更适配人类生存环境。因此，对于那些为与人类紧密协作而被驯化的动物（如犬、马）而言，人类面部表情或许能传递极为丰富的信息。然而，目前尚不明确其他动物——尤其是那些主要为生产目的而被驯化的动物（如山羊）——是否能够识别人类的情绪线索。本研究中，我们针对山羊能否区分人类面部表情展开了探究：实验同时向山羊展示两名陌生人类分别带有不同情绪效价（积极/愉悦或消极/愤怒）的面部图像。两张图像均垂直张贴于测试竞技场一侧的墙面，二者间距为1.3米；山羊从竞技场的另一侧（与墙面相距4.0米）被释放，并可在实验过程中自由探索并与刺激物互动。每组测试时长为30秒，共开展4组测试。整体而言，我们发现山羊更倾向于优先与带有愉悦表情的图像互动，这表明它们能够感知人类面部的情绪线索。当愉悦面孔被置于右侧时，山羊会优先、更频繁且更持久地与积极表情的图像互动；但当愉悦面孔被置于左侧时，则未观察到此类偏好。本研究证实，以生产为目的驯化的动物能够区分不同情绪效价的人类面部表情，并更偏好与积极表情的图像互动。由此可见，驯化对动物认知能力的影响或许比此前设想的更为深远。