Learning to walk changes infants’ social interactions

The onset of crawling marks a motor, cognitive and social milestone. The present study investigated whether independent walking marks a second milestone for social behaviors. In Experiment 1, the social and exploratory behaviors of crawling infants were observed while crawling and in a baby-walker, resulting in no differences based on posture. In Experiment 2, the social behaviors of independently walking infants were compared to age-matched crawling infants in a baby-walker. Independently walking infants spent significantly more time interacting with the toys and with their mothers, and also made more vocalizations and more directed gestures compared to infants in the walker. Experiment 3 tracked infants’ social behaviors longitudinally across the transition from crawling and walking. Even when controlled for age, the transition to independent walking marked increased interaction time with mothers, as well as more sophisticated interactions, including directing mothers’ attention to particular objects. The results suggest a developmental progression linking social interactions with milestones in locomotor development.     

The role of crawling and walking experience in infant spatial memory

This research explored infants' use of place learning and cue learning in a locomotor task across the transition from crawling to walking. Novice and expert crawling and walking infants were observed in a novel locomotor task-finding a hidden goal location in a large space. In Experiment 1, infants were tested with distal landmarks. Infants with fewer than 6 weeks of experience, either crawling or walking, could not find the goal location. All infants with more locomotor experience were more successful. Learning did not transfer across the transition to walking. In Experiment 2, novice and expert crawlers and walkers were tested with a direct landmark. Again, novice crawlers and walkers with fewer than 6 weeks of experience could not find the goal, whereas those with more experience could. Taken together, these findings suggest that infants' spatial learning is inextricably linked to mode of locomotion.     

A study of reaching actions in walking infants

Acquiring motor skills transforms the perceptual and cognitive world of infants and expands their exploratory engagement with objects. This study investigated how reaching is integrated with walking among infant walkers (n = 23, 14.5–15.5 months). In a walk-to-reach paradigm, diverse object retrieval strategies were observed. All infants were willing to use their upper and lower bodies in concert, and the timing of this coordination reflected features of their environment. Infants with an older walking age (months since walking onset) retrieved items more rapidly and exploited their non-reaching hand more effectively during object retrieval than did same-age infants with a younger walking age. This suggests that the actions of the upper- and lower-body are flexibly integrated and that this integration may change across development. Mechanisms that shape sophisticated upper-body use during upright object retrieval are discussed. Infants flexibly integrate emerging motor skills in the service of object retrieval in ways not previously documented.     

Social looking,social referencing and humor perception in 6- and-12-month-old infants

Social referencing refers to infants’ use of caregivers as emotional referents in ambiguous situations (Walden, 1993). Studies of social referencing typically require ambulation, thereby over-looking younger, non-ambulatory infants (i.e., ≤8-months) and resulting in a widespread assumption that young infants do not employ this strategy. Using a novel approach that does not require mobility, we found that when parents provided unsolicited affective cues during an ambiguous-absurd (i.e., humorous) event, 6-month-olds employ one component of social referencing, social looking Additionally, 6-month-olds who did not laugh at the event were significantly more likely to look toward parents than their counterparts who found the event funny. Sequential analyses revealed that, following a reference to a smiling parent, 6-month olds were more likely to smile at the parent, but by 12 months were more likely to smile at the event suggesting that older infants are influenced by parental affect in humorous situations. The developmental implications of these findings are discussed, as well as the usefulness of studying humor for understanding important developmental phenomena.     

Infant distractibility from social events mediates the relation between maternal responsiveness and infant language outcomes

Research demonstrates that contingent and appropriate maternal responsiveness to infant requests and bids for attention leads to better language outcomes. Research also indicates that infants who are less distracted by irrelevant competing stimulation and attend efficiently to audiovisual social events (e.g., faces and voices) show better language outcomes. However, few studies have assessed relations between maternal responsiveness, infant attention to faces and voices, and distractibility, and how together these factors lead to early language outcomes. A newly developed audiovisual protocol, the Multisensory Attention Assessment Protocol (MAAP; Bahrick et al., 2018), allows researchers to examine individual differences in attention to faces and voices and distractibility, and to assess relations with other variables. At 12 months, infants (n = 79) in an ongoing longitudinal study participated in the MAAP to assess intersensory matching of synchronous faces and voices and attention to an irrelevant competing visual distractor event. They also were observed in a brief play interaction to assess infant bids for attention and maternal responsiveness (accept, redirect, or ignore). At 18 months, receptive and expressive language were assessed using the Mullen Scales of Early Learning. Several noteworthy findings emerged: 1) mothers were generally responsive, accepting 74% and redirecting 14% of infant bids, 2) infants who had a greater number of their bids redirected by mothers, and who had better intersensory matching of synchronous faces and voices, showed less attention to the distractor, and 3) infants who showed less attention to the distractor had better receptive language. Findings demonstrate that maternal redirecting of infant attention by mothers who are generally responsive may promote better infant attentional control (lower distractibility) which in turn predicts better receptive language in toddlers.     

Do infants show social preferences for people differing in race?

Do infants develop meaningful social preferences among novel individuals based on their social group membership? If so, do these social preferences depend on familiarity on any dimension, or on a more specific focus on particular kinds of categorical information? The present experiments use methods that have previously demonstrated infants’ social preferences based on language and accent, and test for infants’ and young children’s social preferences based on race. In Experiment 1, 10-month-old infants took toys equally from own- and other-race individuals. In Experiment 2, 2.5-year-old children gave toys equally to own- and other-race individuals. When shown the same stimuli in Experiment 3, 5-year-old children, in contrast, expressed explicit social preferences for own-race individuals. Social preferences based on race therefore emerge between 2.5 and 5 years of age and do not affect social choices in infancy. These data will be discussed in relation to prior research finding that infants’ social preferences do, however, rely on language: a useful predictor of group or coalition membership in both modern times and humans’ evolutionary past.     

Social pretence with mothers and peers at 15 months

Previous research has shown that adults scaffold and direct early infant social pretend play making it difficult to establish infants' own contribution to pretence. To examine infants' social pretence abilities the present study compared infants' social pretend play in interactions with adults and same-age peers, who have similar socio-cognitive competence. Forty-five 15-month-old infants were observed during free-play interactions with their mother and two same-age, same-gender peers. The frequency and duration of parallel and coordinated social pretence were coded during both interactions. Results showed that while infants played pretence with both social partners, they engaged in more and longer coordinated social pretence with their mothers than with peers. Thus, although competent social partners play an important role in scaffolding complex pretence, infants' own socio-cognitive abilities contribute to the development of social pretence and enable them to pretend play with different partners regardless of their competencies.     

Social touch alters newborn monkey behavior

In humans, infants respond positively to slow, gentle stroking—processed by C-tactile (CT) nerve fibers—by showing reductions in stress and increases in eye contact, smiling, and positive vocalizations. More frequent maternal touch is linked to greater activity and connectivity strength in social brain regions, and increases children’s attention to and learning of faces. It has been theorized that touch may prime children for social interactions and set them on a path towards healthy social cognitive development. However, less is known about the effects of touch on young infants’ psychological development, especially in the newborn period, a highly sensitive period of transition with rapid growth in sensory and social processing. It remains untested whether newborns can distinguish CT-targeted touch from other types of touch, or whether there are benefits of touch for newborns’ social, emotional, or cognitive development. In the present study, we experimentally investigated the acute effects of touch in newborn monkeys, a common model for human social development. Rhesus macaques (Macaca mulatta), like humans, are highly social, have complex mother-infant interactions with frequent body contact for the first weeks of life, making them an excellent model of infant sociality. Infant monkeys in the present study were reared in a neonatal nursery, enabling control over their early environment, including all caregiver interactions. One-week-old macaque infants (N = 27) participated in three 5-minute counter-balanced caregiver interactions, all with mutual gaze: stroking head and shoulders (CT-targeted touch), stroking palms of hands and soles of feet (Non-CT touch), or no stroking (No-touch). Immediately following the interaction, infants watched social and nonsocial videos and picture arrays including faces and objects, while we tracked their visual attention with remote eye tracking. We found that, during the caregiver interactions, infants behaved differently while being touched compared to the no-touch condition, irrespective of the body part touched. Most notably, in both touch conditions, infants exhibited fewer stress-related behaviors—self-scratching, locomotion, and contact time with a comfort object—compared to when they were not touched. Following CT-targeted touch, infants were faster to orient to the picture arrays compared to the other interaction conditions, suggesting CT-targeted touch may activate or prime infants’ attentional orienting system. In the No-touch condition infants attended longer to the nonsocial compared to the social video, possibly reflecting a baseline preference for nonsocial stimuli. In contrast, in both touch conditions, infants’ looked equally to the social and nonsocial videos, suggesting that touch may influence the types of visual stimuli that hold infants’ attention. Collectively, our results reveal that newborn macaques responded positively to touch, and touch appeared to influence some aspects of their subsequent attention, although we found limited evidence that these effects are mediated by CT fibers. These findings suggest that newborn touch may broadly support infants’ psychological development, and may have early evolutionary roots, shared across primates. This study illustrates the unique insight offered by nonhuman primates for exploring early infant social touch, revealing that touch may positively affect emotional and attentional development as early as the newborn period.     

Infant touching behaviour during mother–infant face‐to‐face interactions

The study of infant communication during mother–infant interactions has largely focused on infants' distal behaviours, while neglecting their more proximal behaviours, such as touch. Yet, touch is an important modality through which infants and mothers communicate; it is also a vital means through which infants self‐regulate and explore their surroundings. The present study was designed to investigate the touching behaviours of 44, 51/2‐month‐old, healthy, full‐term infants during face‐to‐face mother–infant interactions. A still‐face (SF) procedure was used in order to examine differences in the types and locations of infant touch across normal and perturbed interaction periods, when mothers exhibit changes in their emotional availability. Results revealed that infant touch varied with changes in maternal availability. During the SF period, when mothers were unavailable, infants used more active, soothing, and reactive tactile behaviours (stroke, finger, pat, and pull), and they spent more time touching themselves. In contrast, infants used mostly passive touch (static) during the Normal periods, when their mothers were available. They also spent a significant portion of time touching their mothers. The variations in infant touch across periods suggest that infants communicate their affective states through touch. The findings also support the regulatory and exploratory roles of infant touch, especially during periods of maternal unavailability. Copyright © 2007 John Wiley & Sons, Ltd.     

Social referencing in 10-month-old infants

In Experiment 1, forty 10-month-old infants participated together with an experimenter and a parent in a social referencing encounter. The experimenter or the parent presented an ambiguous toy. Neither of the adults provided information about the toy in order to examine infant spontaneous looking behaviour. The infants looked more at both adults when the experimenter presented the toy. In Experiment 2, forty-four 10-month-old infants participated. The experimenter or the parent provided positive information about an ambiguous toy. The infants played more with the toy when the experimenter provided information than when the parent did. The results are discussed in terms of seeking information from knowledgeable others in ambiguous situations.     

Development of infant leg coordination: Exploiting passive torques

Leg joint coordination systematically changes over the first months of life, yet there is minimal data on the underlying change in muscle torques that might account for this change in coordination. The purpose of this study is to investigate the contribution of torque changes to early changes in leg joint coordination. Kicking actions were analyzed of 10 full-term infants between 6 and 15-weeks of age using three-dimensional kinematics and kinetics. We found 11 of 15 joint angle pairs demonstrated a change from more in-phase intralimb coordination at 6-weeks to less in-phase coordination at 15-weeks. Although the magnitude of joint torques normalized to the mass of the leg remained relatively consistent, we noted more complex patterns of torque component contribution across ages. By focusing on the change in torques associated with hip–knee joint coordination, we found that less in-phase hip–knee joint coordination at 15-weeks was associated with decreased influence of knee muscle torque and increased influence of knee gravitational and motion-dependent torques, supporting that infants coordinate hip muscle torque with passive knee gravitational and motion-dependent torques to generate kicks with reduced active knee muscle torque. We propose that between 6 and 15-weeks of age less in-phase hip–knee coordination emerges as infants exploit passive dynamics in the coordination of hip and knee motions.     

See and be seen: Infant–caregiver social looking during locomotor free play

Face‐to‐face interaction between infants and their caregivers is a mainstay of developmental research. However, common laboratory paradigms for studying dyadic interaction oversimplify the act of looking at the partner's face by seating infants and caregivers face to face in stationary positions. In less constrained conditions when both partners are freely mobile, infants and caregivers must move their heads and bodies to look at each other. We hypothesized that face looking and mutual gaze for each member of the dyad would decrease with increased motor costs of looking. To test this hypothesis, 12‐month‐old crawling and walking infants and their parents wore head‐mounted eye trackers to record eye movements of each member of the dyad during locomotor free play in a large toy‐filled playroom. Findings revealed that increased motor costs decreased face looking and mutual gaze: Each partner looked less at the other's face when their own posture or the other's posture required more motor effort to gain visual access to the other's face. Caregivers mirrored infants' posture by spending more time down on the ground when infants were prone, perhaps to facilitate face looking. Infants looked more at toys than at their caregiver's face, but caregivers looked at their infant's face and at toys in equal amounts. Furthermore, infants looked less at toys and faces compared to studies that used stationary tasks, suggesting that the attentional demands differ in an unconstrained locomotor task. Taken together, findings indicate that ever‐changing motor constraints affect real‐life social looking.     

Joint attention with the mother and the father at 10 months of age

Joint attention capabilities were assessed in 52 10-month-olds observed independently with their mothers and fathers in a semi-structured toy-play condition. Mothers and fathers were indistinguishable in terms of total number of behaviours aimed at engaging their infant in joint attention. However, infants responded more to mothers' bids for attention than to fathers' bids. Contrastingly, infants tended to display more initiating joint attention behaviours while interacting with their fathers. Although parents did not differ in terms of sensitivity, fathers were less intrusive than mothers. Results are discussed in terms of the specificities of mother-infant and father-infant interaction and how the paternal role should be highlighted in the case of infant's joint attention development.     

Differences in caregiver behaviors of infants at-risk for autism and typically developing infants from 9 to 15 months of age

During an object sharing paradigm, we compared infant-caregiver interactions between two groups: i) infants at high-risk (HR) for being diagnosed with Autism Spectrum Disorder (ASD) and ii) low-risk (LR) infants, observed at 9, 12, and 15 months of age. 16 HR infants (14 infants with an older sibling diagnosed with ASD and 2 preterm infants that received a diagnosis of ASD at 2 years) and 16 LR infants (typically developing infants without older siblings diagnosed with ASD) were included in the study. At each visit, infants played with objects in the presence of their caregivers as crawlers or walkers. Previously, we found that HR infants are less likely to share their object play with caregivers at walker ages. The present study found that caregivers of HR infants used greater directive bids including being more proximal to infants and using greater verbal and non-verbal bids to sustain their infant’s attention and to ensure their compliance during the task compared to caregivers of LR infants. Our study emphasizes the bidirectional and dynamic nature of infant-caregiver interactions. Our findings have implications for caregiver training programs that teach parents appropriate strategies to promote early social communication skills in at-risk infants.     

Intentional action processing across the transition to crawling: Does the experience of self-locomotion impact infants’ understanding of intentional actions?

Motor developmental milestones in infancy, such as the transition to self-locomotion, have cascading implications for infants’ social and cognitive development. The current studies aimed to add to this literature by exploring whether and how crawling experience impacts a key social-cognitive milestone achieved in infancy: the development of intentional action understanding. Study 1 used a cross-sectional, age-held-constant design to examine whether locomotor (n = 36) and prelocomotor (n = 36) infants differ in their ability to process a failed intentional reaching action. Study 2 (n = 124) further probed this question by assessing how variability in locomotor infants’ experience maps onto variability in their failed intentional action understanding. Both studies also assessed infants’ tendency to engage in triadic interactions to shed light on whether self-locomotion impacts intentional action understanding directly or indirectly via changes in infants’ interactions with social partners. Altogether, results showed no evidence for the role of self-locomotion in the development of intentional action understanding. Locomotor and prelocomotor infants did not differ in their failed action understanding or levels of triadic engagement (Study 1) and individual differences in days of crawling experience, propensity to crawl during play, and maximum crawling speed failed to predict infants’ intentional action understanding or triadic engagement (Study 2). Explanations for these null findings and alternative influences on the development of intentional action understanding are considered.     

Mother–Infant Joint Attention and Sharing: Relations to Disorganized Attachment and Maternal Disrupted Communication

The normative development of infant shared attention has been studied extensively, but few studies have examined the impact of disorganized attachment and disturbed maternal caregiving on mother–infant shared attention. The authors examined both maternal initiations of joint attention and infants’ responses to those initiations during the reunion episodes of the Strange Situation Procedure at 12 and 18 months of infant age. The mothers' initiations of joint attention and three forms of infant response, including shunning, simple joint attention, and sharing attention, were examined in relation to infant disorganized attachment and maternal disrupted communication. Mothers who were disrupted in communication with their infants at 18 months initiated fewer bids for joint attention at 12 months, and, at 18 months, mothers of infants classified disorganized initiated fewer bids. However, the infant' responses were unrelated to either the infant' or the mother' disturbed attachment. At both ages, disorganized infants and infants of disrupted mothers were as likely to respond to maternal bids as were their lower risk counterparts. Our results suggest that a disposition to share experiences with others is robust in infancy, even among infants with adverse attachment experiences, but this infant disposition may depend on adult initiation of bids to be realized.     

The development of expert face processing: are infants sensitive to normal differences in second-order relational information?

Sensitivity to second-order relational information (i.e., spatial relations among features such as the distance between eyes) is a vital part of achieving expertise with face processing. Prior research is unclear on whether infants are sensitive to second-order differences seen in typical human populations. In the current experiments, we examined whether infants are sensitive to changes in the space between the eyes and between the nose and the mouth that are within the normal range of variability in Caucasian female faces. In Experiment 1, 7-month-olds detected these changes in second-order relational information. Experiment 2 extended this finding to 5-month-olds and also found that infants detect second-order relations in upright faces but not in inverted faces, thereby exhibiting an inversion effect that has been considered to be a hallmark of second-order relational processing during adulthood. These results suggest that infants as young as 5 months are sensitive to second-order relational changes that are within the normal range of human variability. They also indicate that at least rudimentary aspects of face processing expertise are available early in life.     

Babbling development as seen in canonical babbling ratios: A naturalistic evaluation of all-day recordings

Canonical babbling (CB) is critical in forming foundations for speech. Research has shown that the emergence of CB precedes first words, predicts language outcomes, and is delayed in infants with several communicative disorders. We seek a naturalistic portrayal of CB development, using all-day home recordings to evaluate the influences of age, language, and social circumstances on infant CB production. Thus we address the nature of very early language foundations and how they can be modulated. This is the first study to evaluate possible interactions of language and social circumstance in the development of babbling. We examined the effects of age (6 and 11 months), language/culture (English and Chinese), and social circumstances (during infant-directed speech [IDS], during infant overhearing of adult-directed speech [ADS], or when infants were alone) on canonical babbling ratios (CBR = canonical syllables/total syllables). The results showed a three-way interaction of infant age by infant language/culture by social circumstance. The complexity of the results forces us to recognize that a variety of factors can interact in the development of foundations for language, and that both the infant vocal response to the language/culture environment and the language/culture environment of the infant may change across age.     

Social referencing in infants of mothers with symptoms of depression

The present study examined the acquisition of social referencing skills in infants of mothers with symptoms of depression (n = 44). We aimed to determine if a short discrimination training could facilitate infants’ social referencing. Mothers were instructed to pose either joyful or fearful facial expressions to cue infants’ approach/avoidance responses toward an ambiguous object. Maternal expressions were correlated with pleasant or unpleasant events occurring after the infant's response. The results showed that after the intervention, infants looked at their mothers more frequently and reached or avoided the ambiguous object based on the preceding maternal expression. The results suggest that discrimination training procedures can establish social referencing in infants of mothers with symptoms of depression.