The superior olivary complex (SOC), the first locus of the auditory pathway to receive input from both ears and an important structure for sound integration, has been identified as the main neuroanatomical structure involved in binaural beat perception. īinaural beats are, as mentioned in the beginning, an illusory phenomenon, which means that its perceptual basis is not the interference of two sound waves, but a result of their combined neural activity elicited in the auditory pathway. Differences between individuals in the ability to perceive binaural beats were also suggested. Furthermore, Schwarz and Taylor found that participants can control the perception of binaural beats to a certain degree by focusing either on the two presented tones separately, or on the binaural beat percept instead. These thresholds are approximate and assumed to vary interindividually. Below a difference of 3 Hz, the binaural beat is perceived as a rotating tone-a sound that appears to rotate in the head from ear to ear. Up to 20 Hz, the binaural beat is described as a tone fluctuating in loudness, while frequency differences larger than 20 Hz elicit a rough sound. was the first to characterize the percept of the binaural beat depending on frequency differences in more detail. This threshold seems to vary depending on the stimulation technique, though. Beyond frequency differences of 30 Hz, the two tones are perceived separately instead of eliciting the percept of a binaural beat. Third, Perrott and Nelson demonstrated that the maximum difference for the two tones must be around 30 Hz. the frequencies of the two presented tones–of around 400 Hz. Second, binaural beats seem to be best perceived at carrier frequencies-i.e. This is due to the fact that the human auditory pathway can only encode sound waves with frequencies up to 1 kHz. ![]() demonstrated that the two presented frequencies must be of a maximum of 1000 Hz to elicit a binaural beat. First, an early study by Licklider et al. There are, however, a number of constraints to the perception of binaural beats. The illusory nature of the binaural beat, a perceptual phenomenon that has no manifest external source, makes it of interest for research on sound perception and acoustic processing. When, for example, a tone with a frequency of 400 Hz is presented to the right ear and a second tone with a frequency of 420 Hz is presented to the left ear simultaneously, a binaural beat of 20 Hz will occur. This psychoacoustic phenomenon is called the binaural beat. The percept of this third tone is described as being located in the head, or between the ears. When people are presented with two acoustic signals of slightly different frequencies separately to each ear, the percept of a third tone oscillating at the difference of the two frequencies arises. The results of the present systematic review emphasize the need for standardization in study approaches so as to allow for reliable insight into brainwave entrainment effects in the future. The methodological heterogeneity in this field of study ultimately limits the comparability of research outcomes. What is to be noticed is that the fourteen studies included in this review were very heterogeneous regarding the implementation of the binaural beats, the experimental designs, and the EEG parameters and analyses. The results corroborate the impression of an overall inconsistency of empirical outcomes, with five studies reporting results in line with the brainwave entrainment hypothesis, eight studies reporting contradictory, and one mixed results. A sample of fourteen published studies met our criteria for inclusion. ![]() The aim of the present systematic review is, thus, to synthesize existing empirical research. ![]() At first glance, however, the available literature on brainwave entrainment effects due to binaural beat stimulation appears to be inconclusive at best. ![]() Studies, particularly in more applied fields, usually refer to neuroscientific research demonstrating that binaural beats elicit systematic changes in EEG parameters. The brainwave entrainment hypothesis, which assumes that external stimulation at a certain frequency leads to the brain’s electrocortical activity oscillating at the same frequency, provides the basis for research on the effects of binaural beat stimulation on cognitive and affective states. Binaural beats can be perceived in the frequency range of about 1–30 Hz, a range that coincides with the main human EEG frequency bands. Binaural beats are an auditory phenomenon that occurs when two tones of different frequencies, which are presented separately to each ear, elicit the sensation of a third tone oscillating at the difference frequency of the two tones.
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