Task-specific adaptations of postural sway in sitting infants.

When engaging in manual or visual tasks while sitting, infants modify their postural sway based on concurrent task demands. It remains unclear whether these modulations are sensitive to differences in concurrent task demands (holding a toy vs. looking at a toy being held by someone else), and whether the properties of the support surface impact these adaptations. We investigated infants' ability to modify postural sway when holding a toy or visually attending to a toy someone else was holding while sitting on different support surfaces. Twenty-six independently sitting infants sat on solid and compliant surfaces placed on a force plate while looking at or holding a toy. Measures of postural sway were calculated from the center of pressure data. Visually attending to a toy was associated with less sway and lower sway velocity than when holding a toy. Surprisingly, surface compliance did not affect sway and there were no interaction effects. Whereas sway modulations may facilitate infants' performance on both manual and visual concurrent tasks, the visual task placed more constraints on the postural system leading to greater adaptations in postural sway. These findings provide insights into how infants are allocating attention and coordinating perceptual-motor information in developing sitting skills.