Effects of stimulus complexity and incongruity on duration of EEG desynchronization

Abstract

1. 1. Human subjects were exposed to a sequence of visual patterns, each shown twice consecutively. Exposures lasted 3 sec and were separated by intervals of 15 sec. The patterns belonged to eight categories, representing various complexity and incongruity variables. 2. 2. More complex or incongruous patterns evoked, on the average, longer desynchronization than less complex or incongruous patterns (6.4 sec as compared with 5.8 sec). The difference was found to be statistically significant when the data for all eight categories were examined together and when the data for four of the categories (representing Irregularity of Arrangement, Amount of Material, Incongruity and Random Redistribution) were examined separately. 3. 3. No significant difference appeared between first and second presentations of the same patterns or between subjects who were extrinsically motivated (told to attend carefully for the sake of a later recognition test) and not extrinsically motivated, and none of the interactions was significant. There was, however, a significant tendency for desynchronization to grow shorter as the session continued. 4. 4. The findings are discussed in relation to theoretical and experimental work on motivational aspects of exploratory behavior and related phenomena.