Postural influences on the development of infant lateralized and symmetric hand-use.

Within-individual variability is such an apparent characteristic of infant handedness that handedness is believed to consolidate only in childhood. Research showed that manifest handedness is influenced by emerging postural skills (sitting, crawling, and walking). In this investigation, it was proposed that symmetric hand-use (tendency to acquire objects bimanually), rather than lateralized hand-use (the use of one hand more than the other), may be influenced by postural changes. Trajectories of lateralized and symmetric hand-use for object acquisition were examined in 275 infants tested monthly from 6 to 14 months. Multilevel modeling revealed that change in lateralized hand-use is unrelated to developmental transitions in infant posture, whereas the trajectory of symmetric hand-use changes significantly with the development of postural skills.