Conquering fatigue: the battle for engagement

The central aim of this dissertation was to examine how motivation influences fatigue and through what psychophysiological mechanisms it influences cognition. With this aim in mind, task disengagement, which is defined as an affective, cognitive, and motivational state of commitment to mobilize effort in order to reach task goals, while ignoring task-unrelated stimuli (adapted from Matthews et al., 2002), was one of the core concepts. Due to the presumed multifaceted nature of fatigue and task engagement, multiple indicators of task engagement were measured within a well-established fatigue paradigm. Specifically, we used a set of subjective, behavioral, and psychophysiological measures of fatigue and task engagement. Utilizing this approach, this dissertation brings forth at least three major contributions. First, closely following the central aim for the thesis, there is the contribution of the studies towards the formation of a psychophysiological model for mental fatigue, which revolves around the locuscoeruleus norepinephrine neurotransmitter system (LC-NE system). The observed flexibility of this psychophysiological model has pointed out a second contribution of this thesis. Because the negative effects of fatigue appeared to be reversible by manipulating motivation for task engagement, this thesis contains strong evidence against classical resource depletion approaches. A third major contribution of this thesis, is that the objective measurement of task engagement has shown to be very consistent during all studies in this thesis. This observation has a very important implication for the future of applied science research (e.g., organizational and educational psychology), because there is a dire need for strong objective variables. Within these fields, task engagement can serve both as a predictor and outcome variable.