Sitting skill and the emergence of arms-free sitting affects the frequency of object looking and exploration.

The development of sitting changes how much infants are able to explore objects. Infants who can sit with their arms free are likely to explore their environment more effectively than prop sitters, as their hands are free to explore. We sought to quantify how prop sitters differed in the amount of visual and manual exploration of objects from arms-free sitters. Infants younger than 7 months (n = 31) were recruited at sitting emergence, either prop or arms-free sitting without the ability to change positions. Infants were grouped into sitting stages at baseline: prop (n = 17) or wobbly/arms-free (n = 14). Across three visits (baseline, 3 weeks later, 6-8 weeks later), researchers assessed the infants' total gross motor skill, sitting skill, and object looking and active exploration. Infants' gross motor and sitting skill was assessed using the Gross Motor Function Measure (GMFM)-66 total scores and GMFM-88 sitting dimension scores. While researchers supported infants in sitting, object looking and exploration were assessed using a series of three object exploration tasks and scoring modified slightly from the Early Problem Solving Indicator at each visit. Differences between trajectories of prop and wobbly/arms-free sitters for the frequencies of two behaviors, looks and explores, were analyzed using longitudinal multilevel modeling. Prop sitters initially explored toys less frequently, but increased their exploration more quickly, than wobbly/arms-free sitters. Sitting skill predicted minor changes in the development of looking; both stage and skill predicted changes uniquely in the development of exploration. These findings suggest that independent, arms-free sitting changes how capable infants are of exploring objects visually and manually.