Role differentiated bimanual manipulation during a lab-based free play task.

Infants spend a significant portion of their day engaging in play and accumulate immense amounts of object interactions. As infants develop, they perform increasingly complex bimanual actions, such as role differentiated bimanual manipulation (RDBM), where each hand serves a distinct role. RDBM has been well documented in structured lab settings, but these studies restrict the types of toys and postures in which infants can engage. Therefore, previous studies are limited in that they do not simulate everyday infant object interactions. Infants (39 13- and 39 24-month-olds) engaged in a 20-minute lab-based free play task designed to mimic everyday object interactions in order to assess the prevalence of RDBM and to understand the influence of posture, toy size, and toy weight on RDBM. Although both age groups frequently engaged in object interaction, RDBM did not occur as often in the lab-based free play task as found previously in structured settings. Whereas infants engaged in RDBM with toys of various sizes and weights, they favored lightweight toys and preferred to sit while engaging in RDBM. The 13-month-old infants preferred small toys while the 24-month-olds more often incorporated medium and large toys in their interactions. Examining RDBM using a lab-based free play task furthers our understanding of how complex bimanual behaviors emerge in a naturalistic setting where infants can adopt a wide range of postures and interact with a variety of toys.