The Neural Mechanism Of Unconscious Cognitive Conflict And Control

Consciousness has been a difficult and hot topic in scientific studies. Researchers has been trying to reveal the functions and limitations of it through a variety of techniques and approaches. A promising way to study consciousness is establishing a clear boundary between unconsciousness and consciousness, which may be a most important step to reveal the origin and function of consciousness. Traditional studies suggested that cognitive control required consciousness. Previous studies found that recruitment and implementation of cognitive control were strongly dependent on the function of the prefrontal cortex. Since prefrontal itself was related to consciousness, many researchers automatically linked consciousness with cognitive control. It seemed that they thought unconscious cognitive control was impossible. In sharply contrast, recent studies have found that some kinds of cognitive control functions such as conflict control, inhibition control and error processing could be triggered unconsciously. These studies provided direct experimental evidence to the existence of unconsocus cognitive control. In the current paper, the author’s aim is to reveal the mechanism of one aspect of cognitive control functions——conflict control——by using a variety of masking paradigms and approaches. Although researchers in the field of unconscious conflict control have done some preliminary studies, there are still many questions to be answered. For example, the source of unconscious conflict is uncertain; the neural mechanism of unconsicous conflict adaptation is unclear; it is also unclear how different types of conflict are processed in human brain, what brain networks are involved in conflict control and whether unconsicous and conscious conflict control networks are the same or different. In the present study, the author used behavioral, EEG and fMRI methods to explore these questions. Examining the neural mechanisms of unconsicous cognitive control can not only help us better understand cognitive control itself and unconscious information processing, but in the long run, also help us answer the two most difficult scientific questions:(ⅰ) where is consicousness originated from;(ⅱ) what are the functions and limitations of consciousness. Due to the fact that studies on consciousness is still in its infancy, our exploratory research can lay a solid foundation and accumulate empirical evidence for researchers to reveal the origin of consciousness. To investigate the function and limitations of consciousness, all our experiments include a conscious condition.In order to explore and understand the depth and limitations of unconscious information processing, we also explore unconscious semantic conflicts, because compared to perception processing, semantic information processing belongs to a higher level of cognitive processing. If our study further confirms that unconscious conflict and control is independent of consciousness, then it not only helps us explore unconscious cognitive control itself, but also provides inspiration for further studies aimed to construct theories to explore the relationship between cognitive control and consciousness. Conflict-monitoring theory can well explain some conflict control phenomena, but it does not clearly state the function of consciousness in the conflict control loop. Therefore, our study will help expand and update conflict-monitoring theory. Since our study is able to help us reveal the function of consciousness and understand the neural structure generating conscious experience, which is a major challenging problem in neuroscience studies.Therefore exploring unconscious control might have important clinical value, such as treatment sensory loss, coma, vegetative state, micro-conscious patients.The current study includs six experiments which can be divided into two parts: unconscious conflict and unconscious conflict control. In all experiments we used the masked priming paradigm.In the first, second and third experiments, our main concern was the source of unconscious conflict. When introducing a neutral condition, the conflict effect could be separated into facilitation effect and interference effect. The results showed that, compared to conscious conflict, unconscious conflict mainly originated from interference effect while conscious effect mainly from facilitation effect. This might be because the visibility of conflict-induced stimulus was very low and the subjects in this condition could not effectively use the external cues to optimize their behavior. The experiment validated the reliability of the metacontrast masking task, laying foundations for later experiments. In the second experiment we used the classic disocciation logic of semantic and response conflicts in Stroop paradigm. Using EEG time-frequency analysis method, we explored the origin of conflict and how the brain processed different types of conflict. Although we found that unconscious conflict contained only response conflict in behavior, unconscious conflict contained both semantic and response conflict on EEG power. We found that the brain resolved different conflicts via domain general manner. In the third experiment we used the task similar to the second experiment by using a rapid sequence fMRI design. The results showed that although the majority of the similar area activated by semantic and response were the same, the spatial and temporal characteristics were different, revealing the neural network difference when processing unconscious and conscious conflict. In the fourth, fifth and sixth experiments our major concerns were unconscious conflict control. In the fourth experiment by manipulating the proportion of congruent and incongruent tirlas within the same block, we found that unconscious conflict was sensitive to adaptive changes in the proportion of block conflict, leading to N2 and P3 amplitude adjustment, and the forehead theta power changed as a function conflict. In the fifth experiment by mixing the conscious and unconscious trials, we revealed the neural mechanisms of conflict adaptation. The results showed that the conflict adaptation resulted in the changes in midfrontal theta power. More interestingly, we found that Dorsolateral Prefrontal Cortex (DLPFC) was only involved in conscious conflict control but not in unconsicous conflict control. In the sixth experiment, to exclude the possibility that the conflict adaptation was driven by subjective conflict experience and parital error trials but not conflict effect, we explored the impacts of subjective conflict experience and partial error on unconscious conflict by using EEG. The results suggested the existence of conflict adaptation effect regardless of subjective experience and error awareness. Therefore, the unconscious conflict adaptation was not completely driven by error awareness and and subjective conflict experience.After analyzing the experimental results, we can draw the following conclusions: (1) unconscious conflict mainly originates from the interference effect; (2) unconscious conflict contains both semantic conflict and response conflict. The brain resolves unconscious semantic conflict and response conflict not by domain specific manner; (3) unconscious conflict can recruit conflict monitoring and implementation of human brain. Compared to conscious conflict, it shows a different process mechanism; (4) there are similarities and differences between unconscious and conscious conflict control system in terms of quality and quantity, and therefore the neural networks of unconscious and conscious conflict control may partially overlapping and independent, depending on the conflict context. In summary, we find that conflict control is independent of consciousness and that unconscious information has a more lasting regulatory role on the behavior beyond what we have imagined, suggesting that prefrontal cognitive control function is not unique to conscious conflict and human cognitive processing system is flexible. Our study deepens our understanding on not only unconscious information processing, but also the relationship between consciousness and cognitive control, revealing the functions and limitations of conscious awareness. It also raises questions such as what is the unique function of consciousness. We should further study to clarify them.