Performance Decrement During Prolonged Night Driving

Abstract

It is argued that effects of fatigue on performance should be progressive as time goes on. Initial decrements, often found in vigilance tasks, cannot be ascribed to what is usually called fatigue, but rather reflect a change from a state of hyper-vigilance to normal vigilance occurring within the first half hour of the work period. Studies on very long-term performance, in particular longterm driving, have generally failed to show progressive effects. This casts some doubt on the usual implicit assumption that fatigue and long-term work are uniquely related. It is probable that effects of declining diurnal rhythm, monotony, and accumulating lack of sleep will also contribute to fatigue. In an attempt to demonstrate progressive decrement an exploratory experiment was carried out where the effects of long-term work, declining diurnal rhythm, and accumulating sleep loss converge. Subjects carried out a continuous driving task between 2200 and 0600 hours, which was preceded and followed by two driving tests of 45 minutes each. In another condition they had only the pre- and posttest and slept in between. The results showed progressive decrements of performance on several performance measures, including lane drifting and two subsidiary tasks. In general, considerable recovery was observed in the posttest. Although heart rate declined and heart-rate variability increased during the long nightly spell, there are strong arguments against relating heart rate and fatigue. Suggestions for future research are discussed.