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