Visual stimulation method, system and brain-computer interface system

Abstract

The application relates to the technical field of electroencephalogram interfaces, and provides a visual stimulation method, a visual stimulation system and a brain-computer interface system.The method comprises the following steps: presenting a visual stimulation paradigm, controlling the flickering of a grid area of the visual stimulation paradigm in a sinusoidal sampling modulation mode, the visual stimulation paradigm being composed of a background area and a grid area, the contrast of the background area and the grid area being different, the grid area being composed of a line area and a line intersection area, the contrast and width of the line area and the line intersection area being different; synchronously collecting electroencephalogram signals generated by a user under the current visual stimulation paradigm; during the visual stimulation process, the brightness of the background area is controlled to be displayed according to a preset brightness value, the brightness value of the line area is controlled to change in a range higher than the brightness value of the background area, and the brightness value of the line intersection area is controlled to change in a range higher than the brightness value of the line area, so that the stimulation can induce a certain intensity of SSVEP while reducing visual fatigue.

Description

Technical Field

[0001] This invention relates to the field of brain-computer interface paradigm technology, and in particular to a visual stimulation method, system, and brain-computer interface system. Background Technology

[0002] Brain-computer interface (BCI) is a direct communication method between the brain and external devices (most commonly computers or robotic arms). It can be used to replace, assist, improve, enhance, or repair human cognitive or sensorimotor functions. Commonly used non-invasive EEG-based BCI paradigms include BCI based on visual evoked potentials (VEPs), BCI based on slow cortical potentials (SCPs), BCI based on typical event-related potential (P300) components, and BCI based on sensorimotor rhythms (SMRs) for event-related synchronization and event-related desynchronization / synchronization (ERD / ERS).

[0003] In VEP-BCI, the user's neural response to a target stimulus presented in a visual stimulus is used to analyze the target the user is currently fixating on. Specifically, the analysis of the neural signals responding to the target stimulus is based on unique neural response patterns evoked by the stimulus, such as SSVEPs, and these neural signal patterns have a one-to-one correspondence with only one stimulus at a specific time. By presenting stimuli with different flicker frequencies or phases at different time periods, the BCI algorithm can analyze the neural responses evoked by different stimuli at different times, thus enabling the system to determine the target stimulus being fixated on.

[0004] Generally, VEP-BCI is prone to causing visual fatigue. Visual fatigue directly affects user and system performance. The most commonly used stimulus forms in VEP-BCI systems are flickering stimuli (brightness variations) and pattern-changing stimuli. Flickering visual evoked potentials are obtained through a single flickering stimulus, while pattern-changing stimuli are obtained by changing the stimulus pattern. These forms of continuous flickering or pattern-changing stimulation, especially when there are many flickering stimuli presented in the user interface, are particularly prone to causing visual discomfort and cognitive fatigue. Prolonged viewing of visual stimuli can cause dizziness, nausea, and other physical discomfort, which in turn affects the performance of the visual BCI system. For example, the most commonly used stimulus forms in visual BCI systems are black-and-white flickering stimuli and checkerboard stimuli. Black-and-white flickering stimuli use a black image as the background area, and the brightness of the white image varies within the black-and-white range using a sinusoidal sampling modulation method. Checkerboard stimuli also contain two images: a black image and a checkerboard pattern composed of multiple black and white squares. In this stimulus method, the black background remains unchanged, and the brightness of the white squares is modulated using sinusoidal sampling. The flashing area of ​​the black-and-white flickering stimulus is the entire black background area, and the brightness variation range of the white flickering area in the black-and-white stimulus is 0-255, which is a strong contrast. For the checkerboard stimulus paradigm, compared with the black-and-white stimulus paradigm, the flashing area is reduced by half, but the brightness value of the flashing area is still a strong contrast flickering pattern. It can be seen that in the VEP-BCI system, continuous stimulation flashing can easily induce visual discomfort and cognitive fatigue, and the recognition of target stimuli is easily interfered with by background stimuli and surrounding stimuli, thus affecting the speed and accuracy of target stimulus recognition in the visual BCI system. Therefore, how to improve the visual stimuli in the visual BCI system according to human vision and perception conditions, avoid interference from background stimuli and surrounding stimuli when recognizing target stimuli, and ensure that the stimulation can induce a certain intensity of SSVEP while reducing visual discomfort and cognitive fatigue is of particular importance to the development of brain-computer interface technology. Summary of the Invention

[0005] In view of the above problems, the present invention is proposed to provide a visual stimulation method, system and brain-computer interface system that overcomes or at least partially solves the above problems, so as to ensure that the stimulation can reduce visual discomfort and cognitive fatigue while inducing a certain intensity of SSVEP.

[0006] In one aspect, the present invention provides a visual stimulation method, the method comprising:

[0007] A visual stimulus paradigm is presented on the screen, and a sinusoidal sampling modulation mode is used to control the flashing of the grid area of ​​the visual stimulus paradigm. The visual stimulus paradigm is composed of a background area and a grid area superimposed. The contrast of the background area and the grid area are different. The grid area is composed of a line area and a line intersection area. The contrast and width of the line area and the line intersection area are different.

[0008] When displaying the first frame of data of the visual stimulation paradigm, a synchronization signal is sent to the EEG acquisition device to synchronously acquire the EEG signals generated by the user's cerebral cortex under the current visual stimulation paradigm.

[0009] During visual stimulation, the brightness of the background area is controlled to be displayed according to a preset brightness value, the brightness value of the line area is controlled to vary within a range higher than the corresponding brightness value of the background area, and the brightness value of the line intersection area is controlled to vary within a range higher than the corresponding brightness value of the line area.

[0010] Furthermore, the display area of ​​the visual stimulation paradigm is divided into a central visual field and a peripheral visual field according to a preset division ratio;

[0011] The method further includes:

[0012] During visual stimulation, the width of the line intersection area within the peripheral visual field is controlled to be equal to or less than the width of the line area, and the width of the line intersection area within the central visual field is controlled to be equal to, less than, or greater than the width of the line area.

[0013] Furthermore, the method also includes:

[0014] The width of the line area is controlled to change, and the width of the line intersection area is controlled to change with the width of the line area.

[0015] Furthermore, the method also includes:

[0016] During visual stimulation, the number of lines displayed at the intersections of lines within the central field of vision is increased to improve the spatial resolution of the central field of vision.

[0017] Furthermore, the method also includes:

[0018] After increasing the number of lines displayed, the width and / or brightness of each intersection point in the newly formed line intersection area within the central field of view are increased.

[0019] Furthermore, the line intersection points in the line intersection area are squares, dots, rhombuses, or polygons.

[0020] Furthermore, the stimulus sequence of the sinusoidal sampling modulation mode is generated by the following formula:

[0021]

[0022] The sin() function is used to generate a sine wave sequence, i represents the frame index in the stimulus sequence, f and φ represent the frequency and phase values ​​of the coded flicker using joint frequency and phase modulation, and RefreshRate represents the refresh rate of the stimulus display device.

[0023] In a second aspect, the present invention also provides a visual stimulation system, comprising: an electroencephalogram (EEG) acquisition device and a stimulation display device;

[0024] A stimulus display device for displaying a visual stimulus paradigm according to the visual stimulus method described above;

[0025] The EEG acquisition device is used to simultaneously acquire the EEG signals generated by the user's cerebral cortex under the current visual stimulation paradigm when receiving a synchronization signal sent when the first frame of data of the visual stimulation paradigm is displayed on the stimulation display device.

[0026] Thirdly, the present invention also provides a brain-computer interface system, including the visual stimulation system described above.

[0027] Furthermore, the system also includes: a computer device for amplifying, filtering, and performing analog-to-digital conversion on the EEG signals generated by the user's cerebral cortex under the current visual stimulation paradigm; and for real-time processing of the analog-to-digital converted EEG signals to detect the frequency of the SSVEP signal.

[0028] The visual stimulation method, system, and brain-computer interface system provided in this invention offer a highly comfortable visual stimulation paradigm. This paradigm consists of a superimposed background region and a grid region with different contrasts. The grid region is composed of line regions and line intersection regions, each with different contrasts and widths. A sinusoidal sampling modulation mode is used to control the flickering of the grid region in the visual stimulation paradigm. Furthermore, during visual stimulation, the brightness of the background region is controlled to display according to a preset brightness value, and the brightness values ​​of the line regions and line intersection regions are controlled to vary within a range higher than the corresponding brightness values ​​of the background region and line intersection regions, respectively. This ensures that the stimulation can induce a certain intensity of SSVEP while reducing visual discomfort and cognitive fatigue, making it suitable for long-term use in visual BCI systems.

[0029] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0030] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0031] Figure 1 A flowchart of a visual stimulation method provided in an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the visual stimulation paradigm used in the visual stimulation method provided in the embodiments of the present invention;

[0033] Figure 3 This is a diagram illustrating the display control effect of the grid stimulation paradigm in the visual stimulation method provided in this embodiment of the invention.

[0034] Figure 4a A schematic diagram illustrating the contrast and flicker area of ​​the black-and-white stimulus paradigm;

[0035] Figure 4b A schematic diagram illustrating the contrast and flashing area of ​​the checkerboard stimulus paradigm;

[0036] Figure 4c A schematic diagram illustrating the contrast and stimulation flicker area of ​​the grid stimulation paradigm provided in this embodiment of the invention;

[0037] Figure 5 This is a schematic diagram illustrating the visual flickering effect on the screen using a sinusoidal sampling modulation method.

[0038] Figure 6 A comparison chart of the comfort performance of the checkerboard stimulation paradigm and the grid stimulation paradigm proposed in this invention;

[0039] Figure 7 A comparison chart of the stimulus liking performance between the checkerboard stimulus paradigm and the grid stimulus paradigm proposed in this invention;

[0040] Figure 8 This is a comparison chart showing the recognition accuracy of the checkerboard stimulus paradigm and the grid stimulus paradigm proposed in this invention. Detailed Implementation

[0041] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0042] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0043] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined.

[0044] Figure 1 A flowchart illustrating a visual stimulation method according to an embodiment of the present invention is shown schematically. (Refer to...) Figure 1 The visual stimulation method of this invention specifically includes the following steps:

[0045] S11. Present a visual stimulus paradigm on the screen and use a sinusoidal sampling modulation mode to control the grid area of ​​the visual stimulus paradigm to flicker. The visual stimulus paradigm is composed of a background area and a grid area superimposed. The background area and the grid area have different contrasts. The grid area is composed of a line area and a line intersection area. The contrast and width of the line area and the line intersection area are different.

[0046] like Figure 2 As shown, in this embodiment of the invention, the high-comfort visual stimulation paradigm is composed of superimposed background areas and grid areas with different contrasts, wherein the grid area is composed of line areas and line intersection areas with different widths and contrasts.

[0047] Specifically, visual flicker is presented on the screen using a sinusoidal sampling modulation method. The stimulus sequence s(f,φ,i) at frequency f and phase φ in the sinusoidal sampling modulation mode is generated by the following formula:

[0048]

[0049] The sin() function is used to generate a sine wave sequence, where i represents the frame index in the stimulus sequence, f and φ represent the frequency and phase values ​​of the coded flicker using joint frequency and phase modulation, and RefreshRate represents the refresh rate of the stimulus display device. In this embodiment, the refresh rate of the LCD display is 60Hz. In the stimulus sequence, 0 represents the lowest brightness as black, and 1 represents the highest brightness as white.

[0050] S12. When displaying the first frame of data of the visual stimulation paradigm, a synchronization signal is sent to the EEG acquisition device to synchronously acquire the EEG signals generated by the user's cerebral cortex under the current visual stimulation paradigm.

[0051] S13. During the visual stimulation process, the brightness of the background area is controlled to be displayed according to a preset brightness value, the brightness value of the line area is controlled to change within a range higher than the corresponding brightness value of the background area, and the brightness value of the line intersection area is controlled to change within a range higher than the corresponding brightness value of the line area.

[0052] In this embodiment, the brightness setting of the background area in the high-comfort visual stimulation paradigm can be a preset brightness value. Optionally, the brightness value corresponding to the background area is [125, 125, 125]. The brightness of the lines in the grid area varies within a range higher than the background brightness value, such as [192, 192, 192]. The brightness of the line intersection area varies within a range higher than the brightness of the line area, such as [255, 255, 255]. During visual stimulation, display control is performed based on the relationship between the brightness values ​​of the background area, the line area, and the line intersection area.

[0053] The visual stimulation method, system, and brain-computer interface system provided in this invention offer a highly comfortable visual stimulation paradigm. This paradigm consists of a superimposed background region and a grid region with different contrasts. The grid region is composed of line regions and line intersection regions, each with different contrasts and widths. A sinusoidal sampling modulation mode is used to control the flickering of the grid region in the visual stimulation paradigm. Furthermore, during visual stimulation, the brightness of the background region is controlled to display according to a preset brightness value, and the brightness values ​​of the line regions and line intersection regions are controlled to vary within a range higher than the corresponding brightness values ​​of the background region and line intersection regions, respectively. This ensures that the stimulation can induce a certain intensity of SSVEP while reducing visual discomfort and cognitive fatigue, making it suitable for long-term use in visual BCI systems.

[0054] In the VEP-BCI system, continuous flashing stimulation not only easily induces visual discomfort and cognitive fatigue, but also makes target stimulus recognition susceptible to interference from background and surrounding stimuli, thus affecting the speed and accuracy of target stimulus recognition in the visual BCI system and leading to a decrease in both speed and accuracy. Therefore, this invention, based on the visual information processing mechanisms of the central and peripheral visual fields in the human brain's visual processing system, proposes a highly comfortable and long-term usable visual stimulation method suitable for the visual BCI system while maintaining high accuracy.

[0055] Specifically, the display area of ​​the visual stimulation paradigm of the present invention is divided into a central visual field and a peripheral visual field according to a preset division ratio.

[0056] Furthermore, during visual stimulation, the width of the line intersection area within the peripheral visual field can be controlled to be equal to or less than the width of the line area, and the width of the line intersection area within the central visual field can be controlled to be equal to, less than, or greater than the width of the line area. Additionally, the width of the line area can be controlled to vary according to actual application requirements, and the width of the line intersection area can be controlled to vary with the width of the line area.

[0057] In this embodiment, the intersection points of the lines in the visual stimulus paradigm can be set as squares, or the squares can be replaced with dots, rhombuses, or other polygons; this invention does not impose specific limitations on this. The line width of the line area can be appropriately widened or narrowed according to actual application needs. The color of each line intersection point can be set to white, and the intersection point width varies with the line width. In the peripheral visual field, the intersection point width should be equal to or less than the line width; in the central visual field, the intersection point width can be equal to or less than the line width, or it can be greater than the line width.

[0058] Furthermore, during visual stimulation, the lines forming the grid maintain a certain spatial density. The number of lines displayed at the intersections within the central visual field can be increased to improve the spatial resolution of the central visual field. Furthermore, after increasing the number of displayed lines, the width and / or brightness of each intersection point in the newly formed intersection area within the central visual field can be increased to achieve... Figure 3 The display control effect is shown.

[0059] In the human visual information processing system, the central visual field, specifically the fovea, is the most precise and acute area of ​​vision, while peripheral vision is weak, particularly in distinguishing details, colors, and shapes. Because the density of retinal receptors and ganglion cells is higher in the center and lowest at the periphery, the representation of the peripheral visual field in the visual cortex is far less than that of the central visual field. This leads to different sensitivities of the central and peripheral visual fields to visual information processing; for example, the central visual field is sensitive to visual information with high spatial resolution, while the peripheral visual field is sensitive to visual information with low spatial resolution. Therefore, the high-comfort visual stimulation paradigm proposed in this invention designs different visual stimuli for the central and peripheral visual fields based on their different information processing characteristics. Specifically, this invention increases the density of flicker points in the grid area to improve the spatial resolution of flickering stimuli in the central visual field, thereby increasing the amount of visual flickering information input in the visual BCI system and ensuring high accuracy. Furthermore, based on the low spatial resolution of the surrounding field of vision, when a user focuses on the central area of ​​the stimulus image designed in this invention, the flickering points in the surrounding field of vision will be filled by the background lines, thus making the flickering points disappear in the surrounding field of vision. This phenomenon of the flickering stimulus disappearing in the surrounding field of vision can not only improve the user's comfort when focusing on the flickering stimulus by reducing the flickering density, but also reduce the interference of the surrounding visual stimulus on the target stimulus recognition by reducing the amount of flickering information input in the surrounding field of vision, thereby improving the accuracy of the visual BCI system.

[0060] This invention is based on the characteristic that the central / peripheral visual fields of the human visual information processing nervous system have different sensitivities to information of different spatial resolutions. It improves comfort by reducing the density of flicker points in the peripheral visual field; it also improves comfort by reducing the contrast between the stimulus background area and the grid flicker area, changing the traditional high-contrast black / white flicker to a flicker stimulus that varies within a range higher than the brightness value of the background area; moreover, compared with traditional stimulus paradigms, the grid flicker stimulus paradigm of this invention is equivalent to reducing the stimulus flicker area by one-tenth or more, thus significantly improving comfort by reducing the flicker area. Figure 4a , Figure 4b , Figure 4cAs shown, the pure black and white stimulus: the black background remains unchanged, the white area flashes in a sinusoidal modulation, the stimulation flashing area is the entire black background, the gray value of the flashing area changes from 0 to 255, and the contrast is strong; the checkerboard stimulus: the black background remains unchanged, the white small square area flashes in a sinusoidal modulation, the stimulation flashing area is only the white square area, the flashing area is reduced by 50%, the gray value of the flashing area changes from 0 to 255, and the contrast is strong; the flashing grid stimulus proposed in this embodiment of the invention: the gray background remains unchanged, the grid area flashes in a sinusoidal modulation, the stimulation flashing area is only the grid area, the flashing area is about 10% of the entire background area (26784 / 262144=0.102), the gray value of the flashing area changes from 102 to 204 to 255, which is a gradual weak contrast change mode.

[0061] The advantages of this invention in ensuring the high performance of the visual BCI system are reflected in the following aspects: (1) Based on the central amplification effect of the human visual processing nervous system, that is, the visual cortex is mainly activated by the central visual field. Therefore, visual stimuli in the central visual field usually induce a larger response potential than peripheral visual field stimuli. In this invention, the visual flicker information input in the visual BCI system is enhanced by increasing the density of the flicker points in the central visual field grid to ensure high accuracy. (2) According to the low spatial resolution of the peripheral visual field, when the user looks at the central area of ​​the stimulus image designed in this invention, the flicker points in the peripheral visual field will be filled by the line background, thus making the flicker points disappear in the peripheral visual field. This phenomenon of the flickering stimulus disappearing in the peripheral visual field can not only improve the user's comfort when looking at the flickering stimulus by reducing the flicker density, but also reduce the interference of the peripheral stimulus on the target stimulus recognition by reducing the amount of flicker information input in the peripheral visual field, thereby improving the accuracy of the visual BCI system.

[0062] The above-mentioned visual stimulation method will be further illustrated by a specific embodiment below, and experimental evidence will be provided to demonstrate the advantages of the high-comfort visual stimulation method proposed in this invention.

[0063] This implementation case presents a target recognition system based on SSVE-BCI. The system includes an EEG acquisition device, a computer, a stimulus display device, and a BCI interactive interface. The EEG acquisition system is an 8-channel EEG signal acquisition device for the occipital region. It interacts with the computer via serial communication, and the synchronization signal between the stimulus and the EEG is sent in the first frame of the visual stimulus.

[0064] Visual flickering is presented on the screen using a sinusoidal sampling modulation method, see [link / reference]. Figure 5For example, the stimulus sequence s(f,φ,i) at frequency f and phase φ can be generated by formula (1). Here, the sin() function generates the sine wave sequence, i represents the frame index in the stimulus sequence, and f and φ represent the frequency and phase values ​​of the coded flicker using joint frequency and phase modulation (JFPM). The refresh rate of the LCD display is 60Hz. In the stimulus sequence, 0 represents the lowest brightness as black, and 1 represents the highest brightness as white.

[0065]

[0066] To verify the high comfort level of this visual stimulus paradigm and its ability to meet the high accuracy requirements of the visual BCI system, this invention conducts an experimental study to validate its effectiveness. This study employs two stimulus paradigms: the grid stimulus method proposed in this embodiment and the classic checkerboard method, along with five stimulus frequencies: 8.0 Hz, 8.2 Hz, 8.4 Hz, 8.6 Hz, and 8.8 Hz, combined to form ten stimulus conditions. Under each of the ten stimulus conditions, the presentation time was 3 seconds, repeated six times for a total presentation time of 18 seconds. Measurement scales and EEG data were collected from eight participants, and the comfort level and decoding performance of the different stimulus paradigms were discussed through offline analysis. The comfort level and induced visual fatigue level of the two visual stimulus paradigms were assessed through comparative analysis of subjective comfort and visual fatigue scales, and the performance of the stimulus paradigms was evaluated through analysis of offline EEG experimental data.

[0067] The experimental results show (see) Figures 6-8 The grid flickering paradigm proposed in this invention offers significantly greater comfort than the traditional checkerboard paradigm. Participants generally preferred the grid flickering stimulation paradigm proposed in this invention; in the experimental results, lower scores indicated greater comfort and preference for the stimulus. Furthermore, generally, high-comfort visual stimuli tend to lead to lower accuracy in the visual BCI system. However, the high-comfort grid flickering stimulation paradigm in this invention achieves the same accuracy as the traditional checkerboard stimulation paradigm in the SSVEP-BCI system while reducing the amount of flickering stimulus input (p < 0.05), indicating no significant difference in accuracy between the two methods.

[0068] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the embodiments of the present invention are not limited to the described order of actions, because according to the embodiments of the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily essential to the embodiments of the present invention.

[0069] In addition, embodiments of the present invention also provide a visual stimulation system, including: an electroencephalogram (EEG) acquisition device and a stimulation display device;

[0070] A stimulus display device for displaying a visual stimulus paradigm according to the visual stimulus method described in the above embodiments;

[0071] The EEG acquisition device is used to simultaneously acquire the EEG signals generated by the user's cerebral cortex under the current visual stimulation paradigm when receiving a synchronization signal sent when the first frame of data of the visual stimulation paradigm is displayed on the stimulation display device.

[0072] Furthermore, embodiments of the present invention also provide a brain-computer interface system, including the visual stimulation system described above.

[0073] Specifically, the brain-computer interface system includes a stimulation display device, an EEG acquisition device, and a computer device. The stimulation display device is used to display a visual stimulation paradigm according to the visual stimulation method described in the above embodiments. The EEG acquisition device is used to simultaneously acquire the EEG signals generated by the user's cerebral cortex under the current visual stimulation paradigm when it receives a synchronization signal sent when the stimulation display device displays the first frame of data of the visual stimulation paradigm. The computer device is used to amplify, filter, and perform analog-to-digital conversion on the EEG signals generated by the user's cerebral cortex under the current visual stimulation paradigm; and to perform real-time processing on the analog-to-digital converted EEG signals, detecting the frequency of the SSVEP signal.

[0074] Compared with the visual stimulation paradigm of existing visual BCI systems, the visual stimulation method provided by the embodiments of the present invention has the following beneficial effects: The present invention not only ensures high comfort and low visual fatigue of visual stimulation in the visual BCI system, but also ensures high performance of the visual BCI system under the premise of high stimulation comfort. That is, by reducing the amount of input of surrounding visual field flicker information, the interference of surrounding stimuli on target stimulus recognition is reduced, thereby improving the speed and accuracy of target stimulus recognition in the visual BCI system.

[0075] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, any of the claimed embodiments can be used in any combination.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A visual stimulation method, characterized in that, The method includes: A visual stimulus paradigm is presented on the screen, and a sinusoidal sampling modulation mode is used to control the flashing of the grid area of ​​the visual stimulus paradigm. The visual stimulus paradigm is composed of a background area and a grid area superimposed. The contrast of the background area and the grid area are different. The grid area is composed of a line area and a line intersection area. The contrast and width of the line area and the line intersection area are different. When displaying the first frame of data of the visual stimulation paradigm, a synchronization signal is sent to the EEG acquisition device to synchronously acquire the EEG signals generated by the user's cerebral cortex under the current visual stimulation paradigm. During visual stimulation, the brightness of the background area is controlled to be displayed according to a preset brightness value, the brightness value of the line area is controlled to vary within a range higher than the corresponding brightness value of the background area, and the brightness value of the line intersection area is controlled to vary within a range higher than the corresponding brightness value of the line area.

2. The method according to claim 1, characterized in that, The display area of ​​the visual stimulation paradigm is divided into a central visual field and a peripheral visual field according to a preset division ratio. The method further includes: During visual stimulation, the width of the line intersection area within the peripheral visual field is controlled to be equal to or less than the width of the line area, and the width of the line intersection area within the central visual field is controlled to be equal to, less than, or greater than the width of the line area.

3. The method according to claim 1 or 2, characterized in that, The method further includes: The width of the line area is controlled to change, and the width of the line intersection area is controlled to change with the width of the line area.

4. The method according to claim 2, characterized in that, The method further includes: During visual stimulation, the number of lines displayed at the intersections of lines within the central field of vision is increased to improve the spatial resolution of the central field of vision.

5. The method according to claim 4, characterized in that, The method further includes: After increasing the number of lines displayed, the width and / or brightness of each intersection point in the newly formed line intersection area within the central field of view are increased.

6. The method according to claim 2, characterized in that, The line intersections in the line intersection area are squares, dots, rhombuses, or polygons.

7. The method according to claim 1, characterized in that, The stimulus sequence of the sinusoidal sampling modulation mode is generated by the following formula: The sin() function is used to generate a sine wave sequence, i represents the frame index in the stimulus sequence, f and φ represent the frequency and phase values ​​of the coded flicker using joint frequency and phase modulation, and RefreshRate represents the refresh rate of the stimulus display device.

8. A visual stimulation system, characterized in that, include: EEG acquisition equipment and stimulation display equipment; A stimulus display device for displaying a visual stimulus paradigm according to the visual stimulus method as described in any one of claims 1-7; The EEG acquisition device is used to simultaneously acquire the EEG signals generated by the user's cerebral cortex under the current visual stimulation paradigm when receiving a synchronization signal sent when the first frame of data of the visual stimulation paradigm is displayed on the stimulation display device.

9. A brain-computer interface system, characterized in that, Includes the visual stimulation system as described in claim 8 above.

10. The brain-computer interface system according to claim 9, characterized in that, The system also includes: Computer equipment is used to amplify, filter, and perform analog-to-digital conversion on the electroencephalogram (EEG) signals generated by the cerebral cortex under the current visual stimulus paradigm; and to process the converted EEG signals in real time and detect the frequency of the SSVEP signal.

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