## 2 Materials and Methods
### Data Analysis  
The estimated marginal means were charted for the absolute value of frequency band power and its amplitude, which were expressed in microvolts (\(\upmu\)V), for each headset's electrodes. The estimated marginal means were plotted across participants though the analysis was performed according to the electrode-wise schema (one-to-one paired matching between homologous electrodes). In order to compare headset accuracy and reliability when using the same channels, the Emotiv EPOC's 14 electrodes were matched to Brainvision's 14 correspondingly-located electrodes. Thus, the 14 electrodes used in Emotiv were AF3, AF4, F3, F4, F7, F8, FC5, FC6, T7, T8, P8, P7, O1 and O2, while the 14 ones used in Brainvision were FP1, FP2, F3, F4, F7, F8, FC5, FC6, T7, T8, P7, O1, O2 and Oz (see Figure 1). (Note that the EPOC system doesn't have electrodes placed along the midline of the head, and it uses the CMS and DRL electrodes as dual reference points, instead of a single ground electrode as in the Brainvision system. Pooled reference electrodes are shown in green in Figure 1)The estimated marginal means of both amplitude and power were reported in figures to demonstrate visually the detection of arousal, valence and workload, in addition to each EEG's ability to discriminate between high and low psychologically defined states in these three conditions (all these figures are included as Supplementary Materials). For conciseness, we summarize all main findings in the table below (see Table 1A,B). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**(A)**} \\ \hline  & \multicolumn{6}{c}{**EPOC**} & \multicolumn{6}{c}{**Brainvision**} \\ \hline \multirow{2}{*}{**Band**} & \multicolumn{2}{c}{**Mental State**} & \multirow{2}{*}{**z**} & \multirow{2}{*}{**\(p\)**} & \multirow{2}{*}{**\(\mathbf{\mu^{2}}\)**} & \multicolumn{2}{c}{**Mental State**} & \multirow{2}{*}{**z**} & \multirow{2}{*}{**\(p\)**} & \multirow{2}{*}{**\(\mathbf{\mu^{2}}\)**} \\ \cline{2-2} \cline{5-10}  & **Low** & **High** & & & & & **Low** & **High** & & \\ \hline \multicolumn{10}{c}{(ANEW, Arousal)} \\ Delta & 2.02 & 2.16 & \(-\)1.10 & 0.271 & 0.09 & 10.74 & 9.34 & 3.18 & 0.001 & 0.72 \\ Theta & 1.48 & 1.57 & \(-\)1.57 & 0.116 & 0.18 & 8.57 & 7.044 & 3.30 & \textless{}0.001 & 0.78 \\ Alpha & 2.22 & 2.30 & \(-\)1.45 & 0.148 & 0.15 & 13.23 & 11.344 & 3.30 & \textless{}0.001 & 0.78 \\ Beta & 2.20 & 2.11 & 1.51 & 0.132 & 0.16 & 16.53 & 18.784 & \(-\)2.23 & 0.026 & 0.36 \\ Gamma & **0.89** & **0.97** & **\(\mathbf{-2.04}\)** & **0.041** & **0.30** & **14.94** & **18.99** & **\(\mathbf{-3.23}\)** & **0.001** & **0.75** \\ \hline \multicolumn{10}{c}{(ANEW, Valence)} \\ Delta & **1.45** & **1.77** & **\(\mathbf{-2.07}\)** & **0.039** & **0.31** & **6.65** & **8.19** & **\(\mathbf{-3.30}\)** & **\(\mathbf{<0.001}\)** & **0.78** \\ Theta & 2.10 & 1.72 & 1.30 & 0.195 & 0.12 & 5.62 & 5.93 & \(-\)3.30 & \textless{}0.001 & 0.78 \\ Alpha & 2.13 & 1.98 & 0.88 & 0.379 & 0.06 & 10.28 & 10.51 & \(-\)1.38 & 0.167 & 0.14 \\ Beta & 2.50 & 2.18 & 2.10 & 0.036 & 0.32 & 12.50 & 13.55 & \(-\)3.30 & \textless{}0.001 & 0.78 \\ Gamma & **0.52** & **0.70** & **\(\mathbf{-3.04}\)** & **0.002** & **0.66** & **11.27** & **12.21** & **\(\mathbf{-3.17}\)** & **0.002** & **0.72** \\ \hline \hline \end{tabular}
\end{table} 
Table 1: **A**. Grand averaged event-related power amplitudes and nonparametric contrasts for low vs. high mental states in ANEW, IAPS and n-Back Tasks measured by a consumer-grade (EPOC) and a research grade (Brainvision) EEG system. (Statistics were performed on electrode-wise repeated measurements, N = 14). **B**. Grand averaged cumulated power and nonparametric contrasts for low vs. high mental states in ANEW, IAPS and n-Back Tasks measured by a consumer-grade (EPOC) and a research grade (Brainvision) EEG system. (Statistics were performed on electrode-wise repeated measurements, N = 14). Figure 1: Left Panel: Brainvision (32-electrode) EEG system with ground at Cz.