The “Fat Face” illusion: A robust adaptation for processing pairs of faces

• Published in: Vision research (Oxford) 2022-06, Vol.195, p.108015-108015, Article 108015
• Main Authors: Galusca, Cristina I., Fang, Wei, Wang, Zhe, Zhong, Ming, Sun, Yu-Hao P., Pascalis, Olivier, Xiao, Naiqi G.
• Format: Article
• Language: English
• Subjects: Binocular vision; Canada; Depth perception; Face; Face processing; Humans; Life Sciences; Neurons and Cognition; Optical Illusions; Psychology and behavior; Recognition, Psychology; Vision, Binocular; “Fat Face” illusion
• ISSN: 0042-6989; 1878-5646; 0042-6989
• DOI: 10.1016/j.visres.2022.108015

•The “Fat Face” illusion indexes a special perceptual mechanism for multiple faces.•The illusion is not affected by face categories, familiarity, or task requirements.•The visual system augments the perceived size of the face at the bottom.•The illusion relies on binocular vision.•The illusion indexes a visual adaptation to the environment. Converging evidence has demonstrated our remarkable capacities to process individual faces. However, in real-life contexts, we rarely see faces in isolation. It is largely unknown how our visual system processes a multitude of faces. The current study explored this question by using the “Fat Face” illusion: when two identical faces are vertically aligned, the bottom face appears bigger. In Experiment 1, we tested the robustness of this illusion by using faces varied by gender and race, by recruiting participants from different countries (Canadian, Chinese, and French), and by implementing different task requirements. We found that the illusion was stable and immune to variations in face gender or face race, perceptual familiarity, and task requirements. Experiment 2 further indicated that binocular vision was essential for this visual illusion. When participants performed the task with one eye covered, the previously robust illusion completely disappeared. Together, these findings revealed a visual adaptation for processing multiple faces in the environment: the face at the top is perceived as more distant from the viewer and appears smaller in size than the face at the bottom. More broadly, overestimating the size of the bottom face may represent a fundamental mechanism for social interactions, ensuring the deployment of attention to those closest to self.