“…Considering the increasing volume of EEG-BCI databases, it may become feasible to quantify the exact sources of inter-subject/session variability as well as indicators of inter-subject associativity allowing to reduce training sessions to a minimum (Lotte, 2015). Recent advances in deep learning methods demonstrate a potential application that alleviates intraand inter-subject variability in BCI settings (Chiarelli et al, 2018;Fahimi et al, 2018). Meanwhile, recent studies suggest that the quantification of inter-subject associativity could be equally important to increase the efficacy of exclusively machine learning-based transfer learning strategies for covariate shift adaptation (Kang et al, 2009;Kang and Choi, 2014;Wronkiewicz et al, 2015;Saha et al, 2017bSaha et al, , 2019Perdikis et al, 2018).…”