This study investigated the relationship between developmental changes in writing dynamics and the characteristics of developmental disorders in children and adults with typical development. The results showed that the children were significantly delayed in both overall speed and peak maximum speed (the maximum speed achieved when writing words). Kinugasa et al. previously found that IPUT performance time decreased as age increased based on measurements of finger skills [17]. In this study, IPUT execution time was significantly shorter in adults, while developmental changes were observed in both adults and children. However, no correlations were found between the speed item and IPUT execution time (p > .32). This suggests that writing speed is related to factors other than finger dexterity and coordinated movement as measured via IPUT.
Furthermore, we studied the relationship between the strength of the characteristics of the developmental disorder and writing dynamics. Regarding the relationship between ADHD-RS results (which indicated ADHD tendencies) and writing dynamics, positive correlations were found with inattention and pressure SD, respectively. A positive correlation was observed between the positive pressure change SD and the negative pressure change SD, which indicates that increased hyperactivity/impulsivity is related to a greater pen pressure SD. In the DSM-5, one of the behavioral traits listed for children with ADHD is a dislike of engagement in tasks that require sustained mental effort [6]. This includes the continuous performance task (CPT). An earlier study on CPT found a correlation between accuracy rate SD and inattention based on the ADHD-RS [18]. Research has shown that higher carelessness in persons with ADHD is associated with a greater variance in the standard deviation of the volatility of the reaction. Writing tasks require constant attention and mental effort, and it is presumed that participants will show a greater variability of reactions (i.e., variability of writing pressure).
Furthermore, a correlation was found between writing speed and ASD tendencies. Higher “detailed interest” values on the AQ were associated with less time needed to write a word and faster pen speeds. Children with ASD are known to have features that make it easy to pay attention to details [19]. In addition, there is no delay in the processing speed of Wisc-4 [20], and it has been reported that the drawing time is short when drawing a simple figure [21]. Participants with a strong interest in details were suggested to be able to write faster.
In addition, higher AQ “social skill” values were associated with the slowest pen speeds. In this regard, fewer eye movements were reported in the ASD-prone group [22]. It is also known that children with ASD have problems with facial expression recognition, which is closely related to sociality [23]. This could not be elucidated this time, but perhaps social development may also be related to vision. It has been pointed out that eye movements tend to directly reflect the control of the nervous system in the brain, suggesting a relationship between social disorders and eye movements [24].
In this study, we found a correlation between the distribution of writing pressure and ADHD tendencies. Additionally, writing speed was correlated with ASD tendencies, suggesting that the characteristics of each developmental disorder may be captured based on measurements of writing dynamics. However, as the DSM-5 points out the potential coexistence of multiple developmental disorders, it is difficult to complete a differential diagnosis between ADHD and ASD, especially since developmental disorders are expressed through a complex set of behaviors at various levels of severity. Therefore, more research is needed to establish a link between the characteristics of certain developmental disorders and writing. However, the early detection of both ADHD and ASD is still important. To develop a system that enables simple differential diagnoses, we would eventually like to examine the relationship between writing and developmental disorders from various perspectives, including those rooted in brain function measurements.