A wordstem priming task (nondeclarative memory),
and a mental spatial rotation task (declarative memory)
were presented to subjects of an experimental “sleep”
group (n = 11) and of a “wake” control
group (n = 10). Repetition priming effects and
recall of spatial memory were tested after 3-hr retention
intervals, which followed learning and were placed either
in the early or in the late half of the night. Sleep group
subjects slept during the retention intervals while subjects
of the wake group stayed awake. As expected, early retention
sleep was dominated by slow wave sleep (SWS), whereas rapid
eye movement (REM) sleep prevailed during late retention
sleep. After early retention sleep, recall of spatial memory
was superior to that after late retention sleep (p
< .01), and also to that after retention intervals
of wakefulness (p < .05). In contrast, priming
was more effective after late than early retention sleep
(p < .05). It appears that early sleep dominated
by SWS facilitates consolidation of declarative memory
whereas late sleep dominated by REM sleep facilitates consolidation
of nondeclarative memory.