Variations in infants' physical and social environments shape spontaneous locomotion.

Independent locomotion is associated with a range of positive developmental outcomes, but unlike cognitive, linguistic, and social skills, acquiring motor skills requires infants to generate their own input for learning. We tested factors that shape infants' spontaneous locomotion by observing forty 12- to 22-month-olds (19 girls, 21 boys) during free play. Infants were recruited from the New York City area, and caregivers reported that 25 infants were White, six were Asian, four were Black, and five had multiple races; four were Hispanic or Latino. All infants played in four conditions: two environmental conditions (gross-motor toys, fine-motor toys) crossed with two social conditions (alone, together with a caregiver). Infants moved more in the gross-motor toy conditions than in the fine-motor toy conditions. However, the effect of playing with a caregiver differed by toy condition. In the gross-motor toy conditions, playing with a caregiver did not affect how much infants moved, but in the fine-motor toy conditions, playing with a caregiver further depressed infant locomotion. Infants with more walking experience moved more with gross-motor toys but not with fine-motor toys. Differences in the amount of locomotion between conditions were related to how infants used toys and the interactions between infants and caregivers. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Walking and falling: Using robot simulations to model the role of errors in infant walking.

What is the optimal penalty for errors in infant skill learning? Behavioral analyses indicate that errors are frequent but trivial as infants acquire foundational skills. In learning to walk, for example, falling is commonplace but appears to incur only a negligible penalty. Behavioral data, however, cannot reveal whether a low penalty for falling is beneficial for learning to walk. Here, we used a simulated bipedal robot as an embodied model to test the optimal penalty for errors in learning to walk. We trained the robot to walk using 12,500 independent simulations on walking paths produced by infants during free play and systematically varied the penalty for falling-a level of precision, control, and magnitude impossible with real infants. When trained with lower penalties for falling, the robot learned to walk farther and better on familiar, trained paths and better generalized its learning to novel, untrained paths. Indeed, zero penalty for errors led to the best performance for both learning and generalization. Moreover, the beneficial effects of a low penalty were stronger for generalization than for learning. Robot simulations corroborate prior behavioral data and suggest that a low penalty for errors helps infants learn foundational skills (e.g., walking, talking, and social interactions) that require immense flexibility, creativity, and adaptability. RESEARCH HIGHLIGHTS: During infant skill acquisition, errors are commonplace but appear to incur a low penalty; when learning to walk, for example, falls are frequent but trivial. To test the optimal penalty for errors, we trained a simulated robot to walk using real infant paths and systematically manipulated the penalty for falling. Lower penalties in training led to better performance on familiar, trained paths and on novel untrained paths, and zero penalty was most beneficial. Benefits of a low penalty were stronger for untrained than for trained paths, suggesting that discounting errors facilitates acquiring skills that require immense flexibility and generalization.

From description to generalization, or there and back again.

In his target article, Yarkoni prescribes descriptive research as a potential antidote for the generalizability crisis. In our commentary, we offer four guiding principles for conducting descriptive research that is generalizable and enduring: (1) prioritize context over control; (2) let naturalistic observations contextualize structured tasks; (3) operationalize the target phenomena rigorously and transparently; and (4) attend to individual data.

Practice and proficiency: Factors that facilitate infant walking skill.

Infant walking skill improves with practice-crudely estimated by elapsed time since walk onset. However, despite the robust relation between elapsed time (months walking) and skill, practice is likely constrained and facilitated by infants' home environments, sociodemographic influences, and spontaneous activity. Individual pathways are tremendously diverse in the timing of walk onset and the trajectory of improvement, and presumably, in the amount and type of practice. So, what factors affect the development of walking skill? We examined the role of months walking, walk onset age, spontaneous locomotor activity, body dimensions, and environmental factors on the development of walking skill in two sociodemographically distinct samples (ns = 38 and 44) of 13-, 15-, and 19-month-old infants. Months walking best predicted how well infants walked, but environmental factors and spontaneous activity explained additional variance in walking skill. Specifically, less crowded homes, a larger percentage of time in spontaneous walking, and a smaller percentage of short walking bouts predicted more mature walking. Walk onset age differed by sample but did not affect walking skill. Findings indicate that elapsed time since walk onset remains a robust predictor of walking skill, but environmental factors and spontaneous activity also contribute to infants' practice, thereby affecting walking skill.

"Dancing" Together: Infant-Mother Locomotor Synchrony.

Pre-mobile infants and caregivers spontaneously engage in a sequence of contingent facial expressions and vocalizations that researchers have referred to as a social "dance." Does this dance continue when both partners are free to move across the floor? Locomotor synchrony was assessed in 13- to 19-month-old infant-mother dyads (N = 30) by tracking each partner's step-to-step location during free play. Although infants moved more than mothers, dyads spontaneously synchronized their locomotor activity. For 27 dyads, the spatiotemporal path of one partner uniquely identified the path of the other. Clustering analyses revealed two patterns of synchrony (mother-follow and yo-yo), and infants were more likely than mothers to lead the dance. Like face-to-face synchrony, locomotor synchrony scaffolds infants' interactions with the outside world.

Modeling Infant Free Play Using Hidden Markov Models.

Infants' free-play behavior is highly variable. However, in developmental science, traditional analysis tools for modeling and understanding variable behavior are limited. Here, we used Hidden Markov Models (HMMs) to capture behavioral states that govern infants' toy selection during 20 minutes of free play in a new environment. We demonstrate that applying HMMs to infant data can identify hidden behavioral states and thereby reveal the underlying structure of infant toy selection and how toy selection changes in real time during spontaneous free play. More broadly, we propose that hidden-state models provide a fruitful avenue for understanding individual differences in spontaneous infant behavior.

The Importance of Motor Skills for Development.

Motor skills are important for development. Everything infants do involves motor skills - postural, locomotor, and manual actions; exploratory actions; social interactions; and actions with artifacts. Put another way, all behavior is motor behavior, and thus motor skill acquisition is synonymous with behavioral development. Age norms for basic motor skills provide useful diagnostics for "typical" development, but cultural differences in child-rearing practices influence skill onset ages. Whenever they emerge, motor skills lay the foundation for development by opening up new opportunities for learning. Postural control brings new parts of the environment into view and into reach; locomotion makes the larger world accessible; manual skills promote new forms of interactions with objects; and motor skills involving every part of the body enhance opportunities for social interaction. Thus, motor skills can instigate a cascade of developments in domains far afield from motor behavior - perception and cognition, language and communication, emotional expression and regulation, physical growth and health, and so on. Finally, motor skill acquisition makes behavior increasingly functional and flexible. Infants learn to tailor behavior to variations in their body and environment and to discover or construct new means to achieve their goals.

Where Infants Go: Real-Time Dynamics of Locomotor Exploration in Crawling and Walking Infants.

Where do infants go? A longstanding assumption is that infants primarily crawl or walk to reach destinations viewed while stationary. However, many bouts of spontaneous locomotion do not end at new people, places, or things. Study 1 showed that half of 10- and 13-month-old crawlers' (N = 29) bouts end at destinations-more than previously found with walkers. Study 2 confirmed that, although infants do not commonly go to destinations, 12-month-old crawlers go to proportionally more destinations than age-matched walkers (N = 16). Head-mounted eye tracking revealed that crawlers and walkers mostly take steps in place while fixating something within reach. When infants do go to a destination, they take straight, short paths to a target fixated while stationary.

Motor Development: Embodied, Embedded, Enculturated, and Enabling.

Motor development and psychological development are fundamentally related, but researchers typically consider them separately. In this review, we present four key features of infant motor development and show that motor skill acquisition both requires and reflects basic psychological functions. ( a) Motor development is embodied: Opportunities for action depend on the current status of the body. ( b) Motor development is embedded: Variations in the environment create and constrain possibilities for action. ( c) Motor development is enculturated: Social and cultural influences shape motor behaviors. ( d) Motor development is enabling: New motor skills create new opportunities for exploration and learning that instigate cascades of development across diverse psychological domains. For each of these key features, we show that changes in infants' bodies, environments, and experiences entail behavioral flexibility and are thus essential to psychology. Moreover, we suggest that motor development is an ideal model system for the study of psychological development.

It's the journey, not the destination: Locomotor exploration in infants.

What incites infant locomotion? Recent research suggests that locomotor exploration is not primarily directed toward distant people, places, or things. However, this question has not been addressed experimentally. In the current study, we asked whether a room filled with toys designed to encourage locomotion (stroller, ball, etc.) elicits different quantities or patterns of exploration than a room with no toys. Caregivers were present but did not interact with infants. Although most walking bouts in the toy-filled room involved toys, to our surprise, 15-month-olds in both rooms produced the same quantity of locomotion. This finding suggests that mere space to move is sufficient to elicit locomotion. However, infants' patterns of locomotor exploration differed: Infants in the toy-filled room spent a smaller percent of the session within arms' reach of their caregiver and explored more locations in the room. Real-time analyses show that infants in the toy-filled room took an increasing number of steps per bout and covered more area as the session continued, whereas infants in the no-toy room took fewer and fewer steps per bout and traveled repeatedly over the same ground. Although not required to elicit locomotion, moving with toys encouraged infants to travel farther from their caregivers and to explore new areas.

Development (of Walking): 15 Suggestions.

Although a fundamental goal of developmental science is to identify general processes of change, developmental scientists rarely generalize beyond their specific content domains. As a first step toward a more unified approach to development, we offer 15 suggestions gleaned from a century of research on infant walking. These suggestions collectively address the multi-leveled nature of change processes, cascades of real-time and developmental events, the diversity of developmental trajectories, inter- and intraindividual variability, starting and ending points of development, the natural input for learning, and the roles of body, environment, and sociocultural context. We argue that these 15 suggestions are not limited to motor development, and we encourage researchers to consider them within their own areas of research.

Variety Wins: Soccer-Playing Robots and Infant Walking.

Although both infancy and artificial intelligence (AI) researchers are interested in developing systems that produce adaptive, functional behavior, the two disciplines rarely capitalize on their complementary expertise. Here, we used soccer-playing robots to test a central question about the development of infant walking. During natural activity, infants' locomotor paths are immensely varied. They walk along curved, multi-directional paths with frequent starts and stops. Is the variability observed in spontaneous infant walking a "feature" or a "bug?" In other words, is variability beneficial for functional walking performance? To address this question, we trained soccer-playing robots on walking paths generated by infants during free play and tested them in simulated games of "RoboCup." In Tournament 1, we compared the functional performance of a simulated robot soccer team trained on infants' natural paths with teams trained on less varied, geometric paths-straight lines, circles, and squares. Across 1,000 head-to-head simulated soccer matches, the infant-trained team consistently beat all teams trained with less varied walking paths. In Tournament 2, we compared teams trained on different clusters of infant walking paths. The team trained with the most varied combination of path shape, step direction, number of steps, and number of starts and stops outperformed teams trained with less varied paths. This evidence indicates that variety is a crucial feature supporting functional walking performance. More generally, we propose that robotics provides a fruitful avenue for testing hypotheses about infant development; reciprocally, observations of infant behavior may inform research on artificial intelligence.

Can the identity of a behavior setting be perceived through patterns of joint action? An investigation of place perception.

"Behavior settings" are generated by joint actions of individuals in conjunction with the milieu features (or affordances) that are available. The reported research explores the hypothesis that the identity or meaning of a behavior setting can be perceived by means of the patterns of action collectively generated by the setting's participants. A set of computer animations was created based on detailed observation of activities in everyday settings. Three experiments were conducted to assess whether perceivers could extract "structure from motion" (in this case, collective actions) that was specific to the particular behavior setting displayed by way of the animations. Two experiments assessed whether individuals could accurately perceive the identity of the behavior settings with such displays, and a third experiment indirectly examined this possibility by evaluating whether setting possibilities and constraints were recognized. The results offered some support for the hypothesis, and suggested several refinements in how to conceptualize a typology of behavior settings. An ecological approach to place perception is also discussed.