Caregiver reactions to babbling organize turn-taking interactions: Facilitative effects of vocal versus non-vocal responses

Turn-taking interactions are foundational to the development of social, communicative, and cognitive skills. In infants, vocal turn-taking experience is predictive of infants' socioemotional and language development. However, different forms of turn-taking interactions may have different effects on infant vocalizing. It is presently unknown how caregiver vocal, non-vocal and multimodal responses to infant vocalizations compare in extending caregiver-infant vocal turn-taking bouts. In bouts that begin with an infant vocalization, responses that maintain versus change the communicative modality may differentially affect the likelihood of further infant vocalizing. No studies have examined how caregiver response modalities that either matched or differed from the infant acoustic (vocal) modality might affect the temporal structure of vocal turn-taking beyond the initial serve-and-return exchanges. We video-recorded free-play sessions of 51 caregivers with their 9-month-old infants. Caregivers responded to babbling most often with vocalizations. In turn, caregiver vocal responses were significantly more likely to elicit subsequent infant babbling. Bouts following an initial caregiver vocal response contained significantly more turns than those following a non-vocal or multimodal response. Thus prelinguistic turn-taking is sensitive to the modality of caregivers' responses. Future research should investigate if such sensitivity is grounded in attentional constraints, which may influence the structure of turn-taking interactions.

Autistic young people adaptively use gaze to facilitate joint attention during multi-gestural dyadic interactions

LAY ABSTRACT

Autistic people have been said to have 'problems' with joint attention, that is, looking where someone else is looking. Past studies of joint attention have used tasks that require autistic people to continuously look at and respond to eye-gaze cues. But joint attention can also be done using other social cues, like pointing. This study looked at whether autistic and non-autistic young people use another person's eye gaze during joint attention in a task that did not require them to look at their partner's face. In the task, each participant worked together with their partner to find a computer-generated object in virtual reality. Sometimes the participant had to help guide their partner to the object, and other times, they followed their partner's lead. Participants were told to point to guide one another but were not told to use eye gaze. Both autistic and non-autistic participants often looked at their partner's face during joint attention interactions and were faster to respond to their partner's hand-pointing when the partner also looked at the object before pointing. This shows that autistic people can and do use information from another person's eyes, even when they don't have to. It is possible that, by not forcing autistic young people to look at their partner's face and eyes, they were better able to gather information from their partner's face when needed, without being overwhelmed. This shows how important it is to design tasks that provide autistic people with opportunities to show what they can do.

Natural behavior in everyday settings

Infant behaviors-walking, vocalizing, playing, interacting with others, and so on-offer an unparalleled window into learning and development. The study of infants requires strategic choices about what to observe, where, when, and how. We argue that loosening study constraints-by allowing infants and caregivers to do whatever they choose, wherever they choose, and with whatever materials they choose-promises to reveal a deep understanding of the everyday data on which learning builds. We show that observations of infants' natural behavior yield unique insights into the nature of visual exploration, object play, posture and locomotion, proximity to caregiver, and communication. Furthermore, we show that by situating the study of behavior in ecologically-valid settings, researchers can gain purchase on the contextual regularities that frame learning. We close by underscoring the value of studies at every point on the research continuum-from cleverly controlled lab-based tasks to fully natural observations in everyday environments. Acceleration in the science of behavior rests on leveraging expertise across disciplines, theoretical positions, and methodological approaches.

Infant sensorimotor decoupling from 4 to 9 months of age: Individual differences and contingencies with maternal actions

Triadic interactions, wherein infants coordinate attention between caregivers and objects of shared focus, are believed to facilitate infant learning, and emerge around 9-12 months of age (Carpenter et al., 1998). Sensorimotor decoupling, wherein infants look at one percept while manipulating another, or use each hand for different actions, was hypothesized (de Barbaro et al., 2016) to contribute to triadic skills by allowing infants to smoothly shift attention between objects and social partners. We explored the development of Hand-Hand (H-H) and Gaze-Hand (G-H) decoupling in 38 infants at 4, 6, and 9 months. We also tested contingencies between maternal behaviors and infant decoupling: i.e., whether decoupling events followed maternal object-directed actions. Both overall and contingent infant decoupling increased from 4 to 9 months. Decoupling rates (both G-H and H-H) predicted variance in infants' fine and gross motor scores. Contingent G-H decoupling at 6 months predicted BSID-III communication scores at 18 months. Thus the development of infant sensorimotor skills, including decoupling, allows infants to smoothly shift attention and participate in triadic interactions.

The slow emergence of gaze- and point-following: A longitudinal study of infants from 4 to 12 months

Acquisition of visual attention-following skills, notably gaze- and point-following, contributes to infants' ability to share attention with caregivers, which in turn contributes to social learning and communication. However, the development of gaze- and point-following in the first 18 months remains controversial, in part because of different testing protocols and standards. To address this, we longitudinally tested N = 43 low-risk, North American middle-class infants' tendency to follow gaze direction, pointing gestures, and gaze-and-point combinations. Infants were tested monthly from 4 to 12 months of age. To control motivational differences, infants were taught to expect contingent reward videos in the target locations. No-cue trials were included to estimate spontaneous target fixation rates. A comparison sample (N = 23) was tested at 9 and 12 months to estimate practice effects. Results showed gradual increases in both gaze- and point-following starting around 7 months, and modest month-to-month individual stability from 8 to 12 months. However, attention-following did not exceed chance levels until after 6 months. Infants rarely followed cues to locations behind them, even at 12 months. Infants followed combined gaze-and-point cues more than gaze alone, and followed points at intermediate levels (not reliably different from the other cues). The comparison group's results showed that practice effects did not explain the age-related increase in attention-following. The results corroborate and extend previous findings that North American middle-class infants' attention-following in controlled laboratory settings increases slowly and incrementally between 6 and 12 months of age. RESEARCH HIGHLIGHTS: A longitudinal experimental study documented the emergence and developmental trajectories of North American middle-class infants' visual attention-following skills, including gaze-following, point-following, and gaze-and-point-following. A new paradigm controlled for factors including motivation, attentiveness, and visual-search baserates. Motor development was ruled out as a predictor or limiter of the emergence of attention-following. Infants did not follow attention reliably until after 6 months, and following increased slowly from 7 to 12 months. Infants' individual trajectories showed modest month-to-month stability from 8 to 12 months of age.

The quality of caregiver-child interaction is predicted by (caregivers' perception of) their child's interests

This current study examines the extent to which children's interests and caregivers' sensitivity to their children's interests are associated with the quality of caregiver-child interaction, and subsequent learning. Eighty-one caregiver-child dyads (24-30-month old children) completed an online shared book-reading task where caregivers and children read two e-books with pictures and descriptions of objects from different categories-one previously determined to be of low and one of high interest to the child (with one novel word-object mapping introduced in each book). We also obtained separate behavioural indices of children's interests and children's later recognition of newly introduced word-object mappings. Our findings highlight that the quality of caregiver-child interaction is predicted by children's interests and caregivers' perception of children's interests, although we find only limited overlap between our behavioural indices of children's interests and caregiver perception of children's interests. Neither of these factors predicted later novel word recognition. Thus, while the dynamics between higher quality of caregiver-child interaction, children's interests and learning remain inconclusive, caregivers and children appear to be more attentive, enthusiastic and engaged in reading about topics that (caregivers believe) interest the child. Furthermore, learning in itself seems to be successful, regardless of factors involved, through the mere task of shared book reading.

Infant sustained attention differs by context and social content in the first 2 years of life

Sustained attention (SA) is an endogenous form of attention that emerges in infancy and reflects cognitive engagement and processing. SA is critical for learning and has been measured using different methods during screen-based and interactive contexts involving social and nonsocial stimuli. How SA differs by measurement method, context, and stimuli across development in infancy is not fully understood. This 2-year longitudinal study examines attention using one measure of overall looking behavior and three measures of SA-mean look duration, percent time in heart rate-defined SA, and heart rate change during SA-in N = 53 infants from 1 to 24 months across four unique task conditions: social videos, nonsocial videos, social interactions (face-to-face play), and nonsocial interactions (toy engagement). Results suggest that developmental changes in attention differ by measurement method, task context (screen or interaction), and task stimulus (social or nonsocial). During social interactions, overall looking and look durations declined after age 3-4 months, whereas heart rate-defined attention measures remained stable. All SA measures were greater for videos than for live interaction conditions throughout the first 6 months, but SA to social and nonsocial stimuli within each task context were equivalent. In the second year of life, SA measured with look durations was greater for social videos compared to other conditions, heart rate-defined SA was greater for social videos compared to nonsocial interactions, and heart rate change during SA was similar across conditions. Together, these results suggest that different measures of attention to social and nonsocial stimuli may reflect unique developmental processes and are important to compare and consider together, particularly when using infant attention as a marker of typical or atypical development. RESEARCH HIGHLIGHTS: Attention measure, context, and social content uniquely differentiate developmental trajectories of attention in the first 2 years of life. Overall looking to caregivers during dyadic social interactions declines significantly from 4 to 6 months of age while sustained attention (SA) to caregivers remains stable. Heart rate-defined SA generally differentiates stimulus context where infants show greater SA while watching videos than while engaging with toys.

Early development of saliency-driven attention through object manipulation

In the first years of life, infants progressively develop attention selection skills to gather information from visually clustered environments. As young as newborns, infants are sensitive to the distinguished differences in color, orientation, and luminance, which are the components of visual saliency. However, we know little about how saliency-driven attention emerges and develops socially through everyday free-viewing experiences. The present work assessed the saliency change in infants' egocentric scenes and investigated the impacts of manual engagements on infant object looking in the interactive context of object play. Thirty parent-infant dyads, including infants in two age groups (younger: 3- to 6-month-old; older: 9- to 12-month-old), completed a brief session of object play. Infants' looking behaviors were recorded by the head-mounted eye-tracking gear, and both parents' and infants' manual actions on objects were annotated separately for analyses. The present findings revealed distinct attention mechanisms that underlie the hand-eye coordination between parents and infants and within infants during object play: younger infants are predominantly biased toward the characteristics of the visual saliency accompanying the parent's handled actions on the objects; on the other hand, older infants gradually employed more attention to the object, regardless of the saliency in view, as they gained more self-generated manual actions. Taken together, the present work highlights the tight coordination between visual experiences and sensorimotor competence and proposes a novel dyadic pathway to sustained attention that social sensitivity to parents' hands emerges through saliency-driven attention, preparing infants to focus, follow, and steadily track moving targets in free-flow viewing activities.

The distributional and embodied contexts of verbs in caregiver-infant interactions

The process by which infants learn verbs through daily social interactions is not well-understood. This study investigated caregivers' use of verbs, which have highly abstract meanings, during unscripted toy-play. We examined how verbs co-occurred with distributional and embodied factors including pronouns, caregivers' manual actions, and infants' locomotion, gaze, and object-touching. Object-action verbs were used significantly more often during caregiver-infant joint attention interactions. Movement and cognition verbs showed distinct co-occurrences with different contexts. Cognition and volition verbs were differentiated by pronouns. These findings provide evidence for how verb acquisition may be supported by the distributional and embodied contexts in caregiver-infant interactions.

Within arms reach: Physical proximity shapes mother-infant language exchanges in real-time

During everyday interactions, mothers and infants achieve behavioral synchrony at multiple levels. The ebb-and-flow of mother-infant physical proximity may be a central type of synchrony that establishes a common ground for infant-mother interaction. However, the role of proximity in language exchanges is relatively unstudied, perhaps because structured tasks-the common setup for observing infant-caregiver interactions-establish proximity by design. We videorecorded 100 mothers (U.S. Hispanic N = 50, U.S. Non-Hispanic N = 50) and their 13- to 23-month-old infants during natural activity at home (1-to-2 h per dyad), transcribed mother and infant speech, and coded proximity continuously (i.e., infants and mother within arms reach). In both samples, dyads entered proximity in a bursty temporal pattern, with bouts of proximity interspersed with bouts of physical distance. As hypothesized, Non-Hispanic and Hispanic mothers produced more words and a greater variety of words when within arms reach than out of arms reach. Similarly, infants produced more utterances that contained words when close to mother than when not. However, infants babbled equally often regardless of proximity, generating abundant opportunities to play with sounds. Physical proximity expands opportunities for language exchanges and infants' communicative word use, although babies accumulate massive practice babbling even when caregivers are not proximal.

Multimodal pathways to joint attention in infants with a familial history of autism

Joint attention (JA) is an early-developing behavior that allows caregivers and infants to share focus on an object. Deficits in JA, as measured through face-following pathways, are a defining feature of autism spectrum disorder (ASD) and are observable as early as 12 months of age in infants later diagnosed with ASD. However, recent evidence suggests that JA may be achieved through hand-following pathways by children with and without ASD. Development of JA through multimodal pathways has yet to be studied in infants with an increased likelihood of developing ASD. The current study investigated how 6-, 9- and 12-month-old infants with (FH+) and without (FH-) a family history of ASD engaged in JA. Parent-infant dyads played at home while we recorded the interaction over Zoom and later offline coded for hand movements and gaze. FH+ and FH- infants spent similar amounts of time in JA with their parents, but the cues available before JA were different. Parents of FH+ infants did more work to establish JA and used more face-following than hand-following pathways compared to parents of FH- infants, likely reflecting differences in infant motor or social behavior. These results suggest that early motor differences between FH+ and FH- infants may cascade into differences in social coordination.

Variability in infant social responsiveness: Age and situational differences in attention-following

Attention following (AF) is a cornerstone of social cognitive development and a longstanding topic of infancy research. However, there is conflicting evidence regarding the development of AF. One reason for discrepant findings could be that infants' AF responses do not generalize across settings, and are influenced by situational factors. Theories of AF development based on data collected in laboratory paradigms might skew our understanding of infants' everyday AF. To reveal more generalizable patterns of infant AF development, we compared healthy, North American infants' (N = 48) AF developmental trajectories between a controlled laboratory paradigm and a naturalistic, home-based, parent-directed paradigm. Longitudinal micro-behavioral coding was analyzed to compare individual infants' AF between the two settings every month from 6 to 9 months of age. We aimed to (1) examine longitudinal development of infant AF in two settings; (2) compare AF development between settings, and (3) explore differences in adult cueing behaviors that influence AF. We found that longitudinal trajectories of AF differed between home and lab, with more AF at home in earlier months. Additionally, AF at home was related to maternal cueing variables including bid duration and frequency. These results have implications for the assessment of infants' developing social attention behaviors.

Curiosity constructs communicative competence through social feedback loops

One of the most important challenges for a developing infant is learning how best to allocate their attention and forage for information in the midst of a great deal of novel stimulation. We propose that infants of altricial species solve this challenge by learning selectively from events that are contingent on their immature behavior, such as babbling. Such a contingency filter would focus attention and learning on the behavior of social partners, because social behavior reliably fits infants' sensitivity to contingency. In this way a contingent response by a caregiver to an immature behavior becomes a source of learnable information - feedback - to the infant. Social interactions with responsive caregivers afford infants opportunities to explore the impacts of their immature behavior on their environment, which facilitates the development of socially guided learning. Furthermore, contingent interactions are opportunities to make and test predictions about the efficacy of their social behaviors and those of others. In this chapter, we will use prelinguistic vocal learning to exemplify how infants use their developing vocal abilities to elicit learnable information about language from their social partners. Specifically, we review how caregivers' contingent responses to babbling create information that facilitates infant vocal learning and drives the development of communication. Infants play an active role in this process, as their developing predictions about the consequences of their actions serve to further refine their allocation of attention and drive increases in the maturity of their vocal behavior.

Opportunities for learning and social interaction in infant sitting: Effects of sitting support, sitting skill, and gross motor delay

The development of independent sitting changes everyday opportunities for learning and has cascading effects on cognitive and language development. Prior to independent sitting, infants experience the sitting position with physical support from caregivers. Why does supported sitting not provide the same input for learning that is experienced in independent sitting? This question is especially relevant for infants with gross motor delay, who require support in sitting for many months after typically developing infants sit independently. We observed infants with typical development (n = 34, ages 4-7 months) and infants with gross motor delay (n = 128, ages 7-16 months) in early stages of sitting development, and their caregivers, in a dyadic play observation. We predicted that infants who required caregiver support for sitting would spend more time facing away from the caregiver and less time contacting objects than infants who could sit independently. We also predicted that caregivers of supported sitters would spend less time contacting objects because their hands would be full supporting their infants. Our first two hypotheses were confirmed; however, caregivers spent surprisingly little time using both hands to provide support, and caregivers of supported sitters spent more time contacting objects than caregivers of independent sitters. Similar patterns were seen in the group of typically developing infants and the infants with motor delay. Our findings suggest that independent sitting and supported sitting provide qualitatively distinct experiences with different implications for social interaction and learning opportunities. HIGHLIGHTS: During seated free play, supported sitters spent more time facing away from their caregivers and less time handling objects than independent sitters. Caregivers who spent more time supporting infants with both hands spent less time handling objects; however, caregivers mostly supported infants with one or no hands. A continuous measure of sitting skill did not uniquely contribute to these behaviors beyond the effect of binary sitting support (supported vs. independent sitter). The pattern of results was similar for typically developing infants and infants with gross motor delay, despite differences in age.

Proactive or reactive? Neural oscillatory insight into the leader-follower dynamics of early infant-caregiver interaction

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.

The road to conventional tool use: Developmental changes in children's material engagement with artifacts in nursery school

The development of tool use in early childhood is a topic of continuing interest in developmental psychology. However, the lack of studies in ecological settings results in many unknowns about how children come to use artifacts according to their cultural function. We report a longitudinal study with 17 sociodemographically diverse children (8 female) attending a nursery school in Madrid (Spain) and their two adult female teachers. Using mixed-effects models and Granger causality analysis, we measured changes in the frequency and duration of children's object uses between 7 and 17 months of age and in the directional influences among pairs of behaviors performed by teachers and children. Results show a clear shift in how children use artifacts. As early as 12 months of age, the frequency of conventional uses outweighs that of all other types of object use. In addition, object uses become shorter in duration with age, irrespective of their type. Moreover, certain teachers' nonlinguistic communicative strategies (e.g., demonstrations of canonical use and placing gestures) significantly influence and promote children's conventional tool use. Findings shed light on how children become increasingly proficient in conventional tool use through interactions with artifacts and others in nursery school.

Dynamics of the dyad: How mothers and infants co-construct interaction spaces during object play

Studies of dyadic interaction often examine infants' social exchanges with their caregivers in settings that constrain their physical properties (e.g., infant posture, fixed seating location for infants and adults). Methodological decisions about the physical arrangements of interaction, however, may limit our ability to understand how posture and position shape them. Here we focused on these embodied properties of dyadic interaction in the context of object play. We followed 30 mother-infant dyads across the first year of life (at 3, 6, 9, and 12 months) and observed them during 5 min of play with a standard set of toys. Using an interval-based coding system, we measured developmental change in infant posture, how mothers and infants positioned themselves relative to one another, and how they populated interaction spaces with objects. Results showed that mother-infant dyads co-constructed interaction spaces and that the contributions of each partner changed across development. Dyads progressively adopted a broader spatial co-orientation during play (e.g., positioned at right angles) across the first year. Moreover, advances in infants' postural skills, particularly increases in the use of independent sitting in real time, uniquely predicted change in dyadic co-orientation and infants' actions with objects, independent of age. Taken together, we show that the embodied properties of dyadic object play help determine how interactions are physically organized and unfold, both in real time and across the first year of life.

Parent–child interaction during a home STEM activity and children’s handwashing behaviors

We examined correlations between a home-based STEM activity illustrating the importance of soap use during handwashing and children’s (4-to 7-year-olds, N = 81, 42 girls, 39 boys) use of soap when washing their hands. Parents and children either participated in or watched the activity. Children reflected on the activity immediately afterward and a week later. Parent–child interaction during participation related to the frequency of unprompted soap use during handwashing, controlling for performance on other, related cognitive measures. Children whose parents were more goal-directed, and set goals for the interaction, were less likely to use soap spontaneously when handwashing in the subsequent week. The amount of causal knowledge children generated when they reflected on the experience immediately afterward also influenced whether children used soap when washing their hands. Reducing the autonomy children believe they have during a STEM-based activity potentially leads them to not engage in a behavior related to the activity on their own. Overall, these data suggest that parent–child interaction during STEM activities can influence the ways children encode and engage with those activities in their everyday lives. Given that the ways children wash their hands might mitigate the spread of disease, interventions that focus on providing children with the belief that STEM activities are for them might be broadly beneficial to society.

Face-to-face contact during infancy: How the development of gaze to faces feeds into infants' vocabulary outcomes

Infants acquire their first words through interactions with social partners. In the first year of life, infants receive a high frequency of visual and auditory input from faces, making faces a potential strong social cue in facilitating word-to-world mappings. In this position paper, we review how and when infant gaze to faces is likely to support their subsequent vocabulary outcomes. We assess the relevance of infant gaze to faces selectively, in three domains: infant gaze to different features within a face (that is, eyes and mouth); then to faces (compared to objects); and finally to more socially relevant types of faces. We argue that infant gaze to faces could scaffold vocabulary construction, but its relevance may be impacted by the developmental level of the infant and the type of task with which they are presented. Gaze to faces proves relevant to vocabulary, as gazes to eyes could inform about the communicative nature of the situation or about the labeled object, while gazes to the mouth could improve word processing, all of which are key cues to highlighting word-to-world pairings. We also discover gaps in the literature regarding how infants' gazes to faces (versus objects) or to different types of faces relate to vocabulary outcomes. An important direction for future research will be to fill these gaps to better understand the social factors that influence infant vocabulary outcomes.

Physiological arousal explains infant gaze following in various social contexts

Gaze following (GF) is fundamental to central aspects of human sociocognitive development, such as acquiring language and cultural learning. Studies have shown that infant GF is not a simple reflexive orientation to an adult's eye movement. By contrast, infants adaptively modulate GF behaviour depending on the social context. However, arguably, the neurophysiological mechanisms underlying contextual modulation of GF remain somewhat unexplored. In this study, we tested the proposition about whether the contextual modulation of infant GF is mediated by the infant's heart rate (HR), which indicates the infant's physiological arousal. Forty-one 6- to 9-month-old infants participated in this study, and infants observed either a reliable face, which looked towards the location of an object, or an unreliable face, which looked away from the location of an object. Thereafter, the infants watched a video of the same model making eye contact or not making any ostensive signals, before shifting their gaze towards one of the two objects. We revealed that reliability and eye contact acted independently to increase HR, which then fully mediates the effects of these social cues on the frequency of GF. Results suggest that each social cue independently enhances physiological arousal, which then accumulatively predicts the likelihood of infant GF behaviour.

Physiological arousal explains infant gaze following in various social contexts

Gaze following (GF) is fundamental to central aspects of human sociocognitive development, such as acquiring language and cultural learning. Studies have shown that infant GF is not a simple reflexive orientation to an adult's eye movement. By contrast, infants adaptively modulate GF behaviour depending on the social context. However, arguably, the neurophysiological mechanisms underlying contextual modulation of GF remain somewhat unexplored. In this study, we tested the proposition about whether the contextual modulation of infant GF is mediated by the infant's heart rate (HR), which indicates the infant's physiological arousal. Forty-one 6- to 9-month-old infants participated in this study, and infants observed either a reliable face, which looked towards the location of an object, or an unreliable face, which looked away from the location of an object. Thereafter, the infants watched a video of the same model making eye contact or not making any ostensive signals, before shifting their gaze towards one of the two objects. We revealed that reliability and eye contact acted independently to increase HR, which then fully mediates the effects of these social cues on the frequency of GF. Results suggest that each social cue independently enhances physiological arousal, which then accumulatively predicts the likelihood of infant GF behaviour.

Why the parent's gaze is so powerful in organizing the infant's gaze: The relationship between parental referential cues and infant object looking

Parental scaffolding such as looking at and showing objects has long been considered to be helpful for early attention and language development. However, relatively little is known about how parental social multimodal cues work alone or together in guiding an infant's attention toward the referent items. The present study aims to document the dynamics of social referential input during an interactive play session and specify the different types of social cues in directing infant attention. Forty-three parent-infant dyads (infants aged from 5.0 to 18.0 months) in the U.S. completed a short play session recorded by head-mounted camera with eye-trackers. The present findings suggest that joint attention between parent and infant toward the same referent item often co-occurred with other referential input. Infants were more likely to maintain sustained attention to an object under the circumstance that the parent looked at the same item and named it explicitly. This was not the case when parent object looking accompanied other utterances, like "Look!" or the child's name. The present study highlights the importance of multimodal referential input, which sets up enriched opportunities for children to become sensitive to social input and develop sustained attention for further learning.

Children with ASD establish joint attention during free-flowing toy play without face looks

Children's ability to share attention with another person (i.e., achieve joint attention) is critical for learning about their environments in general^1-3 and supporting language and object word learning in particular.^1,4-14 While joint attention (JA) as it pertains to autism spectrum disorder (ASD) is often more narrowly operationalized as arising from eye gaze or explicit pointing cues alone,^2,5,10,15-19 recent evidence demonstrates that JA in natural environments can be achieved more broadly through multiple other pathways beyond gaze and gestures.^2,4,20-31 Here, we use dual head-mounted eye tracking to examine pathways into and characteristics of JA episodes during free-flowing parent-child toy play, comparing children with ASD to typically developing (TD) children. Moments of JA were defined objectively as both the child's and parent's gaze directed to the same object at the same time. Consistent with previous work in TD children,^{4,21,25,30-32} we found that both TD and ASD children rarely look at their parent's face in this unstructured free play context. Nevertheless, both groups achieved similarly high rates of JA that far exceeded chance, suggesting the use of alternative pathways into JA. We characterize these alternate pathways, find they occur at similar levels across both groups, and achieve similar ends: namely, for both groups, targets of JA are named more frequently by parents in those moments than non-jointly attended objects. These findings broaden the conceptualization of JA abilities and impairment in ASD and raise questions regarding the mechanistic role of the face-gaze-mediated JA pathway in ASD.

Shared Multimodal Input Through Social Coordination: Infants With Monolingual and Bilingual Learning Experiences

A growing number of children in the United States are exposed to multiple languages at home from birth. However, relatively little is known about the early process of word learning—how words are mapped to the referent in their child-centered learning experiences. The present study defined parental input operationally as the integrated and multimodal learning experiences as an infant engages with his/her parent in an interactive play session with objects. By using a head-mounted eye tracking device, we recorded visual scenes from the infant’s point of view, along with the parent’s social input with respect to gaze, labeling, and actions of object handling. Fifty-one infants and toddlers (aged 6–18 months) from an English monolingual or a diverse bilingual household were recruited to observe the early multimodal learning experiences in an object play session. Despite that monolingual parents spoke more and labeled more frequently relative to bilingual parents, infants from both language groups benefit from a comparable amount of socially coordinated experiences where parents name the object while the object is looked at by the infant. Also, a sequential path analysis reveals multiple social coordinated pathways that facilitate infant object looking. Specifically, young children’s attention to the referent objects is directly influenced by parent’s object handling. These findings point to the new approach to early language input and how multimodal learning experiences are coordinated socially for young children growing up with monolingual and bilingual learning contexts.

Flexible fast-mapping: Deaf children dynamically allocate visual attention to learn novel words in American Sign Language

Word learning in young children requires coordinated attention between language input and the referent object. Current accounts of word learning are based on spoken language, where the association between language and objects occurs through simultaneous and multimodal perception. In contrast, deaf children acquiring American Sign Language (ASL) perceive both linguistic and non-linguistic information through the visual mode. In order to coordinate attention to language input and its referents, deaf children must allocate visual attention optimally between objects and signs. We conducted two eye-tracking experiments to investigate how young deaf children allocate attention and process referential cues in order to fast-map novel signs to novel objects. Participants were deaf children learning ASL between the ages of 17 and 71 months. In Experiment 1, participants (n = 30) were presented with a novel object and a novel sign, along with a referential cue that occurred either before or after the sign label. In Experiment 2, a new group of participants (n = 32) were presented with two novel objects and a novel sign, so that the referential cue was critical for identifying the target object. Across both experiments, participants showed evidence for fast-mapping the signs regardless of the timing of the referential cue. Individual differences in children's allocation of attention during exposure were correlated with their ability to fast-map the novel signs at test. This study provides first evidence for fast-mapping in sign language, and contributes to theoretical accounts of how word learning develops when all input occurs in the visual modality.

Infants' object interactions are long and complex during everyday joint engagement

As infants interact with the object world, they generate rich information about object properties and functions. Much of infant learning unfolds in the presence of caregivers, who talk about and act on the objects of infant play. Does mother joint engagement correspond to real-time changes in the complexity and duration of infant object interactions? We observed thirty-eight mothers and their first-born infants (cross-sectional, 13, 18, and 23 months) during 2 hours of everyday activity as infants freely navigated their home environments. Behavioral coding explored thousands of infant object interactions within and outside mother joint engagement. Object interactions involving exclusively simple play were shorter than complex play bouts. Critically, mothers' multimodal input (i.e., touching/gesturing toward and talking about the focal object) corresponded with more complex and longer play bouts than when mothers provided no input. Bouts involving complex play and multimodal input lasted 7.5 times longer than simple play bouts absent mother input. Moreover, "action-orienting talk" (e.g., "Twist it", "Feed dolly"), rather than talk per se, corresponded with longer bout duration and complexity. Notably, the association between joint engagement and play duration was not a function of mothers having more time to join. Analyses that eliminated short infant bouts and considered the timing of mothers' behaviors confirmed that mother input "extended" the duration of play bouts. As infants actively explore their environments, their object interactions change moment to moment in the presence of mothers' multimodal engagement. RESEARCH HIGHLIGHTS Mothers and infants were videorecorded for 2 hours at home; researchers coded infants' object interactions and mothers' behaviors (verbal, manual) toward the focal object. Mothers' multimodal joint engagement (i.e., coordinated manual and verbal input) was associated with long and complex infant object interactions. The pragmatics of mothers' talk-namely action-orienting language-related to the duration and complexity of infant object bouts beyond talk per se. Infants' object interactions change in complexity and duration in line with maternal joint engagement, indicating potential mechanisms of real-time learning. This article is protected by copyright. All rights reserved.

Infants Learn to Follow Gaze in Stages: Evidence Confirming a Robotic Prediction

Gaze following is an early-emerging skill in infancy argued to be fundamental to joint attention and later language development. However, how gaze following emerges is a topic of great debate. Representational theories assume that in order to follow adults’ gaze, infants must have a rich sensitivity to adults’ communicative intention from birth. In contrast, learning-based theories hold that infants may learn to gaze follow based on low-level social reinforcement, without the need to understand others’ mental states. Nagai et al. (2006) successfully taught a robot to gaze follow through social reinforcement and found that the robot learned in stages: first in the horizontal plane, and later in the vertical plane—a prediction that does not follow from representational theories. In the current study, we tested this prediction in an eye-tracking paradigm. Six-month-olds did not follow gaze in either the horizontal or vertical plane, whereas 12-month-olds and 18-month-olds only followed gaze in the horizontal plane. These results confirm the core prediction of the robot model, suggesting that children may also learn to gaze follow through social reinforcement coupled with a structured learning environment.

Joint engagement in the home environment is frequent, multimodal, timely, and structured

Infants develop in a social context, surrounded by knowledgeable caregivers who scaffold learning through shared engagement with objects. However, researchers have typically examined joint engagement in structured tasks, where caregivers sit near infants and display frequent, prompt, and multimodal behaviors around the objects of infant action. Which features of joint engagement generalize to the real-world? Despite the importance of joint engagement for infant learning, critical assumptions around joint engagement in everyday interaction remain unexamined. We investigated behavioral and temporal features of joint engagement in the home environment, where objects for play abound and dyad proximity fluctuates. Infant manual actions, mother manual and verbal behaviors, and dyad proximity were coded frame-by-frame from 2-h naturalistic recordings of 13- to 23-month-old infants and their mothers (N = 38). Infants experienced rich, highly structured, multimodal mother input around the objects of their actions. Specifically, joint engagement occurred within seconds of infant action and was amplified in the context of interpersonal proximity. Findings validate laboratory-based research on characteristics of joint engagement while highlighting unique properties around the role of mother-infant proximity and temporal structuring of caregiver input over extended time frames. Implications for the social contexts that support infant learning and development are discussed.

Infant exuberant object play at home: Immense amounts of time-distributed, variable practice

Object play yields enormous benefits for infant development. However, little is known about natural play at home where most object interactions occur. We conducted frame-by-frame video analyses of spontaneous activity in two 2-h home visits with 13-month-old crawling infants and 13-, 18-, and 23-month-old walking infants (N = 40; 21 boys; 75% White). Regardless of age, for every infant and time scale, across 10,015 object bouts, object interactions were short (median = 9.8 s) and varied (transitions among dozens of toys and non-toys) but consumed most of infants' time. We suggest that infant exuberant object play-immense amounts of brief, time-distributed, variable interactions with objects-may be conducive to learning object properties and functions, motor skill acquisition, and growth in cognitive, social, and language domains.

The memory benefits of two naps per day during infancy: A pilot investigation

In infancy, sleep occurs in multiple nap and overnight bouts that change developmentally in quantity and distribution. Though studies suggest that infant memory benefits from a single nap, no work has assessed the relative benefits of different naps (morning vs. afternoon), nor how multiple naps support memory across the day. We investigated the memory benefit of a morning nap, relative to morning wake, and the effect of these intervals on afternoon nap function in 9-month-olds (n = 15). Infants participated in two within-subjects conditions (separated by 1-2 weeks). In the Nap-Nap condition, infants took their morning and afternoon naps; in the Wake-Nap condition, infants were kept awake during morning naptime, but napped unrestricted in the afternoon. Before each nap/wake interval, infants completed an imitation memory task, with memory assessed again shortly after the nap/wake interval. In the Nap-Nap condition, infants showed memory retention across morning and afternoon naps. In contrast, infants tended to forget items learned across morning wake in the Wake-Nap condition. Moreover, morning wake was associated with a significant decline in post-nap retention of items learned in the afternoon. Furthermore, relations between nap slow-wave activity (SWA) and memory varied across naps, with SWA either not predicting (morning naps) or positively predicting (afternoon naps) memory change in the Nap-Nap condition, but negatively predicting afternoon memory change in the Wake-Nap condition. We conclude that two naps per day (rather than one) aids memory at 9 months, and that skipping the morning nap may moderate relations between afternoon nap physiology and memory.

The Origins of Social Knowledge in Altricial Species

Human infants are altricial, born relatively helpless and dependent on parental care for an extended period of time. This protracted time to maturity is typically regarded as a necessary epiphenomenon of evolving and developing large brains. We argue that extended altriciality is itself adaptive, as a prolonged necessity for parental care allows extensive social learning to take place. Human adults possess a suite of complex social skills, such as language, empathy, morality, and theory of mind. Rather than requiring hardwired, innate knowledge of social abilities, evolution has outsourced the necessary information to parents. Critical information for species-typical development, such as species recognition, may originate from adults rather than from genes, aided by underlying perceptual biases for attending to social stimuli and capacities for statistical learning of social actions. We draw on extensive comparative findings to illustrate that, across species, altriciality functions as an adaptation for social learning from caregivers.

An interactionist perspective on the development of coordinated social attention

Infants' ability to coordinate their attention with other people develops profoundly across the first year of life. Mainly based on experimental research focusing on infants' behavior under highly controlled conditions, developmental milestones were identified and explained in the past by prominent theories in terms of the onset of specific cognitive skills. In contrast to this approach, recent longitudinal research challenges this perspective with findings suggesting that social attention develops continuously with a gradual refinement of skills. Informed by these findings, we argue for an interactionist and dynamical systems view that bases observable advances in infant social attention skills on increasingly fine-tuned mutual adjustments in the caregiver-infant dyad, resulting in gradually improving mutual prediction. We present evidence for this view from recent studies leveraging new technologies which afford the opportunity to dynamically track social interactions in real-time. These new technically-sophisticated studies offer unprecedented insights into the dynamic processes of infant-caregiver social attention. It is now possible to track in much greater detail fluctuations over time with regard to object-directed attention as well as social attention and how these processes relate to one another. Encouraged by these initial results and new insights from this interactionist developmental social neuroscience approach, we conclude with a "call to action" in which we advocate for more ecologically valid paradigms for studying social attention as a dynamic and bi-directional process.

Influence of Ideational Praxis on the Development of Play and Adaptive Behavior of Children with Autism Spectrum Disorder: A Comparative Analysis

BACKGROUND

Traditionally, assessment of praxis skills in children with ASD has focused on the evaluation of aspects related to the planning and execution of actions. This study aimed to evaluate the ideational abilities of children with ASD and analyze possible relationships with the development of play and adaptive behaviors.

METHODS

40 children between 4 to 6 years (TD = 20; ASD = 20) were evaluated with the Test of Ideational Praxis, the Revised Knox Preschool Play Scale, and the Adaptive Behavior Assessment System II.

RESULTS

Statistically significant relationships were obtained between ideational praxis and play skills development (r = 0.649; p = 0.01), adaptive leisure behavior (r = 0.338; p = 0.04) and social adaptive behavior (r = 0.319; p = 0.04). Results of multiple linear regression models found a linear relationship between ideational praxis and play development (p = 0.005) and adaptive leisure skills (p = 0.004), but not with social interaction skills (p > 0.05).

CONCLUSIONS

Objective evaluation with a specific ideational praxis assessment facilitates understanding of the ideational abilities and widens understanding of praxis skills and their impact on play and adaptive behaviors in children with ASD.

Revisiting how we operationalize joint attention

Parent-child interactions support the development of a wide range of socio-cognitive abilities in young children. As infants become increasingly mobile, the nature of these interactions change from person-oriented to object-oriented, with the latter relying on children's emerging ability to engage in joint attention. Joint attention is acknowledged to be a foundational ability in early child development, broadly speaking, yet its operationalization has varied substantially over the course of several decades of developmental research devoted to its characterization. Here, we outline two broad research perspectives-social and associative accounts-on what constitutes joint attention. Differences center on the criteria for what qualifies as joint attention and regarding the hypothesized developmental mechanisms that underlie the ability. After providing a theoretical overview, we introduce a joint attention coding scheme that we have developed iteratively based on careful reading of the literature and our own data coding experiences. This coding scheme provides objective guidelines for characterizing mulitmodal parent-child interactions. The need for such guidelines is acute given the widespread use of this and other developmental measures to assess atypically developing populations. We conclude with a call for open discussion about the need for researchers to include a clear description of what qualifies as joint attention in publications pertaining to joint attention, as well as details about their coding. We provide instructions for using our coding scheme in the service of starting such a discussion.

Multimodal coordination of vocal and gaze behavior in mother-infant dyads across the first year of life

Research examining mother-infant interactions indicates a close connection between vocal and gaze behavior. The present longitudinal study examined the development of both intraindividual and dyadic coordination of vocal and gaze behavior in mother-infant dyads at 3, 6, 9, and 12 months. Mother and infant vocalization and gaze behavior during in-home toy play interactions were coded on a moment-by-moment basis and coordinations (i.e., co-occurrences and sequences of behavior) were compared to randomized baselines in order to determine whether coordinate exceeded chance levels. Infants timed their own vocalizations with gaze to partner's face and inhibited vocalizations during gaze to objects at greater than chance levels across the first year. Mother's displayed above-chance intraindividual coordination of vocalizations and gaze to partner's face and objects. Mothers and infants demonstrated dyadic coordination of vocalizations and gaze at above-chance levels, but developmental change and leading-following dynamics varied based on gaze location (i.e., face vs. object). Results emphasize the importance of examining coordination across communication modalities and of considering bidirectional influences on mother and infant vocal and gaze behavior.

What are the building blocks of parent-infant coordinated attention in free-flowing interaction?

The present article investigated the composition of different joint gaze components used to operationalize various types of coordinated attention between parents and infants and which types of coordinated attention were associated with future vocabulary size. Twenty-five 9-month-old infants and their parents wore head-mounted eye trackers as they played with objects together. With high-density gaze data, a variety of coordinated attention bout types were quantitatively measured by combining different gaze components, such as mutual gaze, joint object looks, face looks, and triadic gaze patterns. The key components of coordinated attention that were associated with vocabulary size at 12 and 15 months included the simultaneous combination of parent triadic gaze and infant object looking. The results from this article are discussed in terms of the importance of parent attentional monitoring and infant sustained attention for language development.

Cracking the code: Social and contextual cues to language input in the home environment

Infants use social cues like gaze and touch, typically during joint attention with caregivers, to decipher word meaning. Yet, studies on cues to word meaning primarily rely on structured tasks, where distractors are few compared to the countless objects that vie for attention in the home environment. Forty mothers and their 13-month-old infants were video-recorded during home routines. From transcripts, 3,000+ "naming events" were coded for social (visual and manual) and contextual (location: room and place) cues to the object of reference. Mother and infant visual and tactile attention accompanied naming events with high regularity, and the objects mothers named were specific to room and place. Nested social and contextual cues infuse infants' everyday language experiences in ways that help infants disambiguate word meaning.

Social and emotional contexts predict the development of gaze following in early infancy

The development of gaze following begins in early infancy and its developmental foundation has been under heavy debate. Using a longitudinal design (N = 118), we demonstrate that attachment quality predicts individual differences in the onset of gaze following, at six months of age, and that maternal postpartum depression predicts later gaze following, at 10 months. In addition, we report longitudinal stability in gaze following from 6 to 10 months. A full path model (using attachment, maternal depression and gaze following at six months) accounted for 21% of variance in gaze following at 10 months. These results suggest an experience-dependent development of gaze following, driven by the infant's own motivation to interact and engage with others (the social-first perspective).

Social origins of self-regulated attention during infancy and their disruption in autism spectrum disorder: Implications for early intervention

To understand the complex relationships between autism spectrum disorder (ASD) and other frequently comorbid conditions, a growing number of studies have investigated the emergence of ASD during infancy. This research has suggested that symptoms of ASD and highly related comorbid conditions emerge from complex interactions between neurodevelopmental vulnerabilities and early environments, indicating that developing treatments to prevent ASD is highly challenging. However, it also suggests that attenuating the negative effects of ASD on future development once identified is possible. The present paper builds on this by conceptualizing developmental delays in nonsocial skills as the potential product of altered caregiver-infant interactions following the emergence of ASD during infancy. And, following emerging findings from caregiver-infant dyadic head-mounted eye-tracking (D-ET) research, it also suggests that a multiple pathway model of joint attention can provide mechanistic insights into how ASD alters the ability of caregiver and infant to create a context for infant learning. The potential for this view to inform early intervention is further discussed and illustrated through D-ET data collected prior to and following a brief, parent-mediated intervention for infant ASD. While promising, further research informing how a multiple pathway model of joint attention can inform ASD early intervention is needed.

Using head-mounted eye-trackers to study sensory-motor dynamics of coordinated attention

In this chapter, we introduce recent research using head-mounted eye-trackers to record sensory-motor behaviors at a high resolution and examine parent-child interactions at a micro-level. We focus on one important research topic in early social and cognitive development: how young children and their parents coordinate their visual attention in social interactions. We start by introducing head-mounted eye-tracking and recent studies conducted using this method. We then present two sets of novel analysis techniques that examine how manual actions of parents and children with and without hearing loss contribute to their attention coordination. In the first set of analyses, we investigated different pathways parents and children used to coordinate their visual attention in toy play. After that, we used Sankey diagrams to represent the temporal dynamics of parents' and children's manual actions prior to and during coordinated attention. These two sets of analyses allowed us to explore how participants' sensory-motor behaviors contribute to the establishment and maintenance of coordinated attention. More generally, head-mounted eye-tracking allows us to ask new questions and conduct new analyses that were not previously possible. With this new sensing technology, the results here highlight the importance of understanding early social interaction from a multimodal, embodied view.

The understanding of congruent and incongruent referential gaze in 17-month-old infants: an eye-tracking study comparing human and robot

Several studies have shown that the human gaze, but not the robot gaze, has significant effects on infant social cognition and facilitate social engagement. The present study investigates early understanding of the referential nature of gaze by comparing-through the eye-tracking technique-infants' response to human and robot's gaze. Data were acquired on thirty-two 17-month-old infants, watching four video clips, where either a human or a humanoid robot performed an action on a target. The agent's gaze was either turned to the target (congruent) or opposite to it (incongruent). The results generally showed that, independent of the agent, the infants attended longer at the face area compared to the hand and target. Additionally, the effect of referential gaze on infants' attention to the target was greater when infants watched the human compared to the robot's action. These results suggest the presence, in infants, of two distinct levels of gaze-following mechanisms: one recognizing the other as a potential interactive partner, the second recognizing partner's agency. In this study, infants recognized the robot as a potential interactive partner, whereas ascribed agency more readily to the human, thus suggesting that the process of generalizability of gazing behaviour to non-humans is not immediate.

Social interaction in the emergence of toddler's mealtime spoon use

The use of a spoon for eating is among the important daily skills in early development. The article provides an analysis of how caregiver-toddler interactions guides the attention of toddlers who were first learning how to use a spoon to spoon-related action opportunities that were relevant to the mealtime context. Our analysis revealed several related results. First, caregivers often manipulated objects on the table (i.e., food and dishes), and toddlers were more likely than chance to use their spoon to contact food immediately after watching these caregiver manipulations. Second, toddlers looked more often at the caregiver's hand than at their face. Third, toddlers tended to look at the caregiver's hand when the caregiver was manipulating objects on the table, and after these looks, toddlers were more likely than chance to contact food with their spoon. Finally, the toddlers' choices about when to look at the caregiver were influenced by their own behavior, as if they wanted to know how the caregiver would react to what they had done. We discuss these results in terms of the learning of socially promoted action opportunities for meal-related spoon use.

What leads to coordinated attention in parent-toddler interactions? Children's hearing status matters

Coordinated attention between children and their parents plays an important role in their social, language, and cognitive development. The current study used head-mounted eye-trackers to investigate the effects of children's prelingual hearing loss on how they achieve coordinated attention with their hearing parents during free-flowing object play. We found that toddlers with hearing loss (age: 24-37 months) had similar overall gaze patterns (e.g., gaze length and proportion of face looking) as their normal-hearing peers. In addition, children's hearing status did not affect how likely parents and children attended to the same object at the same time during play. However, when following parents' attention, children with hearing loss used both parents' gaze directions and hand actions as cues, whereas children with normal hearing mainly relied on parents' hand actions. The diversity of pathways leading to coordinated attention suggests the flexibility and robustness of developing systems in using multiple pathways to achieve the same functional end.

The development of mother-infant coordination across the first year of life

Early mother-infant coordinated interactions play a critical role in infant development. The present study describes the development of the dyadic coordination of vocalization and gaze behavior between mothers and infants over the first year of life. In addition to describing developmental trajectories of behavior, the study contributes to our understanding of dyadic coordination by investigating how different measures of coordination relate to one another and how individual behaviors relate to dyadic coordination within the vocal and gaze domains. Thirty dyads were recorded playing together with a standard set of toys when infants were 3, 6, 9, and 12 months of age, and mother and infant vocalization and gaze behaviors were coded from these videos on a moment-to-moment basis. Coordination was analyzed using both cross-recurrence quantitative analysis and event-based measures of analysis. Hierarchical linear modeling was used to examine developmental trajectories of vocalization and gaze coordination. Results indicated that dyadic coordination of the timing of vocalization and gaze behaviors is a very early emerging phenomenon that is supported by both mothers and infants. Vocal coordination did not show developmental change over time, whereas mothers and infants became increasingly coordinated in their gaze behaviors as infants got older. Taken together, findings from this study highlight the importance of considering bidirectional and developmental influences on parent and infant behavior. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Transition From Crawling to Walking Changes Gaze Communication Space in Everyday Infant-Parent Interaction

Acquisition of walking changes not only infants' locomotion itself but also infants' exploratory behavior and social interaction, such as gaze communication. To understand the ecological context in which gaze communication occurs and how it changes with walking development from the point of view of the spatial arrangement of infants, parents, and objects, we analyzed longitudinal data of daily eye contact scenes recorded from head-mounted eye trackers worn by parents as infants grew from 10 to 15.5 months, focusing on infant-parent distance and the number of objects between the dyad. A Bayesian state-space model revealed that the interpersonal distance at which infants initiated eye contact with their parents increased with the time ratio of walking to crawling. This result could not be explained by the developmental change in the amount of time that the infants were far from the parents, which is not limited to the gaze communication context. Moreover, the interpersonal distance at which the parents initiated eye contact with the infants did not increase with the time ratio of walking to crawling. The number of objects on the floor between infants and parents at the time of eye contact increased with interpersonal distance. Taken together, these results indicate that the transition from crawling to walking changes the ecological context in which infants initiate gaze communication to a visual environment characterized by a larger interpersonal distance and, therefore, more objects cluttered between the dyad. The present study has wider implications for the developmental change of shared attention in conjunction with walking development.