Effectiveness of binaural auditory beats in cognition, anxiety, and pain perception: a meta-analysis

Summary
Binaural auditory beats are a perceptual phenomenon that occurs when two tones with slightly different frequencies are presented separately to each ear. It has been revealed that binaural beats can, among other things, influence cognition and mental states. The aim of this meta-analysis was to study the effect of binaural beats on memory, attention, anxiety, and pain perception. Twenty-two studies met our inclusion criteria for this meta-analysis. The results, based on 35 effect sizes, showed a mean, significant, and constant overall effect level (g = 0.45). The results of the meta regression indicated that it does not seem necessary to mask binaural beats with white noise or pink noise. In terms of efficiency, similar effects are obtained with unmasked binaural beats.

Furthermore, the results suggest that exposure to binaural beats before, and during, the task gives greater results than exposure during the task. Exposure time contributed significantly to the model by indicating that longer periods of time are recommended to ensure maximum effectiveness. Our meta analysis adds to the growing evidence that exposure to binaural beats is an effective way to affect cognition, beyond reducing anxiety levels and pain perception without prior training, and that the direction and magnitude of the effect depend on the frequency used, the time of exposure
and when the exhibition takes place.

Conclusion
The objective of this meta-analysis was to provide an overall estimate of the effectiveness of binaural auditory beats on two cognitive functions (memory and attention), as well as on anxiety and analgesia.
We intended to answer two questions: (a) what was the overall magnitude of the effectiveness of exposure to binaural beats on the selected outcomes, and (b) were there attributes of binaural beats that consistently moderated this effectiveness?

This meta-analysis provided strong, though modest, evidence regarding the effectiveness of binaural beats on memory, attention, anxiety, and analgesia. Based on our results, we can observe that exposure to binaural beats alpha (3 ES), beta (10 ES), beta (10 ES), and theta (6 ES) affected the performance of tasks requiring memory, and that this effect depends on the frequency used: positive effect for alpha, beta and
gamma, and negative for the theta frequency (with the exception of studies 2 and 27).

Furthermore, binaural beats have been shown to be effective in reducing the amount of medication required for preoperative anesthesia. Studies 10 and 21 both applied multi-layered binaural beats, while
that study 25 did not report on the frequency used. The effectiveness of binaural beats in reducing anxiety levels after delta/theta exposure was also confirmed in all included studies (k = 5), although study 29 did not mention the frequency used.

Finally, we note that attention was also affected by exposure to binaural sounds. All studies (k = 7), except study number 17, showed positive effects on attention using alpha, beta, and gamma frequencies; based on our results, we can assume that the reduction in efficiency observed in study 17 was due to the time of exposure — only during the task — and to the masking of the binaural rhythm by music.
With respect to these potential moderating variables, the results provided evidence supporting the hypothesis that the time of exposure plays a critical role in the effectiveness of binaural beats, showing a greater effect when exposure occurs before, and during, the performance of a task. Furthermore, it seems that exposure time does not produce an addiction to binaural beats as was initially assumed (Vernon, Peryer, Louch, & Shaw, 2014). On the contrary, our results indicate a positive relationship between exposure time and the magnitude of the effect, which reflects the fact that not only is it advisable to go through an induction phase to ensure that the desired frequency is driven by when the event or task to be measured begins, but also that the exposure time must be long enough to obtain maximum benefit.

In line with this suggestion, it is recommended to conduct an induction phase in order to ensure that the desired frequency is driven by when the event or task to be measured starts, but also that the exposure time is long enough to obtain maximum benefit. Recent studies have shown that to cause changes in almost all cortical regions, exposure to binaural beats must last from 9 to 10 minutes (Jirakittayakorn & Wongsawat, 2017; Seifi Ala, Ahmadi-Pajouh, & Nasrabadi, 2017; Seifi Ala, Ahmadi-Pajouh, & Nasrabadi, 2018).

With respect to the masking of binaural beats, our findings indicated that unmasked beats were associated with larger effect sizes than binaural beats masked by music, but no difference was found when it came to pink noise or white noise. We can hypothesize that the lower efficiency observed with binaural beats embedded in music may be due to some interference between the frequencies found in music and binaural beats, as it has been reported that musical rhythms, even when they are not strictly periodic, cause body movement (London, 2004; McAuley, 2010; Phillips-Silver& Keller, 2012).

With respect to binaural beat frequency, our results indicate that binaural beats with a complex frequency (i.e., multi-layered) produced the greatest effect. Because of the limited number of studies that have looked at multi-layered binaural beats (k = 3), it is plausible that these findings are only valid for surgical procedures and cannot be generalized to a wider range of applications such as improving memory or reducing anxiety. Future studies should address this question and determine whether the reduction in analgesia can be extrapolated to all types of surgical procedures and other areas of cognitive improvement, and whether multi-layered binaural beats offer a greater effect than simple binaural beats.

Although most studies have found significant differences between binaural stimulation and control conditions, it is necessary to identify why some studies could not find such differences. Some variables could potentially explain differences in effectiveness between studies. For example, one of the variables that could play a crucial role in the effectiveness of binaural beats would be the carrier frequency, which would benefit from being studied in future research to determine whether different frequency ranges produce different results. Exposure time, time of exposure (i.e., before and during the task), and the type of sound that was used to mask the binaural beat are other variables that can moderate the effectiveness of the binaural beats that we included in this meta-analysis.

Furthermore, we should not forget that there is a difference in the perception of binaural beats between men and women (Oster, 1973; Tobias, 1965) and that other inter-individual differences could moderate the results. For example, individual mesostriatal dopamine levels — measured directly by the rate of spontaneous eye blinking — have been found to determine the degree to which binaural gamma beats affect cognition (Reedijk et al., 2013; Reedijk et al., 2015). This could potentially be explained by greater sensitivity and a more responsive mesostriatal dopamine system that initiates neural processes more effectively due to a hypodopaminergic state, which can be predicted by the spontaneous blink rate (Jongkees & Colzato, 2016).
This greater sensitivity is common in differences related to extraversion and involves increased sensory reactivity, such as lower hearing and sound thresholds (Smith, 1968; Stelmack & Campbell, 1974), and greater potential amplitudes related to early visual events like the N1 (Rammsayer & Stahl, 2004).

Furthermore, introverts appear to be more sensitive to induced changes in dopaminergic activity, while extroverts show a more effective compensation mechanism by which neurotransmission homeostasis is maintained (Rammsayer, Netter & Vogel, 1993).
It is therefore essential to determine how these variables affect the efficiency of binaural beats and what is the optimal carrier frequency in order to be able to use the most effective parameters and thus get the most out of binaural beats. For the reasons mentioned above, the frequency of binaural beats should be adjusted according to the gender of the listener in order to obtain similar and comparable results taking into account individual differences related to extroversion. One way to reduce these extroversion-related differences could be to use carrier tones at higher frequencies where no significant differences in sensitivity between extroverts and introverts have been observed (Stelmack & Campbell, 1974).

A number of limitations may have influenced the results obtained in the present meta-analysis.
For example, with the exception of study 29, the other studies included had a modest sample size (n < 70) that may compromise statistical power and estimates by overestimating the effectiveness of auditory beats. Publication bias is still a problem in meta-analysis, although the statistical tests performed did not suggest the presence of publication bias. We cannot rule out the possibility that if we had included all studies that were not significant and therefore unpublished, the estimate of effect sizes would have been potentially lower. In addition, more studies are needed as, at present, there is a very small number of studies that have looked at the practical applications of binaural auditory beats.

Also, despite the importance of carrier frequency, we were unable to incorporate it into our analysis, as a large number of the included studies (33%) did not report such information. It is essential to follow the reporting guidelines to make progress in this area. Finally, due to the limited number of studies included (k = 22), interaction effects could not be examined and it is possible that statistical power was not sufficient to perform a meta regression. The associations obtained in meta-regression should be considered with caution, as they have a lower capacity for interpretation than those obtained from randomized comparisons due to their observational and non-causal nature (Thompson & Higgins, 2002).

The results of this meta-analysis are encouraging and should be validated by studies with larger samples to ensure that the observed effectiveness can be replicated and applied to other areas such as implicit and episodic memory. Moreover, the results obtained from the meta regressions should also be confirmed in future studies, as they are limited in that the predictors were not based on theory. It is also essential to validate the idea that exposure before and during the task produces greater efficiency than during the task alone.

Taken together, these findings suggest that binaural auditory beats affect memory, anxiety levels, anxiety levels, attention, and perceived pain passively and automatically, and that the direction and magnitude of the effect are determined by the frequency of the binaural beats and the timing and duration of exposure. The mechanisms that explain how binaural stimulation results in psychophysiological changes are still unknown. Therefore, further work in this area is needed and could lead to a better understanding of this phenomenon and to new practical applications in which binaural beats could prove to be more effective.

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Sources : Efficacy of binaural auditory beats in cognition, anxiety, and pain perception: a meta-analysis. Psychological Research 83, 357—372 (2019).
https://doi.org/10.1007/s00426-018-1066-8

Miguel Garcia-Argibay,
Miguel A. Santed,
José M. Reales
International authors