The relative effects of work hours and circadian factors on pilot performance Arsintescu, L. A.1,3, Colletti, L. M.2,3, Caldwell, J. A.3, and Mallis, M. M.4 1San Jose State University Foundation, Moffett Field, CA; 2QSS Group, Inc., Moffett Field, CA; 3NASA Ames Research Center, Moffett Field, CA; 4Alertness Solutions, Cupertino, CA. INTRODUCTION FIGURES RESULTS Preliminary data have revealed that time of departure (morning versus evening) significantly affected pilot performance during ultra-long-range flights (> 18 hours; Mallis et al., 2005). It is unclear whether the circadian effect or the number of work hours contributed the most to performance decrements from the different departure times. Subsequent analyses were performed to address this issue. PVT Significant main effect of time-of-day on PVT transformed lapses (F(4, 60) = 23.63, p < .001) with a significant linear trend from 21:40 to 05:00 (F(1, 15) = 46.40, p < .001; figure 1). No main effect of departure or interaction. VAS Significant main effect of time-of-day on VAS alertness (F(2 33.7) = 18.21, p < .001) with a significant linear trend (F(1, 15) = 35.45, p < .001; figure 2). KSS Time by departure interaction (F(4, 60) = 2.71, p < .05) due to an increase in sleepiness for the AM group at 00:30 compared to the PM group (figure 3). Significant main effect of time-of-day (F(4, 60) = 43.96, p < .001) due to a significant linear trend (F(1, 15) = 114.24, p < .001). METHODS Figure 1. This figure displays the average number of lapses (reaction times >500 ms) on the PVT during the nighttime to early morning hours (21:00-05:00). Participants N = 17 pilots, male, aged 35 - 60 (M = 48 years, SD = 7.86). Current ATP pilots or retired within the previous 6 months. Flight hours: 3,500 – 34,000 hours (M = 16,665 hours, SD = 8,997.7). Methods Pilots flew a Boeing 747-400 simulator for 19.5 hrs, with either a morning or evening departure. For the first trial, both groups had been awake for approximately an equivalent number of hours (12.33-14.75 hrs); however, the morning group had been flying for 10.5 hrs while the evening group had just started the flight. To determine the degree to which work hours and circadian time affected performance, mixed-effects ANOVA were performed on five trials that occurred at the same clock times (21:40 – 05:00 for both groups). Measures Psychomotor Vigilance Test (PVT) - a hand-held test that delivers a three-mm visual stimulus, which requires the participant to make a pushbutton response within 1.5 seconds with interstimulus intervals ranging from 1 - 10 sec. Visual Analog Scale (VAS) - an adjective such as "anxious" or "sleepy" was placed over the center of a line (100 pixels long) with the words "not at all" appearing at the far left and “extremely” appearing at the far right. Karolinska Sleepiness Scale (KSS) - a nine-point Likert-type scale of subjective sleepiness ranging from “1 = very alert” to “9 = very sleepy, fighting sleep.” CONCLUSIONS These data suggest that with equivalent hours of continuous wakefulness, pilots experienced increased sleepiness and decreased performance, which occurred during the early morning hours corresponding to the circadian nadir. The absence of departure-time main effects suggests that the actual work hours (i.e., number of hours spent in flight) did not significantly attenuate or exacerbate this effect suggesting work hours alone did not significantly influence alertness. The interaction between the departure groups at 00:30 on subjective sleepiness may be due to the fact that the PM group just started the flight so they were more alert because of the high workload experienced during takeoff while the AM group had been flying for approximately 10.5 hrs. Thus, these results suggests that various factors such as circadian and workload may affect performance and alertness; however, work hours alone may not. Figure 2. This figure displays the subjective levels of alertness on VAS during nighttime to early morning hours. REFERENCES Figure 3. This figure displays the subjective ratings of sleepiness on KSS during nighttime to early morning hours. Mallis, M.M., Colletti, L.M., Brandt, S.L., Oyung, R.L., & DeRoshia, C.W. (2005). The effects of ultra-long-range flights on the alertness and performance of aviators. Aviation, Space and Environmental Medicine, 76, 260. Research supported by NASA’s Human Measures and Performance Project of the Airspace Systems Program.