Speech development occurs in highly variable environments; however, little is known about the effect of situational context on emerging infant vocalizations. At 4 time points (4, 6, 9, and 12 months), we longitudinally measured vocalizations of 104 White infant‐caregiver dyads (41 girls) during three play contexts: book‐sharing, toy play, and rattle‐shaking. The frequency of infant vocalizations differed between contexts only at 12 months of age. Meanwhile, caregivers systematically spoke more frequently during book‐sharing than in other contexts from 4 months of age onwards. Book‐sharing elicited more conversational turns at the dyadic level than in other contexts from 9 months of age. Our results show emergence of vocal differentiation of play context by infants and the role of book‐sharing in facilitating early vocal turn‐taking.

Early in life, infants exhibit motor overflow, which can be defined as the generation of involuntary movements accompanying purposeful actions. We present the results of a quantitative study exploring motor overflow in 4-month-old infants. This is the first study quantifying motor overflow with high accuracy and precision provided by Inertial Motion Units. The study aimed to investigate the motor activity across the non-acting limbs during goal-directed action. To this end, we used wearable motion trackers to measure infant motor activity during a baby-gym task designed to capture overflow during reaching movements. The analysis was conducted on the subsample of participants (n = 20), who performed at least four reaches during the task. A series of Granger causality tests revealed that the activity differed depending on the non-acting limb and the type of the reaching movement. Importantly, on average, the non-acting arm preceded the activation of the acting arm. In contrast, the activity of the acting arm was followed by the activation of the legs. This may be caused by their distinct purposes in supporting postural stability and efficiency of movement execution. Finally, our findings demonstrate the utility of wearable motion trackers for precise measurement of infant movement dynamics.

Infants manually contact objects differently depending on their body position and the physical properties of objects. Previous studies have examined these factors separately, in structured laboratory settings, and laid the foundation for the investigation of the interaction of these elements. The current study revisits ideas from structured research in less controlled conditions by investigating how body position and the type of object shape manual contact with objects during free‐flowing play. Nine‐month‐old infants ( N = 80) participated in a semi‐structured dyadic play session with their caregiver, interacting with four objects of two different kinds ‐ two small and graspable objects; and two larger and stationary objects requiring specific actions to elicit an outcome (e.g., button pressing to make balls spin). The dyad was not constrained in terms of positioning, location on the floor, or movement around the room. We examined how the duration and frequency of infants' manual contact with objects varied based on the real‐time interaction between object type and body position. The results indicate that infants contacted objects more frequently while sitting independently compared to other positions. Stationary objects were contacted more frequently but for shorter durations than graspable objects, regardless of the body position. Infants contacted graspable objects longer while sitting independently (compared to other positions), however, stationary objects were contacted with similar durations for all body positions. We found that durations of object contact depend on the interaction between object type and body position, which is more complex than what could be predicted by studies that examined these factors in isolation. These results highlight the need to study multiple interacting elements in less controlled settings.

Little is known about the dynamics of children’s conversations outside of urban Western contexts, where research focuses on one-on-one interactions with parents. Our study addresses this gap, aggregating naturalistic speech data gathered in 10 countries across multiple labs, and using novel speech diarization algorithms to extract and classify different types of conversation. We analyzed 23,000 hours of child-centered audio recordings taken from 844 children (mean age 23 months; 389 girls) across urban, agricultural, and foraging societies. We found that multiparty conversations, involving at least three speakers, are more frequent than any other type of conversation. Across settings, children’s relative exposure to conversation differed based on their age, number of siblings, and mother’s education. We conclude that the kinds of conversation most often studied differ from those children typically encounter. Greater focus on children’s conversations in multiparty contexts may provide a more representative picture of their daily experience with language.