Effect of sleep on memory for task-irrelevant stimuli

Evidence suggests a facilitative effect of sleep on the retention of relevant material. However, little is known about its impact on task-irrelevant material that was acquired incidentally. This study examined recall for task-irrelevant stimuli after 7 h of nocturnal sleep versus nocturnal and diurnal wakefulness. Subjects were instructed to memorize a series of pictures, each of which could appear in one of the four screen corners. Unexpectedly, the subsequent test prompted for the irrelevant picture locations. Recall was better after sleep than after nocturnal wakefulness, but no difference was obtained when sleep was compared to daytime wakefulness.