![Best Carrier Frequency For Binaural Beats Best Carrier Frequency For Binaural Beats](/uploads/1/2/5/8/125841017/447805394.jpg)
Humans can hear binaural beats from a main carrier frequency signal of 1000Hz to 0.5 Hz. The main carrier signal is the median of the two sound wave frequencies which make up the binaural beat.
Binaural beats represent the auditory experience of an oscillating sound that occurs when two sounds with neighboring frequencies are presented to one’s left and right ear separately. Binaural beats are perceived as periodic loudness fluctuations of a sound (Karino et al. 2006). The experience of such oscillations is described as hearing a sound with a frequency equal to the difference in frequencies between the original tones (Oster 1973). For instance, when the left ear is presented with a tone of 320 Hz, and the right ear with a tone of 360 Hz, the subject will perceive a tone that oscillates at a frequency of 40 Hz (i.e., 40 beats per second). In a seminal study, Karino et al. (2006) explored the cortical representation of binaural beat frequencies by applying modulation frequencies of 4.00–6.66 Hz while recording magnetic fields using magnetoencephalography. It was shown that the auditory steady-state responses (ASSR) to binaural beats emerged from the superior temporal, posterior parietal, and frontal cortices, in addition to the auditory cortex. However, beat-generated ASSR in the gamma-frequency seem to originate mainly in the primary auditory cortex (Pastor et al. 2002; Pantev et al. 1996). Even though direct causal links between neural activity and binaural beats are yet to be demonstrated, there is converging evidence that binaural beats are accompanied by, and systematically related to, neural synchronization. Indeed, it has been proposed that binaural beats represent a neural entrainment technique by means of which the brain “takes over” or synchronizes its activity based on external acoustic stimulation (Chaieb et al. 2015). The basic assumption is that listening to binaural beats in a specific frequency band will entrain the same frequency in the brain (Becher et al. 2015). The theoretical idea behind neural entrainment is that the rhythmic oscillatory activity within and between different brain regions can enhance cognitive functioning (see Chaieb et al. 2015 for a review on the effect of binaural beats on cognition and mood). Indeed, in recent years, it has been shown that binaural beats have an impact on the efficiency of allocating attention over time (Reedijk et al. 2015), attentional focusing (Colzato et al. 2015), dual-talk crosstalk effect (Hommel et al. 2016), and creativity (Reedijk et al. 2013). If binaural beats impact cognition via neural synchronization, it is most likely through the frequency of the beat. Whereas short-range communication within brain areas is often linked to neural synchronization in the gamma-frequency (i.e., centered on 40 Hz), long-range communication is related to neuronal phase locking in the slower frequency bands (von Stein and Sarnthein 2000; Schnitzler and Gross 2005). In line with this idea, the increase of gamma band power through neurofeedback improved the top-down control of feature bindings (Keizer et al. 2010a, b). Given this aforementioned link, in the current study, we were interested in searching for converging evidence of whether high-frequency binaural beats (gamma range) enhance the control and management of feature bindings.
Studies of feature-repetition effects commonly show interactions between perceptual features and action-related features: in contrast to complete repetitions and alternations, repeating only some but not all features of a perception–action episode (i.e., of a particular combination of stimulus and response features) hinders performance (Hommel 1998). Later studies have provided evidence that this effect is due to the fact that (a) the co-occurrence of stimulus and response features leads to the binding of the respective feature codes into the so-called event files (Hommel 2004), which are then (b) retrieved whenever at least one of the features is repeated (Beste et al. 2016; Colzato et al. 2005; Keizer et al. 2008; Frings et al. 2007; Kühn et al. 2011; Moeller and Frings 2014; Petruo et al. 2016). The binding part of this scenario seems to be rather immune to all sorts of attentional and instructional variation, while the retrieval part is systematically affected by the degree to which a particular stimulus dimension is attended (e.g., Hommel 2004, 2007). In particular, there is evidence that bindings including irrelevant features are less likely to be retrieved in individuals with high cognitive control abilities, such as individuals high in fluid intelligence (Colzato et al. 2006) and normally developing children as compared to children suffering from autistic spectrum disorder (Zmigrod et al. 2013). Of particular interest for the present investigation, two studies in which neurofeedback training was designed to increase local gamma band activity (Keizer et al. 2010a, b) found greater flexibility in handling (selectively retrieving) visual feature binding costs (which refer to the binding between the two visual features), but not visuomotor binding costs (indicating the binding of visual and action features).
If we assume that high-frequency binaural beats (gamma range) promote cognitive control (Hommel et al. 2016) and that neural synchronization in the gamma-frequency is associated with visual feature bindings (Keizer et al. 2010a, b), we would predict decreased visual feature but not visuomotor binding costs when listening to gamma-frequency beats as compared to a constant tone. If this were the case, we would expect an interaction between visual feature bindings and the kind of beats (gamma-frequency vs. control), with a greater flexibility in handling (selectively retrieving) visual feature binding costs with gamma-frequency beats than with a constant tone. Theoretically, such an interaction would suggest that binaural beats enhance selectivity in updating episodic memory traces. We tested this prediction by adopting a feature-repetition task (i.e., a task known to generate event file effects) and having participants perform it while listening to either high-frequency binaural beats (the gamma group) or to a continuous tone of 340 Hz (the control group).