Time-frequency (TF) data were derived using the S-transform signal processing method, introduced by Stockwell et al. (1996). The S-transform has been explained in our previous papers (Kamarajan et al., 2008; Kamarajan et al., 2012). The S-transform is derived from short-time Fourier transform and continuous wavelet transform, and has a greater flexibility, anti-noise performance, and utility in the processing of non-stationary and complex signals compared to other traditional methods, such as short-time Fourier transform and Wigner-Ville distribution (Yun et al., 2013). This method has been applied in several recent studies to analyze time-frequency signals of event-related oscillation (Jones et al., 2006b; Rangaswamy et al., 2007; Andrew and Fein, 2010; Kamarajan et al., 2012; Kamarajan et al., 2015a; Pandey et al., 2016).
