Overscheduled people often look at sleep as wasted time. If we can multi-task while we’re awake, why not while asleep? That question leads many to consider whether they can learn something while sleeping. For decades businesses have sold recordings designed to play to during sleep in hopes of imparting knowledge, or at least a change in attitude or habits.
While the viability of these techniques is not out of the question, there has been surprisingly little scientific investigation of sleep learning.
Hypnopaedia is a fancy name for sleep learning. In the mid-20th Century serious researchers found positive results, and sleep-learning entered the popular consciousness. It played a part in the plots of the dystopian novels Brave New World and Clockwork Orange and it was associated with brainwashing.
A more positive use of sleep learning was encouraged by people who sold records designed to play while the listener was asleep. Commercially, things haven’t changed much although the recordings you find today are more likely to be digital.
Such hard evidence as we have suggests that these methods can be effective in getting people to remember rote facts. It can also promote simple stimulus-response conditioning. Israeli psychologists were able to make test subjects learn sniffing behavior in response to audible cues. Smell and hearing simple tones can be processes in primitive brain areas. This conditioning worked no matter at what stage of the sleep cycle it was given, although it appeared to be more effective when administered during REM.
Scientists at France's Ecole Normale Supérieur recently showed sleeping people can process and respond to words spoken to them. Whether this processing counts as understanding is a philosophical question (mmost would say it isn't). One researcher told the press he thought the processing bypassed the prefrontal cortex. When they woke up the subjects could not recall the words that were said to them, so this does not exactly meet the definition of sleep learning. Still, it is interesting.
There is some evidence people can solve complex problems more readily if their deliberation is interrupted by sleep. Attacking a tough problem (mathematical, logical, or pragmatic day-to-day) during the day but unable to solve it, people often have better success the next day, after a night of sleep. It is not known which stage, if any, of sleep is the most productive for problem solving.
Further, there is evidence that complex designs, including those with emotional components, often go better after one or more nights of sleep. The familiar admonishment to “sleep on it” appears to be valid.
It's not just mental learning. Physical training such as practicing music, dance and sports causes people to continue to improve for at least a day following a training session. That's been known for a long time. Recent research confirms that sleep plays an important part in that continued learning.
Researchers at Northwesten University found that a 90-minute nap can help solidify learning. They tried teaching new things - both mental and physical - to people and then measured how well the new skills and knowledge stuck. Those who were told to sleep in the lab after the new experiences showed better mastery later on. Experiments showed people taught new piano melodies (while awake) could recall them better if the melodies were played while asleep. This isn’t sleep-learning as originally conceived, but it does employ sleep as part of the overall teaching regimen.