ERP Study Of Pre-attentive And Attentive Processing In Mental Fatigue Induced By Prolonged Vigilance Tasks

Prolonged vigilance tasks refer to that people focus in relatively boring taskscontinuously for a long time, and at the same time, keep alert under the pressure. Theusual prolonged vigilance tasks are the continuous monitoring of important instrument, thelong distance bus driving, and space station activities for a long time. With thedevelopment of modern science and technology, the accidents caused by mechanicalreasons rate decline year by year, however, the proportion of the human error is rising.Mental fatigue induced by prolonged vigilance tasks exists in many occupations, and hasserious effects on the individual’s physical and mental activities. Military and specialprofessions both carried out related research. Studies have shown that after mental fatigue,arousal level reduced, cognitive function declined, and attention function was impaired,which was the most significant. But previous research mostly use subjective evaluation.ERP was employed in the present study in which the MMN and P3a/P3b induced byoddball paradigm and oddball-control paradigm were used to explore the pre-attentive andattentive processing after mental fatigue. At the same time, we set up3mental fatiguemodels by different prolonged vigilance tasks, including the laboratory model, the half scene model, and the simulation monitor model. We use cognitive electrophysiologicalindicators (MMN, P3a, and P3b) to study mental fatigue caused by different prolongedvigilance tasks systematically, and to explore the effect of mental fatigue on pre-attentiveand attentive processing and it’s physiological and psychological mechanism. We hope tofind effective cognitive electrophysiological monitoring indicators, and discuss thesensitivity of the various indicators of mental fatigue monitoring, so as to provide a newway of thinking to solve the mental fatigue real-time monitoring research, and to providetheoretical basis for further research and development of brain fatigue real-timemonitoring device.Set up3mental fatigue models by different prolonged vigilance tasks, including thelaboratory model, the half scene model, and the simulation monitor model. We performedthe ERP experiments respectively before and after mental fatigue, in order to study thechange of pre-attentive and attentive processing after fatigue. Our experiments consistedof three parts: first, laboratory studies use the computer simulation of radar monitor as alaboratory model of prolonged vigilance task. Give participants different rewards andpunishments according to their different performance in experiments. We use ERP andsubjective assessment of fatigue to study mental fatigue caused by laboratory model, andto explore the effect of mental fatigue on pre-attentive and attentive processing, in order toscreen effective fatigue detection indicator. This research use before-after study design.Research indicators are as follows:1. oddball-control MMN, it reflects the mental fatigueeffects on automatic information processing;2. P3a, it reflects the mental fatigue effectson pre-attentive processing;3. P3b, it reflects the mental fatigue effects on selectiveattention processing;4. subjective fatigue questionnaire, it can be used to assess thesubjective feeling of participants under the laboratory model, and to prove whetherlaboratory model has established the effective mental fatigue state. Secondly, the halfscene model, use long-distance transportation drivers as the research subjects. Discuss thelong time driving task’s impacts on pre-attentive and attentive processing. The observationindicators are the same as above. Last, the simulation monitor model, use military driversof a vehicle training base as the research subjects. We do real-time monitoring on thechange of pre-attentive and attentive processing, and inattention-attention transition duringsimulation driving. This research requires to record all EEG signals of subjectscontinuously during simulation driving, and to get the effective MMN from the EEGsignals, in order to analyze the change of automatic information processing in the whole fatigue process.The main results and conclusions of this study are as follows:1. Mental fatigue can impair early stages of the cognitive process, i.e., auditoryperceptual discrimination in the pre-attentive stage. In three mental fatigue models,both the oddball MMN and the oddball-control MMN amplitudes declined afterfatigue. They both can be used as a valid indicator of mental fatigue assessment.2. MMN induced by different sound attributes have different changes after mental fatigue.Frequency MMN and intensity MMN declined after fatigue, but duration MMN has nosignificant change. Therefore, Frequency MMN and intensity MMN can be used toassess and monitor fatigue, however, duration MMN could not be used to evaluatefatigue.3. Through the continuously recording of MMN, we do the real-time monitoring onmental fatigue. We got the curves of brain automatic information processing duringmental fatigue. From the general trend, the capacity of automatic informationprocessing (pre-attentive processing) declined gradually. It indicates that MMN can bea reliable indicator for real-time monitoring of mental fatigue. The results supportedthe conclusion are as follows: in the simulation monitor model, intensity MMNinduced by oddball paradigm, and frequency MMN and intensity MMN induced byoddball paradigm all declined gradually in the process of simulation driving.Frequency MMN induced by oddball paradigm reduced markedly only when doingsimulated driving for4hours, it then maintained low level in the following time. Itdoes not have the characteristics of change over time, so it doesn’t fit for real-timemonitoring of mental fatigue. Therefore, only intensity MMN induced by oddballparadigm, and frequency MMN and intensity MMN induced by oddball paradigm canbe used as the valid indicators for real-time monitoring of mental fatigue.4. After mental fatigue, the capacity of involuntary attention declined, that is the capacityof orientating reflex declined. The declined of the capacity of orientating reflexindicates that the ability of detection and judgment of danger signals may decline aftermental fatigue. The results supported the conclusion are as follows: in three mentalfatigue models, the amplitude of P3a reduced after fatigue. P3a can be used as a validindicator of mental fatigue assessment.5. The effects of mental fatigue caused by prolonged vigilance tasks on selectiveattention are smaller or have no effect. The results supported the conclusion are as follows: in three mental fatigue models, the amplitude of P3b only reduced inlaboratory fatigue model.6. The effects of mental fatigue caused by prolonged vigilance tasks on pre-attentiveprocessing (use MMN to assess) and attentive processing (use P3a and P3b to assess)are not the same. In spite of the decrease of the P3a and MMN after mental fatigue, butthe decline of pre-attentive processing capacity is much larger than attentiveprocessing. It suggests that there is difference between pre-attentive processing andattentive processing after fatigue. The change of pre-attentive processing is moreobvious and sensitive.7. Subjective assessment of mental fatigue shows that the feelings of fatigue worsen aftercompleting the tasks. The scores of subjective fatigue questionnaire are significantlyhigher after fatigue.The results of our study indicate that mental fatigue can impair early stages of thecognitive process, i.e., auditory perceptual discrimination in the pre-attentive stage.; aftermental fatigue, the capacity of involuntary attention declined, that is the capacity oforientating reflex declined; the effects of mental fatigue caused by prolonged vigilancetasks on selective attention are smaller or have no effect; the capacity of automaticinformation processing (pre-attentive processing) declined gradually during prolongedvigilance tasks; the change of pre-attentive processing is more obvious and sensitive thanattentive processing; intensity MMN induced by oddball paradigm, and frequency MMNand intensity MMN induced by oddball paradigm can be used as the valid indicators forreal-time monitoring of mental fatigue; P3a can be used as a valid indicator of mentalfatigue assessment, but it is not fit for real-time monitoring of mental fatigue.