# Dynamic Handwriting Analysis for Neurodegenerative Disease Assessment: A Literary Review
## 2 Typical Experimental Design
### Data Acquisition
#### 2.1.3 Acquisition Protocol  
A crucial step in designing a computerized tool based on handwriting concerns the choice of the most appropriate handwriting tasks to be administered for data acquisition. Some tasks, in fact, may be redundant with other ones; others may even introduce noise in the data. Some recent works [24; 25; 26], in fact, employed ensembles of classifiers, each built on the feature space of every single task, emphasizing how a performance-driven selection of a subset of tasks can improve classification performance against the use of all tasks simultaneously. Generally speaking, handwriting tasks can be classified into simple drawing, simple writing, and complex tasks: they are described in the following paragraphs. It is worth noting that, in order to allow participants to familiarize with the equipment, some preliminary trials are typically required before the effective experimental session is carried out. Drawing Tasks  
Spirals, as well as meanders and circles, have been frequently used for the evaluation of motor performance. Spiral drawing on a digitizing tablet, in particular, was pioneered by [PERSON] [27] for assessing tremor. In fact, it is particularly suited to study motor control deficits in PD patients. The task is very easy to perform and is usually well tolerated. In general, simple drawings have been used for trajectory, tremor, dimension, and velocity evaluations, e.g., References [23; 28; 29]. Fine motor control problems may be caused by a reduced capability to coordinate the fingers and wrist and by a reduced control of wrist flexion. In Reference [28], for example, MCI and AD patients produced less automated, accurate, and regular movement compared to controls when drawing a spiral with the dominant hand. Differentiation between MCI and controls increased when subjects were requested to press a device, with the nondominant hand, while drawing the spiral. In Reference [30], excellent sensitivity in discriminating AD and MCI patients from controls with in-air movement was observed: the task consisted in copying a simple 3-D house with two windows, a door, and a chimney. Drawing a simple figure is very easy to perform and is usually well tolerated by all subjects. Complexity increases in the intersecting pentagon copying task, which is part of the MMSE test. Patients, in fact, typically exhibit constructional apraxia: drawing may contain fewer angles, spatial alterations, lack of perspective, and simplifications [31]. Patients can be unable to perform the task even if they understand what they should do. In particular, they typically show different drawing strategies: some trace the contours of the figure to be copied, others put points first and then connect them with segments, and so on. These issues can be reflected in the dynamic features of handwriting [31; 32]. Writing Tasks  
No-sense words composed by one or more character repetitions, for example _lll_ and _lele_, can be used, e.g., References [22; 33; 34; 35; 36]. These characters are easy to write in a recursive and continuous fashion. One of the most typical evidence of PD is rigidity and tremor; thus, in contrast to controls,which show an automated handwriting, PD may produce slower and more irregular movements. In addition, PD patients may write letters in a more segmented fashion and show micrographia over time within the task [35]. The difficulty to anticipate the upcoming letter, in particular, may be the expression of a general difficulty in producing simultaneous actions. For this reason, this task can be discriminant also in the case of AD [34]. Writing words/sentences is suited to assess agraphia. A sentence requires a high degree of simultaneous processing and may have a higher neuromotor programming load than a sequence of the same characters, since it also involves linguistic skills, attention, and memory (for example, in the case where the sentence must be remembered).