Vocal communication is tied to interpersonal arousal coupling in caregiver-infant dyads

It has been argued that a necessary condition for the emergence of speech in humans is the ability to vocalize irrespectively of underlying affective states, but when and how this happens during development remains unclear. To examine this, we used wearable microphones and autonomic sensors to collect multimodal naturalistic datasets from 12-month-olds and their caregivers. We observed that, across the day, clusters of vocalisations occur during elevated infant and caregiver arousal. This relationship is stronger in infants than caregivers: caregivers' vocalizations show greater decoupling with their own states of arousal, and their vocal production is more influenced by the infant’s arousal than their own. Different types of vocalisation elicit different patterns of change across the dyad. Cries occur following reduced infant arousal stability and lead to increased child-caregiver arousal coupling, and decreased infant arousal. Speech-like vocalisations also occur at elevated arousal, but lead to longer-lasting increases in arousal, and elicit more parental verbal responses. Our results suggest that: 12-month-old infants’ vocalisations are strongly contingent on their arousal state (for both cries and speech-like vocalisations), whereas adults’ vocalisations are more flexibly tied to their own arousal; that cries and speech-like vocalisations alter the intra-dyadic dynamics of arousal in different ways, which may be an important factor driving speech development; and that this selection mechanism which drives vocal development is anchored in our stress physiology.学界普遍认为，人类言语产生的必要前提之一，是个体能够脱离内在情感状态进行发声，但这一能力在人类发育过程中具体何时出现、如何形成，目前仍不明确。为探究这一问题，本研究使用可穿戴麦克风与自主神经传感器，从12月龄婴儿及其照料者处采集了多模态自然场景数据集。研究团队观察到，在全天时段中，婴儿与照料者的发声集群均出现在二者唤醒水平升高的阶段。该关联在婴儿群体中表现得更为显著：照料者的发声与其自身唤醒状态的解耦程度更高，且其发声行为更多受婴儿的唤醒水平影响，而非自身状态。不同类型的发声会引发母婴二人组之间不同的唤醒变化模式。婴儿啼哭多发生于其唤醒稳定性下降之后，且会提升母婴二人组的唤醒耦合程度，同时降低婴儿自身的唤醒水平。类言语发声同样出现在唤醒水平升高的阶段，但会引发更持久的唤醒水平提升，并促使照料者做出更多言语回应。本研究结果表明：其一，12月龄婴儿的发声行为（无论啼哭还是类言语发声）均与其唤醒状态紧密相关，而成人的发声则更灵活地与自身唤醒状态相绑定；其二，啼哭与类言语发声会以不同方式改变母婴二人组的唤醒动态，这或许是推动言语发育的重要因素；其三，驱动发声发育的这一选择机制，根植于人类的应激生理系统。