Electrooculographic and performance indices of fatigue during simulated flight

The investigation evaluated specific components of eye and eyelid movement as predictors of performance decrements resulting from pilot fatigue. Ten partially sleep deprived pilots flew a GAT-1 moving-base flight simulator on a 4.5-h sortie. The scored flight portion consisted of eight legs, each leg made up of two segments, a flight maneuvers task (FMT) and a straight and level flying task (SLT). Error scores were calculated across altitude, airspeed, heading, and vertical velocity. An electrooculogram provided measures of blink rate (BR), blink duration, long closure rate (LCR), blink amplitude (BA), saccade velocity, saccade rate, and peak saccade velocity. Subjective fatigue, workload and sleepiness were estimated using the USAFSAM seven-point forced-choice scales, the Stanford Sleepiness Scale, and the USAFSAM Sleep Survey Form. Error scores increased significantly during the first seven legs of the sortie and decreased slightly for the last leg. Subjective reports of fatigue increased significantly over time and were positively correlated with increased error. For the combined data set and for FMTs alone, BA was the best predictor of changes in error with decreased amplitude corresponding to increased error. BR and LCR were the second and third best predictors, respectively. For SLTs alone, LCR and BA were the first and second best predictors of increased error, respectively. The investigation demonstrated that measurable flying performance decrements do occur due to changes in fatigue and that one can measure physiological correlates of those performance decrements.