# Dynamic Handwriting Analysis for Neurodegenerative Disease Assessment: A Literary Review
## 3 Research Directions
### Parkinson's Disease
#### 3.1.1 Disease Insight
PD handwriting statistically exhibited smaller size and larger velocity fluctuation compared to normal handwriting. These findings were reflected in both experimental data and network predictions. [PERSON] et al. [35] hypothesized that, if it is true that PD patients produce sequential movements in a more segmented fashion, then they should have difficulties in anticipating the forthcoming letter. Their experimental findings revealed that handwriting in PD patients did not exhibit any sign of motor anticipation: although they could write three letters without pauses, PD patients tended to produce each letter in a more independent manner. In order to explain this, the authors suggested that the difficulty in anticipating the upcoming letters may be the expression of a general difficulty in producing simultaneous actions. [PERSON] et al. [73] noticed that all the published studies investigating micrographia in PD examined handwriting only in the horizontal direction, as the handwritten samples analyzed were primarily in Western languages. However, several other languages, as those from Eastern Asia, can be written not only horizontally but also vertically, from top to bottom. Since different directions require different joint coordination patterns and writing horizontally requires more wrist extension than writing vertically, the micrographia reported in horizontal writing may not be generalized to characters written vertically. To investigate on this problem, the authors asked patients and controls to write Chinese character _[PERSON]_. The main finding was that the PD group had a linear decrease in overall character size and horizontal strokes along the writing sequence in the horizontal direction but not in the vertical direction. This observation confirms that micrographia in PD may be associated with wrist extension. [PERSON] et al. [74] obtained results in line with the abovementioned study by [PERSON] et al. [63]: they observed that PD patients experience more dual-task interference during writing than controls when performing a cognitive tone-counting task and a writing task simultaneously. Dual-task interference refers to the decreased performance experienced during dual tasking, i.e., when two motor tasks with different goals are combined. More specifically, the secondary task consisted in counting high and low tones during writing. The results obtained showed that dual-task performance was affected in PD patients. In particular, they suggested that the control of writing at small amplitudes requires more compensation brain-processing resources in PD than controls. [PERSON] et al. [36] investigated handwriting tasks that may be helpful to provide a quantitative method to differentiate between PD patients and healthy controls: circle, star, and spiral drawing; _eel_; and writing a sentence. The drawing and writing tasks were analyzed to evaluate the speed of movement to assess bradykinesia and the size of writing to assess micrographia. In addition, a frequency analysis was carried out to assess rest tremor. The results showed that Parkinson patients tend to be slower than healthy control participants. PD patients also wrote smaller than controls. Furthermore, rest tremor was detected in the group of patients who were clinically assessed as having rest tremor. In a very recent work [75], [PERSON] and [PERSON] proposed a novel paradigm aimed at emulating the early stage of handwriting learning in proficient writers by asking them to produce a familiar \(l\)-shape with a novel, unfamiliar motor plan. In other words, participants were asked to produce the sequence of strokes by using a motor plan different from the one an individual is used to. The authors involved young and elderly healthy participants comparing them with the data of the pathological group of the PaHaW dataset. The authors found that Parkinsonian writing during a familiar movement is characterized by lack of fluency, slowness, and abrupt changes of direction, as the handwriting produced by beginner writers.