Faculty Bibliography

Infants learn nouns during object-naming events-moments when caregivers name the object of infants' play (e.g., ball as infant holds a ball). Do caregivers also label the actions of infants' play (e.g., roll as infant rolls a ball)? We investigated connections between mothers' verb inputs and infants' actions. We video-recorded 32 infant-mother dyads for 2 hr at home (13 month olds, n = 16; 18 month olds, n = 16; girls, n = 16; White, n = 23; Asian, n = 2; Black, n = 1; other, n = 1; multiple races, n = 5; Hispanic/Latinx, n = 2). Dyads were predominantly from middle-class to upper middle-class households. We identified each manual verb (e.g., press, shake) and whole-body verb (e.g., kick, go) that mothers directed to infants. We coded whether infants displayed manual and/or whole-body actions during a 6-s window surrounding the verb (i.e., 3 s prior and 3 s after the named verb). Mothers' verbs and infant actions were largely congruent: Whole-body verbs co-occurred with whole-body actions, and manual verbs co-occurred with manual actions. Moreover, half of mothers' verbs corresponded precisely to infants' concurrent action (e.g., infant pressed button as mother said, "Press the button"). In most instances, mothers commented on rather than instigated infants' actions. Findings suggest that verb learning is embodied, such that infants' motor actions offer powerful cues to verb meanings. Furthermore, our approach highlights the value of cross-domain research integrating infants' developing motor and language skills to understand word learning. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

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. The current study takes a "bottom-up" approach by testing developmental changes in the real-time, moment-to-moment interplay among perceptual, neural, and motor components of action planning using simultaneous video, motion-tracking, head-mounted eye tracking, and electroencephalography (EEG). Preschoolers (n = 32) and adults (n = 22) grasped a hammer with their dominant hand to pound a peg when the hammer handle pointed in different directions. When the handle pointed toward their non-dominant hand, younger children ("nonadaptive planners") used a habitual overhand grip that interfered with wielding the hammer, whereas adults and older children ("adaptive planners") used an adaptive underhand grip. Adaptive and nonadaptive children differed in when and where they directed their gaze to obtain visual information, neural activation of the motor system before reaching, and straightness of their reach trajectories. Nonadaptive children immediately used a habitual overhand grip before gathering visual information, leaving insufficient time to form a plan before acting. Our novel bottom-up approach transcends mere speculation by providing converging evidence that the development of action planning depends on a real-time "tug of war" between habits and information gathering and processing.

Object play yields enormous benefits for infant development. However, little is known about natural play at home where most object interactions occur. We conducted frame-by-frame video analyses of spontaneous activity in two 2-h home visits with 13-month-old crawling infants and 13-, 18-, and 23-month-old walking infants (N = 40; 21 boys; 75% White). Regardless of age, for every infant and time scale, across 10,015 object bouts, object interactions were short (median = 9.8 s) and varied (transitions among dozens of toys and non-toys) but consumed most of infants' time. We suggest that infant exuberant object play-immense amounts of brief, time-distributed, variable interactions with objects-may be conducive to learning object properties and functions, motor skill acquisition, and growth in cognitive, social, and language domains.

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.

Observation is a powerful way to learn efficient actions from others. However, the role of observers' motor skill in assessing efficiency of others is unknown. Preschoolers are notoriously poor at performing multi-step actions like grasping the handle of a tool. Preschoolers (N = 22) and adults (N = 22) watched video-recorded actors perform efficient and inefficient tool use. Eye tracking showed that preschoolers and adults looked equally long at the videos, but adults looked longer than children at how actors grasped the tool. Deep learning analyses of participants' eye gaze distinguished efficient from inefficient grasps for adults, but not for children. Moreover, only adults showed differential action-related pupil dilation and neural activity (suppressed oscillation power in the mu frequency) while observing efficient vs. inefficient grasps. Thus, children observe multi-step actions without "seeing" whether the initial step is efficient. Findings suggest that observer's own motor efficiency determines whether they can perceive action efficiency in others.

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.

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.

The everyday world is populated with artifacts that require specific motor actions to use objects as their designers intended. But researchers know little about how children learn to use everyday artifacts. We encouraged forty-four 12- to 60-month-old children to unzip a vinyl pouch during a single 60-s trial. Although unzipping a pouch may seem simple, it is not. Unzipping requires precise role-differentiated bimanual actions-one hand must stabilize the pouch while the other hand applies a pulling force on the tab. Moreover, kinematic data from six adults showed that the tolerance limits for applying the forces are relatively narrow (pulling the tab within 63° of the zipper teeth while stabilizing the pouch within 4 cm of the slider). Children showed an age-related progression for the unzipping action. The youngest children did not display the designed pulling action; children at intermediate ages pulled the tab but applied forces outside the tolerance limits (pulled in the wrong direction, failed to stabilize the pouch in the correct location), and the oldest children successfully implemented the designed action. Findings highlight the perceptual-motor requirements in children's discovery and implementation of the hidden affordances of everyday artifacts.