Optimized CSD waveforms were submitted to unrestricted, temporal principal components analysis (PCA) derived from the covariance matrix, followed by Varimax rotation of the covariance loadings (Kayser & Tenke, 2003, 2006a), to determine common sources of variance related to N1 sink activity and to quantify its amplitude. The input matrices consisted of 116 variables (samples between −50 and 400 ms) and 12,730 or 15,008 observations stemming from 95 or 112 participants, 2 tasks (face, word) and 67 electrode sites. This approach provides a concise, efficient simplification of the temporal pattern and spatial distribution of neuronal generators, yielding reference-independent CSD factors with unambiguous component polarity and topography (Kayser & Tenke, 2006a; Tenke & Kayser, 2012).
