Children plan manual actions similarly in structured tasks and in free play.

Visually guided planning is fundamental for manual actions on objects. Multi-step planning-when only the requirements for the initial action are directly visible in the scene-necessitates initial visual guidance to optimize the subsequent actions. We found that 3- to 5-year-old children (n = 23) who exhibited visually guided, multi-step planning in a structured tool-use task (hammering down a peg) also demonstrated visually guided planning during unstructured free play while interlocking Duplo bricks and Squigz pieces.

What we don't know about what babies know: Reconsidering psychophysics, exploration, and infant behavior.

Researchers must infer "what babies know" based on what babies do. Thus, to maximize information from doing, researchers should use tasks and tools that capture the richness of infants' behaviors. We clarify Gibson's views about the richness of infants' behavior and their exploration in the service of guiding action - what Gibson called "learning about affordances.

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.

Self-recognition: From touching the body to knowing the self.

Recognizing oneself in a mirror is a classic test of self-concept. A new study has revealed the perceptual-motor foundations of conceptual self-knowledge: infants' success in the mirror test was accelerated after touching a tactile stimulus while viewing themselves in a mirror.

Comparing apples to manzanas and oranges to naranjas: A new measure of English-Spanish vocabulary for dual language learners.

The valid assessment of vocabulary development in dual-language-learning infants is critical to developmental science. We developed the Dual Language Learners English-Spanish (DLL-ES) Inventories to measure vocabularies of U.S.

How mothers help children learn to use everyday objects.

Children must learn specific motor actions to use everyday objects as their designers intended. However, designed actions are not obvious to children and often are difficult to implement. Children must know what actions to do and how to execute them.

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.

Pitfall or pratfall? Behavioral differences in infant learning from falling.

Researchers routinely infer learning and other unobservable psychological functions based on observable behavior. But what behavioral changes constitute evidence of learning? The standard approach is to infer learning based on a single behavior across individuals, including assumptions about the direction and magnitude of change (e.g.

Performance variability and affordance perception: practice effects on perceptual judgments for walking versus throwing.

To judge whether an action is possible, people must perceive "affordances"-the fit between features of the environment and aspects of their own bodies and motor skills that make the action possible or not. But for some actions, performance is inherently variable. That is, people cannot consistently perform the same action under the same environmental conditions with the same level of success.

Learning to Move in a Changing Body in a Changing World.

Infants of all species learn to move in the midst of tremendous variability and rapid developmental change. Traditionally, researchers consider variability to be a problem for development and skill acquisition. Here, we argue for a reconsideration of variability in early life, taking a developmental, ecological, systems approach.

"Go, go, go!" Mothers' verbs align with infants' locomotion.

Caregivers often tailor their language to infants' ongoing actions (e.g., "are you stacking the blocks?").

Gahvora cradling in Tajikistan: Cultural practices and associations with motor development.

In Tajikistan, infants are bound supine in a "gahvora" cradle that severely restricts movement. Does cradling affect motor development and body growth? In three studies (2013-2018), we investigated associations between time in the gahvora (within days and across age) and motor skills and flattened head dimensions in 8-24-month-old Tajik infants (N = 269, 133 girls, 136 boys)) and 4.3-5.

Protracted development of motor cortex constrains rich interpretations of infant cognition.

Cognition in preverbal human infants must be inferred from overt motor behaviors such as gaze shifts, head turns, or reaching for objects. However, infant mammals - including human infants - show protracted postnatal development of cortical motor outflow. Cortical control of eye, face, head, and limb movements is absent at birth and slowly emerges over the first postnatal year and beyond.

Autism: The face value of eye contact.

Inattention to faces in clinical assessments is a robust marker for autism. However, a new study distinguishes diagnostic marker from behavioral mechanism, showing that face looking in everyday activity is equally rare in autistic and neurotypical children and not required for joint attention in either group.

The process of learning the designed actions of toys.

Many everyday objects require "hidden" affordances to use as designed (e.g., twist open a water bottle).

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.

Flexibility in action: Development of locomotion under overhead barriers.

Behavioral flexibility-the ability to tailor motor actions to changing body-environment relations-is critical for functional movement. Navigating the everyday environment requires the ability to generate a wide repertoire of actions, select the appropriate action for the current situation, and implement it quickly and accurately. We used a new, adjustable barrier paradigm to assess flexibility of motor actions in 20 17-month-old (eight girls, 12 boys) and 14 13-month-old (seven girls, eight boys) walking infants and a comparative sample of 14 adults (eight women, six men).

Mothers talk about infants' actions: How verbs correspond to infants' real-time behavior.

Infants learn nouns during object-naming events-moments when caregivers name the object of infants' play (e.g., ball as infant holds a ball).

Real-time processes in the development of action planning.

Across species and ages, planning multi-step actions is a hallmark of intelligence and critical for survival. Traditionally, researchers adopt a "top-down" approach to action planning by focusing on the ability to create an internal representation of the world that guides the next step in a multi-step action. However, a top-down approach does not inform on underlying mechanisms, so researchers can only speculate about how and why improvements in planning occur.

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.

(Hyper)active Data Curation: A Video Case Study from Behavioral Science.

Video data are uniquely suited for research reuse and for documenting research methods and findings. However, curation of video data is a serious hurdle for researchers in the social and behavioral sciences, where behavioral video data are obtained session by session and data sharing is not the norm. To eliminate the onerous burden of curation at the time of publication (or later), we describe best practices in data curation-where data are curated and uploaded immediately after each data collection to allow instantaneous sharing with one button press at any time.