Theory: Handwriting and Signatures - Some basic facts and theory
1. The Physiology of Handwriting Production
Handwriting originates in the brain when a mental picture of letters and words is formed. The signal to try to duplicate the mental picture is sent to the arm and hand through the muscles and nervous system. The actual output is almost never an exact match of the original mental picture.
Let's look at how a human learns to use his or her brain and nervous system to write. Appreciation is extended to Dr. Bryan Found and Dr. Doug Rogers at the Forensic Expertise Profiling Laboratory, School of Human Biosciences at LaTrobe University, Australia, for their voluminous work in this area and for disseminating most of the following information in articles and professional presentations.
2. Automatic Abilities Grow into Patterns
When a baby is born, he/she is equipped with some basic, automatic abilities. He can breathe, cry, suck, move his limbs randomly. For more complex tasks, the baby must learn. Patterns are formed and stored in the brain to trigger messages to the nervous system and muscles to produce movements (behavior). Smiling is a simple behavior that a baby learns early in life. First, he imitates his parents' smiles. As smiles are rewarded by more smiles and hugs from his parents (positive feedback), a pattern is built. Soon, smiling becomes automatic, like breathing. Similarly, the baby learns to reach, grasp, speak and walk. Handwriting is a very complex motor task, not usually learned until the child is 5 or 6 years old and has mastered simpler skills.
3. The Motor Control System
The motor system controls the movement and posture needed for handwriting by contraction and relaxation of muscles. Messages go to and from the muscles and brain via the nervous system. During the learning process, the senses and muscles send messages (feedback) back to the brain to let it know how the sequence, timing and force applied worked out. The brain makes the adjustments needed to give a maximal outcome. Eventually a motor program is formed. This is a set of muscle commands that can be carried out with the correct timing and sequence automatically, without feedback, to give the best possible result.
Handwriting is the result of such stored motor knowledge. Handwriting is distal, meaning that it occurs at the extremities and involves fine motor activity as opposed to a skill like walking which is proximal - a large, or gross motor skill. One reason individuals find it difficult to simulate the handwriting of others is that to do so successfully requires understanding the essence of the writer's motor control program and executing a motor control program that yields a very similar result.
Now, lets do an experiment. Take a clean unlined sheet of paper and write your signature near the top. Next, hold your pen or pencil in your clenched fist and sign your name by moving your wrist and arm. Then bend your arm fully and hold the pencil in the crease at your elbow and sign your name with your elbow guiding the pen. While the second and third signatures do not have the fluency, size and proportion of the first signature, you will see that the same overall pattern prevails. This is because the programs to perform the complex movements required to produce a written word are stored in the brain, not in the muscles. If you want to further prove this to yourself, try to write your first name in the air with your nose or your foot. You can do it, right? The basic information to do this came from your brain, not from the muscles of your shoulder, arm, fingers, or nose.
6. Body as a Machine
Once the basic pattern is established, the muscles and nerves of the shoulder, arm, hand and fingers become important because they certainly effect the appearance of the written line. You can think of the body as a machine, a series of levers and fulcrums (pivot points) with each part influencing the working of the next part in the link. The strength and flexability of the muscles, the position of the pen grip and the overall posture of the writer all affect the output.
7. Variety: The Natural Range of Handwriting
None of the factors that produce handwriting are rigid and unchanging. In addition to the organic factors (physical anatomy and health, mental acuity, etc.) there are environmental factors affecting the handwriting. These include the writing instrument itself, the writing surface and what lies beneath it, and other variables of the writing situation. Because the primary motor pattern is itself a fluid image and because there are so many organic and environmental variables that interact in the production of handwriting, it has become an accepted axiom that a person is unlikely to ever duplicate any signature exactly. Each person has a range of natural variation. But even with this range of variation, each person grows in his or her writing from the classic forms taught in childhood into an individual and identifiable form of written expression.
Handwriting characteristics come in two categories - general, or class characteristics, and individual characteristics. Depending on the cultural setting (time and place) when writing is learned, entire groups of individuals may be taught or trained to write in the same way. When these individuals are first learning to write, there are differences in their ability to do the task, and the results are not all the same, but the true individualizing differences appear over time. As we grow and mature physically and personally, our handwriting becomes more of an individual product - through conscious changes made to fit a mental picture of how we want our writing to appear, or unconsciously.
Handwriting can also be affected by other factors - injury, illness, medication, drug or alcohol use, stress, the writing surface, the writing instrument, or attempted disguise. It is the job of the document examiner to understand these factors as they might relate to a specific situation.
Handwriting is a free-form activity, and there are an infinite number of ways to write even the simplest letter combination. It is highly unlikely that any person will write his or her own name exactly the same way twice in an entire lifetime.
Actually, every person has a range of handwriting variation determined by his or her physical writing ability, training in "penmanship", and other factors. To the experienced expert, a study of known samples of writing can reveal a cluster of individual writing characteristics which can allow the expert to identify or exclude an individual as the author of some questioned writing.
What a forensic document examiner can't tell you about handwriting:
Handedness - Right or Left?
While there are indicators that point to right or left handedness, it is not possible to be certain that the writing was executed with the right or left hand.
Again, while there are indicators that might be more associated with male or female handwriting, it is not possible to be certain of the gender of the writer.
Yes, there are features often associated with the writing of older or younger people, but there is too much crossover to allow for any certainty about the age of the writer.