Cognitive function assessment device and cognitive function assessment program

Abstract

To provide a cognitive function assessment device that can sustain the subject's attention to visual stimuli. [Solution] The cognitive function confirmation device 100 comprises an electroencephalogram (EEG) measuring device 20 for measuring the brain waves of a subject's ultrasound (US), a stimulus generating device 31 for applying a specific frequency idiopathic stimulus 72 to the subject's US and changing the idiopathic stimulus 72 at predetermined timings, an input device 40 for receiving the subject's active response when the idiopathic stimulus 72 changes, and a control device 11 having a determination unit 11d for determining the attentional state from the amplitude of steady-state visual evoked potentials obtained by frequency analysis of the brain waves corresponding to the specific frequency.

Description

Technical Field

[0001] The present invention relates to a cognitive function confirmation device and a cognitive function confirmation program for confirming the attention of a subject based on brain waves.

Background Art

[0002] There is disclosed a driving support device that estimates the degree of driver's inattentiveness from the amplitude of the event-related potential of the brain wave signal (see Patent Document 1).

[0003] Here, although not publicly known, it is conceivable to present a visual stimulus to a subject and use the steady-state visual evoked potential (SSVEP) of the same frequency as the visual stimulus obtained from the brain wave to confirm the cognitive function (specifically, attention) of the subject. However, depending on the subject, the attention to the visual stimulus may not be sustained, and it may be impossible to obtain SSVEP. Also, even when SSVEP can be obtained, there may be no reproducibility when the date and time are different.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a cognitive function confirmation device and a cognitive function confirmation program capable of sustaining the attention of a subject to a visual stimulus.

[0006] To achieve the above objective, the cognitive function confirmation device according to the present invention comprises an electroencephalogram (EEG) measuring device for measuring the brain waves of a subject; a stimulus generating device that provides the subject with an idiosyncratic stimulus of a specific frequency and changes the idiosyncratic stimulus at a predetermined timing; an input device that receives the subject's active response when the idiosyncratic stimulus changes; and a control device having a determination unit that determines the attentional state from the amplitude of a steady-state visually evoked potential obtained by frequency analysis of the brain waves corresponding to a specific frequency.

[0007] According to the cognitive function confirmation device described above, when an idiopathic stimulus changes, the subject responds using the input device, which sustains the subject's attention to the visual stimulus, allowing the judgment unit to stably determine the subject's attentional state.

[0008] To achieve the above objective, the cognitive function confirmation program according to the present invention causes a control device to perform the following actions: change an idiosyncratic stimulus of a specific frequency at a predetermined timing using a stimulus generating device; receive the subject's active response when the idiosyncratic stimulus changes using an input device; and determine the attentional state from the amplitude of steady-state visual evoked potentials obtained by frequency analysis of the subject's brainwaves corresponding to the specific frequency, which is performed by a determination unit. [Brief explanation of the drawing]

[0009] [Figure 1] This is a conceptual diagram illustrating an example of the use of a cognitive function assessment device. [Figure 2] This is a front view showing a part of a cognitive function assessment device. [Figure 3] This is a conceptual block diagram illustrating a cognitive function assessment device. [Figure 4] This is a functional block diagram explaining a cognitive function assessment device. [Figure 5] (A) and (B) are a plan view and a side view illustrating examples of electrode arrangement for an electroencephalogram (EEG) measuring device. [Figure 6] Figures (A) to (C) show examples of the display screen of the stimulus generator when the application software is run. [Figure 7]This diagram shows the frequencies of brainwaves generated in electroencephalogram (EEG) data. [Figure 8] This diagram illustrates the amplitude of SSVEP. [Figure 9] This is a flowchart illustrating an example of how a cognitive function assessment device works. [Figure 10] Figures (A) to (C) show examples of the display screen of the stimulus generating device according to the second embodiment. [Figure 11] Figure 10 shows the display of stimuli in the stimulus generating device in chronological order. [Figure 12] (A) and (B) are diagrams illustrating examples of changes in the difficulty level of the discrimination task. [Figure 13] This is a flowchart illustrating an example of the operation of the cognitive function confirmation device according to the second embodiment. [Figure 14] (A) and (B) are diagrams illustrating examples of changes in the difficulty level of the discrimination task in the cognitive function confirmation device of the third embodiment. [Figure 15] (A) and (B) are diagrams illustrating other examples of changes to the difficulty level of the discrimination task. [Figure 16] (A) and (B) are diagrams illustrating yet another example of a change in the difficulty level of the discrimination task. [Modes for carrying out the invention]

[0010] [First Embodiment] Hereinafter, an embodiment of the cognitive function confirmation device according to the present invention will be described with reference to the drawings.

[0011] Figure 1 is a conceptual diagram illustrating an example of use of the cognitive function confirmation device 100 according to the first embodiment. Figure 2 is a front view showing a part of the cognitive function confirmation device 100. Figure 3 is a conceptual block diagram illustrating the cognitive function confirmation device 100. Figure 4 is a functional block diagram illustrating the cognitive function confirmation device 100. Figures 5(A) and 5(B) are a plan view and a side view illustrating an example of electrode arrangement for the electroencephalogram measurement device 20 of the cognitive function confirmation device 100.

[0012] The cognitive function confirmation device 100 shown in FIGS. 1 to 4 can confirm the cognitive function (attention required for the subject US) of the subject US by determining the attention state of the subject US from the electroencephalogram data. The attention confirmed by the cognitive function confirmation device 100 is exogenous attention and endogenous attention. Exogenous attention is to unconsciously direct attention when a stimulus (including a change in the stimulus) appears in a place where the subject US himself / herself is not directing attention. Exogenous attention is, for example, for the subject US to recognize a change in a signal, a person or a vehicle entering a track, etc. Endogenous attention is for the subject US himself / herself to direct attention to a certain place. Endogenous attention is, for example, looking at the track in the line of sight direction during driving. Although details will be described later, the attention state switches between exogenous attention and endogenous attention according to the progress of the stimulus generated by the cognitive function confirmation device 100. The subject US is, for example, a train driver, a conductor, or other crew members. Also, the subject US is not limited to crew members related to trains, but may also be crew members related to other vehicles such as cars or airplanes, or other people who need to confirm their cognitive function. The cognitive function confirmation device 100 is installed at a station or the like. The confirmation of the cognitive function using the cognitive function confirmation device 100 is performed, for example, before boarding.

[0013] The cognitive function confirmation device 100 includes a device main body 10, an electroencephalogram measurement device 20, an output device 30, and an input device 40. The cognitive function confirmation device 100 operates based on application software or a program stored in the storage device 12 by the control device 11 in the device main body 10 described later.

[0014] As shown in FIG. 1 and the like, the electroencephalogram measurement device 20 measures the electroencephalogram of the subject US. The electroencephalogram measurement is performed about 1 to 2 minutes each time. The measurement result of the electroencephalogram measurement device 20 is recorded as electroencephalogram data in the storage device 12 (see FIG. 3) of the device main body 10 described later.

[0015] The electroencephalogram measuring device 20 is a simple electroencephalograph 21. As illustrated in FIGS. 5(A) and 5(B) etc., the simple electroencephalograph 21 has a reference electrode A disposed on the earlobe ER of the subject US, and an electrode Oz disposed on the mid-posterior head Q1 of the subject US. Note that the simple electroencephalograph 21 may further have an electrode Cz disposed on the mid-center Q2 of the subject US in order to improve the accuracy of electroencephalogram data. The simple electroencephalograph 21 can communicate with the device main body 10 by means of short-range wireless communication, wired communication, or the like. Note that the electroencephalogram measuring device 20 may be any device that measures an electroencephalogram in which steady-state visual evoked potentials (SSVEP) appear, such as a head-mounted type or earphone type simple electroencephalograph, for example.

[0016] The measured electroencephalogram is sampled so that it can be processed by a control device 11 (see FIG. 3) of the device main body 10 described later. The electroencephalogram data is collected at a sampling rate of, for example, 200 Hz to 500 Hz and digitized. Various data processes such as noise processing by a filter, baseline correction, averaging, and frequency analysis are performed on the electroencephalogram data. The data process of the electroencephalogram data may be performed by the electroencephalogram measuring device 20 or may be performed by an electroencephalogram analysis unit 11a of the control device 11 described later.

[0017] As shown in FIG. 3, the device main body 10 has a control device 11 and a storage device 12.

[0018] The control device 11 controls the operations of the electroencephalogram measuring device 20, the output device 30, the storage device 12, etc. The control device 11 reads out a cognitive function confirmation program P1, other computer programs, data, etc. stored in the storage device 12, and executes predetermined information processing (specifically, various processes executed by the cognitive function confirmation device 100). The control device 11 includes an arithmetic processing device such as a CPU (Central Processing Unit).

[0019] As shown in Figure 4, the control device 11 includes an electroencephalogram (EEG) analysis unit 11a, a stimulus generation unit 11b, a response reception unit 11c, and a determination unit 11d. The EEG analysis unit 11a, stimulus generation unit 11b, response reception unit 11c, and determination unit 11d are functions of the control device 11 that operate using corresponding application software. The EEG analysis unit 11a extracts SSVEP EEG from EEG data acquired by the EEG measurement device 20. The stimulus generation unit 11b creates a display pattern for stimuli to be output to the output device 30. The response reception unit 11c receives the response of the subject US when the subject US operates the input device 40 in response to a stimulus. The determination unit 11d evaluates the attention required by the subject US from the EEG (EEG data). Specifically, the determination unit 11d determines the attention state from the EEG of the subject US given a predetermined stimulus. This allows the determination unit 11d to quantitatively confirm a predetermined level of attention from the EEG. Details of the determination unit 11d will be described later.

[0020] The control device 11 performs various data processing to control the main unit 10 and other components. As will be described in detail later, for example, the control device 11, as an electroencephalogram (EEG) analysis unit 11a, performs frequency analysis of EEGs corresponding to specific frequencies acquired from the EEG measurement device 20. The control device 11, as a stimulus generation unit 11b, changes the spontaneous stimulus 72 (see Figure 6(B), etc.) of a specific frequency at predetermined timings using the stimulus generator 31. The control device 11, as a response reception unit 11c, receives the active response of the subject U at the start and change of the spontaneous stimulus 72 using the input device 40. The control device 11, as a determination unit 11d, determines the attention state from the amplitude of the SSVEP.

[0021] The storage device 12 shown in Figure 3 stores programs for various application software that can be executed in the cognitive function verification device 100. The storage device 12 also stores a database 12a related to processing in the cognitive function verification device 100. The storage device 12 is a non-volatile storage medium or non-temporary storage medium NM such as a hard disk or flash memory, and stores cognitive function verification programs P1, etc., for the control device 11 to perform various information processing. Note that the cognitive function verification programs P1, etc., may be provided stored on a storage medium other than the storage device 12, or may be provided by downloading from a server. Furthermore, the storage device 12 temporarily stores data necessary for the control device 11 to perform calculation processing.

[0022] As shown in Figure 2, the output device 30 is a stimulus generator 31 that provides a test stimulus ST to the subject's ultrasound during electroencephalography (EEG) measurement. The stimulus generator 31, as the output device 30, is, for example, a display device such as a display. The stimulus generator 31 displays the test stimulus ST generated by the stimulus generation unit 11b of the control device 11 on the display screen 31a at predetermined timings, through the operation of application software by the control device 11 shown in Figure 3. The spontaneous stimulus 72 (see Figure 6(B), etc.) displayed at the start and during changes induces extrinsic attention.

[0023] The input device 40 detects the subject US's response to a predetermined stimulus FS. The input device 40 has one or more input members 41. The input device 40 is, for example, a keyboard. The input members 41 are, for example, a space key 41a or an enter key 41b. The input device 40 may also be a button device such as a keypad. As will be described in detail later, when the subject US sees a predetermined stimulus FS or an emergency stimulus 72 that draws attention displayed on the stimulus generator 31, the subject US performs an operation by pressing, for example, the enter key 41b as the input member 41. The result of the operation of the input member 41 is output to the response receiving unit 11c of the control device 11. As a response method, instead of pressing the enter key 41b, the subject may press another key, for example, the space key 41a.

[0024] Figures 6(A) to 6(C) illustrate an example of a test stimulus ST displayed on the display screen 31a of the stimulus generator 31 when the application software is executed. Figures 6(A) to 6(C) show the display according to the situation. The dotted triangular line indicates that the image is flashing.

[0025] As shown in Figure 6(A), etc., the display screen 31a of the stimulus generator 31 displays a test stimulus ST related to the estimation of extrinsic or intrinsic attention. The test stimulus ST is a visual stimulus and consists of a steady-state stimulus 71 and an idiosyncratic stimulus 72.

[0026] As shown in Figure 6(A), etc., the steady-state stimulus 71 is a flashing stimulus of a predetermined frequency that is output continuously. The subject US is required to fixate on the steady-state stimulus 71 in advance as the fixation point EP. On the display screen 31a, the steady-state stimulus 71 is displayed, for example, in the line of sight that the subject US should fixate on. The steady-state stimulus 71 is, for example, a flashing circular image, but is not limited to this, and may be a flashing display of other shapes or landscapes. The steady-state stimulus 71 is used to confirm whether the subject US's attention is in a state to receive the idiosyncratic stimulus 72. The frequency of the steady-state stimulus 71 is, for example, 15 Hz. The frequency of the steady-state stimulus 71 can be changed as appropriate, as long as it is different from the frequency of the idiosyncratic stimulus 72 and its integer multiples.

[0027] The spontaneous stimulus 72 is a predetermined stimulus FS of a specific frequency designed to attract the attention of the subject (US). While the spontaneous stimulus 72 is initially a sudden event that elicits extrinsic attention, its persistence shifts attention to intrinsic attention. The spontaneous stimulus 72 is, for example, a flashing image displayed at a predetermined timing in a different location from the steady-state stimulus 71; in other words, a spontaneous flashing display. The frequency of the spontaneous stimulus 72 is, for example, 8Hz to 10Hz. The frequency of the spontaneous stimulus 72 can be changed as appropriate, as long as it is different from the frequency of the steady-state stimulus 71 and its integer multiples. Furthermore, the color, size, shape, and position of the spontaneous stimulus 72 can be changed as appropriate.

[0028] The following describes the tasks (attention tasks) used in cognitive function assessment. As shown in Figure 6(A), in the attention task, the initial screen of the stimulus generator 31 displays the steady-state stimulus 71 from the test stimuli ST. The subject US focuses on the steady-state stimulus 71 as the gaze point EP, thereby bringing the display screen 31a of the stimulus generator 31 into their field of vision. The cognitive function assessment device 100 provides the subject US with a predetermined stimulus FS, etc., to elicit new attention (see Figures 6(B) and 6(C), etc.), and measures SSVEP for the task as an electroencephalogram (EEG) generated by the visual response to a specific frequency. In the attention task, a visual stimulus of a certain frequency is detected, and an EEG of the same frequency as that visual stimulus is detected, utilizing the fact that amplitude amplification occurs in the frequency band of the visual stimulus. Note that SSVEP amplitude also occurs in frequency bands that are integer multiples of the frequency of the visual stimulus. In the attention task, a steady-state visual stimulus (steady-state stimulus 71) and an spontaneous visual stimulus (spontaneous stimulus 72) corresponding to a predetermined stimulus FS are generated, and the amplitude of the SSVEP in the frequency band of the spontaneous stimulus 72 is measured.

[0029] As previously described, when the subject's ultrasound (US) attention is directed to the visual stimulus, which is the idiopathic stimulus 72, an SSVEP with the same frequency as the visual stimulus can be obtained from the electroencephalogram (EEG). However, depending on the subject's US, SSVEP may be obtained in some cases and not in others. Furthermore, even with subject US where SSVEP was obtained, reproducibility may be lacking if the date and time differ. Possible reasons for the inability to obtain SSVEP include the subject's attention not being directed to the visual stimulus, or quickly shifting to something else, resulting in insufficient sustained attention to the visual stimulus. Therefore, during EEG measurement, the display of the idiopathic stimulus 72 is changed over time. In addition, when the idiopathic stimulus 72 changes, the subject is given a task in which they press the Enter key 41b. This task generates the active response of the subject, as described later, and allows for consistent acquisition of SSVEP even when the measurement date and time or subject US differ.

[0030] The stimulus generator 31 changes the spontaneous stimulus 72 at predetermined timings under the operation of the stimulus generation unit 11b of the control device 11. In other words, the stimulus generator 31 changes the stimulus conditions of the spontaneous stimulus 72 at predetermined timings. By changing the spontaneous stimulus 72, the attention of the subject (US) can be sustained. Specifically, the stimulus generator 31 changes one of the following over time: the color, size, shape, position, or frequency of the spontaneous stimulus 72. The stimulus generator 31 may also change the spontaneous stimulus 72 from flashing to disappearing. In one task, the spontaneous stimulus 72 consists of, for example, a first visual stimulus 72a and a second visual stimulus 72b that has a different display from the first visual stimulus 72a. The first visual stimulus 72a is, for example, a white rectangle, and the second visual stimulus 72b is, for example, a gray rectangle. The stimulus generator 31 outputs a spontaneous stimulus 72 according to the subject (US)'s level of ability to distinguish stimulus changes. The level at which the subject US can distinguish between stimulus changes corresponds to the subject US's ability to discriminate between stimuli. The input device 40 receives the subject US's active response via the input member 41 at the start and when the spontaneous stimulus 72 changes. An active response is an action taken by the subject US to maintain attention to the spontaneous stimulus 72, such as pressing the input member 41 at the start or when the spontaneous stimulus 72 changes.

[0031] After the task begins, the first visual stimulus 72a of the spontaneous stimuli 72 is displayed on the display screen 31a of the stimulus generator 31 after a random number of seconds (see Figure 6(B)). The display time of the first visual stimulus 72a is, for example, 4 seconds or more. On the display screen 31a, the first visual stimulus 72a is displayed as, for example, a flashing white rectangle. When the first visual stimulus 72a is displayed, the participant (US) indicates that they have recognized the first visual stimulus 72a by pressing the enter key 41b. The spontaneous stimulus 72 after the start of the task induces extrinsic attention in the participant (US). Subsequently, the participant (US) spontaneously directs their attention to the state of the spontaneous stimulus 72, and this attention becomes intrinsic attention.

[0032] After the appearance of the first visual stimulus 72a, the second visual stimulus 72b is displayed after a random number of seconds (see Figure 6(C)). The display time of the second visual stimulus 72b is, for example, 4 seconds or more. The second visual stimulus 72b is, for example, a variation of the first visual stimulus 72a in color. The idiopathic stimulus 72 changes from white to gray. When the idiopathic stimulus 72 changes, the subject (US) indicates that they have recognized the second visual stimulus 72b by pressing the enter key 41b again. The changed idiopathic stimulus 72, i.e., the change itself, induces extrinsic attention in the subject (US). Subsequently, the subject (US) spontaneously directs their attention to the state of the idiopathic stimulus 72, and this attention becomes intrinsic attention.

[0033] Figure 7 shows the frequency of brain waves generated in electroencephalogram data (steady-state visual evoked potentials). In Figure 7, the vertical axis represents frequency and the horizontal axis represents time. In the example in Figure 7, an idiosyncratic stimulus 72 (predetermined stimulus FS) is given for a predetermined time during the steady-state stimulus 71. As shown in Figure 7, while the SSVEP amplitude (specifically, the solid line L1) appears at a constant frequency H1 of the steady-state stimulus 71, the SSVEP amplitude (specifically, the solid line L2) appears at a specific frequency H2 of the idiosyncratic stimulus 72 a predetermined time t1 after the idiosyncratic stimulus 72 is displayed. The symbol t2 in the figure indicates the duration of the appearance of the SSVEP amplitude corresponding to the idiosyncratic stimulus 72. The cognitive function confirmation device 100 of this embodiment can continuously acquire SSVEP corresponding to the idiosyncratic stimulus 72 by introducing irregular changes to the idiosyncratic stimulus 72 and eliciting an active response from the subject US.

[0034] The details of the determination unit 11d shown in Figure 4 will be explained below.

[0035] The determination unit 11d evaluates attention from the electroencephalogram (ESV) response (SSVEP) to the idiopathic stimulus 72 (predetermined stimulus FS) shown in Figures 6(B) and 6(C) in the EEG related to attention. Specifically, the determination unit 11d evaluates attention (extrinsic attention or intrinsic attention) based on the amplitude of the SSVEP corresponding to a specific frequency H2 in the SSVEP for the idiopathic stimulus 72. The determination unit 11d determines the attentional state based on the degree of attention. For example, when the amplitude of the SSVEP for the idiopathic stimulus 72 is large, the determination unit 11d determines that attention is high and cognitive function is high as an attentional state. When the amplitude of the SSVEP for the idiopathic stimulus 72 is small, the determination unit 11d determines that attention is low and cognitive function is low as an attentional state. This allows for confirmation of the cognitive function of the subject (US).

[0036] Specifically, as shown in Figure 8, the determination unit 11d determines that there is attention (extrinsic or intrinsic attention) or that attention is high if the amplitude of the SSVEP corresponding to the idiopathic stimulus 72 is greater than the determination threshold VX. Conversely, the determination unit 11d determines that there is no attention (extrinsic or intrinsic attention) or that attention is low if the amplitude of the SSVEP corresponding to the idiopathic stimulus 72 is less than the determination threshold VX. The determination threshold VX may be, for example, a general condition value necessary for driving, or it may be set for each subject's electroencephalogram (EEG). The threshold for each subject's EEG is set from the median or average value of the measurement results after measuring EEG multiple times and over multiple days. It is thought that a constant value can be obtained for each subject's EEG as the number of EEG measurements increases, similar to body temperature.

[0037] By appropriately setting the judgment threshold VX and determining attention, it is possible to understand the degree of attention the subject's attention capacity possesses and to quantitatively confirm the attention capacity required for the subject's attention capacity.

[0038] In the attention task, when the spontaneous stimulus 72 is displayed, the subject US presses the enter key 41b as the input member 41 of the input device 40 shown in Figure 2, etc. The act of the subject US pressing the input member 41 is a physical demonstration of the subject US's response to attention. The judgment unit 11d receives the subject US's active response via the input member 41 of the input device 40 through the response reception unit 11c.

[0039] In the above, extrinsic attention or intrinsic attention may be calculated as a numerical value by applying electroencephalogram data to a predetermined conversion formula. Alternatively, extrinsic attention or intrinsic attention may be converted into a level.

[0040] If the judgment unit 11d detects no response from the input device 40 and SSVEP does not appear in the electroencephalogram, it has the subject perform the task again. That is, the stimulus generator 31 generates the spontaneous stimulus 72 again, and the input device 40 again receives an active response from the subject via the input member 41. In the repeated task, the stimulus generator 31 may display the spontaneous stimulus 72 with the same stimulus conditions or change conditions as the previous time, or it may display it with changed stimulus conditions or change conditions. When changing the stimulus conditions, it is preferable to make the changes in the spontaneous stimulus 72 more easily distinguishable.

[0041] Figure 9 is a flowchart illustrating an example of the operation of the cognitive function confirmation device 100. When the operation of the cognitive function confirmation device 100 is started, the control device 11 reads and executes the cognitive function confirmation program P1. Once the cognitive function confirmation program P1 is executed, the control device 11 performs the following operations. In the cognitive function confirmation device 100, electroencephalogram (EEG) data is acquired in real time. The EEG data is subjected to predetermined data processing by the EEG measurement device 20 and the EEG analysis unit 11a for processing by the judgment unit 11d.

[0042] First, the control device 11 starts measuring the brainwaves of the subject (Ultrasound) (step S11). Specifically, the control device 11 runs an application software for confirming cognitive function and, as the stimulus generation unit 11b, displays the steady-state stimulus 71 at the gaze point EP on the display screen 31a of the stimulus generator 31 shown in Figure 6(A), etc.

[0043] As a stimulus generation unit 11b, when the timing for alerting the user arrives (Yes in step S12), the control device 11 displays a predetermined stimulus FS, the special stimulus 72, on the display screen 31a of the stimulus generator 31, as shown in Figure 6(B) (step S13). In this embodiment, the special stimulus 72 is displayed on the display screen 31a at any position other than the display position of the steady stimulus 71. When the special stimulus 72 is displayed, the steady stimulus 71 continues to blink at a predetermined frequency.

[0044] The control device 11, acting as a stimulus generation unit 11b, changes the stimulus conditions of the spontaneous stimulus 72 at predetermined timings while the spontaneous stimulus 72 is being displayed (step S14). Specifically, the spontaneous stimulus 72 changes from a white rectangle (see Figure 6(B)) to a gray rectangle (see Figure 6(C)).

[0045] In steps S13 and S14 described above, the control device 11, acting as a response receiving unit 11c, receives input of response keys related to extrinsic attention. When the spontaneous stimulus 72 is displayed, the subject US presses the enter key 41b on the input member 41 of the input device 40. The subject US also presses the enter key 41b when the display of the spontaneous stimulus 72 changes. In other words, the subject US presses the enter key 41b at the start and when the spontaneous stimulus 72 changes. Pressing the enter key 41b indicates the subject US's physical response to extrinsic attention. When the enter key 41b is pressed, the input device 40 outputs the subject US's response to the response receiving unit 11c as input of a response key related to extrinsic attention. The subject US continues to gaze at the gaze point EP while pressing the enter key 41b.

[0046] After a predetermined time has elapsed, the control device 11, acting as the stimulus generation unit 11b, terminates the display of the special stimulus 72 (step S15).

[0047] After step S15, the control device 11, acting as an electroencephalogram (EEG) analysis unit 11a, extracts the EEG corresponding to SSVEP (step S16). In step S16, predetermined data processing is performed on the EEG data. The EEG analysis unit 11a calculates the magnitude of the SSVEP amplitude at the frequency of the spontaneous stimulus 72.

[0048] If the control device 11 completes a series of tasks to confirm cognitive function (Yes in step S17), the determination unit 11d determines the attentional state (step S18). Specifically, the determination unit 11d quantitatively estimates or determines attention from electroencephalogram data and a determination threshold related to attention. For example, if attention is high, the determination unit 11d determines that cognitive function is high as an attentional state.

[0049] If the control device 11 fails to complete the series of cognitive function assessment tasks (No. in step S17), it returns to step S12. For example, if the number of outputs from the input device 40 does not meet a predetermined number and SSVEP cannot be obtained, it returns to step S12.

[0050] According to the cognitive function confirmation device 100 described above, when the spontaneous stimulus 72 changes, the subject's ultrasound (US) responds with the input device 40, thereby maintaining the subject's attention to the visual stimulus, and the determination unit 11d can stably determine the subject's attention state.

[0051] [Second Embodiment] The following describes an example of a cognitive function confirmation device according to the second embodiment. In the second embodiment, matters similar to those in the first embodiment will not be explained.

[0052] In this embodiment, the configuration of the cognitive function confirmation device 100 is the same as that of the cognitive function confirmation device 100 shown in Figures 3 and 4, etc., but the stimuli displayed on the display screen 31a of the stimulus generator 31 are different from those shown in Figure 6(A), etc.

[0053] Figures 10(A) to 10(C) illustrate an example of a test stimulus ST displayed on the display screen 31a of the stimulus generator 31 in this embodiment. Figure 10(A) shows the display at the start of the stimulus test, Figure 10(B) shows the display when the spontaneous stimulus 72 changes, and Figure 10(C) shows the display when the spontaneous stimulus 72 returns to its original state. The series of displays in Figures 10(A) to 10(C) constitutes one cycle and one task. Each stimulus 72, 73 flashes at a predetermined frequency.

[0054] The display screen 31a shows the gaze point EP, which is the point of focus that the subject (US) should fixate on. In the illustrated example, the gaze point EP is displayed in the center of the display screen 31a. The gaze point EP may be displayed as a steady light or as a blinking light. The subject (US) performs the following attention task while fixing their gaze on the gaze point EP.

[0055] As shown in Figure 10(A), etc., in the cognitive function confirmation device 100 of this embodiment, the display screen 31a of the stimulus generator 31 displays multiple discrimination tasks CK as tasks (attention tasks) for cognitive function confirmation. In the illustrated example, two discrimination tasks CK, specifically the first discrimination task CK1 and the second discrimination task CK2, are displayed. A discrimination task CK is a task in which the user responds when a specific stimulus is presented in response to a normal stimulus. Furthermore, a discrimination task CK is a display of a discrimination task stimulus 73 with an idiosyncratic stimulus 72 as the background.

[0056] The stimulus generator 31 displays two or more discrimination stimulus regions 73r that display discrimination stimulus 73, with each region 72r displaying a different specific frequency, superimposed on the discrimination stimulus region 73r that displays discrimination stimulus 73. The stimulus generator 31 displays the discrimination stimulus 72 from the start of the stimulus test and changes the discrimination stimulus 72 in one of the discrimination stimulus regions 72r at a predetermined timing, as shown in Figure 11. Specifically, for example, the stimulus generator 31 changes the discrimination stimulus 72 of the second discrimination stimulus CK2 on the right from the first visual stimulus 72a to the second visual stimulus 72b. At this time, the discrimination stimulus 72 of the first discrimination stimulus CK1 on the left maintains the display of the first visual stimulus 72a.

[0057] The stimulus generator 31 changes the spontaneous stimulus 72, then changes the spontaneous stimulus 72 again at a predetermined timing, returning the spontaneous stimulus 72 to its state at the start of the stimulus test. In other words, it returns the spontaneous stimulus 72 to the first visual stimulus 72a, which is its state at the start of the stimulus test. This allows for the acquisition of SSVEP (Science Standard Spectrum Output) for one cycle, from the start of display of the spontaneous stimulus 72 to its return after the change, and enables the quantification of cognitive function for each change condition of the spontaneous stimulus 72 or for each difficulty level of the discrimination task CK.

[0058] As described above, the test stimulus ST used in the discrimination task CK is a display in which an adjective stimulus 72 is superimposed on the discrimination task stimulus 73 corresponding to the gaze point of the subject US. As shown in Figure 11, the discrimination task stimulus 73 consists of a normal stimulus 73x and a specific stimulus 73y that is different from the normal stimulus 73x. The specific stimulus 73y is the stimulus among the discrimination task stimulus 73 that the subject US is designated to respond to in the discrimination task CK. In other words, the discrimination task stimulus 73 includes the appearance of a specific stimulus 73y to which the subject US should respond. In the discrimination task CK, the subject US responds by operating the input device 40 when the specific stimulus 73y among the discrimination task stimulus 73 is displayed. In examples such as Figure 10(A), the discrimination task stimulus 73 is displayed by randomly switching between the letters A to Z. If the normal stimulus 73x is, for example, the letters A to Y, and the specific stimulus 73y is, for example, the letter Z, then the subject US operates the input device 40 when the letter Z is displayed as the specific stimulus 73y. Specifically, when the participant US responds to a specific stimulus 73y of the discrimination task stimulus 73, they press, for example, the space key 41a. The frequency of the discrimination task stimulus 73 is, for example, 1 Hz.

[0059] The discrimination task stimulus 73 may consist of a standard stimulus (normal stimulus 73x) that is displayed frequently and a deviation stimulus (specific stimulus 73y) that is displayed frequently. In this case, the normal stimulus 73x is, for example, a random display of numbers (specifically, 1 to 9) at a high frequency. The specific stimulus 73y is distinguishable from the normal stimulus 73x and is displayed at a lower frequency than the normal stimulus 73x. The specific stimulus 73y is, for example, a random display of letters (specifically, A to Z) at a low frequency. The normal stimulus 73x and the specific stimulus 73y can be any distinguishable images and can be changed as appropriate. Distinguishing between letters is more difficult in the discrimination task CK than distinguishing between numbers and letters.

[0060] In the stimulus generator 31, the spontaneous stimulus 72 is displayed from the start of the stimulation test, and one of the multiple spontaneous stimuli 72 changes at a predetermined timing (see Figure 11). Specifically, one of the two spontaneous stimuli 72 shown in Figure 10(A) is changed. Which spontaneous stimulus 72 is changed is random. When the spontaneous stimulus 72 changes, the stimulus generator 31 changes either the color, size, or shape of the spontaneous stimulus 72. As shown in Figure 10(A), the spontaneous stimulus 72 is a first visual stimulus 72a, which is displayed as, for example, a gray rectangle at the start of the stimulation test, and as shown in Figure 10(B), the spontaneous stimulus 72b, which is displayed as, for example, a red rectangle when it changes. The subject US operates the input device 40 when the spontaneous stimulus 72 changes from gray to red. Specifically, when the subject US reacts to the change in the spontaneous stimulus 72, they press, for example, the enter key 41b. Furthermore, the subject US also operates the input device 40 when the spontaneous stimulus 72 changes from red to gray and returns to the state at the start of the stimulation test, as shown in Figure 10(C), after the spontaneous stimulus 72 has changed. The frequency of the spontaneous stimulus 72 is, for example, 8Hz to 10Hz.

[0061] The input device 40 receives an active response from the subject's ultrasound (US) when the spontaneous stimulus 72 changes. The input device 40 also receives an active response from the subject's ultrasound (US) when a specific stimulus 73y appears among the discrimination task stimuli 73.

[0062] The determination unit 11d calculates the discriminative ability of subject US in the discriminative task CK from the response results to a specific stimulus 73y with the spontaneous stimulus 72 as the background in the discriminative task CK, and changes the difficulty level of the discriminative task CK by changing at least one of the spontaneous stimulus 72 and the discriminative task stimulus 73 according to the discriminative ability. The difficulty level of the discriminative task CK is determined, for example, by the contrast level between the spontaneous stimulus 72 and the discriminative task stimulus 73; if the contrast is high, the difficulty level is low, and if the contrast is low, the difficulty level is high.

[0063] Figure 12(A) shows an example of the discrimination task CK for the first trial, and Figure 12(B) shows an example of the discrimination task CK for the second trial. The judgment unit 11d calculates the discrimination ability of the discrimination task CK for the first trial and changes the difficulty level of the discrimination task CK for the second trial according to the calculated discrimination ability. In the examples of Figures 12(A) and 12(B), the contrast between the spontaneous stimulus 72 and the discrimination task stimulus 73 is considered, and the colors of the spontaneous stimulus 72 and the discrimination task stimulus 73 are changed. Alternatively, only the color of the spontaneous stimulus 72 may be changed, or only the color of the discrimination task stimulus 73 may be changed.

[0064] As described above, by calculating discrimination ability for each participant in the US and feeding the results back into the next test, the difficulty level of the discrimination task CK can be adjusted to suit each participant in the US. By performing the discrimination task CK of appropriate difficulty, participants in the US will not focus too much on the discrimination task CK, and the amplitude of the SSVEP for idiopathic stimulus 72 will increase.

[0065] For calculating discrimination ability, signal detection theory is used [1]. In signal detection theory, trials are repeatedly conducted in which the subject is asked to judge whether a stimulus is a signal or noise. In the Nth (N: integer) trial, the subject's response is classified into four trial outcomes, and the number of trial outcomes is counted. Here, a signal trial is a trial in which there is a stimulus to be recognized, and a noise trial is a trial in which there is no stimulus to be recognized. The trial outcomes are (i) a hit (Yes response) in a signal trial, (ii) a miss (No response) in a signal trial, (iii) a false alarm (Yes response) in a noise trial, and (iv) a correct rejection (No response) in a noise trial. Next, the hit rate and false alarm rate are calculated using the above trial outcomes (i) to (iv). The hit rate is the frequency of hits in signal trials. The false alarm rate is the frequency of false alarms in noise trials. Finally, the deep rhyme d', an index of discrimination ability, is calculated using the hit rate and false alarm rate. The deep rim d' is the distance between the mean of the normally distributed signal distribution and the mean of the noise distribution. A small deep rim d' indicates low discrimination ability, while a large deep rim d' indicates high discrimination ability. The magnitude of discrimination ability is determined based on a predetermined value for deep rim d'. Specifically, if the deep rim d' of the Nth trial is greater than or equal to the predetermined value, for example 1.5, the discrimination ability is high, and the difficulty of the task in the (N+1)th trial is increased. Conversely, if the deep rim d' of the Nth trial is less than the predetermined value, for example 1.5, the discrimination ability is low, and the difficulty of the task in the (N+1)th trial is decreased. Note that the predetermined value can be changed as appropriate. The discrimination ability obtained in the Nth trial is fed back into the (N+1)th trial.

[0066] The determination unit 11d reduces the amount of change in the spontaneous stimulus 72 to less than the previous change condition if the amplitude of the SSVEP corresponding to the spontaneous stimulus 72 is not greater than a predetermined value. However, the amount of change in the spontaneous stimulus 72 is set so that the difficulty of the task does not exceed the discrimination ability of the subject US. This makes the discrimination task CK more difficult for the subject US, directing the subject US's attention more toward the spontaneous stimulus 72 and increasing the amplitude of the SSVEP.

[0067] Figure 13 is a flowchart illustrating an example of the operation of the cognitive function confirmation device 100 of this embodiment.

[0068] First, the control device 11 sets the difficulty level of the discrimination task CK as the stimulus generation unit 11b (step S21). Note that step S21 may be omitted in the first measurement.

[0069] Next, the control device 11 starts measuring the brainwaves of the subject (U) (step S22). Initially, the test stimulus ST is not displayed on the display screen 31a of the stimulus generator 31.

[0070] The control device 11, acting as a stimulus generation unit 11b, operates an application software for cognitive function verification at a predetermined timing, causing two discrimination tasks CK to be displayed on the display screen 31a of the stimulus generator 31 shown in Figure 10(A) (step S23). In this embodiment, in each discrimination task CK, the discrimination task stimulus 73 and the spontaneous stimulus 72 are displayed superimposed. In addition, the display of the discrimination task stimulus 73 in the discrimination task CK is randomly switched.

[0071] In step S23 described above, the control device 11, acting as a response receiving unit 11c, receives input of response keys related to intrinsic attention. When a specific stimulus 73y, for example the letter Z, is displayed among the discrimination task stimuli 73, the subject US presses the space key 41a on the input member 41 of the input device 40. When the space key 41a is pressed, the input device 40 outputs the subject US's response to the response receiving unit 11c as input of a response key related to intrinsic attention.

[0072] The control device 11, acting as a stimulus generation unit 11b, changes the stimulus conditions of the spontaneous stimulus 72 at a predetermined timing (step S24). Specifically, the spontaneous stimulus 72 changes from a gray rectangle (see Figure 10(A)) to a red rectangle (see Figure 10(B)).

[0073] In step S24 described above, the control device 11, acting as a response receiving unit 11c, receives input of a response key related to extrinsic attention. When the display of the idiopathic stimulus 72 changes, the subject US presses the enter key 41b on the input member 41 of the input device 40. In other words, the subject US presses the enter key 41b when the idiopathic stimulus 72 changes. When the enter key 41b is pressed, the input device 40 outputs the subject US's response to the response receiving unit 11c as input of a response key related to extrinsic attention.

[0074] After a predetermined time, the control device 11, acting as the stimulus generation unit 11b, restores the display of the spontaneous stimulus 72 to its original state (step S25). In other words, the display of the spontaneous stimulus 72 shown in Figure 10(C) becomes the same as the display of the spontaneous stimulus 72 at the start of the stimulus test shown in Figure 10(A). In step S25, the restoration of the spontaneous stimulus 72 is considered a change in the spontaneous stimulus 72, and the subject US presses the enter key 41b on the input member 41 of the input device 40.

[0075] After step S25, the control device 11, acting as an electroencephalogram analysis unit 11a, extracts electroencephalograms corresponding to SSVEP (step S26).

[0076] The control device 11, acting as a determination unit 11d, calculates the discrimination ability of the discrimination task (step S27). The result of the discrimination ability calculation is fed back when setting the difficulty level of the discrimination task in step S21.

[0077] If the control device 11 completes a series of tasks to confirm cognitive function (Yes in step S28), the determination unit 11d determines the attention state (step S29).

[0078] If the control device 11 fails to complete the series of tasks for confirming cognitive function (No. in step S28), it returns to step S21.

[0079] According to the cognitive function confirmation device 100 of this embodiment described above, by performing multiple discrimination tasks CK, displaying the discrimination task stimulus 73 and the spontaneous stimulus 72 superimposed in the discrimination task CK, and changing one spontaneous stimulus 72, the subject's attention is not dispersed between the discrimination task CK and the spontaneous stimulus 72, and the amplitude of the steady-state visual evoked potential (SSVEP) for the spontaneous stimulus 72 becomes larger, thereby obtaining a sufficient SSVEP amplitude to quantify cognitive function.

[0080] [Third Embodiment] The following describes an example of a cognitive function confirmation device according to the third embodiment. The cognitive function confirmation device of the third embodiment is a partial modification of the cognitive function confirmation device of the second embodiment, and matters similar to those of the second embodiment will not be explained.

[0081] As described above, the determination unit 11d changes the difficulty level of the discrimination task CK by changing at least one of the spontaneous stimulus 72 and the discrimination task stimulus 73 according to the discrimination ability. In particular, in this embodiment, in addition to the contrast between the spontaneous stimulus 72 and the discrimination task stimulus 73, other elements are changed in the spontaneous stimulus 72 and the discrimination task stimulus 73.

[0082] Specifically, when changing the discrimination task CK, the judgment unit 11d changes one of the elements of the idiopathic stimulus 72 (color, size, and shape) and the discrimination task stimulus 73 (color, size, font, and type) in combination. Here, the color, size, font, and type of the discrimination task stimulus 73 specifically refer to the color, size, font, and type of the text. It is preferable that the judgment unit 11d changes three or more elements from the elements of the idiopathic stimulus 72 and the elements of the discrimination task stimulus 73 in combination. In particular, it is more preferable that the judgment unit 11d changes three or more elements, including the elements of the idiopathic stimulus 72 and the elements of the discrimination task stimulus 73 in combination. By increasing the elements that are changed in the idiopathic stimulus 72 and the discrimination task stimulus 73, the number of difficulty patterns for the discrimination task CK can be increased. This makes it possible to set a difficulty level that is more appropriate for the subject US and to obtain more SSVEPs.

[0083] The following are examples of combinations of elements of the idiopathic stimulus 72 to be changed and the elements of the discrimination task stimulus 73. Note that the combinations of elements to be changed are not limited to the examples below; various combinations can be used.

[0084] (Example combination 1) Figure 14(A) shows an example of the discrimination task CK in the first trial, and Figure 14(B) shows an example of the discrimination task CK in the second trial. In the examples in Figures 14(A) and 14(B), the color of the spontaneous stimulus 72 and the color and font (color and font of the text) of the discrimination task stimulus 73 are changed.

[0085] (Example combination 2) Figure 15(A) shows an example of the discrimination task CK in the first trial, and Figure 15(B) shows an example of the discrimination task CK in the second trial. In the examples in Figures 15(A) and 15(B), the color of the spontaneous stimulus 72 and the color and type (color and type of letters) of the discrimination task stimulus 73 are changed.

[0086] (Combination example 3) Figure 16(A) shows an example of the discrimination task CK in the first trial, and Figure 16(B) shows an example of the discrimination task CK in the second trial. In the examples in Figures 16(A) and 16(B), the color and shape of the spontaneous stimulus 72, and the color and type (color and type of letters) of the discrimination task stimulus 73 are changed.

[0087] [Other matters] This invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit.

[0088] In the first embodiment, instead of the steady-state stimulus 71, the discrimination task may be performed at the position of the fixation point EP without superimposing the display of the sudden stimulus 72 as a background.

[0089] In the above embodiment, the determination unit 11d may make a determination based on a learning model obtained by machine learning.

[0090] <References> [1] Shimazu, Naru; Okada, Kensuke: "Basic Methods and Theoretical Development of Signal Detection Theory," Behavioral Measurement, Vol. 49, No. 1 (No. 96), 63-82, 2022. [Explanation of symbols]

[0091] 10...Main unit, 11...Control device, 11a...Electroencephalogram generation unit, 11b...Stimulus generation unit, 11c...Response reception unit, 11d...Determination unit, 12...Storage device, 20...Electroencephalogram measurement device, 21...Simplified electroencephalograph, 30...Output device, 31...Stimulus generation device, 31a...Display screen, 40...Input device, 41...Input component, 41a...Space key, 41b...Enter key, 71...Steady stimulus, 72...Idiopathic stimulus, 72a...First visual stimulus, 72b...Second visual stimulus, 72r...Idiopathic region, 73...Discrimination task stimulus, 73r...Discrimination stimulus region, 73x...Normal stimulus, 73y...Specific stimulus, 100...Cognitive function confirmation device, CK...Discrimination task, EP...Point of fixation, FS...Predetermined stimulus, H2...Specific frequency, ST...Test stimulus, US...Subject

Claims

1. An electroencephalogram (EEG) measuring device for measuring the brainwaves of the subject, A stimulus generating device that provides the subject with a specific frequency of spontaneous stimulation and changes the spontaneous stimulation at predetermined timings, An input device that receives an active response from the subject when the aforementioned spontaneous stimulus changes, A control device having a determination unit that determines the state of attention from the amplitude of steady-state visually evoked potentials obtained by frequency analysis of the electroencephalogram corresponding to the specified frequency, Equipped with, A device for checking cognitive function.

2. The stimulus generating device changes one of the following during the change: color, size, shape, position, and frequency of the spontaneous stimulus. The cognitive function confirmation device according to claim 1.

3. If the stimulus generating device does not detect a response from the input device and the steady-state visual evoked potential does not appear in the electroencephalogram, it will generate the spontaneous stimulus again. The input device then receives an active response from the subject via the input device. The cognitive function confirmation device according to claim 1.

4. The stimulus generating device changes the conditions for the change of the spontaneous stimulus when generating the spontaneous stimulus again. The cognitive function confirmation device according to claim 3.

5. The stimulus generating device outputs the spontaneous stimulus corresponding to the level at which it can distinguish the stimulus change of the subject. The cognitive function confirmation device according to claim 1.

6. The stimulus generating device displays two or more discrimination task stimuli, including the appearance of a specific stimulus to which the subject should respond, as two or more discrimination tasks. It then superimposes two or more discrimination task stimuli onto these discrimination task stimuli, each displaying a different specific frequency, and displays the special stimuli from the start of the stimulation test. At predetermined timings, it changes the special stimuli in one of the special stimuli regions. The input device receives an active response from the subject when the specific stimulus appears. The cognitive function confirmation device according to claim 1.

7. The stimulus generating device, after changing the spontaneous stimulus, changes the spontaneous stimulus again at a predetermined timing, returning the spontaneous stimulus to the state it was in at the start of the stimulus test. The cognitive function confirmation device according to claim 6.

8. The determination unit calculates the subject's discrimination ability from the response results to the specific stimulus in the discrimination task, and changes the difficulty level of the discrimination task according to the discrimination ability. The cognitive function confirmation device according to claim 7.

9. The determination unit changes the difficulty level of the discrimination task by changing at least one of the spontaneous stimulus and the discrimination task stimulus according to the discrimination ability. The cognitive function confirmation device according to claim 8.

10. The determination unit, in changing the difficulty level, changes any combination of the color, size, and shape of the spontaneous stimulus and the color, size, font, and type of the discrimination task stimulus. The cognitive function confirmation device according to claim 9.

11. The stimulation generator changes the spontaneous stimuli of a specific frequency at predetermined timings, The input device receives the subject's active response when the aforementioned spontaneous stimulus changes, The determination unit determines the attentional state from the amplitude of steady-state visual evoked potentials obtained by frequency analysis of the subject's brainwaves corresponding to the specific frequency, To have the control device execute Cognitive function assessment program.

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