trials in each task condition (Go and NoGo) was taken for further analysis. If there were more than 25 artifact-free correct trials in a condition, 25 trials were selected randomly from the pool. The S-transform method was used to obtain the power values in different frequency bands for each successful trial for both task conditions (Stockwell et al., 1996). The S-transform is a variable window of short-time Fourier transform (STFT) or an extension of wavelet transform (WT). It is based on a scalable localizing Gaussian window and supplies the frequency dependent resolution of a time-frequency domain and entirely refers to local phase information. This method has been shown to produce reliable estimates of localized power of nonstationary evoked potential time series (Chu, 1996, Theophanis and Queen, 2000) and has been applied in several studies from our lab to analyze time-frequency signals of EROs (for details see Chen et al., 2009, Jones et al., 2006a, Jones et al., 2004, Jones et al., 2006b, Kamarajan, Porjesz, 2006, Kamarajan, Porjesz, 2004, Kamarajan, Rangaswamy, 2008, Kamarajan et al., 2012, Kang et al., 2012, Padmanabhapillai et al., 2006a, Padmanabhapillai et al., 2006b, Rangaswamy et al., 2007).
