Passage V

In a study of human sleep cycles, subjects in 4 different age groups performed a brief mental task at a scheduled time. Immediately following the task, their oral temperatures were taken and then the time for each subject to fall asleep was measured.

The results were averaged for each group. Figure 1 shows how the average time to fall asleep for the 4 groups varied with the time of day that the task was performed. Figure 2 shows:how the average oral temperature of 2 of the groups varied with the time of day that the task was performed.