Development of Sitting and Reaching in 5- to &Month-Old Infants

Three studies are reported, investigating changes in body engagement by 5to 6-month-old infants as they reach for ObJects in the environment. Infants are distinguished and compared based on their relative ability to maintain a sitting posture without any external body support. The first study demonstrates that manual reaching by sitter infants is coordinated with forward leamng of the trunk, whereas reaching by nonsitters is not. The second study demonstrates that nonsitter infants provided with hip support also show signs of a coordination between reaching of the hand and forward leaning of the trunk. The third study compares nonsitter, nearsitter, and sitter infants as they reach for multiple objects spread across their prehensile space. Results demonstrate expansion in the mapping of infants’ prehensile space and hand use as a function of self-sitting ability. The reported results are discussed as expressions of the interaction between the development of postural, perceptual, and action systems in infancy.