[Visual illusions and the alpha-rhythm EEG].

During flicker stimulation with the alpha-rhythm frequency through the closed eyes 11 from 12 subjects clearly saw illusory objects (in order of descending probability, ring, circle, three-dimensional spiral or spiral spring, funnel, curved crossed bars). The individual optimal stimulation frequency for producing an illusion was always within the alpha range and was closely correlated with the individual dominant alpha frequency (r = 0.86). A supposition is discussed that the effect obtained is based on the quasistroboscopic fixation of the spreading cortical excitation wave of the alpha-rhythm due to its summation with the isorhythmic afferent diffuse cortical excitation evoked by flashes. This phenomenon enables "freezing" of the alpha wave at a certain instant of its spreading and makes it "visible".