# Cross-Subject Classification of Effectiveness in Performing Cognitive Tasks Using Resting-State EEG
## 2 Materials and Methods
### Experimental Design  
Participants were seated comfortably in a soundproof room at 1 m from a 19-inch square monitor. During recording of resting-state EEG participants were instructed to sit calmly with their eyes open. After a 5-min recording of EEG, participants were asked to solve mental tasks, giving equal importance to accuracy and the shortest solution time. Tasks were displayed in gray in the center of a black screen, the size of letters and numbers was the same for all tasks. We presented three types of tasks in pseudo-random order: 60 verbal tasks (anagrams of 5-6 letter words), 60 tasks for complex mental arithmetic including two-digit multiplication and 60 logical tasks to continue arithmetic sequences  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Group/Social-Demographic Status** & **Total, \(n\)** & **Male, \(n\)** & **Age, Mean \(\pm\) StDev** & **AM, \(n\)** & **BM, \(n\)** \\ \hline AM & 12 & 9 & 27.00 \(\pm\) 5.36 & - & - \\ \hline BM & 14 & 5 & 24.64 \(\pm\) 4.47 & - & - \\ \hline HS: DT \textless{} median & 13 & 9 & 25.15 \(\pm\) 5.16 & 7 & 6 \\ \hline MS: DT \textgreater{} median & 13 & 5 & 26.31 \(\pm\) 4.85 & 5 & 8 \\ \hline SAM: DT \textless{} median in AM group & 6 & 5 & 23.83 \(\pm\) 4.17 & - & - \\ \hline SBM: DT \textless{} median in BM group & 6 & 3 & 24.33 \(\pm\) 3.27 & - & - \\ \hline LAM: DT \textgreater{} median in AM group & 6 & 4 & 30.17 \(\pm\) 4.67 & - & - \\ \hline LBM: DT \textgreater{} median in BM group & 6 & 2 & 22.50 \(\pm\) 1.97 & - & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: Social-demographic data for the studied groups (DT—decision time).  
(Table 2). The trial consisted of instructions for the task (2 s), a fixation cross (0.5 s), the task (<40 s), and a black screen during the participant's response (4 s) (Figure 1). Table 1 illustrates examples of the tasks.  
The tasks were presented with a duration limited to 40 s. Participants clicked the left button of the PC mouse when they were ready to respond. If no answer was given within 40 s, the task was considered unsolved and new trial started. Correctness (CA) and decision time (DT) was recorded. DT was calculated from the start of the task to the participant's response. Additional breaks were given every 20 to 30 min or at the request of the participant. The whole experiment usually lasted 2 to 2.5 h. Behavioral data were used to divide participants into groups according to their efficiency: the highly successful (HS) group whose mean DT for correctly answered tasks was below the median (\(n\) = 13; age 25.38 \(\pm\) 5.06 years, range 19-38 years; 8 men, 8 AM) and the moderately successful (MS) group with mean DT above the median (\(n\) = 13; age 26.08 \(\pm\) 4.6 years, range 20-37 years; 6 men, 4 AM). Further, based on the efficiency criteria, we ranked participants inside the AM (\(n\) = 12; age 27 \(\pm\) 5.36 years; 9 men, 7 HS) and BM (\(n\) = 14; age 24.6 \(\pm\) 4.47 years; 5 men, 6 HS) groups. Aiming to find out whether the classification results depended on how successful subjects were at task-solving we performed cross-subject classification of the six most successful participants from the AM group (SAM) against the most successful participants from the BM group (SBM), and vice versa: the six least successful participants from the AM group (LAM) and the six least successful participants from the BM group (LBM) (Table 1).