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Monaural beats are derived from the convergence of two frequencies within a single speaker to create a perceivable pulse or beat. As such they are a purely physical phenomenon; see beats for a more complete discussion of the acoustics. This article deals more in depth with the effect of monaural beats on the human brain. For example, if a 400 Hz tone and a 410 Hz tone are played through a speaker, one would hear a 10 Hz beat amidst the original tones. Monaural beats are similar to binaural beats in that two frequencies are combined to create a perceivable beat; however they vary in two distinct ways. First, binaural beats are created by introducing two different tones, 400 Hz and 410 Hz, via separate speakers (e.g., headphones). Second, binaural beats seem to be “created” or perceived by cortical areas combining the two different frequencies, whereas monaural beats are due to direct stimulation of the basilar membrane.
The most frequently commercialized use of monaural and binaural beats are in software or apps aimed at achieving brainwave entrainment. Brainwave entrainment is the use of masked monaural or binaural beats to induce a specific brainwave state. It is hypothesized that listening to these beats of certain frequencies one can induce a desired state of consciousness that corresponds with specific neural activity. It is widely accepted that patterns of neural firing, measured in Hz, correspond with states of alertness such as focused attention, deep sleep, etc.
While these brain states are what brainwave entrainment is hoping to achieve the effectiveness of monaural and binaural beats are up for debate. There are many companies that produce software for purchase that stand behind their product saying that “research shows” binaural / monaural beats are effective for inducing a desired brainwave state. However no published scientific studies have found statistically significant data that indicates monaural / binaural beats induce a specific brainwave state in human participants. No significant change in human EEG readings were found when using binaural beats to induce a theta brain state. Many applications and software continue to be sold. No evidence supporting their claims has yet been found.