Jeremy Isaac Borjon

Prosodic modifications in caregiver speech are related to infant attention, word learning, and long-term language development, yet how moment-to-moment caregiver prosody relates to infant attentional dynamics during naturalistic interaction remains unclear. Here, we used unsupervised learning to categorize 12,311 caregiver utterances produced during free play across the second year of life (12-24 months) into four prosodic contour types: fall, hill, rise, and valley. Infant visual attention was measured using head-mounted eye-tracking. Proportions of contour types were stable from 12 to 24 months. Despite this stability, specific contours were temporally coordinated with the onset and offset of infant sustained visual attention (SVA). Rise contours coincided with the initiation of SVA in older infants, beginning approximately one second before onset, and valley contours coincided with the period following SVA offset in both age groups. At the dyad level, two patterns emerged. Caregivers who produced higher levels of vocalizations that coincided with the onset or offset of SVA had infants with more SVA episodes and total SVA time overall. Further, caregivers who exhibited a specific prosodic pattern in the two seconds following SVA disengagement, a fall contour in the first second and a valley contour in the following second, had infants with longer average SVA episodes. These results dissociate two facets of dyadic temporal coordination: a broad association between caregiver prosody and the quantity of SVA episodes, and a specific post-disengagement prosodic pattern linked to the duration of SVA.

As developmental science expands globally, its theories and methods must rise to the challenge. Children worldwide develop within caregiving ecologies that often differ from traditional family models. Understanding how infants adapt within these contexts reveals general principles of human development. Achieving this requires structural change: consensus-building, open methods, and theories grounded in the environments where most children actually grow up.

The MacArthur-Bates Communicative Development Inventories (CDIs) are widely used parent-report tools for assessing early language development, including gesture use, expressive and receptive vocabulary, and early morpho-syntactic capacities. While originally developed for typically developing children aged 8 up to 36 months and aimed at detecting developmental language disorder, CDIs have been increasingly applied in studies of neurodevelopmental and genetic conditions, where language development often diverges from typical trajectories. In this review, we synthesize recent literature on the use of CDIs in a range of clinical populations, including autism, Down syndrome, Williams syndrome, cerebral palsy, Angelman syndrome, DDX3X syndrome, 5p deletion syndrome, fragile X syndrome, and others. We highlight condition-specific patterns of expressive vocabulary development, discuss the value of longitudinal data collection using CDIs, and visualize age trends that capture change and variability across developmental pathways. Particular attention is given to methodological considerations such as cross-linguistic adaptations, reporting biases, and the limitations of single-timepoint assessments. While CDIs show promise for tracking language trajectories and informing early support, especially in under-resourced or culturally diverse contexts, challenges remain in ensuring their reliability, validity, and suitability as screening tools. We conclude by emphasizing the importance of longitudinal, cross-condition, and cross-cultural approaches to better understand atypical language development and to improve the utility of CDIs in both research and applied settings.

For human infants, producing recognizable speech is more than a cognitive process. It is a motor skill that requires infants to learn to coordinate multiple muscles of varying functions across their body. This coordination is directly linked to ongoing fluctuations in heart rate; a physiological process that can scaffold behavior. We investigated whether ongoing fluctuations in heart rate coincide with vocal production and word formation in 24-mo-old infants. Infants were most likely to produce a vocalization when heart rate fluctuations reached a peak (local maximum) or trough (local minimum). Vocalizations produced at the peak were longer than expected by chance. Functionally, vocalizations produced just before the trough, while heart rate is decelerating, were more likely to be recognized as a word by naive listeners. Thus, for the developing infant, heart rate fluctuations align with the timing of vocal productions and are associated with their duration and the likelihood of producing recognizable speech. Our results have broad and immediate implications for understanding normative language development, the evolutionary basis and physiological process of vocal production, and potential early indicators of speech and communication disorders.

Producing recognizable words is a difficult motor task; a one‐syllable word can require the coordination of over 80 muscles. Thus, it is not surprising that the development of word productions in infancy lags considerably behind receptive language and is a known limiting factor in language development. A large literature has focused on the vocal apparatus, its articulators, and language development. There has been limited study of the relations between non‐speech motor skills and the quality of early speech productions. Here we present evidence that the spontaneous vocalizations of 9‐ to 24‐month‐old infants recruit extraneous, synergistic co‐activations of hand and head movements and that the temporal precision of the co‐activation of vocal and extraneous muscle groups tightens with age and improved recognizability of speech. These results implicate an interaction between the muscle groups that produce speech and other body movements and provide new empirical pathways for understanding the role of motor development in language acquisition.Research Highlights: The spontaneous vocalizations of 9‐ to 24‐month‐old infants recruit extraneous, synergistic co‐activations of hand and head movements. The temporal precision of these hand and head movements during vocal production tighten with age and improved speech recognition. These results implicate an interaction between the muscle groups producing speech with other body movements. These results provide new empirical pathways for understanding the role of motor development in language acquisition.

This study demonstrates evidence for a foundational process underlying active vision in older infants during object play. Using head-mounted eye-tracking and motion capture, looks to an object are shown to be tightly linked to and synchronous with a stilled head, regardless of the duration of gaze, for infants 12 to 24 months of age. Despite being a developmental period of rapid and marked changes in motor abilities, the dynamic coordination of head stabilization and sustained gaze to a visual target is developmentally invariant during the examined age range. The findings indicate that looking with an aligned head and eyes is a fundamental property of human vision and highlights the importance of studying looking behavior in freely moving perceivers in everyday contexts, opening new questions about the role of body movement in both typical and atypical development of visual attention.

Infant behavior, like all behavior, is the aggregate product of many nested processes operating and interacting over multiple time scales; the result of a tangle of inter-related causes and effects. Efforts in identifying the mechanisms supporting infant behavior require the development and advancement of new technologies that can accurately and densely capture behavior’s multiple branches. The present study describes an open-source, wireless autonomic vest specifically designed for use in infants 8–24 months of age in order to measure cardiac activity, respiration, and movement. The schematics of the vest, instructions for its construction, and a suite of software designed for its use are made freely available. While the use of such autonomic measures has many applications across the field of developmental psychology, the present article will present evidence for the validity of the vest in three ways: (1) by demonstrating known clinical landmarks of a heartbeat, (2) by demonstrating an infant in a period of sustained attention, a well-documented behavior in the developmental psychology literature, and (3) relating changes in accelerometer output to infant behavior.

In adult animals, movement and vocalizations are coordinated, sometimes facilitating, and at other times inhibiting, each other. What is missing is how these different domains of motor control become coordinated over the course of development. We investigated how postural-locomotor behaviors may influence vocal development, and the role played by physiological arousal during their interactions. Using infant marmoset monkeys, we densely sampled vocal, postural and locomotor behaviors and estimated arousal fluctuations from electrocardiographic measures of heart rate. We found that vocalizations matured sooner than postural and locomotor skills, and that vocal-locomotor coordination improved with age and during elevated arousal levels. These results suggest that postural-locomotor maturity is not required for vocal development to occur, and that infants gradually improve coordination between vocalizations and body movement through a process that may be facilitated by arousal level changes.

Young children's visual environments are dynamic, changing moment-by-moment as children physically and visually explore spaces and objects and interact with people around them. Head-mounted eye tracking offers a unique opportunity to capture children's dynamic egocentric views and how they allocate visual attention within those views. This protocol provides guiding principles and practical recommendations for researchers using head-mounted eye trackers in both laboratory and more naturalistic settings. Head-mounted eye tracking complements other experimental methods by enhancing opportunities for data collection in more ecologically valid contexts through increased portability and freedom of head and body movements compared to screen-based eye tracking. This protocol can also be integrated with other technologies, such as motion tracking and heart-rate monitoring, to provide a high-density multimodal dataset for examining natural behavior, learning, and development than previously possible. This paper illustrates the types of data generated from head-mounted eye tracking in a study designed to investigate visual attention in one natural context for toddlers: free-flowing toy play with a parent. Successful use of this protocol will allow researchers to collect data that can be used to answer questions not only about visual attention, but also about a broad range of other perceptual, cognitive, and social skills and their development.