Sound stimulus generation device, sound stimulus generation method, and program

Abstract

Provided is an acoustic stimulation generation device which generates the most suitable acoustic stimulation for a brain wave state of a given subject. This acoustic stimulation generation device includes: a beat frequency determination unit which determines the most suitable beat frequency candidate α for the subject by using a score obtained when a predetermined task has been performed with respect to the subject and a brain wave signal of the subject; and a binaural beat generation unit which generates a binaural beat signal by using the candidate α.

Description

[Technical Field]

[0001] The present invention relates to a technique for generating binaural beat signals. [Background technology]

[0002] There is a conventional technology that presents artificial auditory stimuli to encourage sustained concentration. For example, Non-Patent Document 1 clarifies that when two pure tones with slightly different frequencies, called binaural beats, are presented to both ears and a beat sound (beat sound) corresponding to the frequency difference is presented, brain waves are synchronized, thereby activating concentration. The angular frequency of the reference sound is ω, and a signal x with an angular frequency α added to it is presented to the left ear. L (t) = sin(ω+α)t, and the right ear receives a signal x with the angular frequency α subtracted. R When (t) = sin(ω + α)t is presented, the sum signal y(t) = x L (t)+x R It is heard as (t)=2sinωt cosαt.

[0003] This results in a waveform in which the amplitude of a reference tone with angular frequency ω fluctuates with a beat with angular frequency α, and this beat exhibits an entrainment effect on brain waves. For example, in Non-Patent Document 2, the relationship between the beat frequency of the presented binaural beat and the frequency of the brain response was investigated, and it was confirmed that the same brain wave band as the beat frequency was emphasized, and furthermore, attention during a task improved the day after listening to the binaural beat. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Oster et al., “Auditory Beats in Brain,” Sci American, vol.229, pp.94-102, 1973. [Non-patent document 2] Ross et al., “40-Hz Binaural beats enhance training to mitigate the attentional blink.”Sci Report, vol.10,,pp.7002, 2020. Summary of the Invention [Problem to be solved by the invention]

[0005] In the prior art, it is assumed that the same brain waves are synchronized with the beat frequency, and a fixed beat frequency is set for all subjects, which means that presenting the same sound stimulus to everyone will have the same effect.

[0006] However, since there are individual differences among people, some people may not achieve the desired effect (for example, the effect of improving concentration and attention).

[0007] The present invention aims to provide a sound stimulation generation device, a sound stimulation generation method, and a program that generate sound stimulation that is optimal for the brain wave state of a subject. [Means for solving the problem]

[0008] In order to solve the above problems, according to one aspect of the present invention, a sound stimulation generation device includes a beat frequency determination unit that determines an optimal beat frequency candidate α for a subject using the subject's score when the subject performs a predetermined task and the subject's electroencephalogram signal, and a binaural beat generation unit that generates a binaural beat signal using the candidate α. [Effects of the Invention]

[0009] According to the present invention, it is possible to generate optimal sound stimuli taking into consideration individual differences among subjects. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is a functional block diagram of a sound stimulation generation device according to first and second embodiments. [Figure 2] FIG. 2 is a diagram showing an example of a processing flow of the sound stimulation generation device according to the first and second embodiments. [Figure 3] FIG. 4 is a diagram illustrating an image of processing by a beat frequency determination unit. [Figure 4] FIG. 10 is a functional block diagram of a binaural beat generation unit according to a second embodiment. [Figure 5] FIG. 10 is a diagram showing an example of a processing flow of a binaural beat generating unit according to the second embodiment. [Figure 6] FIG. 10 is a diagram showing an image of processing by a binaural beat generating unit according to the second embodiment. [Figure 7] FIG. 1 is a diagram showing an example of the configuration of a computer to which the present technique is applied. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described. In the drawings used in the following description, components having the same functions and steps performing the same processes will be denoted by the same reference numerals, and duplicated explanations will be omitted. In the following description, the symbols " - " etc. should normally be written directly above the character immediately following it, but due to limitations in text notation, they are written immediately before the character in question. In formulas, these symbols are written in their original positions. Furthermore, unless otherwise specified, processing performed on each element of a vector or matrix is ​​assumed to apply to all elements of that vector or matrix.

[0012] <Key Points of the First Embodiment> In this embodiment, an electroencephalogram band in which power increases when the subject performs well is extracted from the subject's electroencephalogram signal while performing a task and the subject's task performance data, and is determined as a beat frequency candidate.

[0013] First Embodiment FIG. 1 is a functional block diagram of a sound stimulation generation device 100 according to the first embodiment, and FIG. 2 shows the processing flow thereof.

[0014] The sound stimulation generation device 100 includes a beat frequency determination section 110 and a binaural beat generation section 120 .

[0015] The sound stimulation generating device 100 detects an electroencephalogram (EEG) signal x of a subject when the subject is performing a task. eeg The optimal beat frequency for achieving the desired effect is determined using (t) and the subject's score (e.g., time-series data of task performance), and a binaural beat signal (x L (t),x R (t)) is generated and output to a playback device including stereo speakers such as earphones or headphones.

[0016] The sound stimulation generation device 100 is a special device configured by loading a special program into a publicly known or dedicated computer having, for example, a central processing unit (CPU), a main memory (RAM), etc. The sound stimulation generation device 100 executes each process under the control of, for example, the central processing unit. Data input to the sound stimulation generation device 100 and data obtained in each process are stored, for example, in the main memory, and the data stored in the main memory is read out to the central processing unit as needed and used for other processes. At least a portion of each processing unit of the sound stimulation generation device 100 may be configured by hardware such as an integrated circuit. Each storage unit provided in the sound stimulation generation device 100 can be configured, for example, by a main memory such as a RAM (Random Access Memory), or middleware such as a relational database or a key-value store. However, each memory unit does not necessarily need to be provided inside the sound stimulation generating device 100, but may be configured as an auxiliary memory device made up of a semiconductor memory element such as a hard disk, optical disk, or flash memory, and may be provided outside the sound stimulation generating device 100.

[0017] Each part will be explained below.

[0018] <Beat Frequency Determining Unit 110> FIG. 3 is a diagram showing an image of the processing performed by the beat frequency determination unit 110. As shown in FIG.

[0019] The beat frequency determination unit 110 determines the score Score when a predetermined task is performed on a subject and the subject's electroencephalogram signal x measured during the task. eeg (t) and (t) are input, and using these values, the optimum beat frequency candidate α for the subject is determined (S110) and output, where t represents time.

[0020] The score is the task performance (time series data) when a certain task is performed, and is expressed as Score = (Score(1), ..., Score(n), ..., Score(N)). For example, if the task is a question-and-answer task, the task performance is the score for determining whether the question is correct or incorrect. Cor (n)={True, False}, Reaction time from question to answer, Score RT (n), and Score(n) = (Score Cor (n),Score RT (n)) and Score RT =(Score RT (1),…,Score RT (n),…,Score RT (N)) and Median(Score RT ) is Score RT It represents the median score. RT The larger the value of (n), the shorter the reaction time. Here, n represents the question number of the one-question-one-answer task. The total number of questions in this task is N, where n = 1, 2, ..., N. The task questions and EEG signals are associated in advance, and the EEG signal when performing the nth task is expressed as x eeg Also written as (n). x eeg (1),…,x eeg (n),…,x eeg (N) is the EEG signal x eeg (1),…,x eeg (t),…,x eeg(T) represents the time it takes from the start of a task to the completion of all tasks.

[0021] For example, the beat frequency determination unit 110 uses the score Score to determine the electroencephalogram signal x eeg (t) EEG signal x when performance is high eeg high (n) and low EEG signal x eeg low (n) is extracted, for example, using the following formula:

number

[0022] Next, the beat frequency determination unit 110 determines the extracted electroencephalogram signal x eeg high (n), x eeg low (n) are subjected to short-time Fourier analysis, and the average value of the power spectrum for each frequency f is calculated. - X eeg high (f), - X eeg low Calculate (f).

[0023] Finally, the beat frequency determination unit 110 calculates the average value for each frequency f. - X eeg high (f), - X eeg low (f) and EEG power during high performance ( - Xeeg high (f)) is the EEG power during low performance ( - X eeg low (f)) is calculated by the power difference ( - X eeg high (f)- - X eeg low (f)) are sorted in descending order of frequency, and the candidate beat frequencies α={α1,α2,...,α L} and output it.

number

[0024] <Binaural beat generation unit 120> The binaural beat generating unit 120 receives the frequency ω0 of the binaural beat reference sound and the beat frequency candidate α as input, and generates a binaural beat signal (x L (t),x R (t)) is generated (S120) and output. L (t),x R (t)) is a signal corresponding to the subject's brain wave state, which is output to a playback device including stereo speakers such as earphones or headphones, played back by the playback device, and presented separately to the subject's ears. x L (t)=sin(ω0+α t )(t) x R (t)=sin(ω0-α t )(t) In addition, α t is the optimal beat frequency at time t, and in this embodiment, the beat frequency α t is set as a fixed value. For example, the frequency (α1 in this example) that shows the greatest effect among the beat frequency candidates α is permanently set as the beat frequency.

[0025] <Effects> This embodiment emphasizes the same brain wave band as candidate α so that the subject is in a brain wave state when he or she is performing at a high level (for example, in a state of high concentration). Furthermore, unlike conventional techniques, it is possible to generate sound stimuli optimized for each individual (subject).

[0026] <Key Points of the Second Embodiment> In this embodiment, a binaural beat signal with an optimized beat frequency is generated based on beat frequency candidates and the subject's own electroencephalogram state.

[0027] Second Embodiment The following description will focus on the differences from the first embodiment.

[0028] FIG. 1 is a functional block diagram of a sound stimulation generation device 200 according to the first embodiment, and FIG. 2 shows the processing flow thereof.

[0029] The sound stimulation generation device 200 includes a beat frequency determination section 110 and a binaural beat generation section 220 .

[0030] The sound stimulation generating device 200 detects an electroencephalogram signal x of a subject when the subject is performing a certain task. eeg The sound stimulation generation device 200 receives the binaural beat signal and outputs the brain wave signal y of the subject when the binaural beat signal is presented. eeg (t) is input, and the binaural beat signal (x L (t),x R (t)) is generated and output to a playback device including stereo speakers such as earphones or headphones.

[0031] The processing of the beat frequency determination unit 110 is the same as in the first embodiment, and therefore a description thereof will be omitted. However, in this embodiment, L is an integer of 2 or more.

[0032] <Binaural beat generation unit 220> FIG. 4 is a functional block diagram of a binaural beat generating unit 220 according to the second embodiment, and FIG. 5 shows the processing flow thereof.

[0033] FIG. 6 is a diagram showing an image of the processing performed by the binaural beat generating unit 220. As shown in FIG.

[0034] The binaural beat generation unit 220 includes a second binaural beat signal generation unit 221 , an electroencephalogram signal acquisition unit 223 , a power extraction unit 225 , and a determination unit 227 .

[0035] Similarly to the binaural beat generation unit 120, the binaural beat generation unit 220 receives the frequency ω0 of the binaural beat reference sound and the beat frequency candidate α as input, and generates a binaural beat signal (x L (t),x R (t)) is generated (S220) and output. L (t),x R (t)) is a signal corresponding to the subject's brain wave state, and is output to a playback device including stereo speakers such as earphones or headphones, played back by the playback device, and presented separately to the subject's ears. In the first embodiment, the beat frequency is a fixed value, whereas in this embodiment, the beat frequency is a variable. The processing of each part will be described below.

[0036] (Second binaural beat signal generation unit 221) The binaural beat generating unit 221 receives the frequency ω0 of the reference sound of the binaural beat and the beat frequency candidate α, and generates the candidate α included in the candidate α. i The binaural beat signal (x L (t),x R (t)) is generated (S221) and output.

[0037] In addition, x L (t)=sin(ω0+α i )(t) x R (t)=sin(ω0-α i )(t) In this embodiment, the beat frequency α i For example, the frequency (α1 in this example) that shows the greatest effect among the beat frequency candidates α is used first, and then the frequencies α2, ..., α3, ... are sorted in descending order from the most effective to the least effective according to the control of the determining unit 227 described later. L It will change into.

[0038] (Electroencephalogram signal acquisition unit 223) The electroencephalogram signal acquisition unit 223 receives a binaural beat signal (x L (t),x RThe EEG signal y of the subject presented with (t) eeg (t) is acquired (S223) and output.

[0039] For example, the electroencephalogram signal acquiring unit 223 is an existing electroencephalogram measuring device, an interface that receives an electroencephalogram signal measured by an existing electroencephalogram measuring device, or the like.

[0040] (Power extraction unit 225) The power extraction unit 225 extracts the electroencephalogram signal y eeg (t) as input, for example, the time domain EEG signal y eeg (t) is converted into a frequency domain signal by a short-time Fourier transform or the like, and the power Y eeg (k B ,α i ), and the power Y in the previous block section B-1 eeg (k B-1 ,α i ) are extracted (S225) and output. The block sections B and B-1 are time sections used when making a decision in the decision unit 227, which will be described later. B pieces,N B-1 frames (frames for performing short-time Fourier transform, etc.), and for block intervals B and B-1, frequency α i In each case, N B pieces,N B-1 You get the power of k. B ,k B-1 are the indices of the frames included in the block intervals B and B-1, respectively.

[0041] (Judgment unit 227) The determination unit 227 determines the candidate α so that the subject is in a brain wave state when the subject is performing at a high level based on the information based on the brain wave signal. i It is determined whether the same electroencephalogram band as the candidate α is emphasized (S227-1). If it is not emphasized (NO in S227-1), the candidate α i The processes S221, S223, and S225 are repeated using the above. If the process is emphasized (YES in S227-1), the L candidates αi Among the candidates α that have not been used to generate the binaural beat signal, j (S227-5) and select the selected candidate α j The process is controlled to be repeated using

[0042] In this embodiment, the determination unit 227 determines whether N B Individual Power Y eeg (k B ,α i ) and N B-1 Individual Power Y eeg (k B-1 ,α i ) and the difference in frequency distribution d B,B-1 Calculate the difference in frequency distribution d B,B-1 corresponds to the information based on the EEG signal mentioned above. Note that various values ​​can be used to indicate the difference in frequency distribution, and for example, the effect size such as Cohen's d (a standardized value obtained by dividing the difference in the mean values ​​by the sample standard deviation) shown in the following formula can be used.

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number

[0043] The determination unit 227 determines the difference dB,B-1 Based on the magnitude relationship between the candidate α and a predetermined threshold Th, i It is determined whether the same electroencephalogram band as the one in the above is emphasized (S227), and control signals are transmitted to various parts according to the determination result.

[0044] For example, the value d B,B-1 In the case where the difference in frequency distribution is larger as d B,B-1 is equal to or smaller than the predetermined threshold value Th (NO in S227-1), the candidate α used in the binaural beat signal generating unit 220 i The second binaural beat signal generating unit 221 performs processing using the above, and outputs a control signal to each unit to control the electroencephalogram signal acquiring unit 223 and the power extracting unit 225 to repeat the processing.

[0045] The determination unit 227 determines the difference d B,B-1 If is greater than the predetermined threshold Th (YES in S227-1), L candidates α i If all of the L candidates α have been used to generate the binaural beat signal (YES in S227-3), the process ends. i Among the candidates α that are not used to generate the binaural beat signal, j If there exists (NO in S227-3), there are L candidates α i Among the candidates α that have not been used to generate the binaural beat signal, j (S227-5) and select the selected candidate α j The second binaural beat signal generating unit 221 performs processing using the above, and outputs a control signal to each unit to control the electroencephalogram signal acquiring unit 223 and the power extracting unit 225 to repeat the processing.

[0046] In this case, a difference in frequency distribution greater than a threshold value indicates that the brain waves are emphasized at that frequency component. It is believed that the difference between the brain wave state during high performance and other brain wave states is not observed in only one frequency component but in multiple frequency components. In the first embodiment, attention is focused on the difference in one frequency component (e.g., the frequency component that showed the greatest effect) and the brain waves are emphasized only for that frequency component. In contrast, in this embodiment, in order to more closely approximate the brain wave state during high performance, the frequency component to be emphasized is changed each time enhancement of brain waves is confirmed for multiple frequency components that showed an effect, thereby evenly enhancing the brain waves and aiming for a higher effect. The order in which the candidates are selected is not particularly limited. For example, the determination unit 227 may select candidates in descending or ascending order according to the degree of effect, or may select candidates randomly. However, it is believed that selecting candidates in descending order from most effective to least effective can more quickly bring the subject's brain wave state closer to the brain wave state during high performance.

[0047] <Effects> By adopting such a configuration, it is possible to obtain the same effects as in the first embodiment, and furthermore, it is possible to more closely approximate the brain wave state during high performance.

[0048] <Modification> In this embodiment, L candidates α i When all of the candidates have been used to generate the binaural beat signal (YES in S227-3), the process is terminated, but the configuration may be such that the usage state of the candidates is reset and the process of emphasizing the brain waves is repeated again.

[0049] <Other variations> The present invention is not limited to the above-described embodiments and modifications. For example, the various processes described above may not only be executed in chronological order as described, but may also be executed in parallel or individually depending on the processing capabilities of the devices that execute the processes or as needed. Other modifications are possible within the scope of the present invention.

[0050] <Programs and recording media> The various processes described above can be implemented by loading a program that executes each step of the above method into the recording unit 2020 of the computer 2000 shown in Figure 7, and operating the control unit 2010, input unit 2030, output unit 2040, display unit 2050, etc.

[0051] The program describing the processing contents can be recorded on a computer-readable recording medium, which may be, for example, a magnetic recording device, an optical disk, a magneto-optical recording medium, a semiconductor memory, or any other suitable recording medium.

[0052] The program may be distributed, for example, by selling, transferring, or lending portable recording media such as DVDs and CD-ROMs on which the program is recorded. Furthermore, the program may be stored in a storage device of a server computer, and then transferred from the server computer to other computers via a network, thereby distributing the program.

[0053] A computer that executes such a program may first temporarily store the program recorded on a portable recording medium or transferred from a server computer in its own storage device. Then, when executing a process, the computer reads the program stored on its own recording medium and executes the process in accordance with the read program. Alternatively, the computer may read the program directly from a portable recording medium and execute the process in accordance with the program. Furthermore, the computer may execute the process in accordance with the received program each time a program is transferred from a server computer to the computer. Alternatively, the server computer may not transfer the program to the computer, but may execute the process through a so-called ASP (Application Service Provider) service, which realizes the processing function by issuing an execution instruction and obtaining the results. In this embodiment, the program includes information used for processing by a computer that is equivalent to a program (such as data that is not a direct instruction to the computer but has properties that define computer processing).

[0054] Furthermore, in this embodiment, the device is configured by executing a predetermined program on a computer, but at least a part of the processing contents may be realized by hardware.

Claims

1. a beat frequency determination unit that determines an optimal beat frequency candidate α for a subject by comparing and analyzing the EEG signals of the subject at high and low performance frequencies based on the quality of the subject's performance using the score obtained when the subject performs a predetermined task and the EEG signals of the subject; a binaural beat generating unit that generates a binaural beat signal using the candidate α, Sound stimulus generator.

2. A beat frequency determination unit that determines an optimal beat frequency candidate α for a subject using a score when the subject performs a predetermined task and an electroencephalogram signal of the subject; a binaural beat generating unit that generates a binaural beat signal using the candidate α, Let L be any integer equal to or greater than 1, and let i be any of 1, 2, ..., L. The candidates α include L candidates α i Contains, The binaural beat generating unit Candidate α i a second binaural beat signal generating unit that generates a binaural beat signal having a beat frequency of an electroencephalogram signal acquisition unit that acquires an electroencephalogram signal of the subject to which the generated binaural beat signal has been presented; The candidate α is selected so as to be in an electroencephalogram state when the subject is performing at a high level based on information on the electroencephalogram signal. i If the same electroencephalogram band as the candidate α is not emphasized, i If the L candidates α i Among the candidates α that have not been used to generate the binaural beat signal, j Select the selected candidate α j and a determination unit that controls the process to be repeated using the Sound stimulus generator.

3. The sound stimulus generating device of claim 2, The binaural beat generating unit The power Y in the block section B from the electroencephalogram signal acquired by the electroencephalogram signal acquisition unit eeg (k B ,α i ) and the power Y in the previous block section B-1 eeg (k B-1 ,α i ) and a power extraction unit for extracting The determination unit determines the power Y eeg (k B ,α i ) and the power Y eeg (k B-1 ,α i ) and the magnitude relationship between the difference in frequency distribution and a predetermined threshold, i and determining whether the same electroencephalogram band as the information based on the electroencephalogram signal is a difference in the frequency distribution; Sound stimulus generator.

4. The sound stimulus generating device of claim 3, The difference in frequency distribution is a standardized value obtained by dividing the difference in mean values ​​by the sample standard deviation. Sound stimulus generator.

5. The sound stimulus generating device of claim 1, The score includes a correct / incorrect judgment of the question and a reaction time from the question being asked to the answer. Sound stimulus generator.

6. a beat frequency determination step of determining an optimal beat frequency candidate α for the subject by comparative analysis of the EEG signals for each frequency during high performance and low performance based on the quality of the performance using the score obtained when the subject performs a predetermined task and the EEG signals of the subject; and generating a binaural beat signal using the candidate α. Sound stimulus generation method.

7. A program for causing a computer to function as the sound stimulation generating device according to any one of claims 1 to 5.

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