CN115857686A - Visual stimulation method and system and brain-computer interface system - Google Patents
Visual stimulation method and system and brain-computer interface system Download PDFInfo
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Abstract
The invention relates to the technical field of electroencephalogram interfaces, and provides a visual stimulation method, a system and a brain-computer interface system, wherein the method comprises the following steps: presenting a visual stimulation paradigm, and controlling a grid area of the visual stimulation paradigm to flicker by adopting a sine sampling modulation mode, wherein the visual stimulation paradigm is formed by overlapping a background area and the grid area, the background area and the grid area have different contrasts, the grid area is formed by a line area and a line intersection area, and the contrast and the width of the line area and the line intersection area are different; synchronously acquiring electroencephalogram signals generated by a user under a current visual stimulation paradigm; in the process of visual stimulation, the brightness of a background area is controlled to be displayed according to a preset brightness value, the brightness value of a line area is controlled to change within a range higher than the brightness value of the background area, and the brightness value of a line intersection area is controlled to change within a range higher than the brightness value of the line area, so that the visual fatigue can be reduced while certain strength SSVEP is induced by stimulation.
Description
Technical Field
The invention relates to the technical field of brain-computer interface paradigms, in particular to a visual stimulation method and system and a brain-computer interface system.
Background
Brain-computer Interface (BCI) is a direct communication means between the Brain and external devices (most commonly computers or robotic arms, etc.) that can be used to replace, assist, improve, enhance or repair human cognitive or sensorimotor functions. Commonly used BCI paradigms based on non-invasive EEG include BCI based on Visual Evoked Potentials (VEPs), BCI based on Slow Cortical Potentials (SCP), BCI based on the typical event-related potential P300 component, and BCI based on event-related synchronization/synchronization (ERD/ERS) of sensorimotor rhythm (SMR).
In VEP-BCI, the user's neural response to presenting a target stimulus in the visual stimulus is used to resolve the current user gaze target. Specifically, the neural signal response to the target stimulus is analyzed based on unique neural response patterns evoked by the stimulus, such as SSVEPs, and the neural signal patterns have a one-to-one correspondence relationship with only one stimulus at a specific time. By presenting stimuli with different flashing frequencies or phases at different time periods, the BCI algorithm can analyze the neural responses evoked by different stimuli at different times, so that it is possible for the system to judge the target stimulus of fixation.
In general, VEP-BCI is prone to visual fatigue. Visual fatigue directly affects user and system performance. The most commonly used stimulation modalities in the VEP-BCI system are blinking stimulation (brightness variation) and pattern-varying stimulation. Visual evoked potentials in the form of blinking are evoked by a single blinking stimulus, while pattern stimuli are evoked by alternating stimulus patterns. The stimulation form of the continuous flicker or the conversion mode is particularly easy to cause visual discomfort and cognitive fatigue of a user when more flicker stimuli are presented on a user interaction interface. Under the condition of watching visual stimulation for a long time, visual fatigue can cause the discomfort of the user such as dizziness, nausea and the like, and further can influence the performance of a visual BCI system. For example, the most common forms of stimulation in visual BCI systems, black and white blinking stimulation and checkerboard stimulation. The black and white flicker stimulation is that the black picture is taken as a background area, and the brightness of the white picture is changed within a black-white range according to a sine sampling modulation method. The checkerboard stimulation also comprises two pictures, one is a black picture, and the other is composed of a plurality of black and white square grids. In this stimulation mode, the black background remains unchanged and the brightness of the white squares is modulated according to the sinusoidal sampling. The flicker area of the black and white flicker stimulus is the whole black background area, and the brightness variation range of the white flicker area in the black and white stimulus is 0-255, which is the strong contrast. For the checkerboard stimulation paradigm, the flicker area is reduced by half compared to the black and white stimulation paradigm, but the luminance value of the flicker region is still the strong contrast flicker pattern. It can be seen that in the VEP-BCI system, the continuous stimulation flicker is easy to induce visual discomfort and cognitive fatigue, and the recognition target stimulation is easy to be interfered by the background stimulation and the surrounding stimulation, thereby affecting the speed and accuracy of the target stimulation recognition in the visual BCI system. Therefore, how to improve the visual stimulation in the visual BCI system according to the human vision and perception conditions avoids the interference of the background stimulation and the peripheral stimulation when the target stimulation is identified, ensures that the stimulation can reduce the visual discomfort and the cognitive fatigue while inducing SSVEP with certain intensity, and is of particular significance to the development of the brain-computer interface technology.
Disclosure of Invention
In view of the above, the present invention has been made to provide a visual stimulation method, system and brain-computer interface system that overcome or at least partially solve the above-mentioned problems to ensure that stimulation can induce SSVEPs of a certain strength while reducing visual discomfort and cognitive fatigue.
In one aspect of the present invention, there is provided a visual stimulation method, the method comprising:
presenting a visual stimulation paradigm on a screen, and controlling a grid area of the visual stimulation paradigm to flicker by adopting a sine sampling modulation mode, wherein the visual stimulation paradigm is formed by overlapping a background area and the grid area, the background area and the grid area have different contrasts, the grid area is formed by a line area and a line intersection area, and the contrasts and the widths of the line area and the line intersection area are different;
when the first frame data of the visual stimulation paradigm are displayed, a synchronous signal is sent to electroencephalogram acquisition equipment so as to synchronously acquire electroencephalogram signals generated by the cerebral cortex of a user under the current visual stimulation paradigm;
and in the process of visual stimulation, controlling the brightness of the background area to be displayed according to a preset brightness value, controlling the brightness value of the line area to be changed in a range higher than the corresponding brightness value of the background area, and controlling the brightness value of the line intersection area to be changed in a range higher than the corresponding brightness value of the line area.
Further, the display area of the visual stimulation paradigm is divided into a central visual field range and a peripheral visual field range according to a preset division ratio;
the method further comprises the following steps:
and in the process of visual stimulation, controlling the width of the line intersection region in the peripheral visual field range to be equal to or less than the width of the line region, and controlling the width of the line intersection region in the central visual field range to be equal to, less than or greater than the width of the line region.
Further, the method further comprises:
and controlling the width of the line area to change, and controlling the width of the line intersection area to change along with the width of the line area.
Further, the method further comprises:
during the visual stimulation, the display number of the lines is increased in the area of the line intersection in the central visual field range, so that the spatial resolution of the central visual field range is improved.
Further, the method further comprises:
after the display number of the lines is increased, the width and/or the brightness of each intersection in the newly formed line intersection area in the central visual field range are controlled to be increased.
Further, the line intersection points in the line intersection point region are squares, dots, diamonds or polygons.
Further, the stimulation sequence of the sinusoidally sampled modulation pattern is generated by the following equation:
where sin () function is used to generate a sequence of sine waves, i represents the frame index in the stimulation sequence, f and φ represent the frequency and phase values of the coded flicker using a joint frequency and phase modulation, refreshRate represents the refresh rate of the stimulation display device.
In a second aspect, the present invention also provides a visual stimulation system comprising: the device comprises an electroencephalogram acquisition device and a stimulation display device;
a stimulus display device for performing visual stimulus paradigm display according to the visual stimulus method as described above;
and the electroencephalogram acquisition equipment is used for synchronously acquiring electroencephalogram signals generated by the cerebral cortex of the user under the current visual stimulation paradigm when receiving the synchronous signals sent when the stimulation display equipment displays the first frame data of the visual stimulation paradigm.
In a third aspect, the present invention also provides a brain-computer interface system comprising a visual stimulation system as described above.
Further, the system further comprises: the computer equipment is used for amplifying, filtering and carrying out analog-to-digital conversion on the electroencephalogram signals generated by the cerebral cortex of the user under the current visual stimulation paradigm; and carrying out real-time processing on the electroencephalogram signals subjected to analog-to-digital conversion, and detecting the frequency of the SSVEP signals.
The visual stimulation method, the system and the brain-computer interface system provided by the embodiment of the invention provide a high-comfort visual stimulation normal form which is formed by superposing a background area and a grid area, wherein the background area and the grid area have different contrasts, the grid area consists of a line area and a line intersection area, the contrasts and the widths of the line area and the line intersection area are different, a sine sampling modulation mode is adopted to control the grid area of the visual stimulation normal form to flicker, in the process of 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 be changed in a range higher than the corresponding brightness value of the background area, and the brightness value of the line intersection area is controlled to be changed in a range higher than the corresponding brightness value of the line area, so that the stimulation can be ensured to induce SSVEP with certain intensity and simultaneously reduce visual discomfort and cognitive fatigue, and the visual stimulation method is suitable for long-term use of a visual BCI system.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a flow chart of a method for visual stimulation according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a visual stimulation paradigm employed in a visual stimulation method provided by an embodiment of the present invention;
fig. 3 is a diagram illustrating a display control effect of a grid stimulation paradigm in a visual stimulation method according to an embodiment of the present invention;
FIG. 4a is a schematic diagram showing contrast and stimulation flicker area for a black and white stimulation paradigm;
FIG. 4b is a schematic diagram showing contrast and stimulation flicker area of the checkerboard stimulation paradigm;
FIG. 4c is a schematic diagram showing contrast and stimulation flicker area of a grid stimulation paradigm provided by an embodiment of the present invention;
FIG. 5 is a schematic diagram of the effect of visual flicker presented on a screen by a sinusoidal sampling modulation method;
FIG. 6 is a graph comparing comfort performance of a checkerboard stimulation paradigm with a grid stimulation paradigm as proposed by the present invention;
FIG. 7 is a graph of stimulation preference performance versus a checkerboard stimulation paradigm and a grid stimulation paradigm as set forth in the present invention;
fig. 8 is a graph comparing the recognition accuracy of the checkerboard stimulation paradigm and the grid stimulation paradigm proposed by the present invention.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below 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 embodied 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.
As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Fig. 1 schematically shows a flow chart of a visual stimulation method according to an embodiment of the invention. Referring to fig. 1, the visual stimulation method of the embodiment of the present invention specifically includes the following steps:
s11, presenting a visual stimulation paradigm on a screen, and controlling a grid area of the visual stimulation paradigm to flicker by adopting a sine sampling modulation mode, wherein the visual stimulation paradigm is formed by overlapping a background area and the grid area, the background area and the grid area have different contrasts, the grid area is formed by a line area and a line intersection area, and the contrast and the width of the line area and the line intersection area are different.
As shown in fig. 2, the high-comfort visual stimulation paradigm in the embodiment of the present invention is composed of a background area and a grid area with different contrasts superimposed, wherein the grid area is composed of a line area and a line intersection area with different widths and contrasts.
Specifically, visual flicker is presented on a screen by adopting a sinusoidal sampling modulation method, and a stimulation sequence s (f, phi, i) at a frequency f and a phase phi is generated by the following formula when a sinusoidal sampling modulation mode is adopted:
where sin () function is used to generate a sequence of sine waves, i represents the frame index in the stimulation sequence, f and φ represent the frequency and phase values of the coded flicker using a joint frequency and phase modulation, refreshRate represents the refresh rate of the stimulation display device. In this embodiment, the refresh rate of the LCD display is 60Hz. In the stimulation sequence, 0 means that the lowest brightness is black and 1 means that the highest brightness is white.
S12, when the first frame data of the visual stimulation paradigm are displayed, sending a synchronous signal to electroencephalogram acquisition equipment so as to synchronously acquire electroencephalogram signals generated by a user in a cerebral cortex under the current visual stimulation paradigm;
and S13, in the process of visual stimulation, controlling the brightness of the background area to be displayed according to a preset brightness value, controlling the brightness value of the line area to change in a range higher than the corresponding brightness value of the background area, and controlling the brightness value of the line intersection area to change in a range higher than the corresponding brightness value of the line area.
In this embodiment, the brightness of the background region in the high-comfort visual stimulation paradigm may be set to a predetermined brightness value, optionally, the background region corresponds to a brightness value [125, 125, 125], the line brightness of the grid region varies in a range higher than the background brightness value, such as [192, 192, 192], and the brightness of the line intersection region varies in a range higher than the brightness of the line region, such as [255, 255, 255]. In the process of performing visual stimulation, display control is performed based on the magnitude relation of the brightness values of the background region, the line region, and the line intersection region.
The visual stimulation method, the system and the brain-computer interface system provided by the embodiment of the invention provide a high-comfort visual stimulation paradigm which is formed by overlapping a background area and a grid area, wherein the background area and the grid area have different contrasts, the grid area is formed by a line area and a line intersection area, the contrasts and the widths of the line area and the line intersection area are different, the grid area of the visual stimulation paradigm is controlled to flicker by adopting a sine sampling modulation mode, in addition, in 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 corresponding 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 corresponding brightness value of the line area, so that the stimulation can be ensured to induce SSVEP with certain intensity and simultaneously reduce visual discomfort and cognitive fatigue, and the visual stimulation is suitable for long-term use of a visual BCI system.
In the VEP-BCI system, the continuous stimulation flicker not only easily induces visual discomfort and cognitive fatigue, but also identifies the target stimulation easily interfered by the background stimulation and the surrounding stimulation, thereby affecting the speed and accuracy of target stimulation identification in the visual BCI system, resulting in the reduction of the speed and accuracy of target stimulation identification in the visual BCI system. Therefore, the invention provides a visual stimulation mode which is high in comfort degree and suitable for the visual BCI system and can be used for a long time on the premise of ensuring the high accuracy of the visual BCI system based on the visual information processing mechanism of the central visual field and the peripheral visual field in the visual processing system in the human brain.
Specifically, the display area of the visual stimulation paradigm is divided into a central visual field range and a peripheral visual field range according to a preset division ratio.
Further, in the visual stimulation, the width of the line intersection region in the peripheral visual field range may be controlled to be equal to or less than the width of the line region, and the width of the line intersection region in the central visual field range may be controlled to be equal to, less than or greater than the width of the line region. In addition, the width of the line region can be controlled to change according to the actual application requirement, and the width of the line intersection region can be controlled to change according to the width of the line region.
In this embodiment, each line intersection in the line intersection region of the visual stimulation paradigm may be set as a square grid, or the square grid may replace a dot, a diamond, or another polygon, which is not specifically limited in the present invention. The line width of the line region can be widened or narrowed as required by the practical application. The color of each line intersection can be set to be white, the width of the intersection changes with the change of the line width, the width of the intersection is equal to or less than the line width in the peripheral visual field area, and the width of the intersection is equal to or less than the line width in the central visual field area and can also be greater than the line width.
Further, during the visual stimulation, the lines forming the grid keep certain spatial density, and the display number of the lines can be increased in the line intersection area in the central visual field range, so that the spatial resolution of the central visual field range is improved. Further, after the display number of the lines is increased, the width and/or the brightness of each intersection in the newly formed line intersection area in the central visual field range can be controlled to be increased, so that the display control effect shown in fig. 3 can be realized.
In the human visual information processing system, the central visual field, i.e., fovea, is the most accurate and acute region of vision, and peripheral vision is very weak, particularly in distinguishing details, colors and shapes, because the retinal receptors and ganglion cells are more dense in the center and the least dense at the edges, the peripheral visual field is much less characterized in the visual cortex than the central visual field, which results in the central and peripheral visual fields being sensitive to different visual information processing, e.g., the central visual field is sensitive to high spatial resolution visual information and the peripheral visual field is sensitive to low spatial resolution visual information. Therefore, the visual stimulation paradigm with high comfort level proposed in the embodiments of the present invention performs different visual stimulation designs for the central visual field range and the peripheral visual field range based on the information processing characteristics of the central visual field range and the peripheral visual field range that are different. Specifically, the invention ensures high accuracy by increasing the density of the scintillation points in the grid area, improving the spatial resolution of the scintillation stimulation in the central visual field and increasing the input quantity of visual scintillation information in the visual BCI system. In addition, according to the characteristic of low spatial resolution of the peripheral vision field, when a user watches the central area of the stimulation picture designed by the invention, the flicker points of the peripheral vision field are filled with the line background, so that the flicker points disappear in the peripheral vision field.
The invention processes the characteristic that the central/peripheral vision of the nervous system has different sensibility to different spatial resolution information based on human visual information, and improves the comfort level by reducing the density of peripheral vision flicker points; the contrast of the stimulation background area and the grid flicker area is reduced, and the comfort level is improved by changing the traditional black/white flicker with strong stimulation contrast into flicker stimulation in a range higher than the brightness value of the background area; moreover, compared to the conventional stimulation paradigm, the grid flicker stimulation paradigm of the present invention is equivalent to reducing the stimulation flicker area by one tenth or more, and the comfort level is improved by greatly reducing the flicker area, as shown in fig. 4a, 4b, and 4c, the pure black and white stimulation: the black background is not changed, the white area flickers according to sine modulation, the stimulated flicking area is the whole black background, the gray value of the flicking area is changed to be 0-255, and the contrast is strong; and (3) stimulating the checkerboards: the black background is not changed, the white small square grid area flickers according to sine modulation, the stimulated flickering area is only the white square grid area, the flickering area is reduced by 50%, the gray value of the flickering area is changed to be 0-255, and the contrast is high; the embodiment of the invention provides a flicker grid stimulation method, which comprises the following steps: the gray background is unchanged, the grid area flickers according to sinusoidal modulation, the area of the flicker is only stimulated to be the grid area, the area of the flicker is about 10 percent of the whole background area (26784/262144 = 0.102), the gray value of the flicking area is changed to 102-204-255, and the flicking area is in a gradual weak contrast change mode.
The advantage of the design of the invention in ensuring the high performance of the visual BCI system is embodied in that: (1) Based on the central amplification effect of the human visual processing nervous system, i.e., the visual cortex is mainly activated by the central visual field, visual stimuli in the central visual field area will usually induce response potentials of larger magnitude than peripheral visual field stimuli. In the invention, the input amount of visual flicker information in the visual BCI system is enhanced by increasing the density of central visual field grid flicker points so as to ensure high accuracy. (2) According to the characteristic of low spatial resolution of the peripheral vision field, when a user watches the central area of the stimulation picture designed by the invention, the flicker points of the peripheral vision field are filled with the line background, so that the flicker points disappear in the peripheral vision field. The disappearance phenomenon of the flicker stimulus in the peripheral vision field can not only improve the comfort level of a user when watching the flicker stimulus by reducing the flicker density, but also reduce the interference of the peripheral stimulus on the identification of the target stimulus by weakening the input quantity of the flicker information of the peripheral vision field, thereby improving the accuracy of the visual BCI system.
The above-mentioned visual stimulation method is further described below with an embodiment, and experimental evidence is provided for the advantages of the high-comfort visual stimulation method proposed by the present invention.
The embodiment case is a target recognition system based on SSVE-BCI, and the system comprises electroencephalogram acquisition equipment, computer equipment, stimulation display equipment and a BCI interactive interface. The electroencephalogram acquisition system is an electroencephalogram signal acquisition device with 8 channels in the occipital region, data interaction is carried out with a computer device in a serial port communication mode, and synchronous signals of stimulation and electroencephalogram are sent in a first frame of visual stimulation.
A sinusoidal sampling modulation method is used to present a visual flicker on the screen, see fig. 5. For example, the stimulation sequence s (f, φ, i) at the frequency fshaso can be generated by equation (1). Where the sin () function generates a sequence of sinusoids, i represents the frame index in the stimulation sequence, and f and φ represent the frequency and phase values of the encoded flicker using Joint Frequency and Phase Modulation (JFPM). The refresh rate of the LCD display is 60Hz. In the stimulation sequence, 0 means that the lowest brightness is black and 1 means that the highest brightness is white.
In order to verify the high comfort of the visual stimulation paradigm and meet the high accuracy characteristics of a visual BCI system, the invention verifies the effectiveness of the visual stimulation paradigm based on experimental research. Two stimulation paradigms were used in this study: the grid stimulation mode and the classical checkerboard mode provided by the embodiment of the invention, and the stimulation frequencies of 5 types are as follows: 8.0hz,8.2hz,8.4hz,8.6hz and 8.8hz are combined into 10 stimulation conditions, and under the 10 stimulation conditions, the presentation time of each stimulation condition is 3s, and the total presentation time is 18s, and the total presentation time is 6 times. 8 test metrics and EEG data were collected and the comfort and decoding performance of the different stimulation paradigms were discussed by off-line analysis. The comfort and the induced asthenopia degree of the two visual stimulus paradigms are evaluated by comparative analysis of subjective comfort and asthenopia scales, and the performance of the stimulus paradigms is evaluated by analysis of off-line EEG experimental data.
The experimental results show that referring to fig. 6-8, the comfort level of the grid flicker paradigm proposed by the present invention is significantly higher than that of the conventional checkerboard paradigm, and the tested subjects generally like the grid flicker stimulation paradigm proposed by the present invention, and in the experimental result data, the lower the score is, the more comfortable and the more favorable the stimulation is. In addition, generally, the high-comfort visual stimulation generally leads to low accuracy of the visual BCI system, and the high-comfort grid flicker stimulation paradigm in the invention can enable the SSVEP-BCI system to achieve the accuracy consistent with that of the traditional checkerboard stimulation paradigm on the premise of reducing the input amount of flicker stimulation, wherein p is less than 0.05, which indicates that the accuracy of the SSVEP-BCI system in the two modes is not obviously different.
For simplicity of explanation, the method embodiments are described as a series of acts or combinations, but those skilled in the art will appreciate that the embodiments are not limited by the order of acts described, as some steps may occur in other orders or concurrently with other steps in accordance with the embodiments of the invention. Further, those of skill in the art will appreciate that the embodiments described in the specification are presently preferred and that no particular act is required to implement the embodiments of the invention.
In addition, an embodiment of the present invention further provides a visual stimulation system, including: the brain electricity collecting device and the stimulation display device;
a stimulus display device for performing a visual stimulus paradigm display according to the visual stimulus method as described in the above embodiments;
and the electroencephalogram acquisition equipment is used for synchronously acquiring electroencephalogram signals generated by the cerebral cortex of the user under the current visual stimulation paradigm when receiving the synchronous signals sent when the stimulation display equipment displays the first frame data of the visual stimulation paradigm.
In addition, the embodiment of the invention also provides a brain-computer interface system, which comprises the visual stimulation system.
Specifically, the brain-computer interface system includes a stimulation display device, an electroencephalogram acquisition device, and a computer device, where the stimulation display device is configured to perform a visual stimulation paradigm display according to the visual stimulation method described in the above embodiment. And the electroencephalogram acquisition equipment is used for synchronously acquiring electroencephalogram signals generated by the cerebral cortex of the user under the current visual stimulation paradigm when receiving the synchronous signals sent when the stimulation display equipment displays the first frame data of the visual stimulation paradigm. The computer equipment is used for amplifying, filtering and carrying out analog-to-digital conversion on the electroencephalogram signals generated by the cerebral cortex of the user under the current visual stimulation paradigm; and carrying out real-time processing on the electroencephalogram signals subjected to analog-to-digital conversion, and detecting the frequency of the SSVEP signals.
Compared with the visual stimulation paradigm of the existing visual BCI system, the visual stimulation method provided by the embodiment of the invention has the following beneficial effects: the invention not only ensures the high comfort level and the low visual fatigue degree of visual stimulation in the visual BCI system, but also can ensure the high performance of the visual BCI system on the premise of stimulating the high comfort level, namely, the interference of peripheral stimulation on the identification of target stimulation is reduced by weakening the input quantity of peripheral visual field flicker information, thereby improving the speed and the accuracy of the identification of the target stimulation in the visual BCI system.
Moreover, those of skill in the art will appreciate that while some embodiments herein include some features included in other embodiments, not others, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, any of the claimed embodiments may be used in any combination.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A method of visual stimulation, the method comprising:
presenting a visual stimulation paradigm on a screen, and controlling a grid area of the visual stimulation paradigm to flicker by adopting a sine sampling modulation mode, wherein the visual stimulation paradigm is formed by overlapping a background area and the grid area, the background area and the grid area have different contrasts, the grid area is formed by a line area and a line intersection area, and the contrasts and the widths of the line area and the line intersection area are different;
when the first frame data of the visual stimulation paradigm are displayed, a synchronous signal is sent to electroencephalogram acquisition equipment so as to synchronously acquire electroencephalogram signals generated by the cerebral cortex of a user under the current visual stimulation paradigm;
and in the process of visual stimulation, controlling the brightness of the background area to be displayed according to a preset brightness value, controlling the brightness value of the line area to change within a range higher than the corresponding brightness value of the background area, and controlling the brightness value of the line intersection area to change within a range higher than the corresponding brightness value of the line area.
2. The method according to claim 1, wherein the display area of the visual stimulation paradigm is divided into a central visual field range and a peripheral visual field range according to a preset division ratio;
the method further comprises the following steps:
and in the process of visual stimulation, controlling the width of the line intersection region in the peripheral visual field range to be equal to or less than the width of the line region, and controlling the width of the line intersection region in the central visual field range to be equal to, less than or greater than the width of the line region.
3. The method according to claim 1 or 2, characterized in that the method further comprises:
and controlling the width of the line area to change, and controlling the width of the line intersection area to change along with the width of the line area.
4. The method of claim 2, further comprising:
during the visual stimulation, the display number of the lines is increased in the area of the line intersection in the central visual field range, so that the spatial resolution of the central visual field range is improved.
5. The method of claim 4, further comprising:
after the display number of the lines is increased, the width and/or the brightness of each intersection in the newly formed line intersection area in the central visual field range are controlled to be increased.
6. The method of claim 2, wherein the line intersections of the line intersection region are squares, dots, diamonds, or polygons.
7. The method of claim 1, wherein the stimulation sequence of sinusoidally sampled modulation patterns is generated by the following equation:
where sin () function is used to generate a sequence of sine waves, i represents the frame index in the stimulation sequence, f and φ represent the frequency and phase values of the coded flicker using a joint frequency and phase modulation, refreshRate represents the refresh rate of the stimulation display device.
8. A visual stimulation system, comprising: the device comprises an electroencephalogram acquisition device and a stimulation display device;
a stimulus display device for performing a visual stimulus paradigm display according to the visual stimulus method of any one of claims 1 to 7;
and the electroencephalogram acquisition equipment is used for synchronously acquiring electroencephalogram signals generated by the cerebral cortex of the user under the current visual stimulation paradigm when receiving the synchronous signals sent when the stimulation display equipment displays the first frame data of the visual stimulation paradigm.
9. A brain-computer interface system comprising the visual stimulus system of claim 8 as described above.
10. The brain-computer interface system according to claim 9, further comprising:
the computer equipment is used for amplifying, filtering and carrying out analog-to-digital conversion on an electroencephalogram signal generated by the cerebral cortex of a user under the current visual stimulation paradigm; and carrying out real-time processing on the electroencephalogram signals subjected to analog-to-digital conversion, and detecting the frequency of the SSVEP signals.
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