WO2024047732A1 - Acoustic stimulation generation device, acoustic stimulation generation method, and program - Google Patents

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

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

The present invention relates to binaural beat signal generation technology.

There are conventional techniques that present artificial auditory stimuli to encourage continued concentration. For example, in Non-Patent Document 1, 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, the brain waves become synchronized. It has been shown that concentration is activated. Letting the angular frequency of the reference sound be ω, the signal x _L (t)=sin(ω+α)t for the left ear is the signal obtained by adding the angular frequency α, and the signal x _R (t) is the signal obtained by subtracting the angular frequency α for the right ear. When =sin(ω+α)t is presented, the sum signal y(t)=x _L (t)+x _R (t)=2sinωt cosαt is heard in the brain.

This is a waveform in which the amplitude of the reference sound of angular frequency ω is varied by a beat of angular frequency α, and this beat shows the brain wave entrainment effect. For example, in Non-Patent Document 2, they investigated the relationship between the beat frequency of presented binaural beats and the frequency of brain responses, and confirmed that the same brain wave band as the beat frequency was emphasized, and furthermore, the following day after listening to binaural beats, confirmed that attention during the task improved.

In the conventional technology, a fixed beat frequency is set for all subjects on the assumption that the same brain waves as the beat frequency are tuned. In other words, this is an argument that presenting the same sound stimulus to everyone will have the same effect.

However, since there are individual differences between people, the desired effect (for example, the effect of improving concentration and attention) may not be obtained depending on the person.

An object of the present invention is to provide a sound stimulus generation device, a sound stimulus generation method, and a program that generate a sound stimulus that is optimal for the brain wave state of the subject.

In order to solve the above problems, according to one aspect of the present invention, a sound stimulus generation device uses a score obtained when a predetermined task is performed on a subject and an electroencephalogram signal of the subject, The present invention includes a beat frequency determining unit that determines a beat frequency candidate α that is optimal for a subject, and a binaural beat generating unit that generates a binaural beat signal using the candidate α.

According to the present invention, it is possible to generate an optimal sound stimulus in consideration of individual differences among subjects.

FIG. 1 is a functional block diagram of a sound stimulus generation device according to first and second embodiments. FIG. 3 is a diagram illustrating an example of a processing flow of the sound stimulus generation device according to the first and second embodiments. The figure which shows the image of the process of a beat frequency determination part. FIG. 3 is a functional block diagram of a binaural beat generation unit according to a second embodiment. FIG. 7 is a diagram illustrating an example of a processing flow of a binaural beat generation unit according to a second embodiment. FIG. 7 is a diagram illustrating an image of processing by a binaural beat generation unit according to the second embodiment. The figure which shows the example of a structure of the computer to which this method is applied.

Embodiments of the present invention will be described below. In the drawings used in the following explanation, components having the same functions and steps that perform the same processing are denoted by the same reference numerals, and redundant explanation will be omitted. In the following explanation, symbols such as " ^- " used in the text should originally be written directly above the character that immediately follows, but due to text notation limitations, they are written immediately before the character. In the formula, these symbols are written in their original positions. Furthermore, unless otherwise specified, processing performed for each element of a vector or matrix is applied to all elements of that vector or matrix.

<Points of the first embodiment>
In this embodiment, from the subject's brain wave signal while performing a certain task and the subject's task performance data, the brain wave band where the power is high when the subject himself/herself performs well is extracted, and beat frequency candidates are extracted. Determine as.

<First embodiment>
FIG. 1 shows a functional block diagram of a sound stimulus generation device 100 according to the first embodiment, and FIG. 2 shows its processing flow.

The sound stimulus generation device 100 includes a beat frequency determination section 110 and a binaural beat generation section 120.

The sound stimulus generation device 100 inputs the subject's brain wave signal x _eeg (t) while performing a certain task and the subject's score Score (for example, time series data of task performance), and generates a desired effect. Determine the optimal beat frequency to obtain the optimal beat frequency, generate a binaural beat signal (x _L (t),x _R (t)) corresponding to the optimal beat frequency, and use a playback device including stereo speakers such as earphones and headphones. Output to.

The sound stimulus generation device 100 is configured by loading a special program into a known or dedicated computer having, for example, a central processing unit (CPU), a main memory (RAM), etc. It is a special device. The sound stimulus generation device 100 executes each process under the control of, for example, a central processing unit. The data input to the sound stimulus generation device 100 and the data obtained through 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 necessary. and used for other processing. Each processing unit of the sound stimulus generation device 100 may be configured at least in part by hardware such as an integrated circuit. Each storage unit included in the sound stimulus generation device 100 can be configured by, for example, a main storage device such as a RAM (Random Access Memory), or middleware such as a relational database or a key value store. However, each storage unit does not necessarily need to be provided inside the sound stimulus generation device 100, and may be configured with an auxiliary storage device configured from a semiconductor memory element such as a hard disk, an optical disk, or a flash memory. It may be configured to be provided outside the stimulus generation device 100.

Each part will be explained below.

<Beat frequency determination unit 110>
FIG. 3 is a diagram showing an image of the processing of the beat frequency determining section 110.

The beat frequency determination unit 110 inputs the score Score when a predetermined task is performed on the subject and the subject's brain wave signal x _eeg (t) measured during the task, and uses these values to determine the , determines the optimal beat frequency candidate α for the subject (S110) and outputs it. Here t represents time.

The score Score is the task performance (time series data) when a certain task is performed, and is Score=(Score(1),...,Score(n),...,Score(N)). For example, the task is a one-question, one-answer task, and the task performance uses score _Cor (n) = {True, False} to judge whether the question is correct or incorrect, reaction time from asking the question to answering Score _RT (n), etc. Let Score(n)=(Score _Cor (n),Score _RT (n)) and Score _RT =(Score _RT (1),…,Score _RT (n),…,Score _RT (N)). , Median(Score _RT ) represents the median value of Score _RT . The larger the value of Score _RT (n), the shorter the reaction time. Here, n represents the question number of the one-question, one-answer task. Note that the number of questions in this task is N in total, and n=1, 2,...,N. Task problems and brain wave signals are associated in advance, and the brain wave signal when performing the nth task is also expressed as x _eeg (n). x _eeg (1),…,x _eeg (n),…,x _eeg (N) is included in the electroencephalogram signal x _eeg (1),…,x _eeg (t),…,x _eeg (T). T represents the time taken from starting a task to finishing all tasks.

For example, the beat frequency determination unit 110 uses the score to extract an electroencephalogram signal x _eeg high (n) when the performance is high and an electroencephalogram signal x _eeg ^low (n) when the performance is ^low from the electroencephalogram signal x _eeg (t). do. For example, it is extracted using the following formula.

In this example, the electroencephalogram signal when the reaction time is below the median value and a correct answer is taken as the electroencephalogram signal when the performance is high x _eeg ^high (n), and the electroencephalogram signal when the reaction time is longer than the median value and an incorrect answer is made is x eeg high (n). Let the electroencephalogram signal when the performance is low be x _eeg ^low (n). Note that various indicators indicating high performance can be used as the task performance, in addition to determining whether the question is correct or incorrect or the reaction time from asking the question to answering the question.

Next, the beat frequency determining unit 110 performs short ^- time Fourier analysis ^on _the extracted electroencephalogram signals x _eeg ^high (n) and x _eeg ^low (n), and performs short-time Fourier analysis on the extracted brain wave signals ), ^- Calculate X _eeg ^low (f).

Finally, the beat frequency determining unit 110 compares the average values ^-X _eeg ^high (f) and ^-X _eeg ^low (f) for each frequency f, and calculates the brain wave power at high performance ( ^-X _eeg ^high (f)). The frequencies that exceed the ^brain wave power ^{( -} X _eeg ^low (f ₎ ) during low performance ^are sorted in descending order of the power difference ⁽ _- , the beat frequency candidates α={α ₁ ,α ₂ ,...,α _L } are extracted and output.

Candidate α is a vector in which L candidate values α _i of binaural beat beat frequencies are stored. L is any integer greater than or equal to 1, and may be set as appropriate. For example, L may be set to include all frequencies that satisfy ^- X _eeg ^high (f)- ^- X _eeg ^low (f)>0, or ^- X _eeg ^high (f)- ^- X _eeg ^low (f )>0, L may be set to include the top K% of frequencies, or a threshold Th may be set so that ^- X _eeg ^high (f)- ^- X _eeg ^low (f)> You can set L to include all frequencies that satisfy Th, or you can set L to a predetermined integer and select the frequencies that satisfy ^- X _eeg ^high (f) - ^- X _eeg ^low (f)>0. , the top L frequencies may be extracted as candidates α={α ₁ , α ₂ , . . . , α _L }. In this embodiment, L=1.

<Binaural beat generation unit 120>
The binaural beat generation unit 120 receives the frequency ω ₀ of the binaural beat reference sound and the beat frequency candidate α, and generates the binaural beat signal (x _L (t), x _R (t)) using the candidate α. It is generated (S120) and output. The binaural beat signal (x _L (t), x _R (t)) is a signal that corresponds to the brain wave state of the subject, and is output to a playback device including stereo speakers such as earphones and headphones, and is played back by the playback device. , presented separately to the subject's ear. In addition,
x _L (t)=sin(ω ₀ +α _t )(t)
x _R (t)=sin(ω ₀ -α _t )(t)
It is. Note that α _t is the optimal beat frequency at time t, and in this embodiment, the beat frequency α _t is a fixed value. For example, the frequency that shows the greatest effect among the beat frequency candidates α (in this example, α ₁ ) is permanently set as the beat frequency.

<Effect>
According to the present embodiment, the same brain wave band as candidate α is emphasized so that the brain wave state is when the subject is in a high performance state (for example, in a state of high concentration). Further, unlike the conventional technology, it is possible to generate a sound stimulus that is optimized for an individual (target person).

<Points of the second embodiment>
In this embodiment, a binaural beat signal with an optimized beat frequency is generated based on the beat frequency candidate and the brain wave state of the subject himself/herself.

<Second embodiment>
The explanation will focus on parts that are different from the first embodiment.

FIG. 1 is a functional block diagram of a sound stimulus generation device 200 according to the first embodiment, and FIG. 2 shows its processing flow.

The sound stimulus generation device 200 includes a beat frequency determination section 110 and a binaural beat generation section 220.

The sound stimulus generation device 200 inputs the subject's brain wave signal x _eeg (t) while performing a certain task and the subject's score Score (for example, time series data of task performance), and generates a desired effect. Determine the optimal beat frequency candidate to obtain. When generating binaural beats, the sound stimulus generation device 200 inputs the brain wave signal y _eeg (t) of the subject when the binaural beat signal is presented, and generates the binaural beat signal (x _L (t)) corresponding to the optimal beat frequency. ,x _R (t)) and output to a playback device including stereo speakers such as earphones and headphones.

The processing of the beat frequency determination unit 110 is the same as that of the first embodiment, so the explanation will be omitted. However, in this embodiment, L is an integer of 2 or more.

<Binaural beat generation unit 220>
FIG. 4 shows a functional block diagram of the binaural beat generation section 220 according to the second embodiment, and FIG. 5 shows its processing flow.

FIG. 6 is a diagram showing an image of the processing of the binaural beat generation section 220.

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

Similar to the binaural beat generation unit 120, the binaural beat generation unit 220 receives the frequency ω ₀ of the binaural beat reference sound and the beat frequency candidate α as input, and uses the candidate α to generate the binaural beat signal (x _L (t ),x _R (t)) (S220) and outputs it. The binaural beat signal (x _L (t), x _R (t)) is a signal that corresponds to the brain wave state of the subject, and is output to a playback device including stereo speakers such as earphones or headphones, and is played back by the playback device. , presented separately to the subject's ear. 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 explained below.

(Second binaural beat signal generation unit 221)
The binaural beat generation unit 221 inputs the frequency ω ₀ of the binaural beat reference sound and the beat frequency candidate α, _and generates a binaural beat signal (x _L (t), x _R (t)) (S221) and outputs it.

In addition,
x _L (t)=sin(ω ₀ +α _i )(t)
x _R (t)=sin(ω ₀ -α _i )(t)
It is. In this embodiment, the beat frequency α _i is used as a variable. For example, the frequency that shows the greatest effect among the beat frequency candidates α (in this example, α ₁ ) is used first, and then the frequency α 2 is assigned in descending order from the most effective to the least effective under the control of the determination unit ₂₂₇ , which will be described later. ,…,α _L.

(Brain wave signal acquisition unit 223)
The brain wave signal acquisition unit 223 acquires the brain wave signal y _eeg (t) of the subject who is presented with the binaural beat signal (x _L (t), x _R (t)) (S223) and outputs it.

For example, the brain wave signal acquisition unit 223 is an existing brain wave measurement device, an interface that receives brain wave signals measured by the existing brain wave measurement device, or the like.

(Power extraction unit 225)
The power extraction unit 225 inputs the electroencephalogram signal y _eeg (t), converts the time domain electroencephalogram signal y _eeg (t) into a frequency domain signal by short-time Fourier transform, etc., and extracts the power in the block section B. Y _eeg (k _B , α _i ) and the power Y _eeg (k _B-1 , α _i ) in the previous block section B-1 are extracted (S225) and output. Block sections B and B-1 are time sections used when _{making a} judgment in the judgment section 227, which will be described later. For block sections B and B-1, N _B and N _B-1 powers at frequency α _i are obtained, respectively. k _B and k _B-1 are indexes of frames included in block sections B and B-1, respectively.

(Determination unit 227)
The determining unit 227 determines whether or not the same brain wave band as candidate α _i is emphasized so that the target person is in a high performance brain wave state based on the information based on the brain wave signal (S227- 1) If it is not emphasized (NO in S227-1), control is performed to repeat processes S221, S223, and S225 using candidate α _i , and if it is emphasized (YES in S227-1) ), a candidate α _j that is not used for binaural beat signal generation is selected from the L candidates α _i (S227-5), and control is performed to repeat the process using the selected candidate α _j .

In this embodiment, the determination unit 227 receives N _B powers Y _eeg (k _B , α _i ) and N _B-1 powers Y _eeg (k _B-1 , α _i ), and determines the frequency distribution. Calculate the difference d _B,B-1 . This difference in frequency distribution _dB,B-1 corresponds to the information based on the above-mentioned electroencephalogram signal. Various values can be used to indicate the difference in frequency distribution; for example, an effect size such as Cohen's d (standardized value obtained by dividing the difference in mean values by the sample standard deviation) shown by the following formula: can be used.

Here, ^- Y _eeg (k _B ,α _i ) and S _B ² represent the average value and variance of N _B powers Y _eeg (k _B ,α _i ), respectively, and ^- Y _eeg (k _B-1 , α _i ) and S _B-1 ² represent the average value and variance of N _B-1 powers Y _eeg (k _B-1 , α _i ), respectively.

The determining unit 227 determines whether the same brain wave band as candidate α _i is emphasized based on the magnitude relationship between the frequency distribution difference d _B,B-1 and a predetermined threshold Th (S227), A control signal is sent to each part according to the determination result.

For example, when the larger the value d _B,B-1 is, the larger the difference in frequency distribution is, the determination unit 227 performs the following processing. If the frequency distribution difference d _B,B-1 is less than or equal to the predetermined threshold Th (in the case of NO in S227-1), the determining unit 227 uses the candidate α _i used in the binaural beat signal generating unit 220 to determine the second The binaural beat signal generation section 221 performs the processing, and outputs a control signal to each section so as to repeat the processing at the brain wave signal acquisition section 223 and the power extraction section 225.

If the frequency distribution difference _dB,B-1 is larger than the predetermined threshold Th (YES in S227-1), the determination unit 227 determines whether all L candidates α _i were used to generate the binaural beat signal. If it is used (YES in S227-3), the process ends. On the other hand, if there is a candidate α _j that is not used for binaural beat signal generation among the L candidates α _i (in the case of NO in S227-3), the binaural beat signal is selected from among the L candidates α _i. (S227-5 _{), the second binaural beat signal generation unit 221 processes the selected candidate α j ,} and the electroencephalogram signal acquisition unit 223 and the power extraction unit 225 A control signal is output to each part to control the process to be repeated.

In this case, the fact that the difference in frequency distribution is greater than the threshold means that the brain waves are emphasized in that frequency component. It is thought that the brain wave state during high performance and other brain wave states differ not only in one frequency component but in multiple frequency components. In the first embodiment, attention is paid to the difference in one frequency component (for example, the frequency component showing the greatest effect), and brain waves are emphasized only for that frequency component. On the other hand, in this embodiment, in order to more closely approximate the brain wave state during high performance, the frequency components to be emphasized are changed every time brain wave enhancement is confirmed for multiple frequency components that have shown an effect. It aims for higher effects by uniformly emphasizing brain waves. Note that the selection order of candidates is not particularly limited. For example, the determination unit 227 may select candidates in descending or ascending order according to the level of effectiveness, or may select candidates at random. However, it is thought that by selecting candidates in descending order of effectiveness, it is possible to more quickly bring the subject's brain wave state closer to the brain wave state during high performance.

<Effect>
With such a configuration, effects similar to those of the first embodiment can be obtained. Furthermore, it is possible to more closely approximate the state of brain waves during high performance.

<Modified example>
In this embodiment, when all L candidates α _i are used to generate the binaural beat signal (YES in S227-3), the process is finished, but the usage status of the candidates is reset and the process is restarted. A configuration may also be adopted in which processing for emphasizing brain waves is repeated.

<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 capacity of the device executing the process or as necessary. Other changes may be made as appropriate without departing from the spirit of the present invention.

<Program and recording medium>
The various processes described above are performed by causing the recording unit 2020 of the computer 2000 shown in FIG. This can be done by letting

A program that describes this processing content can be recorded on a computer-readable recording medium. The computer-readable recording medium may be of any type, such as a magnetic recording device, an optical disk, a magneto-optical recording medium, or a semiconductor memory.

Further, distribution of this program is performed, for example, by selling, transferring, lending, etc. portable recording media such as DVDs and CD-ROMs on which the program is recorded. Furthermore, this program may be distributed by storing the program in the storage device of the server computer and transferring the program from the server computer to another computer via a network.

A computer that executes such a program, for example, first stores a program recorded on a portable recording medium or a program transferred from a server computer in its own storage device. When executing a process, this computer reads a program stored in its own recording medium and executes a process according to the read program. In addition, as another form of execution of this program, the computer may directly read the program from a portable recording medium and execute processing according to the program, and furthermore, the program may be transferred to this computer from the server computer. The process may be executed in accordance with the received program each time. In addition, the above-mentioned processing is executed by a so-called ASP (Application Service Provider) service, which does not transfer programs from the server computer to this computer, but only realizes processing functions by issuing execution instructions and obtaining results. You can also use it as Note that the program in this embodiment includes information that is used for processing by an electronic computer and that is similar to a program (data that is not a direct command to the computer but has a property that defines the processing of the computer, etc.).

Furthermore, in this embodiment, the present apparatus is configured by executing a predetermined program on a computer, but at least a part of these processing contents may be implemented in hardware.

Claims (7)

1. a beat frequency determination unit that determines an optimal beat frequency candidate α for the target person using a score obtained when a predetermined task is performed on the target person and an electroencephalogram signal of the target person;
   a binaural beat generation unit that generates a binaural beat signal using the candidate α;
   Sound stimulus generator.
2. The sound stimulus generation device according to claim 1, comprising:
   Let L be any integer greater than or equal to 1, let i be any one of 1, 2,...,L, and the candidate α includes L candidates α _i ,
   The binaural beat generation section includes:
   a second binaural beat signal generation unit that generates a binaural beat signal with candidate α _i as the beat frequency;
   an electroencephalogram signal acquisition unit that obtains an electroencephalogram signal of the subject who is presented with the generated binaural beat signal;
   Based on the information based on the brain wave signal, it is determined whether the same brain wave band as the candidate α _i is emphasized so that the brain wave state of the subject is in high performance, and if it is not emphasized. , the process is controlled to be repeated using the candidate α _i , and if the candidate α i is emphasized, the candidate α _j that is not used for generating the binaural beat signal is selected from among the L candidates α _i . a determination unit that controls to repeat the process using the selected candidate α _j ;
   Sound stimulus generator.
3. The sound stimulus generation device according to claim 2,
   The binaural beat generation section includes:
   The power Y _eeg (k _B , α _i ) in block section B and the power Y _eeg (k _B-1 , α _i ) in the previous block section B-1 are determined from the electroencephalogram signal acquired by the electroencephalogram signal acquisition section. It includes a power extraction part that extracts
   The determination unit selects the candidate based on the difference in frequency distribution between the power Y _eeg (k _B , α _i ) and the power Y _eeg (k _B-1 , α _i ) and the magnitude relationship between the power Y eeg (k B , α i ) and a predetermined threshold. Determine whether the same brain wave band as α _i is emphasized,
   The information based on the electroencephalogram signal is the difference in the frequency distribution,
   Sound stimulus generator.
4. The sound stimulus generation device according to claim 3,
   The difference in the 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 generation device according to claim 1, comprising:
   The score includes determining whether the question is correct or incorrect and the reaction time from asking the question to answering the question.
   Sound stimulus generator.
6. a beat frequency determining step of determining an optimal beat frequency candidate α for the target person using a score obtained when a predetermined task is performed on the target person and an electroencephalogram signal of the target person;
   a binaural beat generation step of 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 stimulus generation device according to any one of claims 1 to 5.

Images