This study investigated the effects of display and memory load on the event-related potentials (ERPs) in a visual letter search task combined with selection by color. ERPs were recorded from 10 adult subjects, when they were required to judge if test stimuli, which consisted of a horizontal array of five colored alphabets, contained target letters defined by shape and color. The results showed that the increase of display or memory load caused the enlargement of three different negativities.

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... first and second display load effects were observed in the ERPs at midline central electrode (Cz) between 240-280ms latency range, and in a posterior-distributed negativity that was the maximum at about 650ms after the stimulus onset. The third was the anterior-central negativity that was the largest at Cz about 550ms after the stimulus onset. In contrast to the first two effects, this negativity was enhanced by display or memory load. In discussion, a tentative linkage between these ERP changes and two slave systems of working memory (phonological loop and visuo-spatial sketchpad) was proposed.