Complexity, age and motor competence effects on fine motor kinematics

Prehension is a fundamental skill usually performed as part of a complex action sequence in everyday tasks. Using an information processing framework, these studies examined the effects of task complexity, defined by the number of component movement elements (MEs), on performance of prehension tasks. Of interest was how motor control and organisation might be influenced by age and/or motor competence. Three studies and two longitudinal case studies examined kinematic characteristics of prehension tasks involving one-, two- and three-MEs: reach and grasp (low-complexity); reach, grasp and object placement (moderate-complexity); and reach, grasp and double placement of object (high-complexity). A pilot study established the suitability of tasks and procedures for children aged 5-, 8- and 11-years and showed that responses to task complexity and object size manipulations were sensitive to developmental changes, with increasing age associated with faster movements. Study 2 explored complexity and age effects further for children aged 6- and 11-years and adults. Increasing age was associated with shorter and less variable movement times (MTs) and proportional deceleration phases (%DTs) across all MEs. Task complexity had no effect on simple reaction time (SRT), suggesting that there may be little preprogramming of movements beyond the first ME. In addition, MT was longer and more on-line corrections were evident for the high- compared to the moderate-complexity task for ME1. Task complexity had a greater influence on movements in ME2 and ME3 than ME1. Adults, but not children, showed task specific adaptations in ME2. Study 3 examined performance of children with different levels of motor competence aged between 5- and 10-years. Increasing age was associated with shorter SRTs, and MTs for ME1 only. A decrease in motor competence was associated with greater difficulty in planning and controlling movements as indicated by longer SRTs, higher %DTs and more on-line corrections, especially in ME2. Task complexity affected movements in all MEs, with a greater influence on ME1 compared to Study 2. Findings also indicated that performance in MEs following prehension may be especially sensitive to motor competence effects on movement characteristics. Case studies for two children at risk of Developmental Coordination Disorder (DCD) revealed two different patterns of performance change over a 16-17 month period, highlighting the heterogeneous nature of DCD. Overall, findings highlighted age-related differences, and the role of motor competence, in the ability to adapt movements to task specific requirements. Results are useful in guiding movement education programmes for children with both age-appropriate and lower levels of motor competence.