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Does the “Sleep Effect” on Memory Depend on Sleep or on Night Time?
Olaf Lahl, Ph.D. and Reinhard Pietrowsky, Ph.D.
Numerous investigations demonstrated superior verbal memory performance after
retention intervals of nocturnal sleep as opposed to diurnal wakefulness. However, it
is not clear if the effect is attributable to either sleep or circadian phase. The present
study therefore examined verbal recall after retention intervals of nocturnal sleep,
diurnal wakefulness, and nocturnal wakefulness (sleep deprivation). Forty university
students (range 19-30 years) were randomly assigned to one of the three conditions
and were tested for cued recall of a paired-associate list 7 h after original learning. In
line with previous findings, subjects in the nocturnal sleep condition expressed
superior recall when compared to subjects in the diurnal wakefulness condition.
However, contrary to predictions, recall performance between the nocturnal sleep
and the nocturnal wakefulness condition did not differ significantly. The results raise
some doubt on the generalizability of the beneficial effect of sleep on memory.
| Keywords: sleep, sleep deprivation, memory, retention, circadian phase |
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