Infant motor development predicts the dynamics of movement during sleep

The characteristics of infant sleep change over the first year. Generally, infants wake and move less at night as they grow older. However, acquisition of new motor skills leads to temporary increases in night waking and movement at night. Indeed, sleep-dependent movement at night is important for sensorimotor development. Nevertheless, little is known about how movement during sleep changes as infants accrue locomotor experience. The current study investigated whether infant sleep and movement during sleep were predicted by infants' walking experience. Seventy-eight infants wore an actigraph to measure physical activity during sleep. Parents reported when their infants first walked across a room >10 feet without stopping or falling. Infants in the midst of walking skill acquisition had worse sleep than an age-group estimate. Infants with more walk experience had more temporally sporadic movement during sleep and a steeper hourly increase in physical activity over the course of the night. Ongoing motor skill consolidation changes the characteristics of movement during sleep and may alter sleep state-dependent memory consolidation. We propose a model whereby changes in gross motor activity during night sleep reflect movement-dependent consolidation.     

Avoidance of Heights on the Visual Cliff in Newly Walking Infants

Work with infants on the “visual cliff” links avoidance of drop‐offs to experience with self‐produced locomotion. Adolph's (2002) research on infants' perception of slope and gap traversability suggests that learning to avoid falling down is highly specific to the postural context in which it occurs. Infants, for example, who have learned to avoid crossing risky slopes while crawling must learn anew such avoidance when they start walking. Do newly walking infants avoid crossing the drop‐off of the visual cliff? Twenty prewalking but experienced crawling infants were compared with 20 similarly aged newly walking infants on their reactions to the visual cliff. Newly walking infants avoided moving onto the cliff's deep side even more consistently than did the prewalking crawlers. Thus, in the context of drop‐offs in visual texture, our results show that once avoidance of drop‐offs is established under conditions of crawling, it is developmentally maintained once infants begin walking.     

Effects of Contingent Reinforcement of Actions on Infants' Object‐Directed Reaching

The role of contingency learning was examined in 3‐month‐old infants' reaching movements. Infants in the experimental group experienced 9 min of active training during which they could move their arms in a reach‐like fashion to pull and move a mobile. Infants in the control group experienced 9 min of passive training during which they watched a mobile move. Prior to (pre‐training) and following the mobile experience (post‐training), infants in both conditions were given an opportunity to interact with a rattle placed within and out of their reach. Compared with infants in the control condition, infants in the experimental condition produced reach‐like movements more frequently during the mobile experience; they also showed a greater increase in reaching attempts from pre‐ to post‐training assessments with the rattle. These findings show that reinforcement of arm extensions and retractions increases the frequency of infants' reaching behaviors. This result suggests that the reinforcement of components of infants' behaviors may contribute to the successful assembly of these behaviors. This process could help keep infants engaged during the lengthy transition from prereaching to independent reaching.     

How Mothers Encourage and Discourage Infants' Motor Actions

The content of mothers' emotional, verbal, and gestural communication to their infants was examined under conditions of potential physical risk in a laboratory motor task. Mothers encouraged and discouraged their 12‐ and 18‐month‐old infants to crawl or walk down a sloping walkway. Mothers expressed positive affect on nearly every trial. They rarely expressed purely negative affect in their faces and voices, even when discouraging. Instead, they discouraged infants with a mixture of positive and negative expressions. In both encourage and discourage conditions, mothers coupled their emotional messages with rich verbal and gestural information to elicit infants' attention, regulate their location, guide their actions, and describe the situation and potential consequences of their actions. The content of mothers' communication was attuned to infants' age and locomotor experience.     

Strength of Infants' Bimanual Reaching Patterns is Related to the Onset of Upright Locomotion

Infants typically exhibit a shift from unimanual to bimanual reaching toward the end of their first year, which has been linked to walking onset. Until now, however, it has been unclear whether it was the onset of walking per se that influenced reaching patterns or whether a more general shift to an upright posture might have prompted the reorganization of the motor system. To address this question, the current study longitudinally chronicled the uni‐ and bimanual reaching preferences of 25 infants every 3 weeks starting at 7 months, prior to the onset of pulling‐to‐stand and through the onset of cruising. Experimenters recorded infants' reaching behavior via a semi‐structured reaching procedure and documented their motor development. There was no relationship between the shift from uni‐ to bimanual reaching and the onset of pulling‐to‐stand. However, the onset of cruising was related to a shift in reaching pattern preference, suggesting that the increase in infants' bimanual reaching was prompted by a reorganization of the motor system in which the arms are recruited for use in new ways to support locomotion. We also discuss individual differences in the trajectory of reaching activity in terms of the pitfalls of using age as an explanatory variable.     

Infants' Rapid Learning About Self‐Propelled Objects

Six experiments investigated 7‐month‐old infants' capacity to learn about the self‐propelled motion of an object. After observing 1 wind‐up toy animal move on its own and a second wind‐up toy animal move passively by an experimenter's hand, infants looked reliably longer at the former object during a subsequent stationary test, providing evidence that infants learned and remembered the mapping of objects and their motions. In further experiments, infants learned the mapping for different animals and retained it over a 15‐min delay, providing evidence that the learning is robust and infants' expectations about self‐propelled motion are enduring. Further experiments suggested that infants' learning was less reliable when the self‐propelled objects were novel or lacked faces, body parts, and articulated, biological motion. The findings are discussed in relation to infants' developing knowledge of object categories and capacity to learn about objects in the first year of life.     

Phonemic contrasts under construction? Evidence from Basque

Attunement theories of speech perception development suggest that native‐language exposure is one of the main factors shaping infants' phonemic discrimination capacity within the second half of their first year. Here, we focus on the role of acoustic–perceptual salience and language‐specific experience by assessing the discrimination of acoustically subtle Basque sibilant contrasts. We used the infant‐controlled version of the habituation procedure to assess discrimination in 6‐ to 7‐month and 11‐ to 12‐month‐old infants who varied in their amount of exposure to Basque and Spanish. We observed no significant variation in the infants' discrimination behavior as a function of their linguistic experience. Infants in both age‐groups exhibited poor discrimination, consistent with Basque adults finding these contrasts more difficult than some others. Our findings are in agreement with previous research showing that perceptual discrimination of subtle speech sound contrasts may follow a different developmental trajectory, where increased native‐language exposure seems to be a requisite.     

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.     

Relationship Between Maternal Sensitivity During Early Interaction and Maternal Ability in Perceiving Infants' Body and Face

Maternal sensitivity has been considered an indicator of mother‐infant quality interaction, however little is known about the perception processes associated to this parental behavior style. Here we aimed to explore the relationship between maternal sensitivity during a face‐to‐face interaction with their infants and maternal ability in perceiving infants' body and face. Thirty‐six 6 month‐old infants and their mothers were videotaped during a mother‐infant interaction to identify those with high and low sensitivity. Then, mothers were tested using an inversion effect paradigm requiring the visual discrimination of upright and inverted pictures of whole bodies and faces of their own and unfamiliar infants; this allowed estimation of their configural perceptual processing abilities. Results showed that high‐sensitivity mothers showed reduced body configural processing for others' infants as compared to configural processing of their own infant, whereas low‐sensitivity mothers were engaged in comparable body configural processing independently from infant identity. Infants' face configural processing did not distinguish between high‐ and low‐sensitivity mothers. Our findings suggest that high‐sensitivity mothers have refined their use of configural processing of body postures to be selective for their own infants, suggesting that this visuo‐perceptual strategy makes much more efficient the mothers' ability in detecting, discriminating and recognizing own infant's cues.     

Emotion Regulation Via Maternal Touch

The study of emotion elicitation in the caregiver‐infant dyad has focused almost exclusively on the facial and vocal channels, whereas little attention has been given to the contribution of the tactile channel. This study was undertaken to investigate the effects of touch on infants' emotions. During the time that objects were presented to the dyad, mothers provided tactile stimulation to their 12‐month‐old infants by either (a) tensing their fingers around the infants' abdomen while abruptly inhaling, (b) relaxing their grip around the infants' abdomen, or (c) not providing additional tactile stimulation (control condition). The results revealed that infants in the first condition (a) touched the objects less and waited longer to touch the objects while displaying more negative emotional displays compared to infants in the control condition. However, no apparent differences were found between infants in the second condition (b) and the control condition. The results suggest that infants' emotions may be elicited by specific parameters of touch.     

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.     

Demands on Finite Cognitive Capacity Cause Infants' Perseverative Errors

This research unites traditionally disparate developmental domains—cognition and locomotion—to examine the classic cognitive issue of the development of inhibition in infancy. In 2 locomotor A‐not‐B tasks, 13‐month‐old walking infants inhibited a prepotent response under low task demands (walking on flat ground), but perseverated under increased task demands (descending a staircase). Despite elimination of factors previously associated with infant perseveration, infants still perseverated in the difficult stairs condition. Increasing cognitive load by manipulating task difficulty affected infants' ability to inhibit repeated responses that were no longer appropriate. Evidence supports a cognitive capacity account of infant perseveration, in which infants' performance depends on allocation of cognitive and attentional resources.     

Mothers' Verbal and Nonverbal Strategies in Relation to Infants' Object‐Directed Actions in Real Time and Across the First Three Years in Ethnically Diverse Families

We examined maternal behavioral strategies in relation to infants' object‐directed actions in real time and over developmental time in 206 mother–infant dyads from African American, Dominican immigrant, and Mexican immigrant backgrounds. Mothers were asked to share a set of beads and strings with their infants when children were 14, 24, and 36 months. We coded three types of maternal strategies—eliciting attention, instructive assistance, and encouragement—which could be expressed verbally (e.g., “look”, “turn it”, “good job!”) or physically (i.e., through gestures, hands‐on guidance, or transfer of objects). We also coded infants' unassisted bead‐stringing. Across ethnic groups and ages, mothers' hands‐on guidance and object transfer increased the likelihood that infants would follow with unassisted bead‐stringing during real‐time interaction. Over developmental time, mothers modified their strategies: They displayed fewer attention‐getting strategies and more encouragement across infant ages, and peaked in their provision of instructive assistance when infants were 24 months. Additionally, Mexican mothers displayed more nonverbal strategies (e.g., gestures, hands‐on guidance) than did African American and/or Dominican mothers, who displayed more verbal strategies (e.g., attention‐getting and encouraging language). Developmental and real‐time patterns in mother–infant object‐related interactions generalize across ethnicities, although mothers' emphases on specific strategies are culture specific.     

Locomotion development and infants' object interaction in a day-care environment

This longitudinal study examined the relationship between the development of locomotion and infants' interaction with others involving objects. Observations took place in a multi-person situation—a day-care class—for one-year-old infants for 1 year. The study participants were 13 infants and 7 caregivers (all Japanese). Frequencies of infants’ manual contact with objects and moving before contact with them did not differ according to locomotion developmental level. However, infants who began walking engaged in more social interactions than those who were cruising or crawling. Throughout all locomotor developmental periods, social interactions increased in frequency when more caregivers were present. As infants began to walk, they moved more prior to social interactions, had more frequent bidirectional and triadic social interactions, and moved and interacted more often with others during a single object episode. These results suggest that crawlers' engagement with objects is relatively object-oriented, while for walkers, locomotion seems to be driven by social stimuli. Infants who have begun to walk moved among caregivers and peers in a multi-person environment and developed more elaborated social interactions through objects.     

Infants' Transitions out of a Fussing/Crying State Are Modifiable and Are Related to Weight Status

Currently, about 10% of infants have a weight for length greater than the 95th percentile for their age and sex, which puts them at risk for obesity as they grow. In a pilot obesity prevention study, primiparous mothers and their newborn infants were randomly assigned to a control group or a Soothe/Sleep intervention. Previously, it has been demonstrated that this intervention contributed to lower weight‐for‐length percentiles at 1 year; the aim of the present study was to examine infant behavior diary data collected during the intervention. Markov modeling was used to characterize infants' patterns of behavioral transitions at ages 3 and 16 weeks. Results showed that heavier mothers were more likely to follow their infants' fussing/crying episodes with a feeding. The intervention increased infants' likelihood of transitioning from a fussing/crying state to an awake/calm state. A shorter latency to feed in response to fussing/crying was associated with a higher subsequent weight status. This study provides preliminary evidence that infants' transitions out of fussing/crying are characterized by inter‐individual differences, are modifiable, and are linked to weight outcomes, suggesting that they may be promising targets for early behavioral obesity interventions, and highlighting the methodology used in this study as an appropriate and innovative tool to assess the impact of such interventions.     

Sex Differences in Infants' Ability to Represent Complex Event Sequences

Prior research suggests that when very simple event sequences are used, 4.5‐month‐olds demonstrate the ability to individuate objects based on the continuity or disruption of their speed of motion (Wilcox & Schweinle, 2003). However, infants demonstrate their ability to individuate objects in an event‐monitoring task (i.e., infants must keep track of an ongoing event) at a younger age than in an event‐mapping task (i.e., infants must compare information from 2 different events). The research presented here built on these findings by examining infants' capacity to succeed on an event‐mapping task with a more complex event sequence to determine if the complexity of the event interferes with their ability to form summary representations of the event, and, in short, individuate the objects. Three experiments were conducted with infants 4.5 to 9.5 months of age. The results indicated that (a) increasing the complexity of the objects' trajectories adversely affected infants' performance on the task, and (b) boys were more likely to succeed than girls. These findings shed light on how representational capacities change during the first year of life and are discussed in terms of information processing and representational capabilities as well as neuro‐anatomical development.     

The Cat is out of the Bag: The Joint Influence of Previous Experience and Looking Behavior on Infant Categorization

We examined the effect of 4‐month‐old infants' previous experience with dogs, cats, or both and their online looking behavior on their learning of the adult‐defined category of cat in a visual familiarization task. Four‐month‐old infants' (N = 123) learning in the laboratory was jointly determined by whether or not they had experience with pets at home and how much they shifted their gaze back and forth between the stimuli during familiarization. Specifically, only infants with pets at home who also exhibited high levels of switching during familiarization remembered the individual cat exemplars or formed a summary representation of those cats. These results are consistent with recent theorizing about the processes of how infants' categorical representations are formed, and provide new understanding into how infants' categorization unfolds over time.     

Frustration in Infancy: Implications for Emotion Regulation,Physiological Processes,and Temperament

A study sample of 162 six‐month‐old children was selected from a larger sample of 346 infants on the basis of parents' report of their infants' temperament and a laboratory assessment of temperament. Infants were classified as easily frustrated and less easily frustrated and compared on a number of emotion regulation, physiology, and temperament measures. Results indicated that male and female infants were equally likely to be classified as frustrated and less easily frustrated; however, male infants were less able to regulate physiologically. Easily frustrated infants used different emotion regulation strategies and were observed to be less attentive and more active than less easily frustrated infants when observed in the laboratory. These infants were also characterized by their parents as more active, less attentive, and more distressed to novelty. Infants classified as easily frustrated were more reactive physiologically and less able to regulate physiological reactivity than their less easily frustrated counterparts. It is hypothesized that this cluster of characteristics may constitute a unique temperamental type that may have implications for other types of behavioral functioning. Limitations of the study are that observations are based on a single brief assessment of the infant, modest effect sizes were found, and the study is cross‐sectional.     

Infants' Visual Recognition of Pincer Grip Emerges Between 9 and 12 Months of Age

The development of the ability to recognize the whole human body shape has long been investigated in infants, while less is known about their ability to recognize the shape of single body parts, and in particular their biomechanical constraints. This study aimed to explore whether 9‐ and 12‐month‐old infants have knowledge of a hand‐grasping movement (i.e., pincer grip), being able to recognize violations of the hand's anatomical constraints during the observation of that movement. Using a preferential looking paradigm, we showed that 12‐month‐olds discriminate between biomechanically possible and impossible pincer grips, preferring the former over the latter (Experiment 1). This capacity begins to emerge by 9 months of age, modulated by infants' own sensorimotor experience with pincer grip (Experiment 2). Our findings indicate that the ability to visually discriminate between pincer grasps differing in their biomechanical properties develops between 9 and 12 months of age, and that experience with self‐produced hand movements might help infants in building a representation of the hand that encompasses knowledge of the physical constraints of this body part.     

Infants' Behavioral Strategies for Emotion Regulation With Fathers and Mothers: Associations With Emotional Expressions and Attachment Quality

This study examined 12‐ and 13‐month‐old infants' behavioral strategies for emotion regulation, emotional expressions, regulatory styles, and attachment quality with fathers and mothers. Eighty‐five infants participated in the Strange Situation procedure to assess attachment quality with mothers and fathers. Infants' behavioral strategies for emotion regulation were examined with each parent during a competing demands task. Emotion regulation styles were meaningfully related to infant‐father attachment quality. Although expressions of distress and positive affect were not consistent across mothers and fathers, there was consistency in infant strategy use, emotion regulation style, and attachment quality with mothers and fathers. Furthermore, infants who were securely attached to both parents showed greater consistency in parent‐oriented strategies than infants who were insecurely attached to one or both parents. Limitations of this study include the constrained laboratory setting, potential carryover effects, and a homogeneous, middle‐class sample.