The effects of memory load and stimulus relevance on the EEG during a visual selective memory search task: An ERP and ERD/ERS study

Objective: Psychophysiological correlates of selective attention and working memory were investigated in a group of 18 healthy children using a visually presented selective mernory search task. Methods: Subjects had to memorize one (load 1) or 3 (load3) letters (memory set) and search for these among a recognition set consisting of 4 letters only, if the letters appeared in the correct (relevant) color. Event-related potentials (ERPs) as well as alpha and theta event-related synchronization and desynchronization (ERD/ERS) were derived from the EEG that was recorded during the task. Results: In the ERP to the memory set, a prolonged load-related positivity was found. In response to the recognition set, effects of relevance were manifested in an early frontal positivity and a later frontal negativity. Effects of load were found in a search-related negativity within the attended category and a suppression of the P3-amplitude. Theta ERS was most pronounced for the most difficult task condition during the recognition set, whereas alpha ERD showed a load-effect only during memorization. Conclusions: The manipulation of stimulus relevance and memory load affected both ERP components and ERD/ERS. Significance: The present paradigm may supply a useful method for studying processes of selective attention and working memory and can be used to examine group differences between healthy controls and children showing psychopathology. (c) 2006 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.