Figure 2 shows CSD grand averages for correct trials. CSD estimates (μV/cm2 units; 10-cm head radius) were computed using a spherical spline surface Laplacian (Perrin et al., 1989) with computation parameters (50 iterations; m = 4; smoothing constant λ = 10−5) previously established for a 31-channel recording montage (e.g., Kayser & Tenke, 2006b, 2006c; Tenke et al., 1998). As expected, components have sharper topographies and time courses that more clearly separate the anterior from posterior P3 sources.
