Various personality theories specify that extraversion is related to a low level of arousal. The aim was to relate extraversion to the mechanisms in Sanders' (1983) cognitive-energetical model of choice-reaction time (RT): arousal, activation, and effort. Stimulus degradation and time-uncertainty were manipulated during a long task given to extreme. introverts (N = 22) and extraverts (N = 21). In mean RTs, there was only weak evidence for a stronger slowing during the task in extraverts than in introverts. However, an analysis of the RT-distribution demonstrated a remarkable slowing across time of RTs at the high end of the RT-distribution to degraded stimuli in extraverts, suggesting that arousal is lower in extraverts than in introverts. Extraversion had no such effect on activation. The study of the whole reaction time distribution is also important because in many real-life monitoring tasks, especially if visibility is degraded, the risks may not depend so much on mean RT, but rather on the realistic maximum RT.