Occupational therapists have worked for a long time to improve the activities of daily living for patients with hemiplegia. (Re)acquisition of handwriting ability in target patients is an important item. Many patients with a paralyzed dominant hand have difficulty writing and drawing with their paralyzed hand1. Patients with hemiplegia with a mildly paralyzed dominant hand could practice handwriting using the paralyzed hand. However, handwriting skills are greatly affected when the dominant hand is impaired, even with conditions like minor motor paralysis2. This is because handwriting requires complex coordination of the muscles of the upper extremities 3. If writing is not possible with the dominant hand, patients with hemiplegia who have a paralyzed dominant hand have to write and draw with their non-dominant hand4,5.
In the age of digitalization, handwriting skills are not always necessary. However, it is crucial to retain handwriting ability to prove oneself, such as being asked for a handwritten signature on the back of a credit card 6.
Many patients with hemiplegia complain that their hand prowess is weak when writing. This is due to the fact that the lack of strength in the hands is directly linked to the difficulty in controlling writing pressure.
An easy-to-read character is the one that constitutes a word, has a proper shape and size, and can be clearly distinguished from other characters. Character morphology, writing speed, and fluency can be visually perceived while writing7. These are called handwriting skills and have been analyzed in great detail so far8–10.
Writing (pen) pressure is an important factor in writing easy-to-read characters8. Writing pressure is the pressure applied to the desk when handwriting11. For patients with hemiplegia, we have been searching for a way to obtain stable writing pressure. Vantha changes in writing pressure depended on the writing task and each condition (letters, words, text size, speed, and across a page of text)12.
In this way, when writing pressure changes due to various factors during handwriting, some type of index is required to generalize changes in writing pressure. Furthermore, considering that Japanese language is composed of straight lines and curves, it is necessary to perform a mechanical task to clarify the relationship between basic writing pressure and eye movement12. A previous study reported a method of clarifying handwriting problems in infants was drawing and it also showed that the analysis of changes in writing pressure in drawing can be one of the indicators of handwriting ability13. Furthermore, Nishi et al. showed that a simple tracing test displayed on a tablet terminal could be used to evaluate finger dexterity in patients with cervical spondylotic myelopathy and that writing pressure was one of the indicators14. Therefore, we analyzed the writing pressure variation by drawing a simple line based on the findings of these studies.
Since a drawing task is simpler than writing letters, writing pressure and eye movement can be measured and analyzed during this task. However, writing pressure cannot be physically visualized. Since 2000, digital drawing has become common, and many detailed studies have been conducted on writing pressure.
Previous studies on writing pressure focused on analyzing changes in writing pressure over time and average writing pressure values 15. Murase et al. used repetitive transcranial magnetic stimulation in patients with writer’s cramp to stimulate the premotor cortex at a subthreshold low frequency (0.2 Hz) that exerts an inhibitory effect on the cortex16. The results showed significant improvement in writing pressure fluctuations in patients with writer’s cramp. Gatouillat et al. reported that the pen tip normal force (writing pressure) was not affected by the experiment in which they were instructed to draw a circle under varying speed and rhythm conditions17. Furthermore, Danna et al. showed that increasing pressure (either passively or actively) on the pen impaired drawing accuracy11.
Clinical observation showed that many patients with hemiplegia keep their gaze on the pen tip when writing with paralyzed hands. Additionally, when the patients were instructed to control writing pressure during writing exercises, they kept their gaze on the pen tip. By looking at the pen tip, they appear to confirm the movement and power of their hands and the letters. Based on this phenomenon, we considered that eye movement during writing in patients with hemiplegia might be involved in controlling writing pressure. Many studies have been conducted on eye movements, showing that people use visual information through eye movements when they perform tasks with their hands18.
Eye movements are classified into fixation, smooth pursuit, and saccades19. Saccades are rapid eye movements 20, and they guide hand movements21,22.
Smooth pursuit is an eye movement that slowly follows an object; in recent years, its role is said to be the prediction of motion and collection of visual information (feedback), which are necessary to improve accuracy7,23,24.
Visual information plays a crucial role in handwriting and drawing. Chamberlain et al. reported that accurate visual recognition of objects is central to drawing ability25. Furthermore, Gowen and Miall compared eye movements during tracing and drawing and described visual guidance in eye-hand coordination26. Domkin et al. showed that good vision group had fewer errors in tracing and complex tasks than the low vision group27. Additionally, Tchalenko reported that “close pursuit” and “target locking” modes and their combination are used for eye movements that occur during simple delineation movements28. However, to the best of our knowledge, no reports have investigated changes in eye movement and writing pressure, in patients with hemiplegia as well as healthy people.
Problems in patients with hemiplegia, even with little or no motor paralysis, have been reported to limit eye-hand coordination29–32. Furthermore, obtaining baseline data from patients with hemiplegia is difficult because each individual is affected differently. Thus, we decided to investigate the writing pressure and eye movements during handwriting and drawing with the dominant hand in healthy adults. Results obtained from healthy adults can be used as a reference not only for patients with hemiplegia but also for those with other diseases.
We hypothesized that the writing pressure fluctuation decreases when the line of sight follows the pen tip during drawing (close pursuit type). In contrast, the frequency with which the pen tip is checked decreases, and the writing pressure fluctuation increases when the endpoint of the line is fixed immediately after starting drawing (target locking type).
Students are traditionally taught to draw horizontal lines from left to right when writing Japanese. Thus, drawing horizontal lines from left to right is a familiar task for Japanese people, whereas drawing horizontal lines from right to left is an unfamiliar task even with the dominant hand. If the two have the same result, we predict that this could provide stronger evidence. If visual information is involved in drawing accuracy, teaching patients how to use visual information to control their writing pressure would be a beneficial way to improve their drawing skills.
This study aimed to investigate whether eye movement during a drawing task with the dominant hand in healthy adults affects writing pressure fluctuation.