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Learning to walk expands infants' access to the physical environment and prompts changes in their communicative behaviors. However, little is known about whether walking also shapes infants' proximity to their adult social partners during everyday activities at home. Here we followed 89 infants (42 boys, 47 girls; 92% White, not Hispanic or Latino) longitudinally and documented connections between infant locomotion and infant‐adult proximity on two timescales: (1) across developmental time, by comparing data from a session when infants could only crawl to a later session when they could walk (M walk onset = 12.15 months, range = 8‐15); and (2) in real time, by testing whether the amount of time that infants spent in motion (regardless of their locomotor status) related to their interpersonal distance to adults. The developmental transition to walking corresponded to a significant, but modest, decrease in infant‐adult proximity. Infants' moment‐to‐moment locomotion, however, was strongly related to patterns of interpersonal distance: infants who spent more time in motion spent less time near adults and instigated more proximity transitions, resulting in shorter and more dispersed bouts of proximity throughout sessions. Findings shed new light on how infants' motor achievements can reverberate across other domains of development, and how changes in infant development that researchers often observe over months arise from infants' moment‐to‐moment experiences. [ABSTRACT FROM AUTHOR]

Learning to sit promotes infants' object exploration because it offers increased access to objects and an improved position for exploration (e.g.,). Infants at heightened risk (HR) for autism spectrum disorder (ASD) exhibit delays in sitting and differences in object exploration. However, little is known about the association between sitting and object exploration among HR infants. We examined changes in object exploration as HR infants (N = 19) and comparison infants with no family history of ASD (Low Risk; LR; N = 23) gained experience sitting independently. Infants were observed monthly from 2.5 months until 1 month after the onset of independent sitting. At 12, 18, 24, and 36 months, infants completed standardized developmental assessments, and HR infants were assessed for ASD symptoms at 36 months. Although HR infants began sitting later than LR infants, both groups increased time spent grasping, shaking, banging, and mouthing objects as they gained sitting experience. Groups only differed in time spent actively mouthing objects, with LR infants showing a greater increase in active mouthing than HR infants. Findings suggest that HR infants experience a similar progression of object exploration across sitting development, but on a delayed time scale. [ABSTRACT FROM AUTHOR]

Abstract: Background: Research indicates that social communicative behaviours develop atypically during the second year in Autism Spectrum Disorder (ASD). This study evaluated whether these behaviours also differed in the extent to which they were coordinated across modalities. Aims: To measure joint attention behaviours (e.g., gaze shifts, gestures), vocalisations and their coordination among a cohort of infants with an older sibling with ASD (heightened risk—HR). Methods & Procedures: This prospective longitudinal study examined 50 HR infants at 14, 18 and 24 months. The Early Social Communication Scales (ESCS)—a structured toy‐play task that assesses infant joint attention behaviour—was administered to infants at each age point in the home. Infants’ joint attention behaviours, vocalisations and instances where they overlapped were coded from videos. At 36 months, nine infants received an ASD diagnosis (HR‐ASD), 15 had a significant language delay (HR‐LD) and 26 were classified no diagnosis (HR‐ND). Outcomes & Results: Findings revealed that HR‐ASD infants produced fewer advanced joint attention behaviours, and their vocalisations were less frequent and less advanced than HR‐LD and HR‐ND infants. Notably, HR‐ASD infants also coordinated these behaviours together less frequently than their HR peers. Conclusions & Implications: Differences in the coordination of early communicative behaviours may have negative cascading effects on social and language development for infants who develop ASD. Current intervention practices may be complemented by efforts to increase the coordinated quality of communicative behaviours. [ABSTRACT FROM AUTHOR]