Rapidly maturing technologies for sensing and activity recognition can provide unprecedented access to the complex structure daily activity and interaction, promising new insight into the mechanisms by which experience shapes developmental outcomes. Motion data, autonomic activity, and “snippets” of audio and video recordings can be conveniently logged by wearable sensors (Lazer et al., 2009). Machine learning algorithms can process these signals into meaningful markers, from child and parent behavior to outcomes such as depression or teenage drinking. Theoretically motivated aspects of daily activity can be combined and synchronized to examine reciprocal effects between children’s behaviors and their environments or internal processes. Captured over longitudinal time, such data provide a new opportunity to study the processes by which individual differences emerge and stabilize. This paper introduces the reader to developments in sensing and activity recognition with implications for developmental phenomena across the lifespan, sketching a framework for leveraging mobile sensors for transactional analyses that bridge micro‐ and longitudinal‐ timescales of development. It finishes by detailing resources and best practices to facilitate the next generation of developmentalists to contribute to this emerging area.

Previous accounts of the development of triadic attention identify a ‘‘curious'' shift around nine to twelve months. We introduce a novel approach inspired by distributed and embodied cognition frameworks. In a longitudinal study of five mother-infant dyads, videos of home play interactions were recorded over the infants' first year. We scrutinized the real-time organization of mother-infant sensorimotor activity, including the targets of hands, gaze, and mouth, as the dyad members attended to one another and to toys. We identified a pervasive developmental pattern: At four months, infants converged all sensory modalities on objects introduced by the mother. From six to twelve months, infants showed increasing decoupling of hands and eyes and increasingly elaborate sequences in multi-object play. Concurrently, dyads engaged in increasingly elaborate social exchanges (e.g., turn-taking) as mothers adapted to infants' sensorimotor skills. We therefore theorize that triadic attention emerges not as a novel form of social cognition but as a continuous product of sensorimotor development, scaffolded by parents' expanding social actions.

Previous developmental accounts of joint object activity identify a qualitative “shift” around 9–12 months. In a longitudinal study of 26 dyads, videos of joint object interactions at 4, 6, 9, and 12 months were coded for all targets of gaze and manual activity (at 10 Hz). At 12 months, infants distribute their sensorimotor modalities between objects handled by the parent and others controlled by the infant. Analyses reveal novel trajectories in distributed joint object activity across the 1st year. At 4 months, infants predominantly look at and manipulate a single object, typically held by their mothers. Between 6 and 9 months, infants increasingly decouple their visual and haptic modalities and distribute their attention between objects held by their mothers and by themselves. These previously unreported developments in the distribution of multimodal object activity might “bridge the gap” to coordinated joint activity between 6 and 12 months.

HighlightsPrevious ANS research is largely based on individual peripheral measures.We recorded HR, EDA, pupil size and head and peripheral accelerometry.We found high covariation between ANS indices in infants.Pupil size and EDA showed more complicated patterns.Different patterns were seen between tonic and phasic analyses.