Why does infant stepping disappear and can it be stimulated by optic flow?

Two independent experiments (n = 22 and n = 22) showed that 2-month-old infants displayed significantly more stepping movements when supported upright in the air than when supported with their feet contacting a surface. Air- and surface-stepping kinematics were quite similar (Experiment 2). In addition, when data were collapsed across both experiments, more air steps and more donkey kicks were seen when infants were exposed to optic flows that specified backward compared to forward translation. The findings challenge the currently accepted heavy legs explanation for the disappearance of stepping at 2 months of age and raise new questions about the visual control of stepping.

Air stepping in response to optic flows that move Toward and Away from the neonate.

To shed further light on the perceptual regulation of newborn stepping, we compared neonatal air stepping in response to optic flows simulating forward or backward displacement with stepping forward on a surface. Twenty-two 3-day-olds performed four 60 s trials in which they stepped forward on a table (Tactile) or in the air in response to a pattern that moved toward (Toward) or away (Away) from them or was static (Static). Significantly more steps were taken in the Tactile and Toward conditions than the Static condition. The Away condition was intermediate to the other conditions. The knee joint activity across the entire trial was significantly greater in the Toward than the Away condition. Within-limb kinematics and between-limb coordination were very similar for steps taken in the air and on the table, particularly in the Toward and Tactile conditions. These findings highlight that visual and tactile stimulation can equally elicit neonatal stepping.

The epigenesis of wariness of heights.

Human infants with little or no crawling experience surprisingly show no wariness of heights, but such wariness becomes exceptionally strong over the life span. Neither depth perception nor falling experiences explain this extraordinary developmental shift; however, something about locomotor experience does. The crucial component of locomotor experience in this emotional change is developments in visual proprioception-the optically based perception of self-movement. Precrawling infants randomly assigned to drive a powered mobility device showed significantly greater visual proprioception, and significantly greater wariness of heights, than did controls. More important, visual proprioception mediated the relation between wariness of heights and locomotor experience. In a separate study, crawling infants' visual proprioception predicted whether they would descend onto the deep side of a visual cliff, a finding that confirms the importance of visual proprioception in the development of wariness of heights.

Domain differences in early social interactions.

Different social experiences help children develop distinctions between domains of norms. This study investigated whether mothers respond differently to moral, prudential, and pragmatic norms during the 2nd year, a period that precedes the time when children are able to make explicit distinctions between these norms. Sixty mothers of infants between 11 and 23 months were interviewed. Mothers' reports of their initial interventions, changes in intervention following noncompliance, and emotional reactions depended on normative domain. Initial interventions were less differentiated by domain for mothers of older than for mothers of younger children. These findings suggest that children have social experiences in the 2nd year that are associated with distinctions among normative domains.

Neonatal stepping in relation to terrestrial optic flow.

This experiment examined whether newborn stepping, a primitive form of bipedal locomotion, could be modulated by optical flow. Forty-eight 3-day-old infants were exposed to optical flows that were projected onto a horizontal surface above which the infants were suspended. Significantly more air steps were elicited by exposure to a terrestrial optical flow specifying forward translation than by a rotating optical flow or a static optical pattern. Thus, a rudimentary coupling between optical flow and stepping is present at birth, suggesting a precocious capacity in the newborn to perceive and utilize visual information specifying self-motion. The findings may help the early diagnosis of infants with visual or visual-motor deficits and the development of visually based interventions for disabled infants.

Do Balance Demands Induce Shifts in Visual Proprioception in Crawling Infants?

The onset of hands-and-knees crawling during the latter half of the first year of life heralds pervasive changes in a range of psychological functions. Chief among these changes is a clear shift in visual proprioception, evident in the way infants use patterns of optic flow in the peripheral field of view to regulate their postural sway. This shift is thought to result from consistent exposure in the newly crawling infant to different patterns of optic flow in the central field of view and the periphery and the need to concurrently process information about self-movement, particularly postural sway, and the environmental layout during crawling. Researchers have hypothesized that the demands on the infant's visual system to concurrently process information about self-movement and the environment press the infant to differentiate and functionalize peripheral optic flow for the control of balance during locomotion so that the central field of view is freed to engage in steering and monitoring the surface and potentially other tasks. In the current experiment, we tested whether belly crawling, a mode of locomotion that places negligible demands on the control of balance, leads to the same changes in the functional utilization of peripheral optic flow for the control of postural sway as hands-and-knees crawling. We hypothesized that hands-and-knees crawlers (n = 15) would show significantly higher postural responsiveness to movements of the side walls and ceiling of a moving room than same-aged pre-crawlers (n = 19) and belly crawlers (n = 15) with an equivalent amount of crawling experience. Planned comparisons confirmed the hypothesis. Visual-postural coupling in the hands-and-knees crawlers was significantly higher than in the belly crawlers and pre-crawlers. These findings suggest that the balance demands associated with hands-and-knees crawling may be an important contributor to the changes in visual proprioception that have been demonstrated in several experiments to follow hands-and-knees crawling experience. However, we also consider that belly crawling may have less potent effects on visual proprioception because it is an effortful and attention-demanding mode of locomotion, thus leaving less attentional capacity available to notice changing relations between the self and the environment.

Rediscovering development in infancy.

This commentary endorses J. Kagan's (2008) conclusion that many of the most dramatic findings on early perceptual, cognitive, and social competencies are ambiguous. It supports his call for converging research operations to disambiguate findings from single paradigms and single response indices. The commentary also argues that early competencies must be placed into a longitudinal framework, thereby allowing researchers to (a) identify whether regressive phenomena play a role in skill development, (b) understand what functions (if any) given skills play in their precocious manifestations and whether these functions are comparable in later instantiations of skills, and (c) avoid rich interpretations by identifying how robust a suspected competency is across contexts.

Locomotor experience affects self and emotion.

Two studies investigated the role of locomotor experience on visual proprioception in 8-month-old infants. Visual proprioception refers to the sense of self-motion induced in a static person by patterns of optic flow. A moving room apparatus permitted displacement of an entire enclosure (except for the floor) or the side walls and ceiling. In Study 1, creeping infants and prelocomotor/walker infants showed significantly greater postural compensation and emotional responses to side wall movement than did same-age prelocomotor infants. Study 2 used true random assignment of prelocomotor infants to locomotor-training (via a powered-mobility device) and no-training conditions. Experimental infants showed powerful effects of locomotor training. These results imply that locomotor experience is playing a causal role in the ontogeny of visual proprioception.

Infant differential behavioral responding to discrete emotions.

Emotional communication regulates the behaviors of social partners. Research on individuals' responding to others' emotions typically compares responses to a single negative emotion compared with responses to a neutral or positive emotion. Furthermore, coding of such responses routinely measure surface level features of the behavior (e.g., approach vs. avoidance) rather than its underlying function (e.g., the goal of the approach or avoidant behavior). This investigation examined infants' responding to others' emotional displays across 5 discrete emotions: joy, sadness, fear, anger, and disgust. Specifically, 16-, 19-, and 24-month-old infants observed an adult communicate a discrete emotion toward a stimulus during a naturalistic interaction. Infants' responses were coded to capture the function of their behaviors (e.g., exploration, prosocial behavior, and security seeking). The results revealed a number of instances indicating that infants use different functional behaviors in response to discrete emotions. Differences in behaviors across emotions were clearest in the 24-month-old infants, though younger infants also demonstrated some differential use of behaviors in response to discrete emotions. This is the first comprehensive study to identify differences in how infants respond with goal-directed behaviors to discrete emotions. Additionally, the inclusion of a function-based coding scheme and interpersonal paradigms may be informative for future emotion research with children and adults. Possible developmental accounts for the observed behaviors and the benefits of coding techniques emphasizing the function of social behavior over their form are discussed. (PsycINFO Database Record

Responsiveness to terrestrial optic flow in infancy: does locomotor experience play a role?

Human infants show a peak in postural compensation to optic flow at approximately nine months of age. The current experiment tested whether the magnitude of visual-postural coupling in 9-month-olds increases when terrestrial optic flow is added to a moving room. A secondary objective was to explore whether locomotor experience plays any role in enhancing responsiveness to the additional terrestrial information. Ninety-one infants (experienced creepers, nascent creepers, and prelocomotors) were exposed to two conditions of optic flow: global optic flow (G) and global optic flow minus terrestrial optic flow (G-T). The additional terrestrial optic flow led to significantly higher visual-postural coupling. Consistent with previous findings, locomotor experience had no effect on responsiveness to the G-T condition, though there was weak evidence that the nascent creepers were more strongly influenced by the difference between flow conditions than the other infants. Unexpectedly, the prelocomotor females showed significantly lower visual-postural coupling than the prelocomotor males. These findings support the notion that the ground provides an important source of information for the control of posture and locomotion. The findings also suggest that locomotor experience most likely helps to functionalize smaller (partial), rather than larger (global), optic flow fields for postural control.

Effects of support surface and optic flow on step-like movements in pre-crawling and crawling infants.

Step-like movements were examined in pre-crawling (n=9) and crawling (n=9) 6-13 month-old infants in the air and on a surface in response to a static pattern or optic flows that moved toward or away from the infant. Infants completed six 60-s trials. A significant interaction between locomotor status and support condition revealed that pre-crawling infants made more step-like movements in the air than on a rigid surface. In contrast, crawling infants made an equivalent number of step-like movements in the air and on the surface. Optic flow did not influence the number of step-like movements made by infants. The pre-crawling infant finding is consistent with a finding in a previous study in which two month-old infants were shown to step more in the air than on the ground. This finding is discussed relative to the idea that the infant stepping pattern disappears because the legs become too heavy to lift.

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.

A Darwinian legacy to understanding human infancy: emotional expressions as behavior regulators.

Darwin's influence on the study of emotional responding has largely centered on the study of the production of facial movement patterns. In this paper, we present evidence on the importance of considering facial and vocal patterns as signals that powerfully regulate behavior in infancy and early childhood. We review a series of studies showing that facial expressions and vocal expressions alone can regulate the behavior of infants and, in the case of vocal expressions, do so at ages earlier than most researchers have acknowledged. We also review studies on the enduring effects of social signals, documenting that even 8.5-month-olds show minimal retention of the effects of social signals, some 10-month-olds can retain the effects of social signals for 25 minutes, and 14-month-old can do so for a period of one hour after only two trials of signal exposure. Social signals not only regulate behavior, they also are part and parcel of an important and relatively unstudied phenomenon called affect sharing, which is evident by 11.5 months of age. Finally, we speculate on the constitutive role of social signals, especially those linked to what Ekman has called "basic emotions" in the generation of new emotions, such as pride, shame, and guilt.

Emotional facial expressions in European-American, Japanese, and Chinese infants.

Charles Darwin was among the first to recognize the important contribution that infant studies could make to our understanding of human emotional expression. Noting that infants come to exhibit many emotions, he also observed that at first their repertoire of expression is highly restricted. Today, considerable controversy exists regarding the question of whether infants experience and express discrete emotions. According to one position, discrete emotions emerge during infancy along with their prototypic facial expressions. These expressions closely resemble adult emotional expressions and are invariantly concordant with their corresponding emotions. In contrast, we propose that the relation between expression and emotion during infancy is more complex. Some infant emotions and emotional expressions may not be invariantly concordant. Furthermore, infant emotional expressions may be less differentiated than previously proposed. Together with past developmental studies, recent cross-cultural research supports this view and suggests that negative emotional expression in particular is only partly differentiated towards the end of the first year.

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.

Travel Broadens the Mind.

The onset of locomotion heralds one of the major life transitions in early development and involves a pervasive set of changes in perception, spatial cognition, and social and emotional development. Through a synthesis of published and hitherto unpublished findings, gathered from a number of converging research designs and methods, this article provides a comprehensive review and reanalysis of the consequences of self-produced locomotor experience. Specifically, we focus on the role of locomotor experience in changes in social and emotional development, referential gestural communication, wariness of heights, the perception of self-motion, distance perception, spatial search, and spatial coding strategies. Our analysis reveals new insights into the specific processes by which locomotor experience brings about psychological changes. We elaborate these processes and provide new predictions about previously unsuspected links between locomotor experience and psychological function. The research we describe is relevant to our broad understanding of the developmental process, particularly as it pertains to developmental transitions. Although acknowledging the role of genetically mediated developmental changes, our viewpoint is a transactional one in which a single acquisition, in this case the onset of locomotion, sets in motion a family of experiences and processes that in turn mobilize both broad-based and context-specific psychological reorganizations. We conclude that, in infancy, the onset of locomotor experience brings about widespread consequences, and after infancy, can be responsible for an enduring role in development by maintaining and updating existing skills.

The development of infant detection of inauthentic emotion.

Appreciating authentic and inauthentic emotional communication is central to the formation of trusting and intimate interpersonal relationships. However, when infants are able to discriminate and respond to inauthentic emotion has not been investigated. The present set of studies was designed to investigate infant sensitivity to 3 specific cues of inauthenticity: the contextual congruency of the emotion, the degree of exaggeration of the emotion, and the clarity with which the emotion is communicated. In each experiment, 16- and 19-month-old infants were presented with an emotional communication in which an inauthentic cue was present or absent. Infant behavioral responding to the emotional context was observed and coded. In all 3 experiments, 19-month-old infants, but not 16-month-old infants, detected inauthentic emotional communication and differentially responded to the environment accordingly. These findings demonstrate that infants do not simply take all emotional communication at face value and are sensitive to features of emotional contexts beyond what is expressively communicated by the adult. Possible developmental mechanisms that may account for the observed developmental shift in infant emotional development are proposed, and implications for the present findings on future research in emotion and emotional development are highlighted.

Infant language development is related to the acquisition of walking.

The present investigation explored the question of whether walking onset is related to infant language development. Study 1 used a longitudinal design (N = 44) to assess infant locomotor and language development every 2 weeks from 10 to 13.5 months of age. The acquisition of walking was associated with a significant increase in both receptive and productive language, independent of age. Study 2 used an age-held-constant study with 12.5-month-old infants (38 crawling infants; 37 walking infants) to further explore these findings. Results from Study 2 replicated the differences in infant language development between locomotor groups. Additionally, a naturalistic observation of parent-infant interactions (20 crawling dyads; 24 walking dyads) revealed that language development was predicted by multiple factors in the social environment, but only for walking infants. Possible explanations of the findings (e.g., social, cognitive, neurological) are discussed, and topics for future research are highlighted.

Mothers' tone of voice depends on the nature of infants' transgressions.

Emotional vocal signals are important ways of communicating norms to young infants. The second year is a period of increase in various forms of child transgressions, but also a period when infants have limited linguistic abilities. Two studies investigated the hypothesis that mothers respond with different vocal emotional tones to 3 types of child transgressions: moral (harming others), prudential (harming oneself), and pragmatic (creating inconvenience, e.g., by spilling) transgressions. We used a combination of naturalistic observation (Study 1) and experimental manipulation (Study 2) to record, code, and analyze maternal vocal responses to child transgressions. Both studies showed that mothers were more likely to use intense, angry vocalizations in response to moral transgressions, fearful vocalizations in response to prudential transgressions, comforting vocalizations in response to pragmatic and prudential transgressions, and (in Study 2) playful vocalizations in response to pragmatic transgressions. Study 1 showed that this differential use of vocal tone is used systematically in everyday life. Study 2 allowed us to standardize the context of the maternal intervention and perform additional acoustical analyses. A combination of principal component analysis and linear discriminant analysis applied to pitch and intensity data provided quantitative measures of the differences in vocal responses. These differentiated vocal responses are likely contributors to children's acquisition of norms from early in life.