The Neural Mechanism Of Conflict Monitoring: Evidence From ERP

The successful inhibition of task irrelevant information and the selective attention to task relevant information is pertinent for goal-directed activity, and more generally a requisite for socially appropriate, adaptive behaviour in every day life. For decades, it has been debated at which level of processing the conflict that causes RT interference occurs. The conflict monitoring theory holds that the occurrence of responses conflicts in information processing, thereby triggering compensatory adjustments in cognitive control. So in the conflict monitoring theory, conflict is conceptualized as the simultaneous activation of competing responses. Whether the conflict between different perceptual representations also activates these brain regions is, however, controversial.Interference control involves not noly the inhibiton of inappropriate and conflict response tendencies, but also the suppression of task irrelevant sensory information. Unfortunately, in most studies response conflict has been confounded with stimulus conflict, making it unclear to what extent stimulus conflict is involved. It was, therefore, the primary aim of this thesis to systematically investigate the locus of interference using ERP. The secondary aim of this thesis was to investigate the relationship of conflict monitoring and consciousness。This thesis extended on previous research by systematically investigating the effect of varying the level of conflict in four studies and brain electrical activity correlates of conflict monitoring and interference. To accomplish this, the thesis employed several conflict task as a measure of conflict monitoring and interference control in which distraction sensory information is associated with a conflicting and task irrelevant response that must be inhibited and replaced with the correct target response.Study 1 used S1-S2 matching paradigms in which participants were instructed to discriminate whether the attributes of the first stimulus (S1) were the same as those of the second one (S2) of a pair. Stimuli were defined by three features:color, number note and number magnitude. Using this matching task we can investigate the neural mechanism of two level stimulus conflicts. In addition, to reveal the relationship of conflict monitoring and consciousness, this study investigated how the conflict monitoring system in human brain is modulated by asking participants to attend to one attribute of Stimuli and disregard other attributes.Study 2 used a money feedback experimental paradigm. Specifically, on each trial, two cards were drawn from a deck of eleven, numbered 0 through 10. Before seeing either card, subjects first placed a (?) 1 bet on whether the first or the second card would be higher. Subjects could earn (?)1 if they were right and lost (?)1 if they were wrong. Once the bet was placed, subjects saw card 1, followed 700ms later by card 2. The time interval between display of card 1 and card 2 was the anticipatory period. We investigated the neural correlation of outcome evaluation by analyzing the FRN and P300.Study 3 used prime-target experimental paradigm. We asked subjects to perform a simple color discrimination task on the target color-filled square in which the prime (color words) was masked or not. In some trials the prime was congruent with the target, and in other trials it was incongruent. In addition, we manipulated the semantic distance between prime and target. Study 3 examined the locus of interference in a prime-target color-word Stroop task and the relationship of conflict monitoring and consciousness using electrophysiological chronometric measures (N2, P3 and lateralized readiness potential).Study 4 also used prime-target experimental paradigm. We asked subjects to perform a simple number or letter discrimination task on the target in which the prime was masked or not. This study manipulated response eligibility by using incongruent target that either were ("eligible") or were not ("ineligible") part of the response set. This manipulation allowed for stimuli to be either congruent (CO; prime and target were the same), incongruent at only the stimuli processing level (SI; prime and target were different, but were not part of the response set), or incongruent at both stimuli processing and response levels (RI; prime and target were different and were mapped onto opposite response hands). So study 4 investigated the locus of interference in a prime-target task by experimental separated stimuli conflict and response conflict. This study also investigated the relationship of conflict monitoring and consciousness by masking the prime.So this thesis explores the cognitive and neural mechanism of conflict monitoring, and the major results are as follows:First, the conflict related ERP component include N2, P300 and LRP. In this study two N2 components were clearly delineated:the first of which was increased to stimuli which was incongruent in physical attribute or semantic attribute (stimuli conflict N2), while the second N2 component was consistently observed to increase following the detection of response conflict (response conflict N2). Spatiotemporal dipole analysis showed that all these conflict N2s may arise form ACC. But the fact that stimuli conflict N2 and response conflict N2 showed different scalp and a little different generator suggest that there exist different conflict processing sub-system in the brain.The P3 component was maximal at parietal and increased in latency as there was conflict. In study 1 and study 2 in which experimental task include only stimuli conflict P3 peak latencies were longer for stimuli incongruent trials than stimuli congruent trials. The prolonged P3 latency suggest that incongruent stimuli have more interference on evaluation or categorization of the target. The result of study 1 and study 2 provide evidence that p3 latency is a particularly valuable metric of stimulus processing time in experimental task including only stimuli conflict, In experiment 6 in which experimental task include stimuli conflict and response conflict and prime was masked P3 peak latencies were longer for response incongruent trials than stimuli incongruent trials, indicating that P300 latency is relatively affected by response selection。In experiment 5 in which experimental task also included stimuli conflict and response conflict and prime was not masked P3 peak latencies, however, was not significant different between that of response incongruent trials and that of stimuli incongruent trials. The results of study 4 suggest that P300 latency is not a sensitive tool for separating stimulus-and response-related processes.A number of lines of evidence provide converging support for the suggestion that the LRP can serve as a real-time measure of selective response preparation. The onset of lateralized readiness potential (LRP) may be used to elucidate whether an experimental manipulation affects stages of processing before or after the onset of hand-specific lateralized response activation. The result of Study 4 showed that s-LRP-onset latency for response incongruent stimuli was longer than that of stimulus incongruent stimuli, which was longer than that of congruent stimuli. This results suggest that the inference effect originates from earlier stimulus-related processes and later response-related processes. However response incongruent trials were not significant "initial dip" in study 4. The result of significant sLRP onset and no significant initial dip for response incongruent trials suggest that the lack of initial incorrect response activation is not sufficient proof for accepting that response competition does not play a role in task-execution. It simply suggests that none of the stimulus dimensions able to elicit a response which were processed considerably faster than other dimensions.Second, conflict can occur at numerous levels of information processing, ranging from perceptual representation, to stimulus categorization, to response selection. Evidence for the contribution of stimuli conflict to interference effect comes from study 1 and study 2 that have shown an interference effect when two stimuli were incongruent even when the task was simply to note whether they were the same or not. It has been showed that conflict additionally occurs at the response level. Supportive evidence for a contribution of response conflict to interference comes from the result of RT, P300 latency and sLRP onset. Specifically, the result of study 4 have found longer RTs, longer the latency of the P300 and longer sLRP onset for incongruent-ineligible trials compared to congruent trials, presumably reflecting stimuli (semantic) conflict, and still longer RTs, longer latency of the P300 and longer sLRP onset for incongruent-eligible trials, presumably reflecting response conflict. These results thus confirm that conflict occurs at the response level and the conflict additionally occurs between representations at the level of semantic or conceptual encoding.Third, the relationship between stimuli conflict magnitude and response conflict magnitude. Experiment 3 found stimuli conflict increased as the prime and target distance increased. Semantic distance, however, had primary interference effect on response conflict when experiment task include stimuli conflict and response conflict and showed that response conflict increased as the prime and target distance decreased. Study 4 manipulated the category of prime and target. In this study, when prime and target were different category, they activate two processing module, resulting in stronger stimulus conflict and response conflict and when prime and target were same category, they activate same one processing module, resulting in smaller stimulus conflict and smaller response conflict.Fourth, the relationship between conflict monitoring and consciousness. Awareness of conflict was manipulated, in study 3 and study 4, by using primes that were either invisible, because sandwiched mask, or clearly visible, because presented without a mask. The results showed that prime-induced conflict had a clear effect on ACC activity (higher for incongruent than for congruent primes), not only if the primes were visible but also if primes were invisible. So these results suggest that consciousness of conflict is not a necessary condition for the ACC-related control network to come into play. However, awareness of conflict was manipulated, in study 1, by asking participants to attend to one attribute of Stimuli and disregard other attributes. The results of study 1 showed that the unattended conflict did not activate the ACC related control system when ACC-prefrontal network had been activated by attended conflict. So these results suggest that anterior cingulate cortex (ACC) related neural network is necessary neural substrates for conflict control and conflict monitoring is not contingent on awareness。Fifth, Congruency sequence effects come from bottom-up feature overlap and there is not an automatic conflict-control feedback loop. After controlling for bottom-up repetition effects (including target repetitions, prime repetitions, target-become-prime transitions, and prime-become-target transitions) study 3 and study 4 failed to obtain conflict adaptation effect. These results suggest that conflict monitoring did not play a role in the sequential modulations. Furthermore, we found significant feature overlap effects in all trials andⅡtrials, which provide evidence that feature overlap effect is a contributors to sequential modulations. However, the feature overlap effects did not conform to predictions of the feature integration account. Rather, the feature overlap effects seem to resemble additive benefits of prime and target repetition.In light of the present results and prior related research, we put forth conflict monitoring model involving three stages of information processing which can account for the major results of the thesis.