The influence of a hand preference for acquiring objects on the development of a hand preference for unimanual manipulation from 6 to 14 months.

Development of hand preferences for unimanual manipulation of objects was explored in 90 infants (57 males) tested monthly from 6 to 14 months. From a larger sample of 380 infants, 30 infants with a consistent left hand preference for acquiring objects were matched for sex and development of locomotion skills with 30 infants with a consistent right hand preference for acquisition and 30 with no preference. Although frequency of unimanual manipulations increased during 6-14 month period, infants with a hand preference for acquisition did more object manipulations than those without a preference for acquisition. Multilevel modeling of unimanual manipulation trajectories for the three hand-preference groups revealed that hand preferences for unimanual manipulation become more distinctive with age, and the preference is predicted by the hand preference for object acquisition. Infants with a right and left hand preference for object acquisition develop a right and left (respectively) hand preference for unimanual manipulation. However, the majority of infants at each month do not exhibit hand preferences for unimanual manipulation that are unlikely to occur by chance, even by 14 months. The results are consistent with a cascading theory of handedness development in which early preferences (i.e., for acquisition) are transferred to later developing preferences (i.e., for unimanual manipulation).