Functional Characteristics And Neural Mechanism Of Cognitive Control In Counting Stroop Task With Multiple Distractor Stimuli

Cognitive control refers to the ability to flexibly adapt behavior to current demands by promoting task-relevant information in the face of interference or competition. This ability is central to most higher cognitive functions, including attention, inhibition, working memory, language process and evaluation, etc. Recent years have seen an explosion of research on cognitive control by using neuroscience technique. Many of these researches have examined the functions of cognitive control in monitoring and resolving conflict in the presence of distractor stimuli.On the other hand, Stroop task has been widely used in the researches of cognitive control, while counting Stroop task is an ideal paradigm used in the neuroscience researches on cognitive control. Previous studies only used single distractor stimulus in the Stroop task. However, people usually face multiple distractor stimuli during the cognitive process. It is still an open question whether the functional characteristics and neural mechanism of cognitive control in the context of multiple distractor stimuli would be the same as that in single distractor stimulus.This study aimed to systematically explore the functional characteristics and neural mechanism of cognitive control in counting Stroop task with multiple distractor stimuli by using ERP technique. Three groups of experiments were designed in this study, and each of them consisted of two sub-experiments, which used a different research paradigm. In these experiments, the functional characteristics and neural mechanism of cognitive control in counting Stroop task with multiple distractor stimuli were explored by using digits or Chinese characters as distractor stimuli. For the two distinct components of cognitive control, i.e. the evaluative and executive components, the time course and distribution of them were detailedly analyzed and discussed.The main conclusions of this study are summarized as follows:(1) Stroop effect is a robust phenomenon, which could sensitively reflect adaptive changes in cognitive control. The regulation of cognitive control was influenced by many factors, such as the number and type of distractors, material of stimuli, context of conflict, stimulus type, etc.(2) Cognitive monitoring function could be observed in the two experimental paradigms of cognitive control. Compared to the condition in which the previous and current trials were manipulated, cognitive control could adjust the conflict much more effectively when the proportion of congruent and incongruent trials was varied between blocks of trials. When incongruent trials appeared frequently, the conflict could be dramatically reduced by cognitive control.(3) In the condition of multiple distractor stimuli, the evaluative and executive components could be separated in both of experimental paradigms. However, the sub-components separated in the two kinds of experimental paradigms were associated with the different neural mechanisms. When the proportion of congruent and incongruent trials was varied between blocks of trials, the executive components consisted of episodic control and sensory control components. However, when the previous and current trials were manipulated, the executive components consisted of contextual control and sensory control.(4) Chinese character distractors consumed more cognitive resources than digit distractors in counting Stroop task, and they had more significant influences on counting process. As a result, when Chinese character distractors were presented, cognitive control was impaired by cognitive resource limitation during cognitive executive process.(5) In counting Stroop task with multiple distractor stimuli, N450 and P450, which could be used to reflect conflict detection, had been found in the 400-500 ms time window. N450 distributed mainly on fronto-central region and P450 distributed mainly on lateral fronto-polar region. SP wave, which was considered to be associated with additional meaning analysis, had been found in the 600-800 ms time window, and it distributed mainly on left temporo-parietal areas.(6) In counting Stroop task, the neural mechanism of conflict monitoring in the context of multiple distractor stimuli was the same as that in single distractor case, and Stroop N450 were found at midline sites reversing polarity over the lateral frontal regions under both of these contexts. But the conflict resolution of cognitive control in multiple distractors situation was a longer-lasting continuous process, which was different from that in the single distractor situation. This process consisted of three sub-components of executive function, i.e. episodic control, context control and sensory control. Each of them respectively executed the conflict resolution in different periods. Specifically, episodic control reduced perceptual conflict at 300-390ms over the temporo-parietal regions; context control reinforced conflict monitoring and it started with 400ms and could lasted around 600-800ms; and sensory control regulated response conflict and completed motor response selection at 600-800ms over the midline sites.