Effect of visual feedback on the static and kinetic individual characteristics of handwriting

It has been previously established that handwriting is a motor skill defined in a two dimensional spatial domain, consisted of three major levels through which the motor units
that contain the letter trajectories are retrieved from their motor memory storage and
translated into a process of muscle commands via muscle adjustments. As soon as
individuals start learning how to write they are introduced to a writing system common to a
group of writers connected by geographic, academic, temporal, national or occupational
links. As the writing ability evolves, writers distance themselves from the class system, that
they were taught, develop peculiarities in handwriting and acquire personal writing
characteristics, the so called individual characteristics of handwriting, which are considered
the backbone of forensic handwriting identification. Handwriting is influenced by a number
of genetic, physiological and biomechanical factors. Some factors can change the individual's
writing so drastically that it may be impossible to make an accurate comparison of the
person's normal writing with the person's abnormal writing causing serious problems for
forensic document examiners. However the research regarding the visual feedback is
partially contradictory regarding the degree of its influence on the individual characteristics.
A two-pronged approach was designed in order to investigate the degree of this influence:
Samples of signatures, cursive and block handwriting written with and without visual
feedback were collected by 40 volunteers and were imported in a PC via an opaque pen
tablet using an electronic inking pen. The data was stored and analyzed in a handwriting
movement analysis software module specially designed for this research, that was attached
in the software MovAlyzeR by Neuroscript LLC. Peer reviewed forensic comparison by a
forensic document examined (FDE) between the two groups (that is the group of samples
executed with normal visual feedback versus the group of samples executed without visual
feedback) shows total lack of significant differences between samples of the two different
conditions and the existence of a large corpus of similarities in the design and the pictorial
aspect, regardless of the complexity of the samples. Focusing on the cursive and block
handwriting, six traits linked to the absence of visual feedback where found: change of
overall size, non uniformity of left margins, change of slant, avoidance of pen lifts, inclusion
of extra trajectories and decrease of line quality. Furthermore, it was established that the
absence of visual feedback by itself cannot lead a trained FDE to an erroneous conclusion.
The statistical analysis shows that visual feedback significant influences the duration and
average absolute velocity of the signature execution, since the signature is executed more
slowly under no visual feedback. Further analysis of the cursive handwriting shows that
without visual feedback there is a significant increase in absolute and horizontal size as well
as average pen pressure and a decrease in slant and vertical size while in block handwriting
there is a significant increase in absolute and horizontal size, average pen pressure as well as
duration and a decrease in slant, average absolute velocity and vertical size. The
comparative analysis suggests that the factors of gender, educational level and handedness
creates an insignificant influence during the comparison of the two conditions of the
researched individual characteristics, with the only notable exception of the relationship
between signature duration and educational level due to automation and its results in the
memory retrieval program of the allographs. The combination of the above findings suggests
that all types of writing (signature, cursive and block handwriting) are governed by a single
major open loop motor program, which is not significantly influenced by visual feedback -no
evidence was found that visual feedback intervenes significantly in the procedure of
allograph execution, but is mainly linked with the auxiliary order of macro-managing,
inspection and possibly correction of the overall outcome of the combination of the above
allographs.