As in our previous study (Tenke et al., 2010), ERP waveforms were transformed into CSD estimates (µV/cm2 units; 10 cm head radius; 50 iterations; m = 4; smoothing constant λ = 10−5) using a spherical spline surface Laplacian (Perrin et al., 1989; Kayser & Tenke, 2006a, 2006b; Kayser, 2009). For the time-frequency analyses of these data, the same transform was also applied to the single-trial EEG epochs used to compute these ERPs (averaging the CSD-transformed EEG epochs will yield identical CSD averages).
