Process-based measures of handwriting performance across manual preference

Handwriting is a highly practiced motor skill that relies on the interaction between effector-dependent execution processes and effector-independent motor representations. The present study investigated handwriting performance with the preferred (PH) and non-preferred hand (NPH) in adults using a comprehensive set of process-based measures capturing execution-related fluency, automatization, and force regulation, as well as shape-based pattern stability. Twenty-five participants repeatedly produced a cursive letter "o" under four task conditions (normal, fast, accurate, and a visually constrained task). Execution-related measures revealed robust hand-related differences, with the PH showing higher fluency, greater automatization, and more efficient force regulation across task conditions. Task demands modulated performance in both hands, but fluency and automaticity measures were more sensitive to hand-specific adjustments. In contrast, shape-based measures derived from Dynamic Time Warping (DTW) showed smaller hand-related effects and no significant Hand × Task interaction, suggesting greater similarity in letter-form stability across hands. Classification analyses further indicated that execution-related measures were the most effective in identifying the executing hand across tasks, whereas DTW-based measures showed limited discriminative ability. These findings support a functional dissociation between motor execution and motor pattern stability in handwriting. While execution-related processes remain strongly effector-dependent, the spatial structure of a well-learned letter appears to rely on motor representations that are largely shared across hands. This dissociation highlights the value of combining execution-related and shape-based measures for a more nuanced assessment of handwriting performance.