First, ICA based on the extended Infomax algorithm was applied to ERP signals, and the independent components were extracted. Second, OEMD was performed for each obtained source, and a set of orthogonal IMFs was derived, in which only the IMF of interest based on theta frequency band power and the peak between 200 ms and 450 ms was selected. The combining decomposition is adaptive to the time and frequency content of the data themselves and can separate original ERP signals into orthogonal components with different time scales. Meanwhile, the orthogonality property implies that different IMFs do not have similar frequency content [26]. The algorithm is described in Algorithm 1.
