Is it possible for people to register and retain what is said in their presence while they sleep?
If it is possible, is the learning that takes place during sleep efficient enough to be of practical as well as theoretical significance?
These are the questions of chief concern that researchers have addressed.
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These issues, including research dealing with a number of variables that may have an important influence on sleep learning have produced tentative conclusions concerning the possibility and practicality of learning during sleep.
Dr. Laverne C. Johnson of the United States Navy Medical Neuropsychiatric Research Unit in summarizing a review of the subject said "Information processing during sleep is summarized, and published reports lead to the conclusion that the sleeping brain does receive, process and perhaps even store information presented during sleep."
Learning a New Language Fox and Robbin (1952)
Used three separate 10-person groups to test the effects of hypnopaedia on learning Chinese. The facilitation group was administered a recording during sleep that was 29 minutes long and consisted of 25 Chinese words and their true English translation repeated 15 times. The interference group was administered a recording that consisted of the same 25 Chinese words, repeated 15 times, however, the English translations were incorrect. The control group was administered 29 minutes of music while they slept.
The following morning each group was administered the same recording given to the facilitation group, and tested on their comprehension of the Chinese language. The observable data was significant enough to support the conclusion that learning can occur during sleep.
San Diego State University
Doctors Clarence Leuba and Dorothy Bateman An experiment was conducted with a subject who claimed to recall information broadcast over the radio while she was sleeping. By use of an automatic timer three different songs were played over nine consecutive nights. With no prior knowledge of the songs, she recalled two perfectly and the other with just three minor errors.
Sleep Learning Used As An Aid To Reinforce
Traditional Daytime Learning
Research into sleep learning as an aid to increase and reinforce traditional daytime learning conducted by Dr. William H. Johnson concluded "... that hearing material during sleep can facilitate learning the same material in the waking state." Eight young men were paid $45 with an additional $15 for success, (motivation) if they could recall what was learned during sleep. The volunteers spent eight consecutive nights learning Russian. To ensure they were asleep, accurate recording by EEG was maintained. There were twelve repetitions of a list of ten Russian/English words each night. Each nightly lesson lasted approximately one hour.
Dr. William H. Johnson
The results led Dr. Johnson to say, "...subjects scored higher on the nights upon which they first heard the material to be learned during sleep than when they had not heard the material."
Forty students in a sleep learning program conducted at Duke University were divided into two groups. After both groups were first tested for their ability to remember words under normal circumstances, they were then both assigned a new group of words to learn. Only one group was given instruction whilst sleeping, before being taught the second list of words the next day. The group that heard this list whilst asleep had a significantly higher ability to master the list, leading the researcher to conclude that " The evidence obtained suggests that there is retention of auditory material presented during sleep."
Shedding a Bad Habit Leshan (1942)
Tested the theory of sleep-learning on a group of nail-biting boys attending summer camp. The experimental group consisted of 20 nail-biting subjects, aged 8 to 12 years. There were two control groups: the first consisted of 8 nail-biters, aged 8 to 10 years, the second consisted of 12 nail biters, aged 11 to 14 years.
The experimental group was administered a recording while they slept that said, "My finger-nails taste terribly bitter," repeated 300 times for 54 successive nights. The control group was not administered a recorded message. The researcher found that 40% of the boys in the experimental group stopped biting their nails, confirming Leshan's initial suspicion that people can be influenced by recorded messages during sleep.
San Diego State University
Two New York City researchers concluded after an experiment to teach a list of two word sets "Clearly, pre-presentation of a list of meaningful paired associates during the non-REM stages of sleep benefits subsequent learning of that list."