First, brain waves tend to follow a rhythmic sound, the frequency-following response, which EEG can detect. Second, because each ear feeds mainly the opposite hemisphere, the brain must coordinate both sides to build the beat. The Institute calls this hemispheric synchronization, and a 1982 Army training report defined it as EEG coherence with both sides showing virtually identical electrical patterns. Third, since brain-wave rhythms accompany states such as sleep, relaxation and alertness, steering the rhythm is meant to steer the state. Monroe estimated the synchronized signal runs three to ten times stronger than typical brain rhythms. From sleep-learning tests to binaural beats A radio host introducing Monroe in 1987 credited him with some 400 network programs, and Monroe stressed that his team composed its own music and effects. In 1956 his company began testing whether people could learn during sleep. As chief executive he became the chief subject, with his daughters also sitting in sessions, and counted about 150 runs by early 1958. He says the lab first used frequency-following sounds in 1960, played in open air without headphones. Physicist Tom Campbell, who worked in the lab in the early 1970s, recalls building the first binaural-beat tapes after reading about the effect, aiming at four hertz because Monroe had reported that rate during his own vibrations. More than a pair of tones
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Hemi-Sync: audio and attention
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Hemi-Sync recordings are not one steady beat. Skip Atwater, the Institute's research director, said the frequencies change as the exercise changes, with subtle shifts borrowed from music theory, and Monroe said in a 1992 video that one signal had become seven, with some applications combining as many as 35 patterns. The 1983 Army assessment adds that the signals are barely audible and sometimes masked under sounds such as ocean surf. Atwater called an exercise a recipe: relaxation, breathing, a stated intent and inner perception, with the sound as one ingredient. Sound, not a drug Monroe insisted that Hemi-Sync is only sound. It is not a chemical, it does not invade the body, and the mind can accept or reject it. He described uses from intense wakeful focus to natural sleep, with Focus 10, mind awake and body asleep, between them. Welcoming a Gateway group, he called Hemi-Sync one of the tools, perhaps the basic tool, and said the real subject is learning to use mental tools yourself. Product families and users
The publisher groups its catalog by use. The Gateway Experience is the eight-album home course with spoken guidance; Metamusic blends Hemi-Sync with music; Human Plus teaches a learned cue; titles such as Concentration work while you listen. The Institute's own site now speaks mostly of Monroe Sound Science, so you will meet both names. Professionals adopted the sound too: Atwater told Art Bell's audience that dentists, lawyers, therapists and educators used it, and in 1982 a Defense Information School pilot gave a broadcasting class eight tape exercises. How it differs from generic binaural beats Nancy Walter, the Institute's co-director of research, contrasts Hemi-Sync with a simple binaural beat, which is only the difference between two tones. A steady beat, she says, becomes boring to the brain, which stops responding, while the Institute's recordings keep changing. A.J. Honeycutt, president of Monroe Products, said in 2014 that production still follows Monroe's formulas and ratios and that Hemi-Sync is the Institute's brand. Campbell recalls that Monroe embedded the binaural beats in the sound he already had, and that became Hemi-Sync; Walter says the newer recordings add phase modulation and a 3D soundscape. What the research shows