Change in paired-associate performance across the retention interval.

<p><i>(</i><b><i>A</i></b><i>)</i> Forgetting of semantically related word pairs over a 12-hour retention interval was reduced by nocturnal sleep (black bar) relative to wakefulness during the day (white bar). In contrast, a daytime nap (black hatched bar) had no such effect on forgetting over a 2-hour retention interval compared to wakefulness (white hatched bar). <i>(</i><b><i>B</i></b><i>)</i> For semantically unrelated word pairs, both nocturnal sleep and daytime napping attenuated forgetting over the retention intervals. ** <i>P</i><0.01; *** <i>P</i><0.001.