title: Polarity histogram - a supplementary method for evoked potentials analysis.
abstract: The aim of this study was to evaluate how far the variations in the P300 amplitude of the event-related potentials (ERP) are related to the changes in the frequency of P300 occurrence from the polarity histogram. ERP from Cz (10/20 system) in a task of counting one of two different stimuli ("soft" and "loud" tones) presented in a Bernoulli sequence were recorded. A control situation, i. e. stimuli presentation while the subject is reading a book, was also included. For each subject the two situations were presented according to a completely balanced orthogonal experimental design. The analysis of variance showed statistically significant effect of the task, as well as of the experimental period of the P300 amplitude. For each subject the differences in the P300 amplitudes and the corresponding frequencies of occurrence between the two situations were assessed. The results obtained showed that the changes in the frequency of occurrence are mostly associated with the mere presence of absence of P300. Therefore the polarity histogram provides information particularly valuable for the endogenous ERP components and permits quick identification of these components.
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004569:Electroencephalography; D004585:Electrooculography; D005072:Evoked Potentials, Auditory; D006801:Humans