Controlling posture to see the world: The integration of visual task demands and postural sway in sitting and standing infants.

Our ability to integrate posture with visually demanding tasks is a critical aspect of motor behavior flexibility. When looking at a small object, excessive body movements impair an individual's ability to visually attend to the object. To overcome this problem, we adjust our postural sway to successfully focus on the object. The goal of the current study was to assess whether infants also adjust postural sway when engaged in a challenging visual task. The participants, 19 independently sitting infants (Sitters) and 21 newly independently standing infants (Standers), sat or stood on a force plate while viewing differently sized images displayed on a monitor (smaller images: 8 × 6.5 cm or 3 × 3 cm; larger images: 13 × 16 cm or 13 × 13 cm). Regardless of image size, Standers were less stable than Sitters with larger sway areas and faster sway velocities. Both Sitters and Standers adjusted sway area but not sway velocity, based on image size. Sitters and Standers differed in how they controlled sway dynamics. Standers but not Sitters altered sway dynamics based on image size. Overall, infants used posture-specific adaptive control strategies to make fine-grained adjustments based on image size. The development of the ability to integrate posture with a visually demanding task further emphasizes the capability of advanced complex motor behaviors during infancy, enabling infants to flexibly attend to important aspects of their environment at different postural positions.

Sitting infants alter the magnitude and structure of postural sway when performing a manual goal-directed task.

In typical daily life, adults routinely adapt posture so that balance can be maintained while other goal-directed activities are performed. Interestingly, newly standing infants also control posture based on the demands of a task. It is unknown if the ability to properly adapt postural movements as a goal-directed task is performed emerges soon after the acquisition of independent stance or if it is present at earlier key postural milestones, such as independent sitting. In this study, the postural sway patterns of independently sitting infants were compared while either holding or not holding a toy. Infants exhibited less postural sway when holding the toy. This reduction in sway allowed infants to look at and stabilize the toy in their hand. Thus, the ability to adjust postural movements while performing a concurrent goal-directed task emerges long before the acquisition of independent stance.