Development of role-differentiated bimanual manipulation during the infant's first year.

Role-differentiated bimanual manipulation (RDBM) is a complementary movement of both hands that requires differentiation between actions of the hands. Previous research showed that RDBM can be observed in infants as early as 7 months. However, RDBM could be considered a skill only when its frequency, duration, and use is appropriate for the type of manual task, and there is some evidence of intentionality in use.

Relation of stable hand-use preferences to the development of skill for managing multiple objects from 7 to 13 months of age.

Expression of multiple object management skills (manual acquisition and storage of objects) was examined longitudinally at 7, 9, 11, and 13 months for 38 infants (19 females) whose hand use preference was either stable (consistently right or left across the ages) or nonstable (either no hand-use preference exhibited or inconsistent preference across the ages). Four separate sets of four distinctive objects each were presented singly to the infant's right and left side, with the presentation of each subsequent object contingent on the infant manipulating the previous object. Expression of multiple object management skills significantly increased with age.