Abstract:
When pure tones of different frequencies are presented to each ear simultaneously, a third frequency can often be perceived to be originating from the centre of the brain. In psychological and neurological literature, this auditory phenomenon is referred to as ‘binaural beats’. Binaural beats have become established because of their potential to modulate psychological states, typically to the benefit of the listener. For example, they have been associated with reductions in subjective reports of negative mood or anxiety, and inducing changes in traditional EEG brainwave frequencies. Anecdotal and psychological evidence suggests that individuals listening to binaural beats experience shifts in states of consciousness and general ‘relaxation’. Though it is presumed that changes in individual psychological states are correlated with changes in physiological activity, very few studies examine the direct effects of binaural beat stimulation on the autonomic nervous system (ANS). Two studies have been designed to investigate the effects of binaural beat exposure on physiological recovery after a cognitive stress task, and comparisons have been made across different types of sound. Recordings of skin conductance, heart rate, respiration depth, and respiration rate are employed to infer autonomic recovery processes during post-stress rest periods. In the first study, the stimuli consisted of 6 Hz and 16 Hz frequencies of harmonic binaural beats, a sample of aircraft noise, and a novel stimulus, the Weightless song by Marconi Union. We predicted that lower frequencies of binaural beats would show physiological indications of increased ‘relaxation’. Listening to 6 Hz, and 16 Hz harmonic binaural beats, and Weightless, indicated a relaxation effect compared to silence and aircraft noise in mean change in heart rate, but no differences were found between any sound type exposures in skin conductance or respiration depth. In the second study, the stimuli consisted of 2, 5, 10, and 24 Hz frequencies of regular pure tone binaural beats. Results showed mostly null effects but also included some contradictory patterns of modulation and would require further exploration to be understood. Also, for unknown reasons, data in the second experiment were unexpectedly noisy.