Measurement system, measurement method, and program

Abstract

The present invention makes it possible to reduce the burden on a measurement subject even if there is an increase in the number of times construction of a measurement system is repeated.　This measurement system comprises: a first measurement unit that measures a first potential from a brain signal of a measurement subject who is subjected to first stimuli having uneven stimulation intervals; a second measurement unit that, before the measurement of the first potential, measures a second potential having a stronger signal strength than the first potential from a brain signal of the measurement subject who is subjected to second stimuli having even stimulation intervals and having a shorter stimulation time than the first stimuli; and a determination unit that, before the measurement of the first potential, determines whether the measurement system for measuring the first potential is normal, on the basis of the result of measurement by the second measurement unit.

Description

Measurement system, measurement method, and program

[0001] The present invention relates to a measurement system, a measurement method, and a program.

[0002] Conventionally, techniques for measuring potentials such as ERPs (event-related potentials) have been known. For example, Patent Literature 1 discloses a cognitive ability detection device that detects ERPs from brain signals of a detection subject and detects the cognitive ability of the detection subject based on the detected ERPs.

[0003] International Publication No. 2020 / 138012

[0004] However, there are cases where ERP cannot be measured correctly due to a malfunction of the measurement system. In such cases, conventionally, the measurement system is determined to be abnormal based on the ERP measurement results, and then the measurement system is reconstructed so that the measurement system is normal. Therefore, conventionally, if the construction of the measurement system needs to be reconstructed, the ERP measurement needs to be reconstructed, which poses a problem that the burden on the person being measured increases as the number of times the construction of the measurement system is reconstructed increases.

[0005] Therefore, an object of the present invention is to reduce the burden on the subject even if the number of times the measurement system needs to be reconstructed increases.

[0006] One aspect of the present invention is a measurement system comprising: a first measurement unit that measures a first potential from brain signals of a subject to which a first stimulus having unequal intervals has been applied; a second measurement unit that, before measuring the first potential, measures a second potential having a stronger signal strength than the first potential from brain signals of the subject to which a second stimulus having equal intervals and a shorter stimulation time than the first stimulus has been applied; and a judgment unit that, before measuring the first potential, judges whether the measurement system for the first potential is normal based on the measurement results of the second measurement unit.

[0007] Another aspect of the present invention is a measurement method including a first measurement step in which a computer measures a first potential from brain signals of a subject to which a first stimulus having unequal stimulus intervals has been applied; a second measurement step in which the computer measures a second potential, the second potential having a stronger signal strength than the first potential, from brain signals of the subject to which a second stimulus having equal stimulus intervals and a shorter stimulus time than the first stimulus has been applied; and a determination step in which the computer determines whether or not the measurement system for the first potential is normal based on the measurement results of the second measurement step, wherein the second measurement step and the determination step are performed before the first measurement step.

[0008] Another aspect of the present invention is a program that causes a processor to function as a first measurement unit that measures a first potential from a brain signal of a subject to which a first stimulus having an unequal stimulus interval is given, a second measurement unit that measures a second potential having a stronger signal strength than the first potential from a brain signal of the subject to which a second stimulus having an equal stimulus interval and a shorter stimulus time than the first stimulus is given before measuring the first potential, and a determination unit that determines whether the measurement system of the first potential is normal based on the measurement results of the second measurement unit before measuring the first potential. This specification is intended to include the entire contents of Japanese Patent Application No. 2024-060198, filed on April 3, 2024.

[0009] According to the present invention, even if the number of times the measurement system needs to be reconstructed increases, the burden on the subject can be reduced.

[0010] Fig. 1 is a diagram showing the configuration of a measurement system. Fig. 2 is a diagram showing the configuration of a processing device. Fig. 3 is a diagram showing an example of a waveform for ERP measurement. Fig. 4 is a flowchart showing the ERP measurement procedure.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [1. Configuration of the Measurement System] FIG. 1 is a diagram showing the configuration of a measurement system 1. The measurement system 1 is a system for measuring ERP. ERP is a transient brain potential fluctuation that occurs in response to an external or internal event. ERP is said to include part of cognitive processes such as anticipation, attention, perception, discrimination, decision-making, and memory, and is used for brain function tests and cognitive ability tests. Therefore, the measurement system 1 is applied to places where brain function tests and cognitive ability tests are conducted, such as hospitals. ERP corresponds to a "first potential."

[0012] The measurement system 1 includes a measurement device 2 and a processing device 3. The measurement device 2 includes a plurality of electrodes 2A attached to the head H of the subject P, and measures the brain signals of the subject P using the electrodes 2A. Note that while FIG. 1 shows a case in which three electrodes 2A are attached to the subject P, the number of electrodes 2A attached to the subject P is not limited to three. Furthermore, the number of electrodes 2A provided in the measurement device 2 is not limited to three. Note that the locations at which the electrodes 2A are placed are generally determined in accordance with the International 10-20 System, which is used to measure electroencephalograms, but this does not have to be followed. The processing device 3 corresponds to a "computer."

[0013] The measuring device 2 is communicatively connected to the processing device 3. The measuring device 2 measures brain signals under the control of the processing device 3 and transmits measurement data D indicating the measurement results to the processing device 3. The measuring device 2 and the processing device 3 may be communicatively connected via a wire or wirelessly.

[0014] The processing device 3 is a personal computer (PC). Although Fig. 1 illustrates a case where the processing device 3 is a laptop PC, the processing device 3 may be a desktop PC or a tablet PC.

[0015] The processing device 3 measures potentials such as SSVEP (steady state visual evoked potential), SSAEP (steady state auditory evoked potential), and ASSR (auditory steady-state response) from the brain signals measured by the measuring device 2. When measuring SSVEP, the processing device 3 provides a visual stimulus to the subject P. When providing a visual stimulus to the subject P, the processing device 3 displays an object that the subject P sees using a built-in display or a separate display. When measuring SSAEP or ASSR, the processing device 3 provides an auditory stimulus to the subject P. When providing an auditory stimulus to the subject P, the processing device 3 outputs an object that the subject P hears using a built-in speaker or a separate speaker. SSVEP, SSAEP, and ASSR correspond to "second potentials."

[0016] Furthermore, the processing device 3 measures ERP from the brain signals measured by the measuring device 2. When measuring ERP, the processing device 3 provides the subject P with at least one of a visual stimulus and an auditory stimulus.

[0017] 2. Configuration of the Processing Device The configuration of the processing device 3 will be described in detail with reference to Fig. 2. Fig. 2 is a diagram showing the configuration of the processing device 3.

[0018] The processing device 3 includes a control unit 30, a communication unit 31, a display unit 32, an input unit 33, and a sound output unit .

[0019] Before describing the control unit 30, the communication unit 31, display unit 32, input unit 33, and sound output unit 34 will be described. The communication unit 31 includes communication hardware such as a communication circuit that complies with a predetermined communication standard, and communicates with the measuring device 2 under the control of the control unit 30. The display unit 32 includes a display and displays various information on the display under the control of the control unit 30. The input unit 33 includes a keyboard, mouse, or other input means, detects user operations on the input means, and outputs a detection signal to the control unit 30. The sound output unit 34 includes a speaker and outputs sound under the control of the control unit 30.

[0020] The control unit 30 includes a processor 300 such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and a memory 310. The control unit 30 is connected to a communication unit 31, a display unit 32, an input unit 33, and a sound output unit 34.

[0021] The memory 310 is a memory that stores programs and data. The memory 310 stores a control program 311, a reference value 312, and data to be processed by the processor 300. The memory 310 has a non-volatile storage area. The memory 310 also has a volatile storage area, which constitutes a work area for the processor 300. The memory 310 is constituted by, for example, a read-only memory (ROM) or a random access memory (RAM). The control program 311 corresponds to a "program."

[0022] The reference value 312 is a value to be compared with the contact impedance generated when the electrode 2A comes into contact with the human body.

[0023] The processor 300 functions as a communication control unit 301, a first measurement unit 302, a second measurement unit 303, a third measurement unit 304, a setting unit 305, a judgment unit 306, and an output unit 307 by reading and executing a control program 311 stored in the memory 310.

[0024] [2-1. Communication Control Unit] The communication control unit 301 communicates with the measuring device 2 via the communication unit 31 .

[0025] [2-2. First Measurement Unit] The first measurement unit 302 applies a first stimulus to the subject P. Then, based on the measurement data D received by the communication control unit 301, the first measurement unit 302 measures ERP from the brain signals of the subject P to whom the first stimulus has been applied.

[0026] Here, the first stimulus will be described. The first stimulus is a stimulus that is applied to the subject P multiple times at unequal intervals. In other words, the first stimulus is a stimulus that is not applied at equal intervals. Since noise is superimposed on brain signals, in ERP measurement, multiple stimuli are applied to the subject P to counter noise by averaging. Therefore, the first stimulus is applied to the subject P multiple times.

[0027] The stimulus interval of the first stimulus is, for example, 1 to 3 seconds, which is longer than the stimulus interval of the second stimulus described below. Therefore, the first stimulus has a longer stimulus duration than the second stimulus described below. Generally, ERP measurement requires the application of 20 to 180 stimuli. Therefore, if the stimulus interval is, for example, 1 to 3 seconds, the stimulus duration of the first stimulus is 20 to 600 seconds. Here, the stimulus duration refers to the total time during which the stimuli are applied intermittently, including the time during which the actual stimuli are applied and the time without stimuli between stimuli.

[0028] In this way, the first stimulus is applied to the subject P multiple times at unequal intervals, and the stimulus intervals are long. This is for the following reason: It is known that once the brain memorizes the timing of the next stimulus application, the brain signal strength increases. In general, ERPs measured from brain signals whose signal strength has increased due to habituation may not be potentials generated by cognition, and are therefore unsuitable for testing. Therefore, in order to generate ERPs due to cognition rather than habituation by the brain, the first stimulus is applied at unequal intervals, and the stimulus intervals are long, for example, 1 to 3 seconds.

[0029] Returning to the explanation of the first measuring unit 302, the first measuring unit 302 of this embodiment applies two first stimuli, which are different events, to the subject P. For example, when the first stimulus is a visual stimulus, the first measuring unit 302 applies to the subject P a first stimulus in which a first circle is displayed multiple times at unequal intervals on the display unit 32, and a second circle having a smaller radius than the first circle is displayed multiple times at unequal intervals on the display unit 32.

[0030] The first measuring unit 302 measures ERP from the brain signals indicated by the measurement data D as follows. First, the first measuring unit 302 averages the waveforms of multiple brain signals obtained by applying a first stimulus (first circle) multiple times for a certain event. The first measuring unit 302 also averages the waveforms of multiple brain signals obtained by applying a first stimulus multiple times for a certain event (first circle) and a different event (second circle). The first measuring unit 302 then obtains a waveform for measuring ERP by calculating the difference in amplitude between the two types of waveforms obtained by the average. Hereinafter, the waveform for measuring ERP will be referred to as the ERP measurement waveform.

[0031] 3 is a diagram CH showing an example of a waveform for measuring ERP, in which the vertical axis represents voltage and the horizontal axis represents time elapsed since the stimulus was applied.

[0032] The first measuring unit 302 measures the ERP based on the time from when a stimulus is applied until the subject P reacts, i.e., the latency, and the magnitude of the amplitude. FIG. 3 illustrates an example in which the first measuring unit 302 measures P300, which is a type of ERP. P300, which is a type of ERP, occurs approximately 300 msec after the stimulus is perceived. Therefore, the first measuring unit 302 measures as P300 the potential in the ERP measurement waveform whose amplitude is equal to or greater than a predetermined value approximately 300 msec after the stimulus is started.

[0033] [2-3. Second Measurement Unit] The second measurement unit 303 applies a second stimulus to the subject P. Then, based on the measurement data D received by the communication control unit 301, the second measurement unit 303 measures any one of SSVEP, SSAEP, and ASSR from the brain signals of the subject P to whom the second stimulus has been applied. The SSVEP, SSAEP, and ASSR measured by the second measurement unit 303 are used to determine whether the ERP measurement system is normal. The ERP measurement system includes the electrodes 2A, the measuring device 2, and the processing device 3, and the SSVEP, SSAEP, and ASSR are measured using the same measurement system as the ERP.

[0034] Here, the second stimulus will be described. The second stimulus is a stimulus that is given to the subject P multiple times at equal intervals. In other words, the second stimulus is a stimulus that is given at equal intervals. As described above, noise is superimposed on brain signals, and therefore, in measuring SSVEP, SSAEP, and ASSR, multiple stimuli are given to the subject P to counter noise by averaging. Therefore, the second stimulus is given to the subject P multiple times.

[0035] The second stimulus is applied at an interval of, for example, 0.1 msec, which is shorter than the first stimulus. Therefore, the second stimulus has a shorter duration than the first stimulus. For example, if the interval is 0.1 msec and the number of times the second stimulus is applied is 100, the duration of the second stimulus is 10 seconds. When the interval is 0.1 msec, the duration of the stimulus can be any duration long as the presence or absence of the stimulus can be recognized. However, if the stimulus needs to be emphasized more, the duration may be shorter than half the interval, for example, 0.03 msec.

[0036] In this way, the second stimulus is applied to the subject P multiple times at equal intervals, and the stimulus intervals are short. This is because the second stimulus is not the stimulus used to measure ERP, and therefore the ERP measurement itself is not affected even if the signal strength of the brain signal increases due to brain habituation.

[0037] Returning to the explanation of the second measuring unit 303, because the SSVEP, SSAEP, and ASSR are potentials obtained by a single event, the second measuring unit 303 applies a second stimulus of one event to the subject P. When measuring the SSVEP, the second measuring unit 303 applies a visual stimulus to the subject P. When measuring the SSAEP or the ASSR, the second measuring unit 303 applies an auditory stimulus to the subject P.

[0038] The second measurement unit 303 measures any of SSVEP, SSAEP, and ASSR from the brain signal represented by the measurement data D as follows. First, the second measurement unit 303 averages the waveforms of multiple brain signals obtained by applying multiple stimuli. The averaged waveform has a voltage axis on the vertical axis and a time axis on the horizontal axis. The second measurement unit 303 measures any of SSVEP, SSAEP, and ASSR based on the latency and amplitude. For example, the second measurement unit 303 measures, as the SSVEP, a potential whose amplitude is equal to or greater than a predetermined value approximately 100 msec after the start of stimulation in the averaged waveform. Furthermore, for example, the second measurement unit 303 measures, as the SSAEP or ASSR, a potential whose amplitude is equal to or greater than a predetermined value approximately 50 msec after the start of stimulation in the averaged waveform.

[0039] [2-4. Third Measuring Unit] The third measuring unit 304 measures the contact impedance generated when the electrode 2A comes into contact with the human body. The third measuring unit 304 measures the contact impedance for each electrode 2A. The third measuring unit 304 measures the contact impedance based on the potential generated between the multiple electrodes 2A and the value of the current passed through the electrodes 2A.

[0040] [2-5. Setting Section] The setting section 305 sets the reference value 312 stored in the memory 310 to a value designated by the measurer via the input section 33 .

[0041] [2-6. Determination Unit] The determination unit 306 determines whether the ERP measurement system is normal. If the second measurement unit 303 can measure any one of SSVEP, SSAEP, and ASSR, the determination unit 306 determines that the ERP measurement system is normal. On the other hand, if the second measurement unit 303 cannot measure any one of SSVEP, SSAEP, and ASSR, the determination unit 306 determines that the EPR measurement system is not normal, i.e., that the ERP measurement system is abnormal.

[0042] [2-7. Output Unit] The output unit 307 outputs information via at least one of the display unit 32 and the sound output unit 34.

[0043] 3. Operation Next, the operation of the measurement system 1 will be described with reference to Fig. 4. Fig. 4 is a flowchart showing the procedure for measuring ERP. The flowchart shown in Fig. 4 includes the operation of the measurer and the operation of the processing device 3.

[0044] In measuring ERP, first, the measurer explains the measurement to the subject P (Step S1). In Step S1, the measurer explains to the subject P the time required for the measurement, the equipment to be used for the measurement, the measurement procedure, the application of two types of stimuli, and the requirement that the subject P be able to distinguish between the two types of stimuli and respond accordingly.

[0045] After the explanation of step S1 is finished, the measurer performs pre-treatment for attaching the electrodes 2A and attaches the electrodes 2A to the subject P (step S2). Pre-treatment for attaching the electrodes 2A involves, for example, removing sebum and dead skin cells from the head H of the subject P using alcohol swabs or the like. This reduces the contact impedance, which reduces noise superimposed on the brain signal and improves measurement accuracy.

[0046] When the attachment of the electrodes 2A is completed, the third measurement unit 304 of the processing device 3 measures the contact impedance for each electrode 2A (step S3). The operation of step S3 is performed when the measurer issues an instruction to the processing device 3 to start measuring the contact impedance.

[0047] Next, the third measuring unit 304 determines whether all of the measured contact impedances are equal to or less than the reference values ​​stored in the memory 310 (step S4).

[0048] If the third measurement unit 304 determines that all of the contact impedances are not equal to or less than the reference value (step S4: NO), the output unit 307 outputs a signal indicating that all of the contact impedances are not equal to or less than the reference value (step S5). Note that the output of step S5 may indicate which electrode 2A exceeds the reference value, or may simply indicate that the contact impedance exceeds the reference value without distinguishing between the electrodes 2A.

[0049] When the output of step S5 is performed, the procedure for ERP measurement returns to step S2, and the measurer again performs pre-treatment for attaching the electrodes 2A and attaches the electrodes 2A.

[0050] On the other hand, if the third measuring unit 304 determines that all of the contact impedances are below the reference value (step S4: YES), the output unit 307 outputs a message indicating that all of the contact impedances are below the reference value (step S6).

[0051] When the processing device 3 outputs the result of step S5, the subject starts measuring brain signals (step S7).

[0052] When the measurer starts measuring the brain signal, the second measurement unit 303 of the processing device 3 applies a second stimulus to the subject P and measures any one of the SSVEP, SSAEP, and ASSR (step S8). Step S8 corresponds to the "second measurement step."

[0053] Next, the determination unit 306 determines whether the ERP measurement system is normal or not (step S9). Step S9 corresponds to the "determination step."

[0054] If it is determined that the ERP measurement system is not normal (step S9: NO), the output unit 307 outputs that the ERP measurement system is not normal (step S10).

[0055] When the output of step S10 is performed, in the ERP measurement procedure, if the measurement of step S8 is the first time, the procedure returns to step S7. On the other hand, when the output of step S10 is performed, in the ERP measurement procedure, if the measurement of step S8 is the second time or later, the procedure returns to step S2.

[0056] If the second measurement unit 303 is unable to measure any of SSVEP, SSAEP, and ASSR even after performing the measurement in step S8 multiple times (for example, four times), the output unit 307 outputs, in addition to or instead of the output in step S10, that any of SSVEP, SSAEP, and ASSR cannot be measured. Note that this example of multiple times is merely one example, and the number of times may be two or more.

[0057] Returning to the explanation of step S9, if the determination unit 306 determines that the ERP measurement system is normal (step S9: YES), the output unit 307 outputs that the ERP measurement system is normal (step S11).

[0058] Next, the first measuring unit 302 of the processing device 3 applies a first stimulus and measures the ERP (step S12). Step S12 corresponds to the "first measuring step."

[0059] In step S12, the first measuring unit 302 starts applying the first stimulus (step S121).

[0060] Step S121 will be described in detail. In step S121, the first measurement unit 302 may provide the subject P with a first stimulus that includes the same type of stimulus as the second stimulus provided to the subject P in step S8. That is, if the second stimulus provided to the subject P in step S8 is a visual stimulus, the first measurement unit 302 may provide the subject P with a first stimulus that is a visual stimulus. Also, if the second stimulus provided to the subject P in step S8 is an auditory stimulus, the first measurement unit 302 may provide the subject P with a first stimulus that is an auditory stimulus. In this way, by providing the subject P with a first stimulus that includes the same type of stimulus as the second stimulus, it is possible to measure ERP even if the subject P has a visual or auditory disorder, provided that the ERP measurement system is normal.

[0061] In step S12, when the first measuring unit 302 starts applying the first stimulus, it determines whether or not the stimulus has been applied to the subject P the number of times required for averaging (step S122). That is, in step S122, the first measuring unit 302 determines whether or not application of the first stimulus has ended.

[0062] If the first measuring unit 302 determines that the stimulus has not been applied to the subject P the number of times required for arithmetic averaging (step S122: NO), it continues to apply the first stimulus. On the other hand, if the first measuring unit 302 determines that the stimulus has been applied to the subject P the number of times required for arithmetic averaging (step S122: NO), it measures the EPR using the above-mentioned measurement method (step S123).

[0063] Next, the first measuring unit 302 determines whether or not the EPR has been measured (step S13).

[0064] If the first measuring unit 302 determines that the EPR cannot be measured (step S13: NO), the output unit 307 outputs that the EPR cannot be measured (step S14). Note that when the output of step S14 is performed, if the number of measurements in step S123 is one, the procedure returns to step S7, and if the number of measurements in step S123 is two or more, the procedure returns to step S2.

[0065] On the other hand, if the first measuring unit 302 determines that the ERP has been measured, the output unit 307 displays the ERP measurement results (step S15).

[0066] Next, the effects of this embodiment will be described. Conventionally, when ERP was not measured correctly, the ERP measurement system was determined to be normal or not based on the ERP measurement results, and then the ERP measurement system was reconstructed. Reconstructing the ERP measurement system includes reconstructing the pre-processing for attaching the electrodes 2A, reconstructing the electrodes 2A, correcting malfunctions in the measuring device 2, correcting malfunctions in the processing device 3, and so on. Therefore, when the construction of the ERP measurement system had to be reconstructed, the ERP measurement had to be reconstructed. Conventionally, the increased number of times the construction of the measurement system had to be reconstructed increased the burden on the subject P. Furthermore, conventionally, the increased burden on the subject P meant that there was a limit to the number of times the construction of the ERP measurement system could be reconstructed.

[0067] Therefore, the measurement system 1 of this embodiment measures any one of SSVEP, SSAEP, and ASSR before measuring ERP, and determines whether the ERP measurement system is normal based on the measurement results. As described above, the second stimulus is applied to the subject P multiple times at equal intervals. Because the signal strength of the brain signal increases once the brain memorizes the timing of the next stimulus, the SSVEP, SSAEP, and ASSR measured by applying the second stimulus have stronger signal strength than the ERP measured by applying the first stimulus. In addition, the second stimulus has a shorter stimulation time than the first stimulus. Therefore, the measurement system 1 can quickly determine whether the ERP measurement system is normal, thereby reducing the burden on the subject P even if the ERP measurement system needs to be rebuilt more frequently. Furthermore, because the burden on the subject P can be reduced, the ERP measurement system can be rebuilt more frequently, preventing the ERP measurement from being interrupted due to the burden on the subject P.

[0068] Furthermore, in the past, because the appropriate contact impedance differs for each measurement subject P, the reference value 312 was set to a small value (e.g., 10 kΩ) so as to avoid the need to redo ERP measurements for many measurement subjects P. However, when the reference value 312 is a small value, the number of times pre-treatment for attaching the electrodes 2A increases, and in the past, there was a risk that damage to the skin of the measurement subject P would increase, increasing the burden on the measurement subject P.

[0069] Therefore, in the measurement system 1, when determining whether the ERP measurement system is normal, SSVEP, SSAEP, and ASSR, which have signal intensities stronger than the ERP signal intensity, are measured. Furthermore, in the measurement system 1, the setting unit 305 can set the reference value 312. Therefore, in the measurement system 1, the measurer can set the reference value 312 higher than conventionally (e.g., 100 kΩ to 150 kΩ) to determine whether the ERP measurement system is normal. This reduces the number of pre-treatments required for attaching the electrodes 2A, thereby reducing damage to the skin of the subject P and the burden on the subject P. Conventionally, the reference value 312 was set to an impedance lower than necessary during ERP measurement, increasing the burden on the subject P. However, in the present embodiment, there is no need to lower the reference value 312 more than necessary, thereby reducing the burden on the subject P.

[0070] Furthermore, in the measurement system 1, if any of SSVEP, SSAEP, and ASSR cannot be measured multiple times, the output unit 307 outputs a message to that effect. This allows the measurement subject P to know that they are not responding to stimuli in a shorter time than in ERP measurement, allowing the measurer to decide to end the measurement earlier and reducing the burden on the measurement subject P. Furthermore, because the measurer can quickly know that they are not responding to stimuli, this can contribute to early detection of poor physical condition or mental illness in the measurement subject P.

[0071] 4. Other Embodiments The above-described embodiment merely shows one aspect, and any modifications and applications are possible.

[0072] In the above-described embodiment, the measurement system 1 is configured to measure an ERP as the "first potential." In another embodiment, the measurement system 1 may measure a VEP (visual evoked potential) or an AEP (auditory evoked potential) as the "first potential." In this other embodiment, the first measurement unit 302 measures the VEP or AEP by applying a first stimulus of one event to the subject P.

[0073] In the above-described embodiment, the output unit 307 outputs various information by display or audio output. In other embodiments, the output unit 307 may output various information in other ways, such as by printing or data transmission.

[0074] In the above-described embodiment, the first measuring unit 302 measures P300 as the ERP, as described with reference to Fig. 3. However, the type of ERP measured by the first measuring unit 302 is not limited to P300, and may be ERN (err-related negativity), CRN (correct-response negativity), FRN (feedback-related negativity), or the like.

[0075] The processor 300 may be configured with a single processor or multiple processors. The processor 300 may be hardware programmed to implement corresponding functional units. That is, the processor 300 may be configured with, for example, an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

[0076] 2 is merely an example, and the specific implementation form is not particularly limited. In other words, it is not necessary to implement hardware corresponding to each unit individually, and it is of course possible to implement a configuration in which a single processor executes a program to realize the functions of each unit. Furthermore, some of the functions realized by software in the above-described embodiment may be implemented by hardware, or some of the functions realized by hardware may be implemented by software. In addition, the specific detailed configuration of each unit of the processing device 3 may also be changed as desired.

[0077] Furthermore, the step units of the operation shown in Figure 4 are divided according to the main operation content in order to facilitate understanding of the ERP measurement procedure, and the present invention is not limited by the manner in which the operation units are divided or the names of the operation units. The operation may be divided into more step units depending on the operation content. Furthermore, one step unit may be divided so as to include more operations. Furthermore, the order of the steps may be changed as appropriate within the scope of the present invention.

[0078] The control program 311 of the above-described embodiment may also be non-temporarily recorded on a recording medium that is readable by the processor 300. The recording medium may be a magnetic or optical recording medium or a semiconductor memory device. The control program 311 may also be stored in a server device or the like, and the processing device 3 may download the control program 311 from the server device to achieve the above-described operations.

[0079] 5. Configurations Supported by the Above-described Embodiments The above-described embodiments support the following configurations.

[0080] (Configuration 1) A measurement system comprising: a first measurement unit that measures a first potential from a brain signal of a subject to which a first stimulus is applied at unequal intervals; a second measurement unit that measures a second potential, the second potential having a signal strength stronger than the first potential, from a brain signal of the subject to which a second stimulus is applied at equal intervals and for a shorter stimulation time than the first stimulus before measuring the first potential; and a determination unit that determines whether a measurement system for the first potential is normal based on the measurement results of the second measurement unit before measuring the first potential. According to the measurement system of Configuration 1, when the subject is applied with the second stimulus at equal intervals, the brain memorizes the timing of the next stimulation, and the signal strength of the second potential becomes stronger than the signal strength of the first potential. Therefore, since the signal strength of the second potential is stronger than the signal strength of the first potential and the stimulation time of the second stimulus is shorter than that of the first stimulus, the measurement of the second potential can be performed in a short time. Therefore, it is possible to determine in a short time whether the measurement system for the first potential is normal or not, and even if the number of times the measurement system needs to be reconfigured increases, the burden on the person being measured can be reduced.

[0081] (Configuration 2) The measurement system according to Configuration 1 includes a third measurement unit that measures contact impedance generated by contact between the electrodes measuring brain signals and the human body, a memory unit that stores a reference value to be compared with the contact impedance, and a setting unit that can set the reference value stored in the memory unit, and the second measurement unit measures the second potential when the contact impedance measured by the third measurement unit is equal to or less than the reference value. According to the measurement system of Configuration 2, since the signal strength of the second potential is stronger than the signal strength of the first potential, the reference value can be increased to determine whether the measurement system is normal. This reduces the number of times the process of attaching electrodes to the subject is performed. This reduces damage to the subject's skin and the burden on the subject.

[0082] (Configuration 3) The measurement system according to Configuration 1 or 2, further comprising an output unit that outputs a message indicating that the second potential cannot be measured if the second measurement unit is unable to measure the second potential even after multiple measurements of the second potential. The measurement system of Configuration 3 allows the subject to determine that they are not responding to stimuli in a shorter time than with the first measurement, allowing the measurer to decide to end the measurement earlier and reducing the burden on the subject. Furthermore, the measurer can quickly determine that they are not responding to stimuli, which can contribute to early detection of poor physical condition or a mental illness in the subject.

[0083] (Configuration 4) The measurement system according to Configuration 1 or 2, wherein the first potential is ERP, and the second potential is at least one of SSVEP, SSAEP, and ASSR. According to the measurement system of Configuration 4, it is possible to determine in a short time whether the ERP measurement system is normal by using at least one of SSVEP, SSAEP, and ASSR.

[0084] (Configuration 5) A measurement method including: a first measurement step in which a computer measures a first potential from a brain signal of a subject to which a first stimulus having an irregular stimulus interval is given; a second measurement step in which the computer measures a second potential, the second potential having a stronger signal strength than the first potential, from a brain signal of the subject to which a second stimulus having an irregular stimulus interval and a shorter stimulus time than the first stimulus is given; and a determination step in which the computer determines whether or not a measurement system for the first potential is normal based on the measurement results of the second measurement step, wherein the second measurement step and the determination step are performed before the first measurement step. The measurement method of Configuration 5 achieves the same effects as the measurement system of Configuration 1.

[0085] (Configuration 6) A program that causes a processor to function as a first measurement unit that measures a first potential from a brain signal of a subject to which a first stimulus having an irregular stimulus interval is given, a second measurement unit that measures a second potential having a stronger signal intensity than the first potential from a brain signal of the subject to which a second stimulus having an irregular stimulus interval and a shorter stimulus duration than the first stimulus is given before measuring the first potential, and a determination unit that determines whether a measurement system for the first potential is normal or not based on the measurement result of the second measurement unit before measuring the first potential. The program of Configuration 6 achieves the same effects as the measurement system of Configuration 1.

[0086] 1...measurement system, 2...measuring device, 2A...electrode, 3...processing device (computer), 30...control unit, 31...communication unit, 32...display unit, 33...input unit, 34...sound output unit, 300...processor, 301...communication control unit, 302...first measurement unit, 303...second measurement unit, 304...third measurement unit, 305...setting unit, 306...determination unit, 307...output unit, 310...memory (storage unit), 311...control program (program), 312...reference value, D...measurement data, H...head, P...measurement subject.

Claims

1. A measurement system comprising: a first measurement unit that measures a first potential from the brain signals of a subject to which a first stimulus is given at unequal intervals; a second measurement unit that, before measuring the first potential, measures a second potential, the signal strength of which is stronger than that of the first potential, from the brain signals of the subject to which a second stimulus is given at equal intervals and whose stimulation time is shorter than that of the first stimulus; and a judgment unit that, before measuring the first potential, judges whether the measurement system for the first potential is normal based on the measurement results of the second measurement unit.

2. A measurement system as described in claim 1, comprising: a third measurement unit that measures contact impedance generated by contact between an electrode that measures brain signals and a human body; a memory unit that stores a reference value to be compared with the contact impedance; and a setting unit that can set the reference value stored in the memory unit, wherein the second measurement unit measures the second potential when the contact impedance measured by the third measurement unit is equal to or lower than the reference value.

3. The measurement system according to claim 1 or 2, further comprising an output unit that outputs a message indicating that the second potential cannot be measured if the second measurement unit is unable to measure the second potential even after measuring the second potential multiple times.

4. The measurement system according to claim 1 or 2, wherein the first potential is an ERP, and the second potential is at least one of an SSVEP, an SSAEP, and an ASSR.

5. A measurement method comprising: a first measurement step in which a computer measures a first potential from the brain signal of a subject to which a first stimulus having unequal stimulus intervals has been applied; a second measurement step in which the computer measures a second potential having a stronger signal strength than the first potential from the brain signal of the subject to which a second stimulus having equal stimulus intervals and a shorter stimulus duration than the first stimulus has been applied; and a determination step in which the computer determines whether the measurement system for the first potential is normal based on the measurement results of the second measurement step, wherein the second measurement step and the determination step are performed before the first measurement step.

6. A program that causes a processor to function as: a first measurement unit that measures a first potential from the brain signals of a subject to which a first stimulus having unequal intervals has been applied; a second measurement unit that measures a second potential, the signal strength of which is stronger than that of the first potential, from the brain signals of a subject to which a second stimulus having equal intervals and a shorter stimulation time than the first stimulus has been applied, before measuring the first potential; and a determination unit that determines whether the measurement system for the first potential is normal or not based on the measurement results of the second measurement unit, before measuring the first potential.

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