Postural and lateral asymmetries in the ontogeny of handedness during infancy.

Ten newborn infants who preferred to lie with their heads turned rightward and ten who preferred to lie with their heads turned leftward had their hand-use preferences for reaching assessed at 8 different ages during the period 12-74 weeks postpartum. Eighteen infants maintained stable hand-use preferences throughout this period and the direction of their neonatal head orientation preference predicted the hand they preferred to use. The neonatal head-turn preference was maintained through the first 2 months and induced lateral asymmetries in visual regard and motor control of the hands. These lateral asymmetries are plausible contributors to mechanisms linking neonatal headturn preference to infant hand-use preference. Thus, the dextral bias in handedness may be derived, in part, from the rightward bias in neonatal head-turn preference.