WO2021008086A1

WO2021008086A1 - Visual acuity detection method based on motion visual evoked potential

Info

Publication number: WO2021008086A1
Application number: PCT/CN2019/128990
Authority: WO
Inventors: 徐光华; 郑小伟; 杜成航; 王云云; 梁仍昊; 贾亚光
Original assignee: 西安交通大学
Priority date: 2019-07-17
Filing date: 2019-12-27
Publication date: 2021-01-21
Also published as: CN110251064A

Abstract

A visual acuity detection method based on a motion visual evoked potential, comprising: first designing a concentric ring stimulation paradigm, then designing a stimulation paradigm spatial frequency gradient, then performing building of a brain-computer interface platform and presentation of the stimulation paradigm, performing visual acuity threshold determination on a electroencephalogram result, finally, performing feedback of a visual acuity detection result. According to the method, a concentric ring steady-state motion visual evoked potential (SSMVEP) paradigm for visual acuity examination is designed, and corresponding threshold determining standards are proposed, so that an electroencephalogram objective visual acuity value is obtained. An objective and quantitative measurement method is provided for visual acuity detection in ophthalmologic examination.

Description

Visual acuity detection method based on motor visual evoked potential

Technical field

The invention relates to the technical field of brain-computer interface and optometry inspection, in particular to a visual acuity detection method based on motion visual evoked potential.

Background technique

According to data from the World Health Organization, 253 million people worldwide suffer from visual impairment, and due to population growth and aging, this number may triple. Visual acuity testing is one of the most basic research tasks in ophthalmology. Common visual acuity tests rely on subjects’ subjective feelings and cooperation, such as letter visual acuity scale and rolling E visual acuity scale. For people with communication problems, such as pre-lingual children or toddlers, this type of method is not suitable for visual acuity assessment; adults may also be affected by environmental factors and cause misjudgments; false reports by the examinee cannot be ruled out in forensic examinations And deception.

Brain-computer interface (BCI) and electroencephalogram (EEG), especially scalp electroencephalogram, are new methods for more objective and direct assessment of visual function. In recent years, many scholars have used scanning visual evoked potential (sVEP), steady-state visual evoked potential (SSVEP), pattern visual evoked potential (PVEP) and other methods to complete the detection of visual acuity and contrast sensitivity. However, the current research mainly focuses on determining the threshold of visual function and observing the EEG response by changing some relevant stimulus parameters. These studies did not combine objective EEG tests with subjective psychophysical tests, and there was no exact correlation between stimulation parameters and visual function status. In addition, the traditional checkerboard and grating SSVEP or PVEP paradigm is more likely to cause visual fatigue, which leads to reduced signal quality.

Summary of the invention

In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a visual acuity detection method based on motion visual evoked potential, by designing a concentric ring steady-state motion visual evoked potential (SSMVEP) for visual acuity inspection Paradigm, and put forward the corresponding threshold criteria to obtain the EEG objective visual acuity value, which provides an objective and quantitative measurement method for the detection of visual acuity in eye examinations.

In order to achieve the above objectives, the technical solutions adopted by the present invention are:

The visual acuity detection method based on motion visual evoked potential includes the following steps:

1) Concentric circle stimulation paradigm: Using the SSMVEP method in the brain-computer interface, the periodic contraction and expansion movement of the paradigm pattern texture is drawn by MATLAB using Psychophysics Toolbox programming, which can stably induce SSMVEP; the movement stimulus target appears as light and dark concentric circles In the ring, the distance between the bright area and the dark area is equal; during the stimulus presentation process, the overall brightness and overall size of the paradigm remain unchanged; the phase of the ring is modulated in a sinusoidal manner, forming periodic reciprocating oscillations in both directions of contraction and expansion, and contraction The flip frequency of the expansion movement is defined as the stimulation frequency, and the movement direction changes twice in one cycle;

2) Spatial frequency sweep gradient of stimulus paradigm: Corresponding to the standard logarithmic visual acuity table, a series of concentric circle paradigms are designed as the visual standard for SSMVEP visual acuity detection; corresponding to 1.1 logMAR and the standard logarithmic visual acuity table -0.1 logMAR optotype, by adjusting the spatial frequency of the paradigm, the black-and-white interval of the concentric circles is equal to the human eye angle of view with the black-and-white interval of the letter "E" in the visual acuity table; the spatial frequency is from 1.1 logMAR to each The second 0.1 logMAR decreases linearly to -0.1 logMAR, and the total scan time is 12 seconds;

3) Construction of brain-computer interface platform: Before the experiment, the reference electrode was placed on the subject’s left earlobe, the ground electrode was placed on the subject’s forehead, and the measurement electrode was placed on the occipital area of the head; the electrode was connected to the EEG acquisition module, and enlarged , After filtering, digital-to-analog conversion, output EEG signals to the computer for further data processing;

4) Presentation of the stimulus paradigm: The computer expands the display to present the stimulus paradigm on the high refresh rate display; during the experiment, the user needs to follow the screen prompts to watch the stimulus paradigm; during the experiment, the subject needs to sit in the laboratory every time Perform a monocular test once; collect the EEG signals generated by the user's gaze paradigm through EEG acquisition equipment, and after amplifying, filtering and A/D conversion, the processed EEG signals are input to the computer and performed by canonical correlation analysis (CCA) Feature extraction

5) Visual acuity threshold judgment: Analyze the 12-second SSMVEP signal through a rectangular window with a window length of 2 seconds and a slip duration of 1 second, and obtain the typical correlation coefficient over time curve and the corresponding signal-to-noise ratio SNR, and then Paradigm response value determination; use SNR value to determine the response value of the CCA spectrum. When the SNR is greater than 2.0, the visual evoked potential is significant, and the response value is 1; when the signal-to-noise ratio is not higher than 2.0, the visual evoked potential is not significant, and the response Value is 0; SSMVEP visual acuity value is defined as the spatial frequency value logMAR corresponding to the stimulation paradigm when the final EEG response value is 1;

6) Visual acuity detection result feedback: After completing all stimulation paradigms, the user's objective brain television acuity value is output on the screen.

In the step 5), the rectangular window takes the spatial frequency corresponding to the most central time of the window length, and obtains the corresponding CCA value and SNR value, and then determines according to the threshold determination algorithm.

In the step 5), the experiment obtained the trend of CCA value and SNR value with the logMAR value 1.0-0.0 of the paradigm space frequency, where the CCA value and SNR value both decrease with the logMAR value; the SNR value is used to respond to the CCA spectrum It is judged that the signal-to-noise ratio is defined as the ratio of the square value of the correlation coefficient of the target stimulation frequency 8Hz to the average value of the square value of the correlation coefficient of 10 adjacent points on the CCA spectrum; when the SNR is greater than 2.0, it means that the visual evoked potential is significant, and the response value is 1 ; When the signal-to-noise ratio is not higher than 2.0, the visual evoked potential is not significant, and the response value is 0; the SSMVEP visual acuity value is defined as the stimulus paradigm spatial frequency value logMAR corresponding to the final EEG response value of 1.

The present invention also provides a visual acuity detection system based on motion visual evoked potential, including:

The brain-computer interface platform includes a reference electrode, a ground electrode and a measurement electrode. Each electrode is connected to the EEG acquisition module, and the EEG signal is output to the computer after amplification, filtering, and digital-to-analog conversion;

The computer performs further data processing on the EEG signal, including: based on the concentric circle stimulation paradigm, the stimulation paradigm spatial frequency sweep gradient, the stimulation paradigm presentation, and the visual acuity threshold (the threshold can be preset) is determined ；

The display is connected to the computer to present the aforementioned paradigm; and according to needs, after all stimulation paradigms are completed, the user’s objective brain television acuity value is output through the screen, which can be the same display as the display that presents the paradigm, It can also be another separately connected display.

The beneficial effects of the present invention are:

The invention proposes a visual acuity detection method based on motor visual evoked potentials, which is simple and quick to operate, and solves the problem that the traditional subjective visual acuity test is not objective enough and is not suitable for infants, pre-lingual children, patients with communication difficulties and forensic identification. The following advantages:

(1) The design of the present invention is based on the concentric ring SSMVEP paradigm, the pattern keeps the brightness constant throughout the movement process, reduces the user's visual fatigue, and improves the interaction performance of the brain-computer interface.

(2) The present invention proposes a visual acuity threshold determination method. The analysis method has high accuracy, good robustness, objective, quantitative test results, and rapid sensitivity.

Description of the drawings

Figure 1 shows the contraction-expansion movement process of the concentric ring paradigm of the present invention.

Figure 2 is a schematic diagram of the spatial frequency sweep gradient of the stimulation paradigm.

Fig. 3 is a schematic diagram of the variation of the typical correlation coefficient value and the signal-to-noise ratio with the gradient of the normal scan.

Figure 4 shows the CCA spectrum of a subject (subjective visual acuity 0.4 logMAR).

Figure 5 is a scatter diagram of the comparison between the objective brain television acuity detection value and the subjective visual acuity value.

Detailed ways

The present invention will be described in detail below with reference to the drawings.

1) Concentric ring stimulation paradigm: Using the most practical SSMVEP method in the brain-computer interface, the periodic contraction and expansion movement of the paradigm pattern texture is drawn through MATLAB using Psychophysics Toolbox programming, which can stably stimulate SSMVEP; refer to Figure 1, Movement The stimulus target is expressed as a light and dark concentric ring with the same distance between the bright area and the dark area; during the stimulus presentation process, the overall brightness and overall size of the paradigm remain unchanged; the phase of the ring undergoes a sinusoidal contraction-expansion movement, where:

Where:

f _c ——Motion frequency, that is, the reciprocal of the time required for concentric rings to contract-expand once;

φ(t) is the phase value function of checkerboard contraction-expansion;

By changing the phase function φ(t) from 0 to π, the concentric rings contract, and when the phase function φ(t) changes from π to 0, the concentric rings expand. Referring to Figure 1, in one cycle, two movement directions occur The frequency of the movement direction change is the movement reversal frequency f, which is twice the movement frequency f _c ; since SSMVEP mainly comes from the brain activity stimulated by the change of direction, the energy is mainly concentrated on the movement reversal frequency. The frequency is used as the fundamental frequency of visual stimulation;

2) Spatial frequency sweep gradient of stimulus paradigm: Corresponding to the standard logarithmic visual acuity scale, a series of concentric circle paradigms are designed to serve as the visual standard for SSMVEP visual acuity detection; the paradigm is overall human-oriented by adjusting the screen distance and paradigm size The eye angle of view is 2°; corresponding to 1.1 logMAR and -0.1 logMAR optotypes of the standard logarithmic visual acuity table, by adjusting the spatial frequency of the paradigm, the black-and-white interval of the concentric circles is relative to the human eye’s angle of view and the letters in the visual acuity table. The black-and-white interval of "E" is equal to the viewing angle of the human eye; referring to Figure 2, the spatial frequency decreases linearly from 1.1 logMAR to -0.1 logMAR per second, and the total scanning time is 12 seconds;

3) Brain-computer interface platform construction: Before the experiment, the electrodes were arranged according to the 10/20 system method. The reference electrode was placed on the subject's left earlobe A1, the ground electrode was placed on the subject's forehead Fpz, and six measuring electrodes were placed on the head Occipital area (PO3, PO4, POz, O1, O2, Oz). Inject conductive paste into each measuring electrode to ensure good contact between the electrode and the scalp; the electrode is connected to the EEG acquisition module, and the EEG signal is output to the computer after amplification, filtering, and digital-to-analog conversion for further data processing;

4) Presentation of stimulus paradigm: The computer expands the display to present the stimulus paradigm on the high refresh rate display; during the experiment, the user needs to follow the screen prompts to watch the stimulus paradigm; during the experiment, the subject needs to sit quietly and not be disturbed In the laboratory, the monocular test is performed every time; the EEG signal generated by the user’s gaze paradigm is collected through EEG acquisition equipment, and after amplification, filtering and A/D conversion, the processed EEG signal is input into the computer using typical Correlation analysis (CCA) for feature extraction;

5) Visual acuity threshold determination: The 12-second SSMVEP signal is truncated and analyzed by CCA through a rectangular window (window length of 2 seconds, sliding duration of 1 second), refer to Figure 3, take the stimulus paradigm space in the middle of the window length of 2 seconds The frequency is the abscissa, and the curve of the typical correlation coefficient with the spatial frequency and the corresponding SNR are obtained, so as to determine the paradigm response value; the experiment obtained the CCA value and the SNR value with the paradigm spatial frequency logMAR value (1.0-0.0) Change trend, in which the CCA value and SNR value decrease with the logMAR value; the SNR value is used to determine the response value of the CCA spectrum, and the signal-to-noise ratio is defined as the square value of the target stimulation frequency 8Hz correlation coefficient and 10 adjacent ones on the CCA spectrum The ratio of the average value of the square of the point correlation coefficient; when the SNR is greater than 2.0, the visual evoked potential is significant, and the response value is 1; when the signal-to-noise ratio is not higher than 2.0, the visual evoked potential is not significant, and the response value is 0; SSMVEP visual sensitivity The degree value is defined as the spatial frequency value logMAR of the stimulation paradigm when the final EEG response value is 1;

6) Visual acuity test result feedback: After completing all stimulation paradigms, the user's objective brain television acuity value is output on the screen.

The present invention will be described below in conjunction with embodiments.

The above experiment was carried out on a subject (with a subjective visual acuity of 0.4 logMAR). The electrodes were placed on the subject and the brain-computer interface platform was built according to the above step 3), and the paradigm presentation and EEG signals were performed according to the above step 4) Acquisition; according to the above step 5) for EEG signal analysis and objective brain TV acuity threshold determination, refer to Figure 4, get the paradigm response value: 1,1,1,1,1,1,0,0,0, 0, get the SSMVEP visual acuity test result: 0.4 logMAR.

The EEG data of 11 users in the sample was analyzed and judged, and the objective test results were compared with the subjective test results. Refer to Figure 5, draw a scatter plot and calculate the linear correlation. It can be proved that the objective visual acuity test results are significantly related to the subjective test results (P<0.001).

The present invention can objectively and quantitatively detect the visual acuity of users, establishes a good correlation with subjective psychophysical examination, and realizes the visual acuity of special users such as infants, pre-linguistic children, and forensic examinees. Objective testing methods. The visual acuity detection method based on motion visual evoked potential is convenient, fast, objective and quantitative, and has a good practical prospect.

Claims

The visual acuity detection method based on motion visual evoked potential is characterized in that it comprises the following steps:

1) Concentric circle stimulation paradigm: Using the SSMVEP method in the brain-computer interface, the periodic contraction and expansion movement of the paradigm pattern texture is drawn by MATLAB using Psychophysics Toolbox programming, which can stably induce SSMVEP; the movement stimulus target appears as light and dark concentric circles In the ring, the distance between the bright area and the dark area is equal; during the stimulus presentation process, the overall brightness and overall size of the paradigm remain unchanged; the phase of the ring is modulated in a sinusoidal manner, forming periodic reciprocating oscillations in both directions of contraction and expansion, and contraction The flip frequency of the expansion movement is defined as the stimulation frequency, and the movement direction changes twice in one cycle;

2) Spatial frequency sweep gradient of stimulus paradigm: Corresponding to the standard logarithmic visual acuity table, a series of concentric circle paradigms are designed as the visual standard of SSMVEP visual acuity detection; corresponding to 1.1logMAR and the standard logarithmic visual acuity table -0.1logMAR optotype, by adjusting the spatial frequency of the paradigm, the black-and-white interval of the concentric circles is equal to the human eye's viewing angle with the black-and-white interval of the letter'E' in the visual acuity table; the spatial frequency is from 1.1logMAR per unit 0.1logMAR per second decreases linearly to -0.1logMAR, and the total scanning time is 12 seconds;

3) Construction of brain-computer interface platform: Before the experiment, the reference electrode was placed on the subject’s left earlobe, the ground electrode was placed on the subject’s forehead, and the measurement electrode was placed on the occipital area of the head; the electrode was connected to the EEG acquisition module, and enlarged , After filtering, digital-to-analog conversion, output EEG signals to the computer for further data processing;

4) Presentation of the stimulus paradigm: The computer expands the display to present the stimulus paradigm on the high refresh rate display; during the experiment, the user needs to follow the screen prompts to watch the stimulus paradigm; during the experiment, the subject needs to sit in the laboratory every time Perform a monocular test once; collect the EEG signals generated by the user's gaze paradigm through EEG acquisition equipment, and after amplifying, filtering and A/D conversion, the processed EEG signals are input to the computer and performed by canonical correlation analysis (CCA) Feature extraction

5) Visual acuity threshold determination: Analyze the 12-second SSMVEP signal through a rectangular window with a window length of 2 seconds and a slip duration of 1 second, and obtain the typical correlation coefficient versus time curve and the corresponding signal-to-noise ratio (SNR), In order to determine the response value of the paradigm; use the SNR value to determine the response value of the CCA spectrum. When the SNR is greater than 2.0, the visual evoked potential is significant, and the response value is 1; when the signal-to-noise ratio is not higher than 2.0, the visual evoked potential is not significant , The response value is 0; SSMVEP visual acuity value is defined as the corresponding stimulation paradigm spatial frequency value logMAR when the final EEG response value is 1;

6) Visual acuity test result feedback: After completing all stimulation paradigms, the user's objective brain television acuity value is output on the screen.
The visual acuity detection method based on motion visual evoked potentials according to claim 1, characterized in that: in the step 5), the rectangular window takes the spatial frequency corresponding to the most central time of the window length, and obtains its corresponding The CCA value and SNR value are determined according to the threshold determination algorithm.
The visual acuity detection method based on motion visual evoked potential according to claim 1, characterized in that: in said step 5), the CCA value and SNR value are experimentally obtained with the paradigm spatial frequency logMAR value 1.0-0.0. The CCA value and the SNR value both decrease with the logMAR value; the SNR value is used to determine the response value of the CCA spectrum, and the signal-to-noise ratio is defined as the correlation coefficient between the square value of the target stimulation frequency 8Hz correlation coefficient and the 10 adjacent points on the CCA spectrum The ratio of the average of the squares; when the SNR is greater than 2.0, the visual evoked potential is significant, and the response value is 1; when the signal-to-noise ratio is not higher than 2.0, the visual evoked potential is not significant, and the response value is 0; SSMVEP visual acuity value definition It is the corresponding stimulus paradigm spatial frequency value logMAR when the final EEG response value is 1.