Infant locomotion shapes proximity to adults during everyday play in the U.S.

Learning to walk expands infants’ access to the physical environment and prompts changes in their communicative behaviors. However, little is known about whether walking also shapes infants’ proximity to their adult social partners during everyday activities at home. Here we followed 89 infants (42 boys, 47 girls; 92% White, not Hispanic or Latino) longitudinally and documented connections between infant locomotion and infant-adult proximity on two timescales: (1) across developmental time, by comparing data from a session when infants could only crawl to a later session when they could walk (M walk onset = 12.15 months, range = 8-15); and (2) in real time, by testing whether the amount of time that infants spent in motion (regardless of their locomotor status) related to their interpersonal distance to adults. The developmental transition to walking corresponded to a significant, but modest, decrease in infant-adult proximity. Infants’ moment-to-moment locomotion, however, was strongly related to patterns of interpersonal distance: infants who spent more time in motion spent less time near adults and instigated more proximity transitions, resulting in shorter and more dispersed bouts of proximity throughout sessions. Findings shed new light on how infants’ motor achievements can reverberate across other domains of development, and how changes in infant development that researchers often observe over months arise from infants’ moment-to-moment experiences.     

Behavior of Infant Chimpanzees During the Night in the First 4 Months of Life: Smiling and Suckling in Relation to Behavioral State

This article reports the behavior of 3 newborn chimpanzees in the first 4 months of life, reared by their mothers and living in a community of 14 chimpanzees in a semi‐natural enriched environment. We focused on spontaneous activity during the night partly because sleeping behavior constitutes an essential part of the infants' activity. Observation during the night also had the advantage of keeping the influence of the mothers' activity as well as the environmental stimulation constant throughout the observation period. We report several interesting findings. Behavioral states defined through overt features such as open or closed eyes were variable during the night, with the rapid eye movement (REM) and non‐REM sleep patterns alternating much as they do in human infants. Although crying is one of the distinctive behavioral states in the case of human infants, the chimpanzee infants did not cry like humans. Suckling behavior was often accompanied by open eyes until the end of the first 2 months. Thereafter, suckling with the eyes closed became more prominent. Although there were no explicit stimuli, the newborns showed neonatal smiling with the eyes closed during REM sleep periods. However, neonatal smiling disappeared within the first 2 months and was replaced by social smiling with open eyes. Taken together, the results suggest a strong similarity between human infants and chimpanzee infants in terms of developmental changes in spontaneous activities at around 2 months of age.     

Object Interaction and Walking: Integration of Old and New Skills in Infant Development

Manual skills such as reaching, grasping, and exploring objects appear months earlier in infancy than locomotor skills such as walking. To what extent do infants incorporate an old skill (manual actions on objects) into the development of a new skill (walking)? We video recorded 64 sessions of infants during free play in a laboratory playroom. Infants’ age (12.7–19.5 months), walking experience (0.5–10.3 months), and walking proficiency (speed, step length, etc.) varied widely. We found that the earlier developing skills of holding and exploring objects were immediately incorporated into the later developing skill of walking. Although holding incurred a reliable cost to infants’ gait patterns, holding and exploring objects in hand were relatively common activities and did not change with development. Moreover, holding objects was equally common in standing and walking. However, infants did not interact with objects indiscriminately: Object exploration was more frequent while standing than walking, and infants selectively chose lighter objects to carry and explore. Findings suggest that the earlier appearance of some skills may serve to motivate and enrich later appearing skills.     

Longitudinal links between maternal factors and infant cognition: Moderation by infant sleep

The current study examined the moderating role of infant sleep in the link between maternal factors (i.e., maternal education, depressive symptoms, sleep disturbance) and infant cognition. Data come from 95 African American parent–child dyads. At 3 months of age, infant sleep was objectively measured using videosomnography and actigraphy, from which measures of sleep regulation and consolidation were calculated. Mothers also self‐reported their level of education, depressive symptoms, and sleep quality. At 6 months of age, infants completed cognitive assessments, including a measure of general cognitive ability and observed attention behavior. Findings revealed that infant sleep quality interacted with maternal education and sleep disturbances to predict cognition. Specifically, the link between maternal education and infants’ attention behavior was significant and positive for infants with better regulated sleep, but not for infants with poorly regulated sleep. Similarly, the link between maternal sleep disturbance and infant cognition depended on infant sleep quality. For infants with poorer sleep consolidation, increased maternal sleep disturbance predicted poorer infant general cognitive ability. For infants with better sleep consolidation, maternal sleep disturbance was positively related to both general cognitive ability and attention behavior. These findings suggest that infant sleep quality moderates the impact of environmental factors on cognitive functioning.     

The Relations between Reactivity at 4 Months and Behavioral Inhibition in the Second Year: Replication across Three Independent Samples

This paper examines the predictive relations between two infant temperamental biases assessed at 4 months and inhibited behavior during the first 2 years of life in three independent samples from two research laboratories. Although each sample used slightly different criteria for classifying infants, the results across samples were consistent. Infants of both genders who displayed high levels of motor activity and distress to unfamiliar events were more inhibited at 14 months of age. By 24 months, there were significant sex differences: Boys identified as high reactive were more inhibited than high reactive girls.     

Posture Development in Infants at Heightened versus Low Risk for Autism Spectrum Disorders

Evidence suggests that children and adults diagnosed with autism spectrum disorders (ASD) exhibit difficulties with postural control. Retrospective video studies of infants later diagnosed with ASD indicate that infants who eventually receive an ASD diagnosis exhibit delays in postural development. This study investigates early posture development prospectively and longitudinally in 22 infants at heightened biological risk for ASD (HR) and 18 infants with no such risk (Low Risk; LR). Four HR infants received an autism diagnosis (AD infants) at 36 months. Infants were videotaped at home at 6, 9, 12, and 14 months during everyday activities and play. All infant postures were coded and classified as to whether or not they were infant‐initiated. Relative to LR infants, HR infants were slower to develop skill in sitting and standing postures. AD infants exhibited substantial delays in the emergence of more advanced postures and initiated fewer posture changes. Because posture advances create opportunities for infants to interact with objects and people in new and progressively more sophisticated ways, postural delays may have cascading effects on opportunities for infant exploration and learning. These effects may be greater for infants with ASD, for whom posture delays are more significant.     

Walking Ability is Associated with Social Communication Skills in Infants at High Risk for Autism Spectrum Disorder

Achievement of early motor milestones in infancy affords new opportunities for social interaction and communication. Research has shown that both motor and social deficits are observed in infants who later develop autism spectrum disorder (ASD). This study examined associations between motor and Social communication skills in 12‐month‐old infant siblings of children with ASD who are at heightened risk for developmental delays (N = 86) and low‐risk, typically developing infants (N = 113). Infants were classified into one of three groups based on their walking ability: walkers (walks independently), standers (stands independently), or prewalkers (does not yet stand or walk independently). Social communication and cognitive skills were assessed with two standardized assessments (Communication and Symbolic Behaviors Scales [CSBS] and Mullen Scales of Early Learning) and compared across the three walking groups. Results demonstrated that high‐risk walkers showed superior Social communication skills, but commensurate cognitive skills, compared to high‐risk prewalkers. In contrast, Social communication and cognitive skills were largely comparable for low‐risk infants, regardless of walking status. Findings suggest that for high‐risk infants, who are already vulnerable to developmental delays and ASD, independent walking may facilitate the emergence of Social communication abilities. Pivotal motor milestones may serve as useful indicators of Social communication delays and targets for intervention.     

Infants born preterm and infants born full-term generate more selective leg joint movement during the scaffolded mobile task

Infants born very preterm (PT), prior to 32 weeks gestation, are at increased risk of developing cerebral palsy. Children with spastic cerebral palsy have impaired selective leg joint movement, which contributes to lifelong walking limitations. We investigated whether infants born PT generated more selective hip–knee joint movement (e.g., hip flexes as knee extends) while participating in a scaffolded mobile task. Infants born PT and infants born full-term (FT) at 4 months corrected age participated in a scaffolded mobile task for 2–3 consecutive days. The scaffolded mobile task required infants to raise their legs vertically over a virtual threshold. Three threshold heights (low, middle, and high) were used to test whether the middle and high heights encourage infants to move their legs more selectively. Fifteen infants born FT learned the task and showed more selective hip–knee movement at each of the three threshold heights on the day that they learned, compared with their baseline spontaneous kicking. Thirteen infants born PT learned the task and showed more selective hip–knee movement on their learning day, but only when the middle and high thresholds were used. The results show that the scaffolded mobile task effectively encouraged infants to generate more selective hip–knee joint movement.     

Development of Infant Pointing from 10 to 12 months: The Role of Relevant Caregiver Responsiveness

Infants’ pointing frequency is a predictor of their later language abilities. Yet, predictors of pointing frequency in the first year of life are not well understood. Study 1 explored what factors in infants and caregivers at 10 months would predict the pointing frequency of infants at 12 months (N = 35). Infant‐driven predictors were infants’ fine‐motor skills and point‐following abilities. Caregiver‐mediated predictors were caregivers’ pointing frequency and responsiveness toward infants’ pointing. Relevant caregiver responsiveness at 10 months predicted infants’ pointing frequency at 12 months, controlling for the other factors and infants’ prior pointing frequency. Study 2 explored whether child‐level factors influence caregivers’ responsiveness (N = 49). We examined the hand shape of infants’ pointing (whole‐hand versus index‐finger) and the presence of point‐accompanying vocalizations. Infants’ vocalization‐accompanied points were more likely to elicit relevant responses from caregivers, while hand shapes played a less pronounced role. Together, the findings reveal an early emerging mutual relationship between infant pointing and caregiver behavior such that certain characteristics of infant pointing predict caregivers’ responsiveness, and relevant responsiveness toward infants’ pointing predicts the increase in infants’ pointing frequencies.     

Developmental Change in Action Perception: Is Motor Experience the Cause?

Human actions are complex stimuli containing several perceptual dimensions an observer could attend to. Research indicates that attention to the perceptual dimensions of action undergoes a process of perceptual narrowing between 4 and 10 months, during which infants’ attention to configural and temporal information in action decreases over time, while attention to hand information is maintained. This research explored whether infants’ active experience with grasping is related to perceptual narrowing in action. Across two studies, we tested 6‐month‐old infants’ attention to changes in these action dimensions and also assessed their grasping ability. Infants who were more proficient at grasping showed a pattern more consistent with perceptual narrowing (decreasing attention to configural and temporal information) relative to those less proficient at grasping, especially for attention to configural information. In addition, attention to hand information appears to undergo U‐shaped development between 4 and 10 months, as 6‐month‐olds did not recover attention to the hand change. These findings add to a growing body of research showing that infants’ motor experience broadly influences their perception of others’ action and may follow a complex developmental pathway that diverges from perceptual narrowing over the first year.     

Effects of Maternal Responsiveness on Infant Responsiveness and Behavior in the Still‐Face Task

The effects of maternal responsiveness on infant responsiveness and behavior in the Still‐Face Task were longitudinally examined through infants' first 3 months. Maternal vocal responsiveness and infant vocal and smiling responsiveness significantly increased when infants were 2 months of age. Mothers showed continuity of individual differences in vocal responsiveness from the infants' newborn period. Maternal responsiveness predicted infant responsiveness within and across sessions. Compared with infants with low‐responsive mothers, infants with high‐responsive mothers were more attentive and affectively engaged during the Still‐Face Task from 1 month of age. Infants with high‐responsive mothers discriminated between the task phases with their smiling at 1 month, a month before infants with low‐responsive mothers did so. Infants in both groups discriminated between the phases with their attention and nondistress vocalizations throughout their first 3 months. Results suggest that maternal responsiveness influences infant responsiveness and facilitates infants' engagement and expectations for social interaction.     

Does surprise enhance infant memory? Assessing the impact of the encoding context on subsequent object recognition

A discrepancy between what was predicted and what is observed has been linked to increased looking times, changes in brain electrical activity, and increased pupil dilation in infants. These processes associated with heightened attention and readiness to learn might enhance the encoding and memory consolidation of the surprising object, as suggested by both the infant and the adult literature. We therefore investigated whether the presence of surprise during the encoding context enhances subsequent encoding and recognition memory processes for the items that violated infants' expectations. Seventeen-month-olds viewed 20 familiar objects, half of which were labeled correctly, while the other half were mislabeled. Subsequently, infants were presented with a silent recognition memory test where the previously labeled objects appeared along with new images. Pupil dilation was measured, with more dilated pupils indicating (1) surprise during those labeling events where the item was mislabeled and (2) successful retrieval processes during the memory test. Infants responded with more pupil dilation to mislabeling compared to correct labeling. Importantly, despite the presence of a surprise response during mislabeling, infants only differentiated between the previously seen and unseen items at the memory test, offering no evidence that surprise had facilitated the encoding of the mislabeled items.     

Six‐Month‐Old Infants Prefer Speech with Raised Formant Frequencies

Voices can be characterized by their fundamental frequency as well as by speech timbre characteristics, such as formant frequencies. While infants' responses to fundamental frequency characteristics are well established, very little is known about how infants respond to changes in formant frequencies. This study tested whether 6‐month‐old infants prefer listening to speech with raised formant frequencies over speech with lowered formant frequencies. Naturally spoken utterances were acoustically manipulated to render raised‐formant and lowered‐formant stimuli that only differed in the formant frequencies, while keeping fundamental frequency and other acoustic characteristics constant. Infants in an infant‐controlled listening procedure listened longer to the raised‐formant than to the lowered‐formant stimuli. These results provide the first evidence that infants distinguish and show preferences for variations in formant frequencies in adult speech.     

Neurobehavioral Consequences of Prenatal Exposure to Smoking at 6 to 8 Months of Age

Between 400,000 and 800,000 infants are born in the United States each year to women who smoked cigarettes during their pregnancy. Whereas the physical health consequences to infants of prenatal exposure to smoking are well established, the early neurobehavioral consequences are less well understood. This study investigated the neurobehavioral consequences of prenatal exposure to smoking using an epidemiologically derived sample of 454 infants who were drawn from a larger sample of 1,292 infants whose families were recruited at birth. Results indicated that, on average, infants who were exposed to higher levels of prenatal smoking exhibited less positive affect and greater irritability. Moreover, among male infants, elevated levels of prenatal exposure to smoking were associated with lower levels of approach, gross motor movement, reactivity, and attention. There was no evidence that the effects of prenatal exposure to smoking on infant neurobehavioral functioning were mediated by physical growth parameters (infant weight and head circumference) that are also known to be affected by prenatal exposure to smoking.     

Evidence of Early Strategies in Learning to Walk

Learning to walk is a dynamic process requiring the fine coordination, assembly, and balancing of many body segments at once. For the young walker, coordinating all these behavioral levels may be quite daunting. In this study, we examine the whole‐body strategies to which infants resort to produce their first independent steps and progress over the first months of walking experience. Six infants were followed weekly from the onset of independent upright locomotion for 8 weeks, and then every other week until 4 months of walking experience. The walking kinematics from the infants' earliest steps were cluster‐analyzed and the infants were classified into 3 groups. Follow‐up comparisons with kinematics recordings were used to quantify the infants' strategies more precisely and track how these early forms of walking evolved over time. Results revealed that in the first weeks of independent walking, 3 infants used a stepping strategy, 1 used a twisting strategy, and 2 used a falling strategy to move their body forward and perform their first unsupported steps. As the infants gained walking experience, their walking patterns became more similar. These findings indicate that infants discover different solutions to use their body and control their balance when beginning to walk. With time, infants adopt a more efficient solution that incorporates and integrates elements of the different strategies.     

Maternal Attention‐Directing Strategies and Infant Focused Attention During Problem Solving

Forty‐nine mother‐infant dyads participated in the study. Mothers were observed during free play with their infants to assess their attention‐directing strategies. Infants were observed during the Bayley to assess their focused attention abilities. Assessments were made when infants were 10 and 18 months. Whereas consistently high levels of maintaining over time were modestly associated with better infant focused attention at 18 months, consistently high levels of redirecting were moderately associated with poorer infant focused attention at 18 months. Additionally, more focused attention was associated with higher Bayley scores at both ages. Although the direction of effects could not be determined, the findings suggest links between maternal attention‐directing strategies (maintaining and redirecting) during play and infant attentional abilities during problem solving.     

Peripheral Stimulus Localization by Infants of Moving Stimuli on Complex Backgrounds

This study examined the effect of attention in young infants on the saccadic localization of dynamic peripheral stimuli presented on complex and interesting backgrounds. Infants at 14, 20, and 26 weeks of age were presented with scenes from a Sesame Street movie until fixation on a moving character occurred and then presented with a second segment in the scene in which the character movement occurred in a new location. Localization of the moving character in the new location was faster when the infant was engaged in attention than when inattentive, for scenes in which the character moved from one location to another, or scenes in which the character stopped moving and characters in new locations began moving. However, localization of the character was slower during attention when the first character disappeared and a different character appeared in a new location. We also found a decrease in the linear component of the main sequence in the saccade characteristics over the three testing ages, and attention affected the main sequence for infants at the two oldest ages. These results partially replicate prior findings showing that attention to a focal stimulus affects localization of peripheral stimuli, but suggest that the nature of the stimuli being localized modifies the role of attention in affecting eye movements to peripheral stimuli.     

Infant Affect During Parent—Infant Interaction at 3 and 6 Months: Differences Between Mothers and Fathers and Influence of Parent History of Depression

Fifty families participated in mother‐infant and father‐infant still‐face interaction at infant ages 3 and 6 months as part of a study of affect in early parent‐infant relationships. Infants' positive and negative affect and parents' positive affect and physical play were coded from videotapes. Consistent with previous research, during the normal condition, mothers displayed more positive affect than did fathers, and fathers were more likely than mothers to display physical play. Infants were more positive with mothers than with fathers. Parents' positive affect but not parent gender predicted infants' positive affect at 6 months. During the still‐face condition, infants of parents with a lifetime history of depression were more likely to display negative affect and less likely to display positive affect than infants with no such parent history. Infants' affect was unrelated to parents' current level of depressive symptoms, which indicates the value of considering family history of psychopathology when examining individual differences in infants' affect.     

Experienced crawlers avoid real and water drop-offs,even when they are walking

Crawling experience was recently linked to crawling and walking infants’ avoidance of falling on real and water cliffs, whereas walking experience had no effect on walkers’ avoidance behavior (Burnay et al., 2021). In the current study, the behavior of 25 infants was analyzed on the Real Cliff/Water Cliff apparatus using a longitudinal study design. Infants were tested as experienced crawlers (M_crawling = 2.93 months, SD = 1.07), novice walkers (M_walking = 0.68 months, SD = 0.29), and experienced walkers (M_walking = 4.90 months, SD = 0.92). Infants avoided falling on both cliffs when tested as experienced crawlers and their behavior was not different when tested as novice or experienced walkers. These findings confirmed the effect of crawling experience on crawling and walking infants’ avoidance of falls from heights and into water and the transfer of perceptual learning from crawling to walking postures.     

A Cross‐National Investigation of the Relationship Between Infant Walking and Language Development

The acquisition of walking has recently been linked with infant language development (Walle & Campos, 2014). If this relation reflects the consequence of an epigenetic event, then it should be present regardless of when the infant typically begins to walk, the infant's culture, and the infant's native language. This study sought to replicate the previously reported link between walking and language development in American infants and investigate whether this relation exists cross‐nationally in typically developing Chinese infants exposed to Mandarin. Urban Chinese infants not only provide a distinct linguistic and cultural population in which to study this relation but also typically begin walking approximately 6 weeks later than American infants. Our results demonstrated that (1) walking infants in both the American and Chinese samples had greater receptive and productive vocabularies than same‐aged crawling infants, (2) differences between crawling and walking infants were proportionally similar in each sample, and (3) the walking‐language relation was present for both noun and non‐noun vocabularies. These findings provide further support of a relation between infant walking onset and language development, independent of age. Avenues for future research of the processes involved in this relation, as well as additional populations of interest to investigate, are discussed.