Effects of size-brightness and complexity of non-meaningful stimulus material on EEG desynchronization

Abstract

Latency and duration of EEG desynchronization were measured while Ss were exposed to nine slides varying in complexity and size-brightness. There was a positive relationship between duration of EEG desynchronization and the simple stimulus impact va'iable but no effect due to nonmeaningful complexity levels. There was no relation between duration of latency period and either stimulus complexity or sizebrightness. The results were evaluated in the context of the "collative variables" hypothesis and the alerting scanning, and integrative postulates for EEG desynchronization phenomena.Debate about the significance of EEG desynchronization as a product of external stimuli has revolved about the alerting-orientation hypothesis (Bishop, 1933) , the scanning hypothesis (Walters, 1953), and the integrative hypothesis (Klein & Krech, 1952 showed that "amount of material" influenced duration of EEG desynchronization, it is not clear from these studies whether simple stimulus intensity variables or information content variables were being manipulated. Both studies employed levels of complexity based on symbolically meaningful stimulus material. The present study examined duration of EEG desynchronization in response to three stimulus intenSity levels with three complexity gradients comprised of information-free stimulus materials. SubjectsFifteen students from the University of Calgary were randomly selected within the limits of displaying more than 25% or less than 90% alpha over the recording time of the experiment. ApparatusA Grass Model 7 polygraph was used to record EEG on one channel with a 7P3A preamplifier and a 7DAB driver amplifier. A second channel marked time DAVID GIBSDN, GARRY BAKER AND ELAINE RATHIE THE UNIVERSITY OF CALGARYin sec (paper speed was 25 rom per sec), while a third registered the beginning and end of each stimulus pattern presentation. A monopolar recording was taken from the left OCCipital lobE' of each S by means of a single silver disc electrode. There was a reference electrode on the corresponding ear and a ground electrode attached to the arm.The S was placed in a reclining position faCing a blank wall in a darkened room. The E and apparatus were in an adjoining room from which the S could be viewed through a one-way window. A 35 rom Kodak Carousel 800 projector was used to present the slides. Each slide was presented for 3 sec with an interval of 17 sec.Stimulus slides, Nine negative (white on black) stimulus slides were graduated by three degrees of complexity and three levels of size. The smallest size occupied 25% of the projection surface, the middle size 50%, and the largest slide 100%. The least complex design comprised three straight lines of equal length arranged in random drop-stick fashion. The middle level of complexity engaged six lines of random arrangement, and so on. The "designs" displayed no harmonious relationship and afforded limited opportunity for cognitive association by Ss. This impression is confirmed by Ss' reports. A second series of slides involving syllables an...