Forty hertz EEG (36 - 44 Hz) correlates of automatic and effortful cognitive processing



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In order to assess the efficacy of 40 Hz EEG (36-44 Hz) as an index of amount of effort required by attentional mechanisms during complex cognitive processing, a visual search paradigm was utilized in which subjects were given 600 consecutive training trials in either a consistent mapping (CM) or variable mapping (VM) situation. Four subjects were trained in each condition. Each trial consisted of a sequence of 20 frames presented at a rate of 90 msec per frame. Load was varied by placing either 2 or 4 distractors per frame. Subjects were required to detect appearance of a memory item during the visual array. In the CM condition items which were used as memory targets never appeared as distractors and vice versa; while in VM trials a memory item on one trial would appear as a distractor in other trials. Results indicated that all subjects trained in CM condition demonstrated significant differences in 40 Hz activity between the load conditions, but there was no significant change in 40 Hz levels during the course of trials. VM subjects had a dramatic decrease in 40 Hz levels over time. Inspection of data suggested that VM subjects had an initial load effect which either disappeared or attenuated with training. Analysis of percent error score showed a similar pattern. Results are cognizant with earlier reports on the two- process model of information processes. 40 Hz EEG appears to be a sensitive indicator of the amount of attentional effort required to perform cognitive tasks.



Attention, Electroencephalography