JP2015226723A - Brain wave detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device that does not cause a user and/or persons around to feel "troublesomeness" or "discomfort" for a change in light in brain wave detection that can be used for a BMI device utilizing steady state visually evoked potential (SSVEP).SOLUTION: A brain wave detecting device includes a target light emitter for emitting target light disposed at a position that can be visually recognized by a user, brain wave detection means for detecting a brain wave of the user, and steady state visually evoked potential detection means for detecting the presence of steady state visually evoked potential generated in the brain wave when the user visually recognizes the target light emitted by the target light emitter. The target light is the light whose color characteristics change repetitively in a change width that is not discriminated by a human.

Description

  The present invention relates to an electroencephalogram detection apparatus, and more particularly, to an electroencephalogram detection apparatus that detects a steady state visual evoked potential (SSVEP). The electroencephalogram detection apparatus of the present invention can be used for electroencephalogram detection in a brain machine interface (BMI) apparatus.

  In a human cranial nerve network, an electroencephalogram (EEG) in a different form (change in frequency and intensity) is generated in accordance with a stimulus such as vision and hearing. Therefore, conventionally, research and development of a BMI that measures the brain waves generated by applying various visual and auditory stimuli to humans and controls the operation of any machine / device using the measured brain waves as input information. Is underway. According to such a control system using BMI, since the operation control of the machine / device can be achieved regardless of the operation by the human body movement, the driver operating the vehicle operates the operation of the machine / device. It is possible to control the operation of machines and devices even in situations where physical movement is restricted.

  As an example of the technology related to the BMI device as described above, for example, in Japanese Patent Application Laid-Open No. H10-228688, a “event-related potential” generated in a user's brain wave when a specific stimulus is given to the user is detected. A device for adjusting an electroencephalogram identification method for performing operation control of the device is disclosed. In this publication, the request identification method based on the electroencephalogram signal is adjusted based on the feature amount extracted from the waveform of the event-related potential accumulated for a certain period from the time when the stimulus changes. Thus, it has been proposed to reduce the burden of calibration for accurately measuring the electroencephalogram. One example of the stimulus given to the user is a change in the hue of the video.

  Further, in Patent Document 2 by a part of the applicant of the present application, in the brain wave of a human who watches the light blinking at a certain frequency, the stationary visual stimulus induction that appears in synchronism with the frequency of the blinking light. One aspect of improving a BMI device utilizing potential (SSVEP) is disclosed. In the configuration described in the publication, first, in order to reduce the glare and flickering feeling of blinking light received by an observer, the blinking frequency of the light to be watched is the critical fusion frequency (flashing but continuously lit. (Frequency: CFF: Critical Fusion Frequency, usually approximately 34 Hz) or higher. However, the signal amplitude of SSVEP by flashing light of CFF or higher is very weak, and it is difficult to detect a signal with a high S / N ratio as it is. Therefore, paying attention to the fact that the frequency of the SSVEP signal matches the frequency of the flashing light, the cross spectrum value (cross-correlation function value) between the driving signal of the flashing light source and the electroencephalogram signal is calculated, and the cross spectrum value is high ( That is, a configuration is proposed in which it is determined that the observer is gazing at the light source having the frequency of the flashing light (when the driving signal of the flashing light source and the electroencephalogram signal are synchronized).

  Further, in Patent Document 3 by the applicant of the present application, as one form for practical application of the BMI device, the BMI device using the SSVEP is operated arbitrarily by the driver while driving a vehicle such as an automobile, for example, When applied as an input means for operation of wipers, air conditioners, headlamps, audio, etc., the brightness of the light emitted by the flashing light source can be adjusted by the ambient brightness, body temperature, etc. in order to improve operability BMI control devices have been proposed. And in patent document 4 by the present applicant, in the BMI device using SSVEP, the stochastic resonance phenomenon caused by causing the user to visually recognize the background light blinking at a random frequency simultaneously with the blinking target light, A configuration has been proposed in which SSVEP is amplified to improve the detection accuracy or S / N ratio of the electroencephalogram and shorten the detection time.

International Patent Publication 2008/059878 JP2011-15788 JP2012-128512 JP 2014-71825 A

Aquadam David Lewis, Journal of Optical Society of America, 32, 247-274, 1942 (MacAdam, David Lewis, “Visual sensitivities to color differences in daylight”, Journal of Optical Society of America, Vol. 32, No.5, pp.247-274, 1942.)

  As described in Patent Documents 2-4 above, when a user gazes at a light source that blinks at a certain blinking frequency, it synchronizes with the blinking frequency that appears in the electroencephalogram from the visual cortex of the user's brain. In the BMI device that detects whether or not the SSVEP has been detected and determines whether or not the user is gazing at the blinking light source, the intensity of the SSVEP changes depending on the blinking frequency of the blinking light source. In general, when the blinking frequency is lower than the critical fusion frequency or about 40 Hz or less, the intensity of SSVEP is relatively strong and easy to detect. However, when the blinking frequency of the blinking light source is lower than the critical fusion frequency, i.e., when the observer can recognize the blinking of the light source, as already mentioned, the observer will be aware of the blinking light source, i.e., the flickering of light. You may feel annoyance. In addition, when the blinking of a light source is in a state that can be recognized by a person, it is easier for people around the light source to be careful of the light source (because there is only light that can be recognized blinking in the peripheral vision, pay attention to the light. The flashing of the light source may be felt uncomfortable not only by the user of the device but also by the people around it. However, if the blinking frequency of the light source is made higher than the critical fusion frequency, as already mentioned, the intensity of SSVEP becomes weak as it is, and the detection accuracy can be greatly reduced.

  By the way, the blinking light used in the above SSVEP detection is due to increase / decrease of light intensity or repetition of turning on / off the light source. According to the research and development by the inventors of the present invention, Also when the color characteristics of the light source (hue, saturation) are repeatedly changed (rather than blinking), or when the light color characteristics are switched repeatedly so that multiple different color characteristics of light occur alternately It was found that significant intensity SSVEP was generated. The SSVEP having such a significant intensity has a color characteristic switching frequency (hereinafter referred to as “switching frequency”) of CFF or less, and a color characteristic change width (hue and / or saturation change). This occurs even when the width is in a range indistinguishable by humans and can be detected. For light in which such color characteristics are switched with a change range that cannot be distinguished by a person, there is no problem that the person feels “inconvenienced” by the change in light. The range of change in the color characteristics that cannot be distinguished by humans is known as “MacAdam ellipse” on the chromaticity diagram (Non-patent Document 1). In the present invention, the above knowledge is used in the application of stimulation light to the user and the detection of SSVEP.

  Thus, one object of the present invention is to provide an electroencephalogram detection that can be used for a BMI device using the SSVEP as described above, with a variation range in which the color characteristic is indistinguishable by humans as light given as a stimulus to the user. Repetitively periodically changing or switching light is employed so that the user and / or the surrounding people do not “inconvenience” or “discomfort” in the light change.

  According to the present invention, the above-described problem is an electroencephalogram detection device that detects a steady visual stimulus evoked potential, a target light emitter that emits target light disposed at a position that can be visually recognized by the user, and a user EEG detection means for detecting a brain wave of the subject, and stationary visual stimulus induction for detecting the presence of a steady visual stimulus evoked potential (SSVEP) generated when the user visually recognizes the target light emitted from the target light emitter in the brain wave This is achieved by an apparatus including a potential detecting means, wherein the target light is light whose color characteristics change periodically and periodically with a change width indistinguishable by humans.

  In the above-described electroencephalogram detection apparatus according to the present invention, basically, the user watches the target light emitter that emits the target light in the same manner as the electroencephalogram detection process of the BMI apparatus using the conventional SSVEP. Thus, SSVEP generated in the visual cortex of the user is detected. In that case, conventionally, the target light used to make the user gaze at the detection of SSVEP was flashing light, that is, light whose light intensity repeatedly increases and decreases, but in the present invention, as target light, In this case, light whose color characteristics are repeatedly changed periodically with a change width indistinguishable by a person is used. Here, “light whose color characteristics change repeatedly within a range of change indistinguishable by humans” typically means that the color characteristics are on the chromaticity diagram at an arbitrarily set frequency. It may be light that changes repeatedly within the range of the McAdam ellipse. More specifically, for example, the color characteristic of the light emitted from the target light emitter is based on the first color characteristic state corresponding to a certain point on the chromaticity diagram and the first color characteristic state. It is alternately switched to the second color characteristic state in which hue and / or saturation is changed within the range of the MacAdam ellipse on the chromaticity diagram. In this case, according to experiments, even when the color characteristic switching frequency is 40 Hz or less or CCF or less, it is possible to detect SSVEP having a significant intensity, and the change in the color characteristic is indistinguishable from the color characteristic. Due to the range, it has been found that a change in color characteristics is not substantially recognized by a user who is gazing at the target light. Therefore, in the detection of SSVEP, it is possible to achieve a state in which “no bother” or “discomfort” is not given to the change in the light that becomes the stimulus.

  As described above, the electroencephalogram detection apparatus of the present invention may be used for electroencephalogram detection in a BMI apparatus that performs operation control of an arbitrary machine or apparatus. In that case, specifically, it is determined whether or not the user gazes at (or is) the target light by detecting the presence or absence of SSVEP. Based on the determination result, any machine / device is determined. Operation control such as operation start or stop is executed. In the configuration in which the electroencephalogram detection device is used for electroencephalogram detection in the BMI device, for example, as a target light emitter, a plurality of target lights whose color characteristics are switched or changed at different frequencies are used. Target light emitters may be provided. Then, since the SSVEP induced by each target light is synchronized with the switching of the respective color characteristics, there is an SSVEP having substantially the same frequency as the switching frequency of the color characteristics of each target light in the electroencephalogram. By detecting whether or not, it is possible to determine whether or not the user is gazing at any of the target light emitters. When it is determined that the target light emitter is being watched, the operation control of the control object such as a machine / device associated with the target light emitter is executed.

  In the above-described electroencephalogram detection apparatus of the present invention, the target light emitter is an arbitrary light source having an arbitrary shape, for example, a quadrangle, a circle, or an elephant that schematically represents a mechanical device of a controlled object to be associated. It may be. The color characteristic of the target light may be appropriately selected by the user (when the user selects a certain color characteristic, the color characteristic is changed or switched within a change range that cannot be distinguished from the selected color characteristic. It will be.) In the embodiment, a light source such as an LED, a CRT, or a strobe can be used as the light emitter. Further, the electroencephalogram detection means may be any device for detecting an electroencephalogram normally used in this field, and typically, a plurality of electroencephalogram detection means are fixed to the head surface around the visual cortex of the user. You may comprise an electrode and the signal processing apparatus which measures the electric potential of each electrode sequentially, and processes the signal from an electrode in arbitrary aspects.

  Thus, according to the above configuration, in the detection of SSVEP, as the target light to be watched by the user as a stimulus for inducing SSVEP, the light whose color characteristics are repeatedly changed with a change width indistinguishable by a person is adopted. By doing so, the problem in the detection of the conventional SSVEP that the user feels “inconvenience” or “discomfort” due to the change of the light as the stimulus can be solved. In particular, in the case of the present invention, the switching frequency of the color characteristics can be set to CCF or less, specifically, 10 Hz to 40 Hz, so that the user does not feel “comfort” or “discomfort”. This is advantageous in that the band that can be used as the switching frequency can be expanded to a lower range, and the degree of freedom in selecting the switching frequency is increased. Furthermore, since the strength of SSVEP generally increases as the frequency decreases, the SSVEP S / N ratio and detection accuracy are expected to be improved by using a lower frequency range. The

  Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention.

FIG. 1A is a diagram for explaining the configuration of a BMI apparatus in which the electroencephalogram detection apparatus of the present invention is incorporated. FIG. 1B shows the arrangement of electrodes attached to the subject's head. FIG. 2 is a diagram for explaining the generation of SSVEP used in the electroencephalogram detection apparatus of the present invention. (A) is a case where light blinking at a frequency higher than CFF is used as the stimulation light, and (B) is a case where light blinking at a frequency lower than CFF is used as the stimulation light. (C) is a case in which light whose color characteristics change periodically is used as stimulation light according to the present invention. FIG. 3 is a chromaticity diagram in human vision for explaining “MacAdam ellipse” (Md in the figure) described in Non-Patent Document 1. In the figure, the ellipses in the areas labeled 4 (A) and 4 (B) are shown in FIGS. 4 (A) and 4 (B). The example of the switching range of the color characteristic of the stimulating light utilized for generation | occurrence | production of SSVEP is shown. 4 (A) and 4 (B) are diagrams showing in more detail on the chromaticity diagram changes in the color characteristics of the stimulating light used for the generation of SSVEP in the electroencephalogram detection apparatus of the present invention. It is. (A) is the case where the point Sd on the chromaticity diagram which is the reference when changing the color characteristics is the green point (x, y) = (0.294, 0.596), and (B) is the color This is a case where the point Sd on the chromaticity diagram that serves as a reference for changing the characteristics is the blue point (x, y) = (0.147, 0.063). FIG. 5 shows an example of the power spectrum of the brain wave of the subject who gazes at the target light whose color characteristics are periodically switched in the electroencephalogram detection apparatus of the present invention. (A) shows the chromaticity of the target light between the point of coordinates (x, y) = (0.294, 0.596) and the point of coordinates (x, y) = (0.323, 0.573) on the chromaticity diagram. In the case of switching at a switching frequency of 26.6 Hz (hue direction), (B) shows the chromaticity of the target light as coordinates (x, y) = (0.294,0.596) on the chromaticity diagram. This is a case where switching is performed at a switching frequency of 26.6 Hz between the coordinates (x, y) = (0.285, 0.495) (saturation direction). (C) shows the chromaticity of the target light between the point of coordinates (x, y) = (0.294, 0.596) and the point of coordinates (x, y) = (0.323, 0.573) on the chromaticity diagram. This is an example in which switching is performed at a switching frequency of 13.33 Hz, in which an SSVEP appears at a frequency (overtone) that is an integral multiple of the frequency (basic sound) that matches the switching frequency. FIG. 6A shows an actual measurement example of the change in SSVEP intensity with respect to the switching frequency. “Hue” is a case where the color characteristic of the target light is periodically changed in the hue direction, and “saturation” is a case where the color characteristic of the target light is periodically changed in the saturation direction. FIG. 6B is a graph showing a change in the accuracy rate of the determination as to whether or not the subject gazes at the target light based on the detection of SSVEP with respect to the length of the EEG sampling time in the FFT conversion. . F1, F2, and F3 are ratios at which the subject determined that the subject gazes at the light source by detecting SSVEP when the subject gazes at the light source with the switching frequency set to 13.33 Hz, 20.00 Hz, and 26.67 Hz, respectively. (Accuracy rate).

DESCRIPTION OF SYMBOLS 100 ... Light emitter 110 ... Target light light emitter Br ... Human brain el ... Electrode apparatus

  The present invention will now be described in detail with reference to a few preferred embodiments with reference to the accompanying drawings. In the figure, the same reference numerals indicate the same parts.

Configuration of Device Referring to FIG. 1A, the electroencephalogram detection device of the present invention may be applied to a portion of the BMI device that executes electroencephalogram detection. In the basic configuration, the BMI device measures the brain wave of the light source device 100 carrying the light emitter 110 that emits the target light to be visually recognized by the user and the visual cortex of the user who visually recognizes the light emitter. And processing devices 200 to 500 that perform signal processing and control operation of an arbitrary device based on the detected signal in the electroencephalogram.

  The light emitter 110 is typically configured such that the color characteristics (hue, saturation) of the emitted light are periodically switched between two states, as will be described in detail later. Further, as shown in the figure, a plurality of light emitters 110 may be provided, and in that case, the switching frequency of the color characteristics of the light emitted from each light emitter may be normally set different from each other. In such a configuration, when the user focuses on one target light emitter 110 with both eyes focused, SSVEP is generated in the user's visual cortex in synchronization with the target light switching frequency. It becomes. Then, the target light emitter 110 (each of which has a plurality of light emitters) is associated with a device to be operated and controlled, and the user gazes at one target light emitter 110 and watches the target light emitter 110. When the presence of the SSVEP synchronized with the target light is detected, the operation control for the device associated with the target light is executed. Specifically, as the target light emitter 110, any light emitting device that uses an LED, a CRT, or the like and whose hue and / or saturation of light is periodically variable may be used. As will be described later, when detecting SSVEP due to a periodic change in the color characteristics of light according to the present invention, the switching frequency is CFF (flashing that appears to be continuously lit but flashing. It can be any frequency lower than the frequency (usually approximately 34 Hz). The color of the target light and the duty ratio at the time of switching may be appropriately selected so as not to cause discomfort depending on the ease of use of the user.

  The measurement of the user's electroencephalogram may be performed in a normal manner in this field. The electrode device that senses the potential change of the visual cortex VF may be configured or arranged so as to be able to measure the potential at the measurement point according to the International 10-20 method (for example, the measurement point is shown in FIG. ) According to the international 10-20 method, as shown schematically in C), Cz, Oz, O1, O2, Ground: Forehead, Ref .: Earlobe. Then, the potential signal sensed by the electrode device is input to the processing device, where it is first amplified and A / D converted in the normal manner, and then digitized potential signal, ie, An FFT transformation is performed on the electroencephalogram signal, and a power spectrum of the electroencephalogram signal is generated (200). When the user gazes at the target light of one target light emitter 110, and thus SSVEP is generated, in the generated power spectrum, the switching frequency of the target light that the SSVEP is gazing at is roughly set. Since it is expected to appear as a maximum value in the coincident frequency band, the presence or absence of the maximum value is inspected in the frequency band including the switching frequency of the target light emitter 110 in the power spectrum. When a maximum value is detected at a frequency substantially equal to the switching frequency, SSVEP detection is thereby achieved (300). When there are a plurality of target light emitters 110 as shown in FIG. 1A, a power spectrum in a frequency band including a switching frequency of each of the target lights is calculated, and at each switching frequency. It is checked for the presence of a local maximum. As will be described later, in the inspection for the presence or absence of the maximum value, not only the intensity of the frequency (basic sound) substantially matching the switching frequency but also the intensity of the doubled frequency (harmonic sound) may be referred to. .

  Thus, when the SSVEP corresponding to the target light of the target light emitter 110 is detected, the processing device generates a control command to the device to be controlled associated with the target light (command generation: 400). Then, in order to execute control of the device in accordance with such a control command, an operation of a related drive device or the like is executed (device control: 500). The device to be controlled may be a wiper, an air conditioner, a headlamp, an audio, or the like when the BMI device of the present invention is used as a device operating means by a driver of a vehicle such as an automobile. Further, it may be used for powering on / off an arbitrary device, channel operation or volume adjustment of a television or radio.

As described in the “Background Art” and “Summary of Invention” sections regarding SSVEP due to periodic changes in the color characteristics of light, when a person watches a light source that blinks at a certain blinking frequency, SSVEP (stationary visual stimulus evoked potential) synchronized with the blinking frequency appears in the electroencephalogram from the visual cortex of the brain. Whether or not the user is gazing can be determined. In an attempt to use a BMI device for determining whether or not a person is gazing at a blinking light source by detecting such SSVEP, the blinking light, that is, the light intensity is periodically used as the light to be gazed at by the person. Increasing or decreasing light or light that repeatedly turns on and off was used. In that case, the blinking frequency is the critical fusion frequency, as schematically shown in FIG. 2A, so that the observer watching the light source does not feel “no bother” with the flickering of the light. If higher flashing light is used, generally, the higher the flashing frequency, the more the intensity of SSVEP tends to decrease. Therefore, as it is, only SSVEP having a relatively low intensity is detected. On the other hand, as shown in FIG. 2B, when the blinking frequency is lower than the critical fusion frequency or about 40 Hz or less, the intensity of SSVEP is relatively strong, but the observer who watches the light source blinks the light source. Because it can be recognized, the flickering of the light may feel “annoying”, and for those around it, it is easy to be careful of blinking, and it may feel uncomfortable. As a light source to be watched by a user of the apparatus, a light source having a blinking frequency of not more than a critical fusion frequency or not more than about 40 Hz has been supposed to be not very advantageous in practice.

  By the way, as described in the “Summary of the Invention” section, as described above, the SSVEP generated when a person gazes at the light has a color characteristic as schematically illustrated in FIG. For example, when a person gazes at periodically changing light, for example, it also occurs when two people having different hues and / or chromas are gaze at each other. In this case, the SSVEP is generated even if the change width of the light color characteristic is not recognized by humans.

  More specifically, referring to the chromaticity diagram of FIG. 3, with respect to the ability to discriminate against the difference in color characteristics of human light, an arbitrary point on the chromaticity diagram, for example, Sd, is used as a reference, and from there, a broken line It is known that a change in hue or saturation within the range of the ellipse Md drawn in (1) is not recognized by humans (Non-Patent Document 1—this ellipse is generally referred to as a “MacAdam ellipse”). The range of “McAdam's ellipse” is different for each reference point as shown in the figure). However, as shown in FIG. 2C, light having a color characteristic at a certain point on the chromaticity diagram and light whose hue or saturation is changed within the range of the McAdam's ellipse from the point are alternately displayed. When the observer gazes, the observer himself / herself does not notice the change in the color characteristics, but the SSVEP synchronized with the switching frequency of the color characteristics is detected in the electroencephalogram. For example, as shown in FIG. 4 (A) (enlarged view of the region marked with 4 (A) in FIG. 3), as the light of the reference point Sd on the chromaticity diagram, the green point (x, y) = (0.294,0.596) light and a point Hg (x, y) = (0.323,0.573) changed from the reference point Sd in the hue direction (within a range in which it is confirmed that a change in color characteristics cannot be recognized by humans) ) And the light of the reference point Sd (x, y) = (0.294, 0.596) and the reference point Sd (change in color characteristics to humans). A light source (switching frequency = 26.67 Hz) that is alternately switched with the light at the point Cg (x, y) = (0.285,0.495) changed in the saturation direction (within the range in which it is confirmed that cannot be recognized) In each case, when the subject is gazed, as shown in FIGS. 5 (A) and 5 (B), the frequency substantially matching the switching frequency in the power spectrum of the subject's brain wave In the number, a local maximum is observed. (It should be understood that in the results of FIGS. 5A and 5B, the switching frequency is lower than CFF.) Also, FIG. 4B (in FIG. 3). As shown in Fig. 4 (B), the blue point (x, y) = (0.147,0.063) light and the reference point are used as the light at the reference point Sd on the chromaticity diagram. A light source that alternately switches the light at the point Hg (x, y) = (0.151,0.076) changed in the hue direction (within a range in which it is confirmed that a change in color characteristics cannot be recognized by humans) from Sd, In addition, the light at the reference point Sd (x, y) = (0.294,0.596) and the reference point Sd were changed in the saturation direction (within a range in which it was confirmed that a change in color characteristics could not be recognized by humans). Similarly, when the subject gazes at the light source that alternately switches the light of the point Cg (x, y) = (0.154,0.075), the color characteristics are switched in the power spectrum of the subject's brain wave. Abbreviated to frequency Maximum values were observed at the matching frequencies.

  Therefore, in the present invention, as the target light to be watched by the user or the subject, light that is switched in two different states within a range in which the color characteristic cannot be recognized by a person is employed. In this case, even if the switching frequency is set to be lower than the critical fusion frequency in the case of blinking light, the user or the subject cannot recognize the change in the color characteristics, so it is not possible to feel “annoyance” due to the flickering of light. Therefore, the selection range of the switching frequency can be expanded on the low frequency side.

Example of Device Operation Referring again to FIG. 1A, in the BMI device to which the electroencephalogram detection device of the present invention is applied, a plurality of target lights are emitted on the light source device 100 as shown. Light emitters 110 (F1, F2, F3) are provided, and the switching frequency of the color characteristics of the respective light emitters 110 is set to be different from each other. The color characteristic that is the standard for switching may be arbitrarily selected by the user, and the color characteristic that is the switching destination for the selected standard color characteristic is as follows. The color characteristic is changed from the reference color characteristic to the hue direction or the saturation direction within a range in which it is confirmed that the change in the color characteristic cannot be recognized (see FIG. 4). Further, since the switching frequency may be CFF or less, for example, F1 = 13.33 Hz, F2 = 20.00 Hz, F3 = 26.67 Hz, and the like may be set. Then, the light source device 100 is disposed at a distance of about 50 cm from the user's eyes, and the light emitter 110 emits the target light having the color characteristics set as described above, and in the vicinity of the user's visual cortex. A potential signal representing an electroencephalogram is measured through the attached electrode. As already mentioned, A / D conversion of the potential signal, generation of an electroencephalogram power spectrum by FFT conversion, and a maximum value in the vicinity of the switching frequency of each target light Presence detection is performed. These processes may basically be executed in a normal manner in SSVEP electroencephalogram detection.

  In particular, in the detection of the presence or absence of a local maximum value in the vicinity of the switching frequency (F1, F2, F3) of each target light, basically, the switching frequency of the target light is centered in the electroencephalogram power spectrum. The maximum value or the maximum value in the predetermined range is extracted as a feature value, and it is determined whether or not the feature value exceeds a predetermined threshold value. When the feature value exceeds the threshold value, SSVEP The occurrence of may be determined. As illustrated in FIG. 6A, the intensity of SSVEP changes depending on the magnitude of the switching frequency and the change direction of the color characteristics (hue direction or saturation direction). And / or a different value may be set for each change direction of the color characteristic. Further, in the spectrum of the electroencephalogram generated by SSVEP, a maximum value appears at a frequency (basic sound) that substantially matches the switching frequency of each target light, and depending on conditions as illustrated in FIG. The maximum value appears even at a frequency (overtone) twice the switching frequency. Therefore, a value obtained by adding the power in the overtone to the power in the base tone may be used as the feature amount for determining whether or not SSVEP is generated.

  Further, according to an experiment, the accuracy of detecting the occurrence of SSVEP improves as the EEG sampling time for generating an EEG power spectrum, that is, the EEG measurement time used for executing the FFT transform increases. Referring to FIG. 6 (B), the subject is caused to gaze at the light sources of F1, F2, and F3, and the FFT conversion is executed from the EEG data obtained at that time with different EEG sampling time lengths. The power spectrum is generated, and in the generated power spectrum, whether or not the presence of the SSVEP can be detected is determined by determining whether or not the power value at each switching frequency> the threshold value. However, as shown in the figure, at any frequency, the proportion (correct answer rate) at which the subject determined that the subject was gazing at the light source increased with the extension of the brain wave sampling time. However, the longer the measurement time of the electroencephalogram, the longer the control instruction to the device / device that is controlled by the BMI device. Therefore, in an actual BMI apparatus, the electroencephalogram sampling time may be appropriately set in consideration of the accuracy and the time delay of the control instruction to the device / apparatus.

  As described above, when an SSVEP for a certain target light is detected, the operation control of the associated device / device is executed.

  Thus, according to the present invention described above, in the detection of SSVEP, the stimulus light to be watched by the user is light that periodically changes within a range where the color characteristics cannot be recognized by humans, so Even at the switching frequency, it is possible to achieve a state in which the user does not feel bothered by the flickering of light. According to such a configuration, the frequency band of the detected SSVEP can be expanded to a lower frequency range, and an improvement in the S / N ratio and detection accuracy is expected.

  Although the above description has been made in relation to the embodiment of the present invention, many modifications and changes can be easily made by those skilled in the art, and the present invention is limited to the embodiment exemplified above. It will be apparent that the invention is not limited and applies to various devices without departing from the inventive concept.

Claims (1)

An electroencephalogram detection device for detecting a steady visual stimulus evoked potential,
A target light emitter that emits target light arranged at a position visible by the user;
An electroencephalogram detection means for detecting the electroencephalogram of the user;
A stationary visual stimulus evoked potential detecting means for detecting the presence of the steady visual stimulus evoked potential generated by the user visually recognizing the target light emitted from the target light emitter in the brain wave,
An apparatus in which the target light is light whose color characteristics are repeated periodically with a change width indistinguishable by humans.

Images