# Predicting the Onset of Freezing of Gait Using EEG Dynamics
## 2 Materials and Methods
### Experimental Design  
The patients were in their off state, having had no medications for at least 12 h when they participated in this study. They performed the TUG task, starting with the participants seated. The participants were instructed to stand up and walk towards a target location in a large corridor. The target location was marked on the floor using a box with dimensions of 0.6 m \(\times\) 0.6 m, positioned 6 m away from the starting position to allow for multiple FOG episodes. The participants were instructed to turn within the marked box. In the TUG tasks, the participants were asked to perform either a 180\({}^{\circ}\) or a 540\({}^{\circ}\) turn. Turning within a box elicits freezing episodes in PD patients. The researcher initially demonstrated the task and the direction to turn within the box, and the participants followed the researcher's example. The experiment was video recorded and reviewed by two clinical researchers to identify freezing episodes.  
As described in [17], we considered two variants of the TUG task: the classical TUG task and the TUG task with a voluntary stopping element. As shown in Figure 1A, the classical TUG task was employed as it elicits freezing in PD patients [19]. We considered two seconds immediately preceding the freezing episode as the transition to freezing. The period of two seconds before this transition period was regarded as normal walking.  
In the TUG tasks with the voluntary stopping element (Figure 1B), the researcher guided the participant in the voluntary stopping by providing verbal instructions such as \"stop\" and \"walk\". In these TUG trials, the target box was located 10 m away from the starting position. The box was located 10 m from the starting position in these TUG tasks so as to prevent participants from anticipating exactly when they might receive the instruction to stop walking. Furthermore, verbal instructions to stop walking were generally provided to the participants while they were walking back to the chair after turning inside the box. The participants were required to stop as soon as they heard the researcher say \"stop\", and they resumed walking when the researcher said \"walk\", usually in 5-10 s. We defined two seconds when the researcher said \"stop\" and the participants were preparing to stop walking as the transition to voluntary stop. We also considered two seconds before the \"stop\" instruction as normal walking. The participants were randomly asked to perform a standard TUG task or TUG task with voluntary stopping to avoid any habituation effects.  
Even though we strived to have an equal number of normal walking, transition to FOG, and voluntary stopping, this was not accomplished. The well-being of the patients was given the top priority, and we stopped the experiment for any PD patients who expressed difficulty in continuing with the experiment. Hence, we could not collect an equal number of trials for normal walking, transitions to FOG, or voluntary stopping. Table 1 shows the number of normal walking trials, the number of transitions to FOG, and the transitions to voluntary stopping for each participant.