Eye-tracking measures and human performance in a vigilance task

Background: Visual scanning is necessary for aviation safety and similar vigilance tasks, but little is known about its characteristics in such tasks, including possible changes with alertness and fatigue. We explored concurrent eye movements and human performance during a vigilance task designed to require frequent visual scanning. Effects of time and auditory stimuli were examined. Method. A corneal-reflectance, PC-based system (Eyegaze Development System, LC Technologies) provided eye movement measures. Stimuli were four digits in a rectangular array, changed at an event rate of 4 s for a task duration of 30 min. There were 20 subjects who were asked to respond to specific, infrequent signal arrays by bar press, under both 50 dBA white noise and 90 dBA intermittent and unpredictable sound-burst conditions, counterbalanced for order. Results. With time-on-task, subjective fatigue ratings increased, dwell time defined as the total duration of fixations on target digits decreased, number of fixations decreased, and fixations were further from target digits in both conditions. Fixation durations [mean (M) = 258 ms; standard deviation (SD) = 54 ms] did not change significantly with time or condition. Off-target visual scan-paths were less frequently followed by hits than were on-target scan-paths in both conditions. With the sound-burst condition, fixations were closer to target digits and hit rates increased. Conclusions. Dwell time, number, and accuracy of fixations on target objects decreased with time on task, and inaccurate scan-paths were often associated with performance errors. Sound bursts increased fixation accuracy and hit rate. The results provide a basis for visual scan analyses during vigilance tasks, with applications to alertness monitoring and prediction.