The Impact Of Concurrent Working Memory Task On Stroop Interference Task:Evidence From EEG Oscillations

Cognitive control is a key function for human beings to adapt flexibly and dynamically to the complex and ever-changing environment. It represents the ability to select a weaker, but task-relevant stimulus or behavior while ignoring or inhibiting the stronger, but task-irrelevant one. Working memory refers to the ability of temporary information storage and manipulation in the brain. While different, a huge body of evidence has convinced researchers that the two constructs are to some degree overlapped. However, to what extent the concurrent working memory tasks influence cognitive control is far from conclusive. Many pervious behavioral studies suggested that under different conditions, working memory would increase or decrease the interference effect of concurrently performed cognitive control tasks. However, the underlying neural oscillatory correlates of such a modulation effect of working memory on Stroop interference is still largely unknown.Based on this, in the current study, we take a dual-task paradigm to study the effect of visual working memory load on the Chinese Stroop interference effect. In experiment1, we asked32healthy campus students to successively perform the single Stroop task and the Stroop task with concurrent working memory load (working memory load stimuli occurs before Stroop stimuli). At the same time, we concurrently recorded participants’ behavioral and EEG data. We found that under the dual task, the interference effect as represented by RTs or theta-band ERSP, reduced compared with the single Stroop task. What’s more, the correlation between the modulation effect of WM on interference effect represented in RTs and its corresponding in ERSP is significant. With Loreta, we further identified a source in left middle frontal area may explain such a modulation effect of working memory on theta-band interference effect. At the same time, frontal alpha rhythm, which although also represented interference effect in the single Stroop task, was not affected by working memory load.In experiment2, we included another13healthy students to respectively perform the single Stroop task, the dual task with visual working memory load presented before the Stroop stimuli (duall), the dual task with visual working memory load presented simultaneously with the Stroop stimuli (dua12). On analyzing the RTs, we found that the interference of duall decreased compared with the single Stroop task; whereas the interference of dual2increased compared with the single Stroop task. This indicates that the reduction effect of working memory load on Stroop interference is not due to the additional visual encoding period before the Stroop stimuli, but working memory per se.In conclusion, this study indicates the effect of working memory load on Stroop interference effect can be represented by theta-band oscillations. This modulation reflects the reduction of cognitive control under working memory load. On the other hand, although frontal alpha rhythm was also involved in cognitive control, its function may be different from theta-band’s. This was reflected by the dissociation between alpha and theta rhythms under working memory load. The interference effect in alpha rhythm was not affected by working memory load, this may be because that alpha-band activity is not sensitive to the change in the level of cognitive control.