Continuously Awake versus Suddenly Awakened Alert Crews: When Do You Want Your Decrement?

Previous research on “alert” crew performance under sudden arousal from sleep indicated performance decrements would persist for varying periods of time depending on task characteristics. These studies did not, however, address the alternative of continuously awake crews. Twelve males performed a dual axis, compensatory tracking task under two modes of standby alertness–continuously awake vs sleep-alert. Performance, oral temperature, and subjective ratings of fatigue were acquired during three intervals: pretest, 2000–2200; test, 0200–0400; and posttest, 0800–1000. For the awake mode the test performance in the middle of the night was indistinguishable from the pretest performance, but the posttest performance was markedly worse. For the sleep-alert mode tracking performance was noticeably degraded following sudden awakening, but posttest performance was virtually identical to pretest performance (Figure 1). From the pretest to the test interval, oral temperature decreased to a much greater extent for the sleep-alert mode than for the continuously awake mode (Figure 2). Under both modes, feelings of subjective fatigue increased from pretest to test intervals. At posttest, even greater fatigue was reported for the continuously awake mode, while some recovery was reported for the sleep-alert mode (Figure 3). For alert duty one must consider probability of required performance, error tolerances, and future performance requirements prior to scheduling decisions.