## 2 Materials and Methods
### Procedure  
All participants performed the handwriting tasks while they were comfortable seated in front of a desk. Handwriting samples were collected through a digitizer tablet (WACOM Intuos 29 \(\times\) 12, active area 24.06 cm \(\times\) 30.48 cm, manufacturer: Wacom, Saitama, Japan) that recorded the pen tip movements (Intuos2 Ink Pen XP-110 with a ballpoint refill, manufacturer: Wacom, Saitama, Japan). This tablet does not display the pen trace, but was overlaid with a paper on which participants performed the handwriting tasks. Using the inking pen enabled participants to write naturally while seeing the ink trace produced. Pen tip position (x and y coordinates) and pressure were recorded by the table with 0.001 cm of spatial resolution and 100 Hz sampling rate. We used the software MovAlyzeR (NeuroScript LLC, Tempe, AZ, USA) [34] for setting-up the entire experimental procedures. Participants used their dominant hand to perform handwriting tasks and were instructed to write at their more comfortable speed. Subjects were asked to perform the writing tasks according to the instructions by the experimenter and shown by a brief animated movie of the task. The writing tasks had to be performed in 10 conditions, each task in a separate box. The dimensions were 2 cm \(\times\) 12 cm for Tasks 1-8 and 3 cm \(\times\) 12 cm for Tasks 9 and 10. The tasks were printed on a horizontally oriented A4 sheet (Figure 1). In previous work [16], we asked healthy subjects to write separated l-loops in two fashions: in the normal counterclockwise fashion and clockwise fashion (denoted as Tasks 1 and 3 in Table 2), i.e., as they are used to and in the opposite direction, respectively (Figure 2 reports an example of the tasks and the direction of the pen tip).  
\begin{table}
\begin{tabular}{l c c c} \hline \hline  & **PD** & **Healthy** & **Two-Tailed \(t\)-Test** \\  & **N = 13** & **N = 14** & _df = 25_ \\ \hline Gender & 7 men and 6 women & 8 men and 6 women & \(p>0.05\) \\ \hline Age (years) & 64.4 \(\pm\) 1.5 & 60 \(\pm\) 1.9 & \(p>0.05\) \\ \hline Education (years) & 9.4 \(\pm\) 1.2 & 11.3 \(\pm\) 1.3 & \(p>0.3\) \\ \hline Handedness score & 76.7 \(\pm\) 12.2 & 69.4 \(\pm\) 12.1 & \(p>0.6\) \\ \hline MoCA corrected & 21.6 \(\pm\) 0.7 & 22.1 \(\pm\) 0.8 & \(p>0.6\) \\ \hline BDI & 3.2 \(\pm\) 0.7 & 2.5 \(\pm\) 0.8 & \(p>0.5\) \\ \hline Disease Duration & 44.1 \(\pm\) 5.6 & & \\ (months) & & & \\ \hline Modified & 1.5 \(\pm\) 0.1 & & \\ [PERSON] \& [PERSON] score & & \\ \hline UPDRS III & 20.6 \(\pm\) 2.6 & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Demographic characteristics and data about clinical evaluation of the subjects participating in the experiments. Features are reported in terms of mean \(\pm\) SEM.  
Hereinafter we refer to these conditions as habitual and novel, respectively. Ten handwriting tasks composed the protocol, which is based on the same paradigm used in [16], and includes other handwriting modalities: free and guided conditions, which consist of drawing the loops freely (Tasks 1, 3, 5, 7 in Table 2) or following a set of visual cues (Tasks 2, 4, 6, 8 in Table 2); simple and complex (multiple) conditions, which consist of drawing single l-loops (Tasks 1, 2, 3, 4 in Table 2) or a set of multiple, connected l-loops with different heights (the word _\"elle\"_, Tasks 5, 6, 7, 8 in Table 2);  
which consists of drawing a set of multiple, connected l-loops, twice bigger than the other tasks, following a sequence of dots (Tasks 9, 10 in Table 2).  
Boxes related to the first eight tasks had a straight baseline at 0.8 cm from the bottom, those related to the guided tasks contained blue dots located at the starting and ending points, crossing points, and maximum curvature points of the l-loops. Table 2 reports for each task the instructions provided and an example of a subject's execution. For free tasks, we provided no constraints on the number of repetitions.