Development of handedness for role-differentiated bimanual manipulation of objects in relation to the development of hand-use preferences for acquisition during infancy
Handedness development during infancy could be represented as a progressive expansion of a hand-use preference across a wider range of increasingly complex skills. The goal of the present study was to explore the development of role-differentiated bimanual manipulation (RDBM) during infancy as an expansion of the development of handedness for acquiring objects and unimanual manipulation. Infants were categorized according to their handedness status for acquiring objects (right-hand, left-hand, or no distinct hand-use preference). This status was determined from nine monthly assessments performed during 6-14 month period and resulted in a sample of 90 normally developing infants (30 right-handers, 30 left-handers, and 30 no preference infants). These infants were tested monthly from 9 to 14 months for unimanual manipulation and RDBM handedness. The results of the multilevel analyses showed that lateralization of handedness for toy acquisition increased during 6-12 month interval and decreased thereafter. Lateralization of handedness for unimanual manipulation and RDBM increased during 9-14 month period. Furthermore, handedness for toy acquisition was found to be positively related to handedness for unimanual manipulation, which, in its turn, was positively related to handedness for difficult, but not simple, RDBM. Also, handedness for toy acquisition was positively related to handedness for difficult RDBM. Thus, it was concluded that handedness for toy acquisition concatenates into unimanual handedness which further influences the development of RDBM handedness
