The transition from crawling to walking affects infants' social actions with objects

This study examined the unique and interactive roles of age and locomotor posture (crawling vs. walking) in explaining changes in infants' social actions with objects. Fifty infants were observed longitudinally at 11 and 13 months of age for 1 hour per visit during spontaneous object activities at home. At 11 months, all infants were crawlers; by 13 months, half were walkers. The age-held-constant longitudinal design permitted an investigation of whether social actions with objects change as a function of locomotor posture, while holding age constant. Number of object engagements, duration of object episodes, and location of objects were totaled. To address the question of infants' social actions with objects, the frequency of object bids was assessed and the type of bids was described. At 13 months of age, infants spent more time in object activities and were more likely to share objects with mothers. Age-related changes were enhanced for walkers: They were more likely to engage with distal objects than crawlers, perhaps because of an elevated vantage point; they were more likely to transport objects from place to place and to approach mothers to offer objects to them, presumably due to freeing of the hands and a more efficient upright posture when locomoting. Together, these findings indicate that the development of walking plays a facilitative role in infants' social actions with objects independent of age effects. Thus, developmental changes in posture can restructure the nature of infants' physical and social environment