Sleep-learning (also known as sleep-teaching, hypnopædia, or hypnopedia) is an attempt to convey information to a sleeping person, typically by playing a sound recording to them while they sleep. Research on this has been inconclusive. Some studies have largely discredited the technique's effectiveness, while others have found that the brain indeed reacts to stimuli and processes them while we are asleep 
In 1927 Alois Benjamin Saliger invented the Psycho-Phone for sleep learning: "It has been proven that natural sleep is identical with hypnotic sleep and that during natural sleep the unconscious mind is most receptive to suggestions."
Since the electroencephalography studies by Charles W. Simon and William H. Emmons in 1956, learning by sleep has not been taken seriously. The researchers concluded that learning during sleep was "impractical and probably impossible." They reported that stimulus material presented during sleep was not recalled later when the subject awoke unless alpha wave activity occurred at the same time the stimulus material was given. Since alpha activity during sleep indicates the subject is about to awake, the researchers felt that any learning occurred in a waking state.
In 2012 research from the Weizmann Institute of Science indicated that classical conditioning can occur during sleep by using odor recognition. "During sleep, humans can strengthen previously acquired memories, but whether they can acquire entirely new information remains unknown. The nonverbal nature of the olfactory sniff response, in which pleasant odors drive stronger sniffs and unpleasant odors drive weaker sniffs, allowed us to test learning in humans during sleep."
- In Hugo Gernsback's 1911 story Ralph 124C 41+, one finds the Hypnobioscope, a sleep learning device.
- In Aldous Huxley's 1932 novel Brave New World, it is used for the conditioning of children into the novel's fictional future culture. In the novel, sleep-learning was discovered by accident when a Polish boy named Reuben Rabinovitch was able to recite an entire radio broadcast in English after a radio receiver was left on in his sleep. The boy was unable to comprehend what he had heard via hypnopædia, but it was soon realized that hypnopædia could be used to effectively make suggestions about morality.
- In the BBC Radio series Journey into Space (1953–1958), during the second and third parts of the trilogy, there were said to be Martians abducting people from the Earth and conditioning them to obey instructions or to make them believe things that were not true. The inception of this conditioning involved putting the subject into a hypnotic sleep and appraising them of a certain situation; once they awoke they would believe it, regardless of the validity.
- In a 1961 episode of My Three Sons, "A Lesson In Any Language", Mike connects a phonograph to an automatic timer to play Spanish lessons while he sleeps. Steve and Bub ultimately end up sleeping in the room and are able to speak fluent Spanish the following day.
- In Anthony Burgess's 1962 novel A Clockwork Orange, it is used to reverse the effects of the Ludovico Technique, a form of classical conditioning, which was used on the main character Alex to make him incapable of violent behavior. The conditioning was a new technique which was supposed to rehabilitate violent criminals in a short period of time, but which resulted in Alex attempting to commit suicide. This reflected very badly on the government, which had sanctioned the experiment, so hypnopædia was used to undo the conditioning.
- In a 1963 episode of The Patty Duke Show, "The Conquering Hero", Cathy tries to help a failing basketball player pass a quiz. She suggests that the latest scientific method of "subconscious learning" will help. She records the lessons on a tape which plays repeatedly while he is asleep. He passes the quiz after the answers "come to him" while looking at the questions.
- In the 1965 movie The Monkey's Uncle, a college student connects a phonograph to an automatic timer, which plays to sleeping students the voice of a girl reading their lessons aloud. This backfires in class, however — when asked to give an oral report, the students speak, but in the girl's voice.
- In the 1966 novel Flowers for Algernon, a mentally retarded 35 year old, Charlie Gordon, has an operation to increase his intelligence. Professor Nemur and Dr. Strauss then give Charlie a "teeching mashine that werks like T.V." Charlie explains to Professor Nemur that "I dint think I was goin to get smart anyway." (sic)
- In a 1988 episode of the BBC2 sitcom Red Dwarf, "Me2", Arnold Rimmer uses sleep-learning tapes such as Learn Esperanto While You Sleep and Learn Quantum Theory While You Sleep, to the dismay of his bunkmate Dave Lister.
- In the 1990 movie Dragon Ball Z: The Tree of Might, Chi-Chi packs for her son Gohan a tape recorder so he can learn while he sleeps on a camping trip.
- In a 1992 episode of The Simpsons, "Bart's Friend Falls in Love", Homer orders hypnosis tapes which are supposed to induce weight loss. However, the mail-order company sends him vocabulary builder tapes instead, and Homer gets fatter and fatter while his vocabulary increases, through hypnopædia.
- In a 1996 episode of Dexter's Laboratory, "The Big Cheese", Dexter hooks himself up to a gramophone that repeats his lesson for a French class test the next morning. The gramophone gets stuck at the phrase omelette du fromage, and Dexter finds out the next morning that it is all he is capable of saying.
- In a 1997 episode of Friends, "The One with the Hypnosis Tape", Chandler borrows from Rachel a smoking-cessation audiocassette, to which he listens while he is asleep. The tape tells him that he is "a strong, confident woman" who doesn't need to smoke. He stops smoking, but also begins acting effeminately.
- In a 2001 episode of Homestar Runner, "A Jorb Well Done", Coach Z attempts to overcome his speech impediment with the word "job" (which he pronounces as "jorb"). After unsuccessfully trying several methods, Strong Sad gives him a tape of him repeating the word job thousands of times, "from when (he) was practicing the dictionary". Coach Z takes it home and listens to it while he sleeps, and the next day is able to pronounce "job" correctly, but forgets Homestar's name.
- The twins Hank and Dean Venture, of the animated television program The Venture Bros., are homeschooled through the use of hypnopædic beds.
- In the 1997 PC game Outpost 2: Divided Destiny, one of the items available for research was hypnopædia, which allowed scientists to be trained more quickly.
- Sleep and learning, for the science that ties sleep to learning
- Educational technology
- Mozart effect
- Ackerman, Jennifer (2007). Sex Sleep Eat Drink Dream. Houghton Mifflin Books. ISBN 0-618-18758-8. p. 171 "But most scientist agree that learning during sleep--that is actively acquiring new knowledge--is probably impossible. Certainly, attempts to teach slumbering adult subjects vocabulary or foreign languages or lists of items has failed miserably."
- Turkington, Carol (2003). 12 Steps to a Better Memory. Simon and Schuste. ISBN 0-7434-7575-5. p. 9 "While it is popularly believed that a person can learn and remember while sleeping, in fact research has shown that learning does not take place while you are sound asleep...However, there is some evidence suggesting that you can learn while you are very drowsy, or even in a very light sleep. The material must be presented at just the right time; if you are not sleepy enough, the material will wake you up, and if you're too deeply asleep, the materials won't make an impression at all. In addition, complex material involving reasoning or understanding can't be learned while in a drowsy state."
- "Learning while you sleep may be possible". The Telegraph. 2014. Retrieved 2014-12-13.
Once the participants were asleep, the testing continued but with an entirely new list of words to ensure that responses would require the extraction of word meaning rather than a simpler pairing between stimulus and response. Brain activity showed that the participants continued to respond accurately, although more slowly, even as they lay completely motionless and unaware.
- "Psycho-Phone". The New Yorker. 1933. Retrieved 2010-11-18.
Well, sir, since 1927, Mr. Saliger has sold more than 2500 Psycho-phones ...
- Fromm, Erika; Ronald E. Shor (1972). Hypnosis. Aldine/Atherton. ISBN 978-0-202-30856-2. 020230856. p. 78 Referring to Charles W. Simon and William H. Emmons EEG, Consciousness, and Sleep, Science, 1956, 124, 1066-1069.
- Kleitman, Nathaniel (1987). Sleep and Wakefulness. University of Chicago Press. ISBN 0-226-44073-7. Page 125
- Arzi, A.; Shedlesky, L.; Ben-Shaul, M.; Nasser, K.; Oksenberg, A.; Hairston, I. S.; Sobel, N. (2012). "Humans can learn new information during sleep". Nature Neuroscience 15 (10): 1460–1465. doi:10.1038/nn.3193. PMID 22922782.
- Amanda L. Chan (29 August 2012). "Sleep Learning May Be Possible: Study". Huffington Post. Retrieved 3 September 2012.
- Hypnopaedia -Sleep Learning
- Emmons William H., Simon Charles W. The Non-Recall of Material Presented During Sleep. American Journal of Psychology. 1956 Mar;69(1):76-81.
- Fox, B.H.; Robbin, J.S. (1952). "The Retention of Material Presented During Sleep". Journal of Experimental Psychology 43: 75–79. doi:10.1037/h0057555.
- Fox, B.H. (1968). Current research in Hypnopaedia. Macdonald & Co. [PDF]
- Leshan, L. (1942). "The Breaking of a Habit by Suggestion During Sleep". Journal of Abnormal & Social Psychology 37 (3): 406–408. doi:10.1037/h0057703.