Variability of Grip Kinetics during Adult Signature Writing

Abstract

Grip kinetics and their variation are emerging as important considerations in the clinical assessment of handwriting pathologies, fine motor rehabilitation, biometrics, forensics and ergonomic pen design. This study evaluated the intra- and inter-participant variability of grip shape kinetics in adults during signature writing. Twenty (20) adult participants wrote on a digitizing tablet using an instrumented pen that measured the forces exerted on its barrel. Signature samples were collected over 10 days, 3 times a day, to capture temporal variations in grip shape kinetics. A kinetic topography (i.e., grip shape image) was derived per signature by time-averaging the measured force at each of 32 locations around the pen barrel. The normalized cross correlations (NCC) of grip shape images were calculated within- and between-participants. Several classification algorithms were implemented to gauge the error rate of participant discrimination based on grip shape kinetics. Four different grip shapes emerged and several participants made grip adjustments (change in grip shape or grip height) or rotated the pen during writing. Nonetheless, intra-participant variation in grip kinetics was generally much smaller than inter-participant force variations. Using the entire grip shape images as a 32-dimensional input feature vector, a K-nearest neighbor classifier achieved an error rate of % in discriminating among participants. These results indicate that writers had unique grip shape kinetics that were repeatable over time but distinct from those of other participants. The topographic analysis of grip kinetics may inform the development of personalized interventions or customizable grips in clinical and industrial applications, respectively.

Long Term Consistency of Handwriting Grip Kinetics in Adults

“…In this paper, we only consider authentic signatures, i.e., 12,000 (600 signatures x 20 participants) from phase one and 4680 (300 x 12-|-180 x 6) from phase two. The authentic signatures from phase one were previously reported in a topographic kinetic analysis [20]. The bogus sij:natures were not considered in this study; however, an analysis based on the bogus signatures has been presented in Ref.…”

“…Further details regarding the calibration procedure and the instrumentation set-up can be found in Refs. [20] and [7].…”

Grip Kinetic Profile Variability in Adult Signature Writing

“…To collect the required data, the instrumentation setup shown in Figure 1 was used. Grip force signals, which are the forces applied by the fingers on the pen barrel, were acquired at 250 Hz via an instrumented writing utensil adorned with an array of Tekscan 9811 force sensors [1,8]. A custom-made data acquisition box transferred these signals to the data collection computer where they were saved for processing.…”

“…Signature writing is a well-learned [1] but highly complex perceptual motor task [2,3], invoking the coordinated activation of both proximal (e.g., thenar) and distal (e.g., trapezius) muscles [4], relying upon the central role of proprioception and the secondary role of vision [5], integrating kinesthetic input [6] and harnessing shortterm memory [7]. The complexity of these biomechanical and cognitive systems introduces variations between and within individuals [2].…”

“…However, studies of handwriting grip kinetic variability in the adult population is very limited [3]. Recently, we studied the variability of grip kinetics associated with signature writing in adults [1,13] and found that the variability of kinetic topographies (i.e., grip shape) between individuals was much higher than the variability within an individual, even when considering signatures collected over several months. These findings encouraged the study of variations in a summative handwriting grip kinetic profile, which is the time series of total force variation over the course of a signature.…”