Principal components and varimax-rotated components in event-related potential research: some remarks on their interpretation.

Some properties of principal components analysis (PCA) and simple structure rotation, which are relevant to the study of event-related potentials (ERPs), were examined both in theory and with simulated data. The analysis casts some doubt on whether it is useful and desirable to rotate the loading pattern of a PCA of ERPs to simple structure. The evidence presented is more in favour of the unrotated solution. In particular we were able to demonstrate with simulated data that a solution rotated to simple structure may lead to false conclusions about the functional independence of ERP peaks. Beyond this, the more general question is asked of whether principal components should be accepted as basic waveforms, i.e. as physiologically meaningful entities which, for example, represent different ERP generators.