Early development in autism: How developmental cascades help us understand the emergence of developmental differences.

Many theories of autism spectrum disorder (ASD) focus on a single system or factor as an explanatory mechanism for autism symptoms and behavior. However, there is growing recognition that ASD is a complex, multisystem neurodevelopmental condition with origins in prenatal life. Researchers therefore need a conceptual framework that allows examination of the interplay between multiple interacting domains and systems and the ways in which they extend their influence beyond the individual into the surrounding environment. The developmental cascades perspective suggests that even relatively small perturbations in early emerging behaviors in domains that are not traditionally linked may influence subsequent achievements across these areas. In this chapter, we illustrate how a developmental cascades framework can be used to inform the study of developmental differences. The developmental cascades perspective provides us with conceptual and methodological tools for considering how variation in children's real time behavior can provide new insights into sources of variation in their developmental trajectories and outcomes. It also suggests approaches for intervention that leverage targeted skills in novel ways, creating opportunities to support development in other domains and fine-tune caregiver behavior to create powerful moments for infant learning.

Equifinality in infancy: The many paths to walking.

Many different pathways can lead to the same result or developmental outcome. What are the developmental routes that result in the onset of walking? In this longitudinal study, we documented patterns of infant locomotion during everyday activities at home for 30 prewalking infants. Using a milestone-based design, we focused on observations spanning the two months before the onset of walking (M age at walk onset = 11.98 months, SD = 1.27). We examined how much time infants spent in motion and when they moved, whether they were more likely to do so while prone (crawling) or upright with support (cruising or supported walking). Results showed immense variability in infants' practice regimes en route to walking-some infants spent relatively similar amounts of time crawling, cruising, and supported walking at each session, others preferred one method of travel over the alternatives, and some switched between different types of locomotion from session to session. In general, however, infants spent a larger share of their movement time in upright positions compared to prone. Finally, our densely sampled dataset revealed a clear feature of locomotor development: infants follow many distinct and variable paths to walk onset, regardless of the age at which it is attained.

Dynamics of the dyad: How mothers and infants co-construct interaction spaces during object play.

Studies of dyadic interaction often examine infants' social exchanges with their caregivers in settings that constrain their physical properties (e.g., infant posture, fixed seating location for infants and adults). Methodological decisions about the physical arrangements of interaction, however, may limit our ability to understand how posture and position shape them. Here we focused on these embodied properties of dyadic interaction in the context of object play. We followed 30 mother-infant dyads across the first year of life (at 3, 6, 9, and 12 months) and observed them during 5 min of play with a standard set of toys. Using an interval-based coding system, we measured developmental change in infant posture, how mothers and infants positioned themselves relative to one another, and how they populated interaction spaces with objects. Results showed that mother-infant dyads co-constructed interaction spaces and that the contributions of each partner changed across development. Dyads progressively adopted a broader spatial co-orientation during play (e.g., positioned at right angles) across the first year. Moreover, advances in infants' postural skills, particularly increases in the use of independent sitting in real time, uniquely predicted change in dyadic co-orientation and infants' actions with objects, independent of age. Taken together, we show that the embodied properties of dyadic object play help determine how interactions are physically organized and unfold, both in real time and across the first year of life.

Infant locomotion shapes proximity to adults during everyday play in the U.S.

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.

Bidding on the go: Links between walking, social actions, and caregiver responses in infant siblings of children with autism spectrum disorder.

The development of walking is associated with a shift in how neurotypical infants initiate social interactions. Walking infants are more likely to locate objects in distant places, carry them, and then share those objects by approaching caregivers and using gestures to show or offer their discoveries (i.e., moving bids). The simultaneous organization of the behaviors necessary to generate moving bids requires the coordination of multiple skills-walking, fine motor skills, and gesturing. Infants with an elevated likelihood (EL) for autism spectrum disorder (ASD) exhibit differences and delays in each of these behaviors. This study investigated interconnections between infant walking, social actions, and caregiver responses in 18-month-old EL infants with diverse developmental outcomes (ASD, non-ASD language delay, no diagnosis). We observed 85 infant-caregiver dyads at home during everyday activities for 45 minutes and identified all times when infants walked, instances of walking paired with social action (i.e., approaching the caregiver, approaching while carrying an object, producing a moving bid), and whether caregivers responded to their infants' social actions. There were no group differences in infants' production of social actions. Caregiver responses, however, were more clearly modulated by outcome group. While all caregivers were similarly and highly likely to respond to moving bids, caregivers of EL-ASD infants were substantially more likely to respond when their infants simply approached them (with or without an object in hand). Taken together, this research underscores the complexity of EL infant-caregiver interactions and highlights the role that each partner plays in shaping how they unfold.

Cascades in action: How the transition to walking shapes caregiver communication during everyday interactions.

New motor skills supply infants with new possibilities for action and have consequences for development in unexpected places. For example, the transition from crawling to walking is accompanied by gains in other abilities-better ways to move, see the world, and engage in social interactions (e.g., Adolph & Tamis-LeMonda, 2014). Do the developmental changes associated with walking extend to the communicative behaviors of caregivers? Thirty infants (14 boys, 16 girls; 93% White, not Hispanic or Latino) and their caregivers (84% held a college degree or higher) were observed during everyday activities at home during the two-month window surrounding the onset of walking (M infant age = 11.98 months, range = 8.74-14.86). Using a cross-domain coding system, we tracked change in the rates of co-occurrence between infants' locomotor actions and caregivers' concurrent language and gesture input. We examined these relations on two timescales-across developmental time, as infants transitioned from crawling to walking, and in real time based on moment-to-moment differences in infant posture. A consistent pattern of results emerged: compared to crawling, bouts of infant walking were more likely to co-occur with caregiver language and gestures that either requested or described movement or provided information about objects. An effect of infants' real-time behavior was also discovered, such that infants were more likely to hear language from their caregivers when they moved while upright compared to prone. Taken together, findings suggest that the emergence of walking reorganizes the infant-caregiver dyad and sets in motion a developmental cascade that shapes the communication caregivers provide. (PsycInfo Database Record (c) 2022 APA, all rights reserved).