The ‘social brain’, consisting of areas sensitive to social information, supposedly gates the mechanisms involved in human language learning. Early preverbal interactions are guided by ostensive signals, such as gaze patterns, which are coordinated across body, brain, and environment. However, little is known about how the infant brain processes social gaze in naturalistic interactions and how this relates to infant language development. During free-play of 9-month-olds with their mothers, we recorded hemodynamic cortical activity of ´social brain` areas (prefrontal cortex, temporo-parietal junctions) via fNIRS, and micro-coded mother’s and infant’s social gaze. Infants’ speech processing was assessed with a word segmentation task. Using joint recurrence quantification analysis, we examined the connection between infants’ ´social brain` activity and the temporal dynamics of social gaze at intrapersonal (i.e., infant’s coordination, maternal coordination) and interpersonal (i.e., dyadic coupling) levels. Regression modeling revealed that intrapersonal dynamics in maternal social gaze (but not infant’s coordination or dyadic coupling) coordinated significantly with infant’s cortical activity. Moreover, recurrence quantification analysis revealed that intrapersonal maternal social gaze dynamics (in terms of entropy) were the best predictor of infants’ word segmentation. The findings support the importance of social interaction in language development, particularly highlighting maternal social gaze dynamics.

“社交大脑”由对社交信息敏感的区域组成，据说控制着人类语言学习的机制。早期的前语言互动是由明示信号引导的，例如凝视模式，这些信号在身体、大脑和环境之间协调。然而，人们对婴儿大脑如何在自然互动中处理社交凝视以及这与婴儿语言发展的关系知之甚少。在 9 个月大的婴儿与母亲自由玩耍期间，我们通过 fNIRS 记录了“社交大脑”区域（前额皮质、颞顶叶连接处）的血流动力学皮层活动，以及微编码的母亲和婴儿的社交目光。通过分词任务评估婴儿的语音处理能力。使用联合复发量化分析，我们检查了婴儿的“社交大脑”活动与人际（即婴儿协调、母亲协调）和人际（即二元耦合）水平上社会凝视的时间动态之间的联系。回归模型显示，母亲社会凝视的个人动态（但不是婴儿的协调或二元耦合）与婴儿的皮质活动显着协调。此外，重复量化分析表明，母亲内心的社会凝视动态（就熵而言）是婴儿分词的最佳预测因子。研究结果支持了社会互动在语言发展中的重要性，特别强调了母亲的社会注视动态。