## 2 Methodology
### Data Preparation and Evaluation  
The EEG data are collected after each participant has completed a concentration test, as described in Figure 2, while playing each of the three virtual reality (VR) video games listed in Table 2. To measure the level of cognitive concentration elicited in each volunteer (player), based on the spectral power density (PSD) of the EEG, individual alpha frequency (IAF), and frontal alpha asymmetry (FAA), the following EEG data processing was conducted: \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Classification**} \\ \hline  & **Challenging Puzzlers** & **Casual Games** & **Exergames** \\ \hline \multirow{3}{*}{**Characteristics**} & Challenging activities & Easy to play & Physical activity \\  & Enjoyable & Attractive design & Challenges \\  & Playful work & Enjoyable & Motivation \\ \hline \multirow{3}{*}{**Objective**} & Education & Distraction & Calories burning \\  & Training & Quick hitch & Increase heart rate \\ \cline{1-1}  & Concentration & & Coordination \\ \cline{1-1}  & Absorption & & Attention \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics and objectives. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Video Games**} \\ \hline  & **1: Cubism** & **2: Angry Birds** & **3: Beat Saber** \\ \hline \multirow{3}{*}{**Properties of the game**} & Calm music & Upbeat music & Rhythical music \\  & Pastel color & Saturated color & Neon colors \\ \cline{1-1}  & Use of control or hands & Use of control or hands & Use of control \\ \cline{1-1}  & Interaction with objects & Interaction with objects & Interaction with objects \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of video games. Participants were outfitted with an EEG device during the games to measure the brain's electrical activity in different frequency bands, including the alpha band. EEG data were recorded at a sampling rate of 500 Hz for a period of 15 min. Each of the three games lasted 15 min, with a brief 5-min break between each. The games were chosen to provide a variety of difficulty levels, as well as different genres of games, to assess cognitive skills while playing. * EEG data were processed to analyze the brain's electrical activity in different frequency bands, including the alpha band (8-12 Hz). PSD in the alpha band was compared to activity in the other frequency bands to measure concentration. PSD in the alpha band was calculated using the Welch method: \[S_{xx}(f)=\frac{1}{N_{FFT}\cdot\Delta}\cdot\sum_{i=0}^{M-1}\frac{|X_{i}(f)|^{2} }{N_{avg}}\] (1) where \(S_{xx}(f)\) is the power spectral density at frequency \(f\), \(N_{FFT}\) is the number of points used in the FFT, \(\Delta\) is the time interval between overlapping signal segments, \(M\) is the total number of signal segments, \(X_{i}(f)\) is the Fourier transform of the \(i\)th EEG signal segment, and \(N_{avg}\) is the number of segments averaged in the Welch method. * The IAF of each participant was measured using a custom algorithm to detect the individual frequency of the alpha wave in the frequency spectrum of each participant. The computation of these average IAF values is described in detail in Algorithm 1. Alpha wave activity was analyzed at each participant's frequency to determine if any activity change could indicate a state of concentration.