The development of bimanual role differentiation in infants and young children.

Abstract

Bimanual role differentiation involves two hands engaged in qualitatively different movements, collaborating toward a common goal. This thesis explored the development of role differentiated hand use in infants and young children in four separate experiments, by examining: (a) developmental progressions, (b) the integration of unimanual with bimanual actions, (c) the presence, strength and consistency of bimanual lateralization, (d) the influence of task context, and (e) the collaborative relationship between the hands. In Experiment 1, the repertoire and lateralization of hand use was investigated in 30 term infants observed at 14 mo in 3 min of toy play. In Experiment 2, 26 of these infants were retested at 19 mo. In Experiment 3, hand use frequency, lateralization and context effects were examined in 36 children, aged 3 to 5 years, with a variety of toys. Bimanual reaches were examined using frame-by-frame motion analysis in Experiment 4. The data revealed that at 14 mo, only a quarter of the contacts were role differentiated, but they took up a third of the contact time. By 19 mo, unimanual contacts had decreased, and bimanual contacts increased. While 3 to 5 year olds demonstrated over 50% role differentiated toy play, the frequency of unimanual and bimanual contacts varied with the toy indicating a context effect. While both babies and preschoolers had a bimanual preference, it was not exclusive, as each group also explored the toys with their nonpreferred hand. Lateralization was stable for 60% of the infants between 14 and 19 mo. The frequency of right to left contacts changed with the type and position of toy presentation, but the bimanual preference remained stable for 3-5 year olds. Several rules of collaboration were identified: There was a functional asymmetry in the bimanual reaches and an order effect, with the preferred right hand initiating the reach and making first object contact; the duration of the reach was affected by order, with the first hand reaching faster, but it was not affected by lateralization, toy, or position; and finally, there was no evidence of a tight coupling of the hands in this self-paced toy playing task.