Infants' organization of pull-to-stand behaviors during play: A longitudinal investigation.

Pulling-to-stand (PTS) is an important transitional posture which may facilitate the shift to walking, but infants still frequently PTS even after learning to walk. Using a group of 13 infants who had learned to PTS about three weeks prior, we aimed to track how gains in PTS, standing, and walking experience contributed to infants' selection of more skilled PTS strategies and reorganized how infants used PTS to facilitate free play. We tracked spontaneous PTS over 10 biweekly laboratory sessions and video-coded functional measures of PTS skill, including hand-, knee-, and foot-use (e.g., lateral sides, hand- and foot-steps), and how infants used PTS during play, including behaviors immediately following PTS. Results showed infants frequently adopted skilled half-kneel strategies en route to PTS even though they were slower than symmetric PTS strategies. Most PTS involved asymmetrical and diagonal activation of the hands and legs, offering a stable center of gravity, and lateralized foot preferences were strong and stable. Other functional measures of PTS skill revealed increased efficiency over time, as infants PTS using fewer alternating hand-steps. Initially, infants PTS using stationary objects and then interacted with objects and mothers, but over time, infants increasingly PTS using the stairs and stair rails and engaged in more locomotor exploration following PTS. Even months after its initial onset, infants continued to refine PTS strategies and efficiency and used PTS differently for object interactions and locomotor exploration during play, which highlights the importance of tracking patterns of interlimb coordination during PTS and goal-directed behavior in context.