Sleep-learning (also known as hypnopædia or hypnopedia) is an attempt to convey information to a sleeping person, typically by playing a sound recording to them while they sleep. Although sleep is considered an important period for memory consolidation, scientific research has concluded that sleep-learning is not possible. It appears frequently in fiction. History In 1927, Alois Benjamin Saliger invented the Psycho-Phone for sleep learning, stating: "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. In fiction Sleep-learning is found in influential science fiction and other literature. The following examples are listed chronologically by publication or original air date, when known. 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 Robert Heinlein's 1948 novel Space Cadet, the character Matt Dodson is taught to speak Venutian (the language of the planet Venus) while under drug-aided hypnosis. He surprises his Venus-born friend Oscar by spontaneously reproving him when Oscar utters a curse in Venutian. (Later in the novel, Matt appears to have forgotten what he learned and relies on Oscar for translation.) 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