Standardized varimax descriptors of event related potentials: evaluation of psychiatric patients

A large normative data base of visual and auditory event related potentials (ERPs) was collected. Factor analysis (PCVA) was used to extract factor wave shapes that accurately reconstructed these normal ERPs with appropriate "factor scores." The mean value and standard deviation (SD) of the normative factor score distribution were computed separately for each stimulus, factor, and electrode. This enabled reconstruction of any individual ERP as a combination of these standardized Varimax descriptors, with z-transformation of the required factor scores giving objective statistical assessment of ERP wave shape. Statistical probability factor z-score topographic maps were constructed, color coded in SDs from the normative means. The incidence of significant individual deviations from these normative mean values was at or near chance levels in test groups of normal subjects. For many of these new ERP descriptors, significant deviations from the norms were found for single features in from 20% to as much as 63% of the patients in particular diagnostic categories. Factor z-scores were used to construct multivariate discriminant functions that accurately and replicably separated (1) normal from schizophrenic from demented subjects and (2) schizophrenic from bipolar depressed subjects.