What are the effects of sleep listening on language skills and aren't there any negative effects of it on overall physiological health? Are there any studies or your personal experiences proving that you can improve your language skills just by listening while you are sleeping?
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. .."