As situation was not counterbalanced, the effect of situation in that heavy traffic and heavy traffic with fog led to more sleepiness, may be an effect of the increased workload induced by traffic and weather, an effect of time on task, or a combination of both.
There was a significant effect of time on task (road segment) F = 2.4 5165) (p = 0.04), and of Session (day/night) F = 14.6(1165) (p < 0.01) the average number of line crossings to the left, see Fig. 4. Open image in new window Fig. 4 Line crossings left, day and night for road segment 1 6 along the road.
There was also a significant effect of time on task (road segment) F = 3.9 5165)(p < 0.01), and of Session (day/night) F = 15.9(1165) (p < 0.01) on Blink duration, see Fig. 3. Open image in new window Fig. 3 Blink duration, day and night for road segment along the road 1 6.
In order to control for the effect of time on task but avoid confounding results during overtaking, passing situations and change in speed limits, fixed road segments along the road way were selected for the analysis, see Table 2. Road segment is used as a factor for time on task.
There was a significant effect of time on task (road segment) F = 29.03 5159) (p < 0.01), and of Session (day/night) F = 264,8(1159) (p < 0.01) on KSS, see Fig. 2. Open image in new window Fig. 2 Average Karolinska Sleepiness Scale, day and night for road segment along the road 1 6.
The absence of time effect in this study could be explained by the fact that participants were extensively trained with the SART both in the days preceding and immediately before the fMRI session, which could have reduced the effect of time on task during the functional acquisition.
Statistical analysis of these measures revealed significant effect of time-on-task but no effect of group.
Again, there was a main effect of time-on-task, with percent hits falling during later minutes, F 4,216) = 31.27, P <.001, and partial η =.37.
In the main analyses, the reaction times were included in the regression model to account for any effect of time-on-task in the main result.
There was a significant main effect of time-on-task, F 4,216) = 9.07, P <.001, and partial η =.14, with the number of false alarms falling during later minutes.
Furthermore, only the stable control system seems to be altered as an effect of time-on-task (TOT) (Olsen et al. 2013), suggesting that this network may be particularly prone to the effects of cognitive fatigue (Cook et al. 2007).
