Electrophysiological brain activity fluctuations during a long period of task engagement

Humans generally fail to maintain their task performance during a long period of task involvement, leading to performance declines and mental fatigue increases. This phenomenon is called the time-on-task effect or vigilance decrement. It is still unclear whether the impairment of time-on-task is taskspecific or not. Although some theoretical frameworks of vigilance decrement have been proposed in the literature, there is still no agreed framework generalizing to all fatigue-related findings. To address these questions, we conducted a selective visual attention task for 2 hours 20 minutes and provided monetary rewards in the early and late blocks. We also adopted the 80-minute sustained attention EEG dataset with motivation manipulation in the interval of 60-80 minutes. We explored the effects of time-on-task on selective attention and sustained attention, and investigated the modulations of motivation in these studies. We also examined the differences between vigilance and congruency. For data analysis methods, we applied the ERP, time-frequency analysis, automatic dynamic function connectivity detection approach, temporal PCA, and single-trial analysis, obtaining indicators of ERPs (e.g., N1, P2, N2, P300), ERSP (e.g., delta and theta bands), frequency-specific dynamic functional connectivity (fdFC) across different studies. Our results found that cognitive functions in selective attention were impaired by time-on-task and partially restored by motivation manipulation. Similarly, cognitive processes involved in sustained attention were degraded by vigilance decrement and partially and transiently improved by providing rewards. We also demonstrated different influences between vigilance and congruency in conflicting tasks. Overall, this dissertation elucidates the effects of prolonged task involvement on different types of attentional tasks and provides evidence for the theoretical framework of motivational control and energetical costs. Keywords: mental fatigue, time-on-task, vigilance decrement, selective attention, sustained attention, congruency