Physically-coupled bimanual coordination in children

Abstract

This thesis explores physically-coupled bimanual coordination amongst typically developing (TD) children, as well as children with unilateral spastic cerebral palsy (USCP). Unlike TD children, who acquire bimanual skills through activities of daily living (ADLs), children with USCP exhibit sensorimotor impairments to half side of their body, that impede their ability to learn and adapt two-handed skills into ADLs. While bimanual training is increasingly being incorporated into rehabilitation, the evidence for its effectiveness in improving the functional capacity of children with USCP against standard care is modest at best. This thesis argues that there is a fundamental gap in the knowledge, thus impeding our understanding, of how bimanual skills develop and manifest under both TD and USCP conditions. Specifically, much of what we know about bimanual development in children comes from studies on uncoupled bimanual tasks, where the hands control two independent objects. Conversely, there has been a minimal effort to systematically quantify the behaviours underlying ubiquitous physically-coupled bimanual coordination, where the hands manipulate a common shared object. Bimanual coordination of TD children and children with USCP was explored through four experiments that incorporated different forms of physical coupling (visual and haptic feedback), mechanics (modulating object stiffness), and congruence. This was achieved using instrumented objects, a robotic interface and novel metrics developed within this thesis that enable the elucidation of various synergies between the two hands to be quantified. The findings from this thesis provide important implications for understanding the normal and impaired behaviour of bimanual action amongst TD children and children with USCP, as well as amongst healthy adults. Specific contributions of this thesis come from (1) development and application of a suite of instrumented objects and robotic interfaces to study the broader spectrum of physically-coupled bimanual tasks, (2) development of novel metrics, e.g. grip-load monotonicity to quantify and stratify normal and pathological behaviours in early childhood development, and (3) a deeper understanding of the interplay between haptic and visual feedback in shared object manipulation tasks. The results provide evidence that physical coupling may facilitate bimanual coordination, especially in the presence of haptic feedback. Therefore, this thesis proposes that true physical interaction during bimanual activities may provide a new opportunity for the rehabilitation of children with USCP.