Sleep learning during stage 2 and REM sleep.

Pairs of subjects were presented with a 20-item picture series at bedtime. In the latter part of the night, a tape-recorded series of 10 words, the verbal equivalent of half the original series of pictures, was repeated 10 times during either Stage 2 or REM sleep. Morning recall and recognition for repeated words was found to be facilitated following repetition during Stage 2 sleep, but relatively unaffected following repetition during REM sleep. However, adjusting for recall, the number of additional words elicited through recognition was found to be significantly greater for REM repeated words than for Stage 2 repeated words. It was suggested that retrieval limitations, perhaps as a result of REM state dependency, rather than storage inhibition may be the main locus of the initial recall failure. By comparison, Stage 2 sleep would seem to present both a lower barrier to memory storage and retrieval compatibility with wakefulness.