Figure 2.

Study design. Subjects were tested on two nights (early versus late retention condition), with the order balanced across subjects. On the early retention condition, learning of the texts took place between 2215–2300 h, followed by a retention interval of ∼3 h. On the late retention condition, subjects first slept between 2300–0200 h (to “consume” SWS). Learning took place between 0215–0300 h, followed by a 3-h retention interval with subsequent retrieval testing. The experimental sleep group slept during the retention interval, and retrieval was tested 15 min after awakening. The control group remained awake in the retention intervals.