Smiles are universal but nuanced facial expressions that are most frequently used in face-to-face communications, typically indicating amusement but sometimes conveying negative emotions such as embarrassment and pain. Although previous studies have suggested that spatial and temporal properties could differ among these various types of smiles, no study has thoroughly analyzed these properties. This study aimed to clarify the spatiotemporal properties of smiles conveying amusement, embarrassment, and pain using a spontaneous facial behavior database. The results regarding spatial patterns revealed that pained smiles showed less eye constriction and more overall facial tension than amused smiles; no spatial differences were identified between embarrassed and amused smiles. Regarding temporal properties, embarrassed and pained smiles remained in a state of higher facial tension than amused smiles. Moreover, embarrassed smiles showed a more gradual change from tension states to the smile state than amused smiles, and pained smiles had lower probabilities of staying in or transitioning to the smile state compared to amused smiles. By comparing the spatiotemporal properties of these three smile types, this study revealed that the probability of transitioning between discrete states could help distinguish amused, embarrassed, and pained smiles.

微笑是普遍但微妙的面部表情，最常用于面对面的交流，通常表示娱乐，但有时传达负面情绪，如尴尬和痛苦。尽管先前的研究表明，这些不同类型的微笑之间的空间和时间特性可能不同，但没有研究彻底分析这些特性。本研究旨在使用自发的面部行为数据库阐明微笑传达娱乐、尴尬和痛苦的时空特性。关于空间模式的结果表明，与愉快的微笑相比，痛苦的微笑表现出更少的眼睛收缩和更多的整体面部紧张；尴尬和好笑的微笑之间没有发现空间差异。关于时间属性，尴尬和痛苦的微笑比逗乐的微笑更加紧张。此外，尴尬的微笑比逗乐的微笑表现出从紧张状态到微笑状态的逐渐变化，而痛苦的微笑与逗乐的微笑相比，停留或过渡到微笑状态的概率更低。通过比较这三种微笑类型的时空特性，本研究揭示了在离散状态之间转换的概率可以帮助区分开心、尴尬和痛苦的微笑。