It has been suggested that cognitive and executive functioning is accompanied by specific brain wave oscillations. Overall, the brain activity within alpha rhythm (7.5 – 12.5 Hz in adults) has been associated with vigilance, inhibitory processes, attention, working memory, perceptual abilities, and information processing speed. Some authors have concluded that oscillations in alpha rhythm indirectly enhance performance in such a way that they filter out irrelevant information and prevent disruptions caused by conflicting stimuli (Klimesch et al., 2007; Rihs et al., 2007; Tuladhar et al., 2007).
One way of ensuring induction of electrical activity in the brain is through binaural beats (BB). BB are subjective auditory sensations caused by presenting tones of slightly different frequencies separately to each ear. As a result, the listener perceives sound with an amplitude that changes with a frequency equal to the difference of frequency in the presented tones, and these two frequencies are integrated at the cortical level into the above-mentioned binaural beat. If the difference in frequencies corresponds to the alpha range (7.5 – 12.5 Hz), then the electrical activity of both hemispheres should merge into one synchronized activity.
In this study, consisting of 50 university/college students, each participant was randomly assigned to either an experimental or control group. The subjects took a computer-administered test consisting of a training period and actual test. During the task, a person is asked to retain randomly presented series of 3 to 7 defined letters. The letters were presented one at a time for 800 milliseconds. After the presentation of each letter, a simple mathematical equation appears on the screen (ex. (2*3) + 7 = ?)
The participant has to assess whether the proposed solution is correct. The mathematical operation is presented to each participant for a specific amount of seconds calculated from his/her individual tempo as measured during his/her individual rehearsal task + 2 SDs. Afterwards, a letter comes up for 800 ms. This process is presented anywhere between 3 and 7 times. Afterwards, a set of letters (a table of all possible letters) is presented to the participant. The participant has to choose the letters that were presented in that trial. The whole task consists of 3 series of each set size. The set sizes range from 3 to 7 letters plus the mathematical operations. In total, 75 letters and 75 mathematical operations are administered to the participant. After completing the AOSPAN task, two scores related to the assessment of working memory capacity were computed. The first score, the Ospan score, has an absolute scoring method, and it represents the sum of all correctly recalled sets of letters in the correct order. The second additional score reflects the total number of errors made solving the mathematical operations.
The baseline measure of the AOSPAN was obtained at the beginning of the experiment. After the first completion of the AOSPAN, participants were randomly assigned to either music with a BB or music without a BB. All participants then listened to a 12 minute long recording of one of the recordings. After those 12 minutes they were asked to retake
the AOSPAN. Both the experimental and control group were exposed to the same procedure with the exception of the inclusion of BB in the music in the experimental condition. Completing the experiment took approximately 50 minutes.
The results of the study illustrate that BB frequencies corresponding to alpha range of brain activity had a temporary positive effect on the capacity of working memory. Participants undergoing a 12-minute BB stimulation of 9.55 Hz frequency achieved a significant increase in the capacity of their working memory in comparison to a control group, which was not exposed to BB stimulation. Participants exposed to BB just for 12 minutes showed an improvement in their working memory capacity on average by 4.6 points in their score. In terms of the control group, this group either remained unchanged by means of measured performance, or deteriorated by the maximum of one set on average (deterioration of 2.45 points). Thus, the ultimate difference between the experimental and control group represents the difference of 1-2 correctly recalled sets, roughly a range of 7 – 13 %. While the experimental group improved by an average of slightly more than one remembered letter, the control group deteriorated by almost 3 letters in total. The overall mean difference between the two groups was, on average, 4 correctly recalled letters.
Although this study presents findings that confirm the authors’ hypothesis and further validates previous studies, the sample was composed of young, healthy students. It would be interesting to see results achieved by individuals with memory or other cognitive deficits, older individuals, or people without university/college experience. Additionally, it would be appropriate to extend the time between the solving of the two AOSPAN tasks to reduce the potential effect of fatigue on the test subjects.
Kraus, J., & Porubanova, M. (2015). The effect of binaural beats on working memory capcity. Studia Psychologica 38 (2), 135-145.