Space-time invariance in adult handwriting

Handwriting quality is commonly evaluated off-line using either subjective or pattern recognition techniques based on the static final output. Skilled performance is characterised in terms of legibility and as a minimisation of spatial variability. However, these techniques are subject to error, and provide little information about the underlying dynamics producing the movement. This study employed temporally sensitive techniques to investigate the relationship between spatial (i.e. legibility) and the kinematic (i.e. dynamic) aspects of handwriting production. Each of 18 adult subjects (7 male, 11 female) wrote the pseudo-word MADRO-NAL 10 times in their natural cursive handwriting. Horizontal (x), vertical (y) and pressure (z) coordinate data were collected using a Wacom 1212-R graphics tablet controlled by a laboratory computer. Spatio-temporal aspects of the x, y and z velocities of the stylus were analysed both between trials and within subjects using coherence analysis. Subjects previously rated as good handwriters by three independent judges displayed a greater degree of temporal consistency than the less proficient writers. The results showed that spatial inconsistencies are related to dynamic variability and demonstrated that the methodology employed can provide a useful tool for the quantitative assessment of handwriting quality. (C) 1997 Elsevier Science B.V.