# Preprocessing for Lessening the Influence of Eye Artifacts in EEG Analysis
## 2 Experimental Setup
### Equipment and Procedure  
The procedure employed follows the directions described by [PERSON] et al. in [PERSON] et al. (2017). The stimuli were presented to the participants by using the software piece Presentation via Sennheiser HD219 headphones. An individual hearing threshold was determined for each participant by playing the royalty free track 'Casual Friday' by Bjokib [[https://bjokib.com/casual-friday-royalty-free-music-free-download/](https://bjokib.com/casual-friday-royalty-free-music-free-download/)]([https://bjokib.com/casual-friday-royalty-free-music-free-download/](https://bjokib.com/casual-friday-royalty-free-music-free-download/)), which was irrelevant to the study. The procedure employed to determine such thresholds were: The playback loudness level started clearly above the hearing threshold and it was manually decreased until the participants reported they stopped hearing the sound; then, the test track was played clearly below the hearing threshold and the loudness was manually increased until the participants reported hearing the sound. The average between these two loudness levels was considered the hearing threshold. After that, the playback loudness level was set to 50 dB above the individually determined hearing threshold.  
The audio tracks were played in the following order: Magic Flute, Emperor Waltz, Universal Mind, Adios Nonino, and, lastly, the speech track. The resting period between the pieces of music was  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Id** & **Age** & **Sex** & **Number of Clean Channels** \\ \hline \(S_{9}\) & 21 & Female & 12 \\ \(S_{10}\) & 21 & Female & 12 \\ \(S_{12}\) & 29 & Male & 14 \\ \(S_{18}\) & 23 & Male & 14 \\ \(S_{19}\) & 20 & Female & 11 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Participants’ data.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Track** & **Trial** & **Duration (in mins)** \\ \hline The Magic Flute & 1 & 7:13 \\ Emperor Waltz & 2 & 5:31 \\ Universal Mind & 3 & 7:54 \\ Adios Nonino & 4 & 8:07 \\ Speech & 5 & 1:20 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Track lengths and their correspondence with the trial numbers.  
determined by the subjects themselves. Each track started after pressing a button whenever they were still, comfortable, and ready to listen to the next piece. Once the button was pressed, the audio track started after an informative message and 3 s of silence.  
The EEG data were recorded by using OpenVibe v2.2.0 software with a 16-channel TMSi Porti system with water-based electrodes. A total of 14 electrodes were placed on the scalp according to the modified combinatorial nomenclature of the 10-20 system for the placement of electrodes [18]; the specific electrode locations employed were: Fz, F3, F4, FCz, Cz, C3, C4, T7, T8, CPz, Pz, P3, P4, POz. Furthermore, one electrode was placed vertically at the right eye (EOG) and one as ground on the forehead. The TMSi system takes the average of all electrodes as reference. The data were collected at a 2048 Hz sampling rate. The beginning and end of each musical piece was marked with a trigger into the EEG data.  
The EEG data of all the participants were imported into Matlab 2018b [19] and the processing was made mostly with the FieldTrip toolbox [20].