Facial expressions contribute to nonverbal communication, social coordination, and interaction. Facial expressions may reflect the emotional state of the expressor, but they may be modulated by the presence of others, for example, by facial mimicry or through social display rules. We examined how deliberate facial expressions of happiness and anger (smiles and frowns), prompted by written commands, are modulated by the congruency with the facial expression of background faces and how this effect depends on the age of the background face (infants vs. adults). Our main interest was whether the quality of the required expression could be influenced by a task-irrelevant background face and its emotional display. Background faces from adults and infants displayed happy, angry, or neutral expressions. To assess the activation pattern of different action units, we used a machine classifier software; the same classifier was used to assess the chronometry of the expression responses. Results indicated slower and less correct performance when an incongruent facial expression was in the background, especially when distractor stimuli showed adult faces. Interestingly, smile responses were more intense in congruent than incongruent conditions. Depending on stimulus age, frown responses were affected in their quality by incongruent (smile) expressions in terms of the additional activation or deactivation of the outer brow raiser (AU2), resulting in a blended expression, somewhat different from the prototypical expression for anger. Together, the present results show qualitative effects on deliberate facial expressions, beyond typical chronometric effects, confirming machine classification of facial expressions as a promising tool for emotion research.

面部表情有助于非语言交流、社会协调和互动。面部表情可能反映表达者的情绪状态，但它们可能会受到他人在场的调节，例如面部模仿或社交展示规则。我们研究了由书面命令引发的刻意的快乐和愤怒的面部表情（微笑和皱眉）如何受到与背景面部表情的一致性的调节，以及这种效果如何取决于背景面部的年龄（婴儿与成人） ）。我们的主要兴趣是所需表情的质量是否会受到与任务无关的背景脸及其情绪表现的影响。成人和婴儿的背景面孔表现出快乐、愤怒或中性的表情。为了评估不同动作单元的激活模式，我们使用了机器分类器软件；相同的分类器用于评估表达反应的计时。结果表明，当背景中的面部表情不一致时，尤其是当干扰刺激显示成人面孔时，表现会更慢且更不正确。有趣的是，在一致的情况下，微笑反应比不一致的情况下更强烈。根据刺激年龄的不同，皱眉反应的质量会受到不协调（微笑）表情的影响，即外提眉器（AU2）的额外激活或停用，导致混合表情，与愤怒的原型表达有些不同。总之，目前的结果显示了对刻意面部表情的定性影响，