Scientists already knew that getting some decent shut-eye after studying helps to consolidate learning, but new research suggests that sleeping in between study sessions is even more effective.
“Our results suggest that interleaving sleep between practice sessions leads to a twofold advantage, reducing the time spent relearning and ensuring a much better long-term retention than practice alone,” explains psychological scientist Stephanie Mazza of the University of Lyon.
Researchers assigned 40 French adults to one of two groups: a sleep group and a wake group. Both were presented with 16 French-Swahili word pairs and tasked with studying each for seven seconds, before being prompted to type the French translation.
The correct pair was shown for four seconds and any mistranslations were presented again, until each was correctly translated.
Twelve hours later, participants were tasked with translating the pairs again, until they could translate all 16 correctly.
But the wake group performed the first session in the morning and the second in the evening, while the sleep group performed the former in the evening and the latter the next morning.
Participants in the sleep group could recall roughly 10 words on average, while the wake group could only recall 7.5 on average.
Those who had slept needed only three attempts to recall each of the pairings, while the wake group needed six.
The effects lasted over time too, with participants in the sleep group able to recall 15 pairs after a week and those in the wake group only able to remember 11. The memory boost was noticeable as much as six months later.
“Memories that were not explicitly accessible at the beginning of relearning appeared to have been transformed by sleep in some way,” says Mazza. “Such transformation allowed subjects to re-encode information faster and to save time during the relearning session.”