## Appendix B Trends in Number of Publications for EEG-Based Emotion Recognition
### Classification of Articles by Online Database and Journal  
There are a total of 285 articles, published by 34 online databases. Classifications of articles by online database and journal are shown in Tables A2 and A3, respectively.  
In Table A2, we specify our top ten online article databases. Each of these hosted a minimum of five article publications that matched our search criteria. Of these, Science Direct had the highest percentage of articles (103 articles, 36.1%). The likely reason for this is that Science Direct publishes a coterie of different journals, such as Neurocomputing; International Journal of Psychophysiology; Biomedical Signal Processing and Control; Computers in Biology, Medicine, Brain, and Cognition; Brain Research; and Computers in Human Behavior. All of these journals publish EEG-based emotion recognition system articles. Similarly, Springer Link also hosts a cross-section of journal articles from various fields. Consequently, their database recorded the second-highest number of articles: 27 articles, or 9.5% of our total research articles. Other online databases are IEEE Xplore (23 articles, or 8.1%), Frontiers (22 articles, or 7.7%), Taylor & Francis (16 articles, or 5.6%), and Wiley Online Library (12 articles, or 4.2%).  
Table A3 shows the number of articles in each journal publication. We only documented journals with more than two published articles. Most of these journals were related to neuroscience, biology, physiology, computer science, electronic engineering, and healthcare. Of these, PLOS ONE published 10 articles (or 3.5%); International Journal of Psychophysiology and IEEE Transactions on Affective Computing each published 9 articles (or 3.2%).  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Online Database** & **Number of Articles** & **Timeframe** & **Online database** & **Number of Articles** \\ \hline Science Direct & 103 & 2005–2016 & Wiley Online Library & 12 & 2007–2015 \\ Springer Link & 27 & 2006–2016 & Plos.org & 10 & 2012–2016 \\ IEEE Xplore & 23 & 2006–2016 & World Scientific & 8 & 2010–2016 \\ Frontiers & 22 & 2010–2016 & Hindawi & 6 & 2013–2016 \\ Taylor \& Francis & 16 & 2006–2016 & Oxford & 6 & 2008–2016 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Classification of articles based on the online database.  
\begin{table}
\begin{tabular}{l c c} \hline \hline
**Journal (Impact Factor IF, Citation C)** & **Number of Articles** \\ \hline PLOS ONE (IF: 2.806, C: 188) & 10 \\ \hline International Journal of Psychophysiology (IF: 2.582, C: 360), IEEE Transactions on & 9 \\ Affective Computing (IF: 3.149, C: 1593) & \\ \hline Frontiers in Human Neuroscience (IF: 3.209, C: 73), Neuroimage (IF: 5.835, C: 283), & 7 \\ Frontiers in Psychology (IF: 2.323, C: 71) & \\ \hline Neurocomputing (IF: 3.317, C: 185), Neuropsychologia (IF: 3.197, C: 321), Social & 6 \\ Neuroscience (IF: 2.255, C: 185) & \\ \hline Frontiers in Neuroscience (IF: 3.566, C: 102), Neuroscience Letters (IF: 2.180, C: 139), & 5 \\ Clinical Neurophysiology (IF: 3.866, C: 149) & \\ \hline IEEE Transactions on Information Technology in Biomedicine (IF: 2.493, C: 558), & \\ Sensors (IF: 2.677, C: 30), Social Cognitive and Affective Neuroscience (IF: 3.937, C: 99), Biological Psychology (IF: 3.070, C: 40), Brain and Cognition (IF: 2.432, C: 194), & 4 \\ Schizophrenia Research (IF: 3.986, C: 227) & \\ \hline IEEE Transactions on Autonomous Mental Development (IF: 1.638, C: 49), Journal of & \\ Visualized Experiments (IF: 1.325, C: 5), Behavioural Brain Research (IF: 3.002, C: 39), & \\ Computers in Human Behavior (IF: 3.435, C: 31), Psychiatry Research (IF: 2.528, & 3 \\ C: 18), Cognitive Affective \& Behavioral Neuroscience (IF: 3.263, C: 42), Cognitive & \\ Neurodynamics (IF: 1.828, C: 17), Journal of Neural Transmission (IF: 2.392, C: 86) & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Classification of articles based on the journal.