As in our previous study (Kayser et al., 2010), OERP 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). To determine their common sources of variance, CSD waveforms were submitted to temporal PCA derived from the covariance matrix, followed by unrestricted Varimax rotation of the covariance loadings (Kayser & Tenke, 2003, 2006c). The input data matrix consisted of 301 variables (time interval −100 to 1,400 ms) and 8,036 observations stemming from 41 participants, 4 odor conditions, and 49 electrode sites. By virtue of the reference-independent Laplacian transform (see Tenke & Kayser, 2012, for a review), CSD factors have an unambiguous component polarity and topography.
