Development of role-differentiated bimanual manipulation in infancy: Part 3. Its relation to the development of bimanual object acquisition and bimanual non-differentiated manipulation.

This third paper in a series of three related developmental trajectories of bimanual object acquisition and non-differentiated bimanual manipulation (NDBM) to patterns of role-differentiated bimanual manipulation (RDBM) development to help identify the sequence of events that might predict (and potentially facilitate) the development of RDBM skill. Ninety infants were tested monthly from 6 to 14 months of age for object acquisition, and from 9 to 14 months for NDBM and RDBM. The results did not support the hypothesis proposing that the onset of RDBM would require decoupling of the hands in unimanual acquisition, but supported the prediction that coupling of the hands in bimanual acquisition would predict increasing expertise in the RDBM skill. The relation between the bimanual object acquisition and RDBM was found to be mediated by NDBM, which prompts the hypothesis that bimanual acquisition of objects facilitates the development of NDBM, which, in its turn, facilitates the development of the RDBM skill.