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Fig. 2. Study design. Subjects were tested on two nights (early- vs. late-night condition) with the order balanced across subjects. On the early-night condition, the first rating (judgment 1) took place at 10:15 to 11:00 PM, followed by a 3-hour interval filled with sleep or wakefulness and a second rating (judgment 2). On the late-night condition, subjects first slept between 11:00 PM and 2:00 AM (to "consume" SWS). Judgment 1 took place at 2:15 to 3:00 AM, followed by a 3-hour interval of sleep or wakefulness and subsequently by judgment 2. The experimental sleep group slept during the 3-hour interval, and judgment 2 took place 15 minutes after awakening. The control group remained awake during these intervals.
