Infant vocalisations differ in relation to autonomic arousal. Distress vocalisations remain coupled to arousal whereas speech-like vocalisations increasingly decouple over development.Although caregiver responsiveness associates with infant emotional and communicative development, it remains unclear whether responsiveness is linked to arousal-vocalisation coupling, if associations differ between speech-like and distress vocalisations, and what types of response most associate with decoupling.Using day-long home recordings from infants aged 5-18 months, we examined associations between infant arousal, vocalisation type, and caregiver responsiveness. Arousal-vocalisation coupling was quantified using ROC analyses; pointwise ROC comparisons tested coupling differences across arousal. We examined whether caregiver contingency associated with coupling strength; and which types of response - immediate vs delayed, at high vs low infant arousal - showed the strongest associations. Our results showed it is not overall contingency but selective responding during elevated arousal that associates with stronger coupling for both cries and canonical vocalisations, with a heightened effect for cries: immediate responses showed stronger associations that increased over development.These findings have theoretical implications for understanding how early caregiving relates to the functional differentiation of infant vocal signals: selective responsivity may reinforce the alarm function of crying whilst maintaining the functional differentiation between distress and speech-like vocalisations.

Infants develop communicative display through proto-conversations with caregivers. Infant vocalisations elicit responses, shaping dyadic arousal. Infant and caregiver therefore grow together as a communicative and regulatory unit. In typical development autonomic arousal is initially closely linked to distress vocalisations, while communicative vocal display gradually becomes more independent of arousal over time. Individual differences in developmental trajectories suggest variation in these patterns. Using day-long home recordings from 5-18 month-old infants we examined how infant autonomic arousal relates to vocal behaviour and caregiver responsivity. We found a functional hierarchy in arousal–vocalisation coupling consistent with functional flexibility theory. Caregiver responsivity was arousal-contingent: higher rates of both 2-second and 5-second contingent responses during elevated arousal were associated with stronger coupling at medium–high arousal levels. Consistent with selective reinforcement theory, the more immediate window showed greater specificity and stronger effects than the proximal window. Within arousal levels, caregiver divergence in intensity and affect predicted fewer high-intensity and increased low-intensity vocalisations at moderate (but not elevated) arousal. Overall, findings suggest two interacting developmental mechanisms: broad caregiver responsivity supporting symbolic language via functional flexibility, and arousal-specific responsivity supporting a distress ‘alarm’ function. Variation in arousal-contingent caregiver responses may help characterise both typical and atypical developmental trajectories.

Despite strong evidence that children learn more effectively from face-to-face interactions than from screens, we still understand relatively little about the dynamic, adaptive processes through which inter-personal contingency enhances attention and learning during live interactions. In this study, we investigate how social signals during early interactions operate across multiple hierarchical levels, ranging from low-level salience cues to higher-order features. Specifically, we examine how mothers dynamically and reciprocally adjust their behaviours across these levels in response to their infants’ attention during play. To achieve this, we developed a suite of novel, information-theory-based methods to quantify naturalistic audio-visual-semantic behaviours. Using time-series analyses, we assessed moment-by-moment associations between infant attention and both lower-order features (e.g., spectral flux of ambient noise and maternal vocalizations, maternal face and hand movement) and higher-order features (e.g., speech information rate, facial expression novelty, semantic surprisal, and toy naming) in tabletop interactions involving 67 mother-infant dyads (5- and 15-month-olds). Our findings suggest that, from early infancy, the information infants perceive is continuously and dynamically modulated across multiple hierarchical levels, contingent on their behaviour and attention. When infants focus on objects, mothers reduce low-level sensory input, minimising distractions. Conversely, increases in object naming and high-level information content associate with increases in sustained attention. These results indicate that maternal behaviours are both driven by and predictive of infant attention, and that, even from early development, attention involves interactive processes which unfold across multiple levels, from salience to semantics.

Almost all early cognitive development takes place in social contexts. At the moment, however, we know little about the neural and micro-interactive mechanisms that support infants’ attention during social interactions. Recording EEG during naturalistic caregiver-infant interactions (N=66), we compare two different accounts. Traditional, didactic perspectives emphasise the role of the caregiver in structuring the interaction, whilst active learning models focus on motivational factors, endogenous to the infant, that guide their attention. Our results show that, already by 12-months, intrinsic cognitive processes control infants’ attention: fluctuations in endogenous oscillatory neural activity associated with changes in infant attentiveness. In comparison, infant attention was not forwards-predicted by caregiver gaze or vocal behaviours. Instead, caregivers rapidly modulated their behaviours in response to changes in infant attention and cognitive engagement, and greater reactive changes associated with longer infant attention. Our findings suggest that shared attention develops through interactive but asymmetric, infant-led processes that operate across the caregiver-child dyad.

ABSTRACT Joint attention (JA) has been found to correlate with many developmental outcomes. However, little is known about how naturalistic JA is established and develops during early infancy. In this study, free‐flowing tabletop toy play between infants at 5 and 15 months and their mothers ( N = 48 dyads; 65% white) was observed to (1) examine changes in JA, (2) investigate whether infants become better leaders or followers of JA, and (3) explore the role of intentionally mediated forms of communication. JA episodes increased in frequency and duration, and initiations of JA became more evenly distributed between members of the dyad. Older infants became better at leading as well as following their mothers' attention behaviors and more frequently directed their attention towards their partner, though this had minimal impact on the organization of episodes of JA.

Previous research shows that infant vocal output varies with fluctuations in autonomic arousal. It remains unclear, however, how infants transition from reflexive vocal production to being able to produce vocalisations independent of internal state. Using naturalistic daylong recordings with wearable devices, we demonstrate that early vocalisations occur at heightened levels of autonomic arousal, measured via heart rate, in infants aged 4-21 months (n=92), but that this relationship becomes progressively decoupled over development. Daylong heart rate time series discriminated vocalisation timing above chance (ROC AUC = 0.64), and hierarchical linear mixed effects modelling demonstrated this relationship became significantly weaker over age. Arousal also strongly associated with the acoustic features of infants’ cry and non-cry vocalisations, with vocalisations produced at higher arousal being higher-pitched and more variable in pitch, more harmonic and longer in duration. The influence of arousal on non-cry acoustic features diminished significantly with age, as opposed to cry acoustics which remained tied to arousal. This differential developmental trajectory suggests the emergence of parallel vocal pathways: one remaining tied to physiological state for fixed affective signals such as cries and laughs, and another increasingly decoupled from internal states for the functionally flexible signals critical to verbal communication. We also found that mothers who contingently responded to a greater proportion of their infants’ non-cry vocalisations had infants who were significantly more decoupled, suggesting that caregiver responsivity may play a role in this progressive process.

Infant vocal production is closely linked to autonomic arousal yet the developmental transition from reflexive vocal production to vocalisations produced independent of internal state remains unclear. Using naturalistic daylong recordings from wearable devices, we examined the relationship between vocal output and heart rate in 92 infants aged 4 to 21 months. Early vocalisations occurred predominantly at heightened levels of autonomic arousal, but this coupling weakened progressively with age. Daylong heart rate time series associated with vocalisation timing above chance (ROC AUC = 0.64) and hierarchical linear mixed effects modelling confirmed a progressive developmental decoupling. Arousal also strongly associated with the acoustic features of both cry and non-cry vocalisations, with higher arousal associated with higher and more variable pitch, more harmonicity and longer duration. Notably, the influence of arousal diminished with age for non-cry vocalisations but remained stable for cries. This differential developmental trajectory suggests the emergence of parallel vocal pathways: one remaining tied to physiological state for fixed affective signals such as cries and laughs, and another increasingly decoupled from internal states for the functionally flexible signals critical to speech communication. Importantly, infants whose mothers responded contingently to a greater proportion of non-cry vocalisations showed significantly greater decoupling, suggesting that caregiver responsivity plays a role in this developmental trajectory.

During development we transition from co-regulation (where regulatory processes are shared between child and caregiver) to self-regulation. Most early co-regulatory interactions aim to manage fluctuations in the infant’s arousal and alertness; but over time, co-regulatory processes become progressively elaborated to encompass other functions such as socio-communicative development, attention and executive control. The fundamental aim of co-regulation is to help maintain an optimal ‘critical state’ between hypo- and hyper-activity. Here, we present a dynamic framework for understanding child-caregiver co-regulatory interactions in the context of psychopathology. Early co-regulatory processes involve both passive entrainment, through which a child’s state entrains to the caregiver’s, and active contingent responsiveness, through which the caregiver changes their behaviour in response to behaviours from the child. Similar principles, of interactive but asymmetric contingency, drive joint attention and the maintenance of epistemic states as well as arousal/alertness, emotion regulation, and socio-communicative development. We describe three ways in which active child-caregiver regulation can develop atypically, in conditions such as Autism, ADHD, anxiety and depression. The most well-known of these is insufficient contingent responsiveness, leading to reduced synchrony, which has been shown across a range of modalities in different disorders, and which is the target of most current interventions. We also present evidence that excessive contingent responsiveness and excessive synchrony can develop in some circumstances. And we show that positive feedback interactions can develop, which are contingent but mutually amplificatory child-caregiver interactions that drive the child further from their critical state. We discuss implications of these findings for future intervention research, and directions for future work.

During early life, we develop the ability to choose what we focus on and what we ignore, allowing us to regulate perception and action in complex environments. But how does this change influence how we spontaneously allocate attention to real-world objects during free behaviour? Here, in this narrative review, we examine this question by considering the time dynamics of spontaneous overt visual attention, and how these develop through early life. Even in early childhood, visual attention shifts occur both periodically and aperiodically. These reorientations become more internally controlled as development progresses. Increasingly with age, attention states also develop self-sustaining attractor dynamics, known as attention inertia, in which the longer an attention episode lasts, the more the likelihood increases of its continuing. These self-sustaining dynamics are driven by amplificatory interactions between engagement, comprehension, and distractibility. We consider why experimental measures show decline in sustained attention over time, while real-world visual attention often demonstrates the opposite pattern. Finally, we discuss multi-stable attention states, where both hypo-arousal (mind-wandering) and hyper-arousal (fragmentary attention) may also show self-sustaining attractor dynamics driven by moment-by-moment amplificatory child-environment interactions; and we consider possible applications of this work, and future directions.

In this article we examine how contingency and synchrony during infant-caregiver interaction helps children to learn to pay attention to objects; and how this, in turn, affects their ability to direct caregivers’ attention, and to track communicative intentions in others. First, we present evidence that, early in life, child-caregiver interactions are asymmetric. Caregivers dynamically and contingently adapt to their child more than the other way around, providing higher-order semantic and contextual cues during attention episodes which facilitate the development of specialised and integrated attentional brain networks in the infant brain. Then, we describe how social contingency also facilitates the child’s development of predictive models; and, through that, goal-directed behaviour. Finally, we discuss how contingency and synchrony of brain and behaviour can drive children's ability to direct their caregivers’ attention voluntarily; and how this, in turn, paves the way for intentional communication.

During development we transition from coregulation (where regulatory processes are shared between child and caregiver) to self-regulation. Most early coregulatory interactions aim to manage fluctuations in the infant's arousal and alertness; but over time, coregulatory processes become progressively elaborated to encompass other functions such as sociocommunicative development, attention and executive control. The fundamental aim of coregulation is to help maintain an optimal ‘critical state’ between hypo- and hyperactivity. Here, we present a dynamic framework for understanding child–caregiver coregulatory interactions in the context of psychopathology. Early coregulatory processes involve both passive entrainment, through which a child's state entrains to the caregiver's, and active contingent responsiveness, through which the caregiver changes their behaviour in response to behaviours from the child. Similar principles, of interactive but asymmetric contingency, drive joint attention and the maintenance of epistemic states as well as arousal/alertness, emotion regulation and sociocommunicative development. We describe three ways in which active child–caregiver regulation can develop atypically, in conditions such as Autism, ADHD, anxiety and depression. The most well-known of these is insufficient contingent responsiveness, leading to reduced synchrony, which has been shown across a range of modalities in different disorders, and which is the target of most current interventions. We also present evidence that excessive contingent responsiveness and excessive synchrony can develop in some circumstances. And we show that positive feedback interactions can develop, which are contingent but mutually amplificatory child–caregiver interactions that drive the child further from their critical state. We discuss implications of these findings for future intervention research, and directions for future work.

Neural entrainment to slow modulations in the amplitude envelope of infant-directed speech is thought to drive early language learning. Most previous research with infants examining speech-brain tracking has been conducted in controlled, experimental settings, which are far from the complex environments of everyday interactions. Whilst recent work has begun to investigate speech-brain tracking to naturalistic speech, this work has been conducted in semi-structured paradigms, where infants listen to live adult speakers, without engaging in free-flowing social interactions. Here, we test the applicability of mTRF modelling to measure speech-brain tracking in naturalistic and bidirectional free-play interactions of 9-12-month-olds with their caregivers. Using a backwards modelling approach, we test individual and generic training procedures, and examine the effects of data quantity and quality on model fitting. We show model fitting is most optimal using an individual approach, trained on continuous segments of interaction data. Corresponding to previous findings, individual models showed significant speech-brain tracking at delta modulation frequencies, but not in alpha and theta bands. These findings open new methods for studying the interpersonal micro-processes that support early language learning. In future work, it will be important to develop a mechanistic framework for understanding how our brains track naturalistic speech during infancy.### Competing Interest StatementThe authors have declared no competing interest.

The capacity to pay attention underpins all subsequent cognitive development. However, we understand little about how attention control is instantiated in the developing brain in real-world settings. We recorded naturalistic attention patterns, together with autonomic arousal and brain activity, in 5- and 10-month-old infants during free play. We examined whether changes in autonomic arousal and brain activity associate with changes in moment-by-moment attentional engagement, and whether they anticipate attention changes, or follow on from them. Early in infancy, slow-varying fluctuations in autonomic arousal forward-predicted attentional behaviours. Later in infancy, fluctuations in fronto-central theta power after but not before an attentional shift associated with changes in infants’ attentiveness, predicted the length of infants’ attention durations and modulated changes in arousal. Together, our results suggest that the modulation of real-world attention involves both arousal-based and cortical processes and what changes with developmental time is how these lower- and higher-order endogenous factors modulate real-world attention. As attentional systems mature, stronger associations emerge between attentional behaviour, cortical activity, and autonomic arousal.

Temporal coordination during infant-caregiver social interaction is thought to be crucial for supporting early language acquisition and cognitive development. Despite a growing prevalence of theories suggesting that increased inter-brain synchrony associates with many key aspects of social interactions such as mutual gaze, little is known about how this arises during development. Here, we investigated the role of mutual gaze onsets as a potential driver of inter-brain synchrony. We extracted dual EEG activity around naturally occurring gaze onsets during infant-caregiver social interactions in N=55 dyads (mean age 12 months). We differentiated between two types of gaze onset, depending on each partners’ role. ‘Sender’ gaze onsets were defined at a time when either the adult or the infant made a gaze shift towards their partner at a time when their partner was either already looking at them (mutual) or not looking at them (non-mutual). ‘Receiver’ gaze onsets were defined at a time when their partner made a gaze shift towards them at a time when either the adult or the infant was already looking at their partner (mutual) or not (non-mutual). Contrary to our hypothesis we found that, during a naturalistic interaction, both mutual and non-mutual gaze onsets were associated with changes in the sender, but not the receiver’s brain activity and were not associated with increases in inter-brain synchrony above baseline. Further, we found that mutual, compared to non-mutual gaze onsets were not associated with increased inter brain synchrony. Overall, our results suggest that the effects of mutual gaze are strongest at the intra-brain level, in the ‘sender’ but not the ‘receiver’ of the mutual gaze.

Shared picture-book reading is well-recognized as beneficial for children's early language development, especially where "dialogic book-sharing" techniques are used. Possible benefits of dialogic book-sharing to other aspects of child development have been little investigated, and it has not been widely studied in European populations. We conducted a randomized trial of dialogic book-sharing in Children's Centers in the UK, with parents of 2- to-4-year-old children, hypothesizing that it would benefit parenting and a range of child developmental outcomes. Intervention group parents (n = 110) received 7, weekly, group training sessions, and control parents (n = 108) the usual center input. Parenting and a range of child outcomes (language, attention, executive function, social development, and emotional-behavior difficul-ties) were assessed on 3 occasions: before, after, and 4-6 month following intervention. For all study outcomes we compared controls with each of the Intention-to-Treat population and the per-protocol population (participants attending the requisite number of sessions); and, for primary child outcomes only, the population of parents who engaged well with the intervention. There were substantial benefits of dialogic book-sharing training to parental behavior during book-sharing, especially for sensitivity and cognitive scaffolding. For all 3 sets of comparisons there were small-medium effects of on child expres-sive language, and, for the per protocol and engaged populations, similar sized effects on child receptive language and attention. There was no evidence of benefit of dialogic book-sharing for the other areas of child development; we suggest that specific intervention components need to be added to standard dialogic book-sharing to effect change in these areas.(c) 2022 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

We know that infants' ability to coordinate attention with others toward the end of the first year is fundamental to language acquisition and social cognition. Yet, we understand little about the neural and cognitive mechanisms driving infant attention in shared interaction: do infants play a proactive role in creating episodes of joint attention? Recording electroencephalography (EEG) from 12-mo-old infants while they engaged in table-top play with their caregiver, we examined the communicative behaviors and neural activity preceding and following infant- vs. adult-led joint attention. Infant-led episodes of joint attention appeared largely reactive: they were not associated with increased theta power, a neural marker of endogenously driven attention, and infants did not increase their ostensive signals before the initiation. Infants were, however, sensitive to whether their initiations were responded to. When caregivers joined their attentional focus, infants showed increased alpha suppression, a pattern of neural activity associated with predictive processing. Our results suggest that at 10 to 12 mo, infants are not routinely proactive in creating joint attention episodes yet. They do, however, anticipate behavioral contingency, a potentially foundational mechanism for the emergence of intentional communication.

While much variance in general intelligence or g is genetic, a substantial environmental component suggests a possible role for parent-child interaction. In particular, previous evidence suggests the importance of parental scaffolding, or provision of cognitive structure to shape child behaviour. A role for scaffolding is consistent with the proposal that, in adult cognition, a critical aspect of g is decomposition of complex problems into a structure of simpler parts. Building on previous work, we recruited 162 parents attending Children's Centres with a child aged 2–4 years, and examined parental scaffolding during a book-sharing activity. Scaffolding was measured as the first principal component of a variety of parental behaviours, including sensitivity, focusing attention, extending comprehension, and promoting child participation. Child g was measured as the first principal component of a broad cognitive battery, including language, attention, working memory, and executive function. Importantly, we assessed contributions of the parent's own intelligence, education, and family income. Though these variables were all associated with both child g and parental scaffolding, scaffolding remained predictive of child g even once the influence of these variables was removed. In contrast to the correlation with cognitive proficiency, scaffolding did not predict child pro-social behaviour. We suggest that parental scaffolding supports the child's development of a broad skill of attentional structuring, promoting the across-the-board cognitive proficiency that is reflected in g.

Current approaches to analysing EEG hyperscanning data in the developmental literature typically consider interpersonal entrainment between interacting physiological systems as a time-invariant property. This approach obscures crucial information about how entrainment between interacting systems is established and maintained over time. Here, we describe methods, and present computational algorithms, that will allow researchers to address this gap in the literature. We focus on how two different approaches to measuring entrainment, namely concurrent (e.g., power correlations, phase locking) and sequential (e.g., Granger causality) measures, can be applied to three aspects of the brain signal: amplitude, power, and phase. We guide the reader through worked examples using simulated data on how to leverage these methods to measure changes in interbrain entrainment. For each, we aim to provide a detailed explanation of the interpretation and application of these analyses when studying neural entrainment during early social interactions.

It has been argued that a necessary condition for the emergence of speech in humans is the ability to vocalise irrespective 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 vocalisations 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.

Although associations between joint attention and infant development have been extensively investigated (e.g., Carpenter et al., 1998; Donnellan et al., 2020; Mundy & Newell, 2007), the question of how, exactly, interactive behaviours support infant learning remains widely debated (Abney et al., 2020; Tomasello et al., 2007). Hudspeth and Lewis (this issue, DOI 10.1159/000515681) suggest that measures of joint attention in early interaction with an adult partner might merely reflect the ability of the infant to sustain their attention. This theory places infant object engagement at the forefront of attention and learning in joint interaction, in contrast to more traditional views that emphasise infants’ engagement with the attentional behaviours of their adult partner (e.g., Carpenter et al., 1998). First, we discuss Hudspeth and Lewis’s comments on methodological issues to do with defining sustained attention. Next, we consider an important point that they do not mention – namely, the inconsistencies in defining joint attention in the literature. We end by exploring endogenous and exogenous influences on sustained and concurrent looking in early interaction, as well as their implications for understanding infant learning.