Human motor development and hand laterality: a kinematic analysis of drawing movements

This study examines the developmental profiles of basic 'open-loop' drawing movements on the non-dominant ha nd (ND) in comparison with the dominant h and (D). Fifty-three right-handed children aged 7-14 years and 15 adults ag ed 27-43 years were era mined. Each subject drew lines and circles of diffe rent sizes at maxim um velocity with a pressure-sensitive pen on a computer graphics tablet. Small lines were drawn at 90 degrees to the axis of the f orearm (lines using wrist movements (LWM)) and along the axis of the forear m (lines using elbow movements (LEM)). Larger lines were drawn at 90 degree s to the axis of the forearm (LEM). At both extremities, the movement frequ encies of the proximally generated drawing movements increased in a paralle l fash ion at different levels. In LWM,the rig ht-left-differences (RLD) we re high in 7- to 8-year-old children; until puberty, the ND hand reached al most the performance of the D hand. In contrast, the RLD of the LFM increas ed at the same ti me. As adulthood approaches, frequencies of all drawings increased further while the LWM on the ND side remained stable. In adults, there were similar RLD for all line drawings involving predominantly flexio n and extension movements. When drawing circles, the RLD were highest, thou gh stable in all age groups. Hand laterality of pen use changes over time; these changes are dependent on complexity (combined/sequential cf. flexion- extension muscle activation) a nd on topography (proxima I cf. distal movem ents). Distinct developmental profiles of motoneuronal populations of the c ortex may be responsible for the distinct hand laterality effects and the d ecreasing variability of motor patterns. The drawing abilities and developm ental changes on the untrained ND hand indicate that effector-specific prac tice plays a minor role. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.