[Method for estimation of ERP topography instability degree and its application in the experimental task of target letter discrimination].

A new method for estimation of human event-related potential (ERP) topography instability was developed. It was applied to the visual ERPs evoked in the experimental task of target letter discrimination. Periods of stable topography corresponding to the main ERP waves and those of unstable topography between them were revealed. Dependence of stability and instability characteristics on relevance of stimuli was disclosed: mean ERP magnitude (potential field power) of stable periods and duration of N1-P3a unstable interval were higher for target letters than for nontarget ones. Possible mechanisms of these effects are discussed.