In the two-process model, the circadian process primarily influences what?

• A. Timing of wakefulness
• B. Sleep architecture
• C. REM onset
• D. Sleep intensity

Answer: (A)

In the two-process model, Process C (the circadian rhythm) gates when we feel alert and when we are inclined to sleep, aligning our sleep-wake pattern with the day-night cycle. Because of this, its primary influence is the timing of wakefulness—when you’re likely to be awake and when you’ll feel sleepy enough to sleep. Sleep intensity and the depth of sleep are more tied to Process S, the homeostatic drive that builds with wakefulness and dissipates during sleep. Sleep architecture and REM onset are shaped by both processes and other factors, but the circadian signal mainly determines the daily schedule of wakefulness and sleep rather than the specific depth or the exact timing of REM.