Perhaps one of the most interesting practical applications of an understanding of handwriting processes is in the world of forensic handwriting analysis. Handwriting forgery is the alteration of what, through years of training, has become second nature. When a person sits down to forge a signature, they simultaneously imitate the features of another person’s handwriting and avoid the characteristics of their own. This process of imitation and avoidance is a conscious rejection of the writer’s inherent writing process – where the creation of strokes is programmed – in favour of a system where he or she relies more on visual feedback, on copying or tracing. Observing what happens when a writer avoids the processes that their brains have become accustomed to using is a fantastic way of understanding what these processes are. As I strive for a clearer understanding of how we write, I have taken this opportunity to share my research with my blog readers.
I’ve been making my way slowly through a paper by Caligiuri, Mohammed, Found and Rogers on forensic document examination. It shows that that the kinematics (movements) of handwriting display different characteristics when a person signs their own signature from when they forge someone else’s. Forged signatures are produced with less kinematic efficiency ie. the writer produces movement sequences less efficiently. Forged signatures also violate what is called the ‘isochrony principle’. Caligiuri et al’s article explains this rule as follows: ‘The isochrony principle states that the velocity of voluntary movement increases with the extent of the movement, thus keeping movement time approximately constant’.
I am afraid that this explanation left me unsatisfied and still a little confused, so I dug deeper. I found an article explaining this rule in the behaviour of monkeys. If a macaque needs to reach an object, she adjusts the speed of her arm movement so that the time required to make the grabbing movement remains constant, no matter how far away the object. This is an automatic information processing system that makes perfect sense. If an object is closer, the monkey has to gear down her movement in order to grab it accurately. In contrast, if the object is further away, she gears up, because she has a longer distance over which to choreograph her movement.
So, returning to humans, this means that when you are making your own signature, and need to make it smaller, you will make more slowly than you would if it were twice the size. Like the monkey who covers a smaller distance, the minuteness of the stroke requires greater precision, and thus a slower movement. However, because the strokes are shorter, your signature will take approximately the same time as if you had made it really large. Your brain, like the monkey’s hand, is producing and regulating motor movements automatically. Calgiuiri et al found that if you are forging a signature, you are less likely to adhere to this principle. In forgery, large strokes take longer than smaller ones. This abandonment of the isochrony principle is because the forger’s brain is using a relatively un-programmed set of movements – it is relying on constant visual feedback. There’s still more work to be done in this area, though. As Caligiuri et al acknowledge, the processes involved in producing a stylised signature (i.e. one made up of unrecognisable characters) might be different from producing a text-based one (where individual characters can be picked out).
Caligiuri et al’s study has formed interesting connections with the acquisition of handwriting abilities when we are children. Interestingly, when we are very tiny, aged 5-6 and first learning how to write, our handwriting conforms to the isochrony principle. However, between ages 6-8, we show less evidence of isochrony as we rely more on visual feedback. Then, as we gain experience and confidence, aged above 8, we begin to conform again, and develop a more automatic handwriting motor program. As a child grows, he or she migrates towards what are called the ‘lognormal’ characteristics of better mastered handwriting. Like a child in the intermediate stage, who has not yet formed his or her style, a forger relies heavily upon visual feedback, upon copying the features of the letters that they see before them. When Caligiuri et al did their study, they allowed their forgers three ‘practice runs’, in order to test whether a forged signature might become programmed with practice. Even after eighteen goes, their forgeries were still with less kinematic efficiency, and without adherence to the isochrony principle.
This use of the digitising tablet is where Caligiuri et al’s study has obvious limitations. As we know, forgers rarely attach themselves to digitising equipment and allow neurologists to study their brain performance. Most evidence regarding forgery exists as a static sample, seen after the fact. So how can these fascinating revelations about the brain processes involved in forgery be applied in practice? Caligiuri et al, in their discussion, recognise that the primary aim of the study was to test the kinematic efficiency of forged signatures, and thus the use of dynamic samples was necessary. So, indeed, the findings have limited applications for investigating static signatures. However, they do also state that the study’s findings support existing findings about the ‘degraded quality’ of forged signatures. In short, I think more work needs to be done on connecting the observations about the dynamic qualities of forged signatures with the analysis of historical or contemporary static forgeries. The last five years has seen some exciting studies in this area, such as using grey-level analysis of static scans to infer the pressure that was applied when the signature was made. I’ll be reading these excitedly, as the analysis of these ‘pseudodynamic’ features may be very useful in medieval palaeography.
What was useful for me, trying to learn more about handwriting processes, was what this study reveals about how our brain is programmed to produce a natural signature. Caligiuri et al’s findings show how the brain, when it is asked to produce a forged signature, has to abandon its pre-programming and revert to the same kind of dependence on visual feedback as it had when the person was a child.
 Michael P. Caligiuri, Linton A. Mohammed, Bryan Found, Doug Rogers, ‘Nonadherence to the isochrony principle in forged signatures’. Forensic Science International. 2012.
 Luisa Sartori, Andrea Camperio-Ciani, Maria Bulgheroni, and Umberto Castiello, ‘Reach-to-grasp movements in Macaca fascicularis monkeys: the Isochrony Principle at work’. Front Psychol. 2013;4:114.
 B. Found, D. Rogers, ‘Contemporary issues in forensic handwriting examination. A discussion of key issues in the wake of the Starzecpyzel decision’. Journal of Forensic Document Examination. 1995;8:1-31
 A. Vinter, P. Mounoud, ‘Isochrony and accuracy of drawing movements in children; effects of age and context’. In: J. Wann, A.M. Wing, N. So˜vik (Eds.), Development
of Graphic Skills (London, 1991), 113–114.
 R Plamondon, C O’Reilly, C Rémi , T Duval, ‘The lognormal handwriter: learning, performing, and declining’. Front Psychol. 2013;Dec 19;4:945,10.
 J.F. Vargas, M.A. Ferrer, C.M. Travieso, J. B. Alonso, ‘Offline Signature Verification Based on Pseudo-Cepstral Coefficients’. Proc. of the 10th Int. Conference on Document Analysis and Recognition (ICDAR ’09), Barcelona, Spain, 26-29 July, 2009, 126 – 130.