International audience In real traffic conditions, air traffic controllers rated alertness and tension according to time of day (recordings every 6 hr) and time on duty (1st vs. 2nd half of afternoon shifts). The 2 measures were inversely correlated on the 2nd shift half, suggesting a compensatory effect of increased tension on decreased alertness. Task performance was decreased at 7:00, overall in a free recall task, and according to list length (9-vs. 6-item) and presentation modality (visual vs. auditory) in a recognition task. The data suggest that changes in controllers' memory processes with time of day depend on the processing strength induced by task characteristics.