A study of event-related potentials of visual working memory capacity

Abstract

Objective To explore the electro-physiological changes of visual working memory (WM) and the issues related to its capacity limitation.Methods Delayed sample matching duty was used to observe the characteristics of event-related potential (ERP) changes of 18 participants under the evoking of 5 types of stimuli items (consisting of stimulus arrays:2 items,3 items,4 items,6 items and 9 items).The results of ERP analysis were presented by statistical parametric mapping (SPM) oft value.Results At the presentation of 400 ms of memory array,a big negative slow wave was observed in bilateral posterior parietalis and lateral occipitalia,and its amplitude increased gradually with the number of stimulus items increasing from 2 to 4,reaching to the maximum at 4 items; and then,it started to decrease when the number increased to 6 and 9; this reaction lasted for the entire memory retention phase;the amplitude of each array was not totally the same,with significant difference (P＜0.05).The SPM(t)results of ERP showed significant effects in bilateral parietal-occipital sites at 450-800 ms (between 3 and 2 items) and 350-990 ms (between 4 and 2 items).Conclusion Negative slow waves evoked by visual memory stimula in parietal-occipital site reflect the memory retention of visual WM.There is a limitation in visual WM capacity,and functional sites of brain related to its limitation of capacity may locate in the parietal-occipital sites. Key words: Visual working memory; Memory capacity; Event-related potential; Statistical parametric mapping