# Dynamic Handwriting Analysis for Neurodegenerative Disease Assessment: A Literary Review
## 3 Research Directions
### Parkinson's Disease
#### 3.1.1 Disease Insight
[63] tested the hypothesis that PD patients are more vulnerable to a moderate level of secondary task load than elderly or young controls due to a heightened variability in the motor system. Patients and the two control groups were requested to write a sentence under four load conditions: start writing after they heard the recorded word \"start\"; ignore auditory presented digits while writing; repeat orally the presented digits; and subtract the number 2 from each presented digit and pronounce the outcome aloud. The results obtained showed that, in contrast to young and elderly controls, PD patients tended to increase movement time and normalized jerk when the secondary task consisted primarily of motor load. Furthermore, it was shown that PD patients did not reduce writingsize because of a high level of mental load: this suggested that writing in an automated fashion does not cause micrographia. [PERSON] et al. [60] investigated whether PD patients can have difficulty in increasing stroke size, decreasing stroke duration, or both during the execution of noncomplex handwriting tasks. To this end, they designed an experiment comprising simple writing patterns, such as straight lines and circles, requesting participants to vary writing size and speed. Although the different handwriting patterns affected movement time and writing size significantly, patients did not show increasing difficulty in maintaining writing size and/or stroke duration because of a decrease of pattern complexity: thus, it was argued that the complexity of a pattern is likely to not be a relevant factor in handwriting. In Reference [64], [PERSON] et al. addressed the problem of determining whether practice modifies the temporal and spatial features of handwriting in PD patients. The findings obtained showed that PD patients can change their performance thanks to practice, suggesting that practice may help them to partly overcome bradykinesia. Nevertheless, they never reached the performance level obtained by the elderly control group. [PERSON] et al. [65] hypothesized that the cause of micrographia in PD patients can be associated with the concurrent processing demands that result from the coordination and control of fingers, wrist, and arm during writing and processing of future words. In their experiments, patients and controls were requested to write four different phrases of various word counts. All phrases started with an _llll_ pattern, and this pattern was repeated later in the phrase. PD patients reduced stroke size when the number of words increased in the phrase, i.e., when the processing demand increased. This finding suggested that the motor system of PD patients anticipates increased processing demands by reducing stroke size rather than increasing stroke duration. [PERSON] et al. [66] compared PD patients to elderly people and young adults with respect to their ability to use visual feedback to control handwriting size. Participants wrote sequences of cursive _l_-shaped loops on a digitizer display, which enabled the authors to distort the visual feedback without the participant's knowledge by altering the vertical dimension of handwriting. The results showed that controls gradually corrected loop size by enlarging (or reducing) the size of the entire loop sequence. Conversely, PD patients showed an entirely different response: instead of correcting for the distortions, they progressively amplified its effect. This suggested that PD patients do not adapt their visuomotor map in response to the distorted visual feedback of handwriting. Instead, they seem to rely constantly on the visible trace feedback during the ongoing movement. The authors thus hypothesized that they either plan their writing based on the visual feedback of their previous strokes or that they attempt to track the ongoing, distorted handwritten trace. [PERSON] et al. [67] evaluated the ability of PD patients to increase stroke size independently of stroke duration for different sizes.