CN111045517A - SSVEP visual stimulator and stimulation method - Google Patents
SSVEP visual stimulator and stimulation method Download PDFInfo
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Abstract
The invention discloses a design method of an SSVEP visual stimulator, which can be used for designing a brain-computer interface visual stimulator and has the advantages of stable flicker frequency, high accuracy and good synchronism. The visual stimulator controls the visual stimulation pattern to be changed in light and shade at a certain frequency, and the change rule is in a sine wave form. By adjusting the gray value of each frame of the stimulation pattern, stimulation flicker can be realized, and the achievable frequency range of the visual stimulation frequency is large. The visual stimulation frequency generation module can calculate the amplitude and the gray value corresponding to each frame under different frequencies in a mode of sampling the sinusoidal signal. Displaying different frequencies and corresponding gray values on a computer display through a VGA interface to realize visual stimulation; the visual stimulator can transmit information and set and modify parameters to the visual stimulation paradigm through a graphical user interface.
Description
Technical Field
The invention relates to the field of brain-computer interfaces, in particular to an adjustable SSVEP visual stimulator and a stimulation method.
Background
The brain-computer interface system is a system for realizing the communication and control between the human brain and the computer or other electronic equipment by utilizing the human brain bioelectric signals, and is a brand new communication and control method. At present, electroencephalogram signals for realizing a brain-computer interface are mainly divided into evoked potentials and spontaneous electroencephalogram signals, the evoked potentials are divided into P300 and visual evoked potentials, and the spontaneous electroencephalogram signals are divided into time-related synchronous or time-related desynchronizing potentials, cortical slow potentials and spontaneous electroencephalogram signals.
Compared with other electric signals, the visual evoked potential has relatively stable waveform characteristics, has unique corresponding relation with visual stimulation, is easy to detect, has little relation with the strength of the automatic control capability of a user, and is suitable for being used as an input signal of a brain-computer interface, wherein the visual steady evoked potential, namely SSVEP, is widely applied to the brain-computer interface system due to the characteristics of stable waveform and obvious spectrum characteristics.
The stimulation modes of the visual stimulator applied to the SSVEP brain-computer interface system at present mainly include LED lamp flickering and computer display displaying. However, the visual stimulator using LED light flashing is inconvenient to modify and cannot display complex content, and thus is difficult to apply to complex application scenarios, and therefore, it is increasingly used as a display device for visual stimulation, and although the computer display can display more complex and accurate images and implement more experimental paradigm designs than the LED light flashing, the conventional flashing stimulation of the visual stimulator is limited by the refresh frequency of the display, so that the frequency that the flashing stimulation can implement is limited, thereby limiting the research on visual steady state induction applied to the computer display.
The most important performance indexes of the visual stimulator based on the SSVEP are the stability and the accuracy of the visual stimulation frequency, how to increase the stimulation frequency and the synchronism between the visual stimulator and an electroencephalogram signal acquisition system. However, the visual stimulator implemented by software programming in the windows system can cause the frame loss of the visual stimulation graph while the electroencephalogram signal is processed due to the multitasking characteristic of the windows system, thereby affecting the stability and accuracy of the visual stimulation signal.
Disclosure of Invention
The invention aims to solve the technical problems that the existing visual stimulator realized by software programming in a windows system causes the frame missing of a visual stimulation graph while processing an electroencephalogram signal, so that the stability and the accuracy of the visual stimulation signal are influenced, and the traditional flicker stimulation is limited by the refreshing frequency of a display, so that the frequency of the realization of the flicker stimulation is limited and cannot be adjusted.
The invention is realized by the following technical scheme:
an SSVEP visual stimulator comprises a VGA control module, a stimulation frequency generation module, a storage module and an image transmission module;
the VGA control module comprises a scanning time sequence generation module and an image description module;
the image transmission module: transmitting the input user-defined graph and the visual stimulation frequency to be adjusted to the VGA control module;
the stimulation frequency generation module: sampling a sinusoidal signal of a visual stimulation frequency, calculating sampled data, and loading amplitude values and gray values corresponding to different visual stimulation frequencies calculated by the stimulation frequency generation module into a storage module;
the scan timing generation module: generating a line synchronizing signal, a field synchronizing signal and a digital signal type of graphic stimulation signal;
the image description module: reading the amplitude and the gray value corresponding to the visual stimulation frequency from the frequency generation module, generating RGB signals and visual stimulation frequency control signals through the amplitude and the gray value, generating parameter information of the size, the shape and the quantity of the graph according to the received user-defined graph, and transmitting the parameter information to the interface control display module;
the interface control module: and displaying and flashing visual stimulation graphs through the graph stimulation signals, the RGB signals, the visual stimulation frequency control signals and the parameter information.
The visual stimulation graph is used as a target selection item, the graph can be displayed in a display, the visual stimulator makes a required graph on a PC (personal computer) end graphical user interface of the image transmission module and transmits the graph through the PC end graphical user interface, a synchronous dynamic random access memory is used for storing received picture data in the image transmission module realized by FPGA (field programmable gate array) design, and then the stored graph is transmitted and displayed in a rectangular frame. The synchronous dynamic random access memory chip is internally provided with a storage array, a row is firstly appointed when data is written in, then a column is appointed, and then an accurate cell can be found so as to achieve the purposes of reading, writing and transmission, so that the image transmission module can realize the adjustment of different visual stimulation frequencies.
The stimulation frequency generation module firstly samples all adjustable visual stimulation frequencies by taking the refresh frequency of a display as a sampling frequency to obtain the amplitude values and the gray values of different data frontal stimulation frequencies, stores the amplitude values and the gray values, reads the corresponding gray values according to different visual stimulation frequencies after the visual stimulation frequencies are input by the visual stimulator, and transmits the gray values to the image and description module to assign the user-defined image. The stimulation frequency generation module does not need to use a traditional counter frequency division mode to obtain the visual stimulation frequency, so that the visual stimulation frequency is not limited by the refresh frequency of the display, the visual stimulation frequencies with different frequencies can be realized, and the accuracy and the stability are realized.
The image transmission module, the stimulation frequency generation module and the VGA control module are designed and realized in the FPGA, and the FPGA is a semi-custom circuit, so that the defects of the custom circuit are overcome, a digital system is overcome, and the functions of any digital device can be completed. The invention can verify the correctness of the design in advance through software simulation. Compared with a visual stimulator realized by software programming under a windows system, the visual stimulator can not cause the frame loss of a visual stimulation graph while carrying out electroencephalogram signal processing, thereby not influencing the stability and the accuracy of the visual stimulation signal.
The computer display can display clearer and more complex graphs and can more conveniently and automatically define the parameters of the graphs such as shape, size and the like compared with a mode of realizing visual stimulation by flashing an LED lamp by taking a computer display screen as a display.
Further, the operation principle of the stimulation frequency generation module includes:
the stimulation frequency generation module samples a sinusoidal signal of the visual stimulation frequency, and the sampling frequency is the refresh frequency of the display;
the stimulation frequency generation module calculates the sampled sinusoidal signals to obtain stimulation sequences corresponding to the corresponding frequencies and amplitudes of the sinusoidal signals;
the stimulation frequency generation module adjusts the gray value corresponding to each frame of the stimulation sequence according to a sine wave form;
and the stimulation frequency generation module outputs the data generated after the stimulation sequence is processed in a file form and loads the data into the storage module.
Further, the working principle of the VGA control module includes:
when each frame of a field synchronizing signal generated by the scanning time sequence generating module starts, the field synchronizing signal can generate a high pulse with a fixed width;
when each line of the line synchronizing signal generated by the scanning time sequence generating module starts, the line synchronizing signal can generate a high pulse with a fixed width;
the VGA time sequence of the scanning time sequence generation module sequentially carries out synchronous pulse, back porch pulse, display pulse and front porch pulse according to a reference driving clock, and scans the line synchronous signal in the effective pulse of the field synchronous signal;
the image description module generates parameter information of the size, shape and quantity of the graph according to the received custom graph and transmits the parameter information to the interface control display module;
the image description module reads corresponding amplitude and gray value from a stimulation sequence corresponding to the stimulation frequency of the stimulation frequency generation module according to the stimulation frequency, and generates RGB signals and stimulation frequency control signals through the amplitude and gray value;
and the VGA control module transmits the graphic stimulation signal, the RGB signal and the visual stimulation frequency control signal to the interface control module.
Further, the interface control display module comprises a VGA interface drive display device and a display;
the VGA interface drives display equipment to transmit the received graphic stimulation signal, the received RGB signal, the received stimulation frequency control signal and the received parameter information to a display;
and the displayer displays the received graphic stimulation signal, the RGB signal, the stimulation frequency control signal and the parameter information which are output by the VGA interface driving equipment, so as to stimulate the graphic.
Furthermore, the image transmission module comprises a PC end graphical user interface, a main control module, a static memory control module and a synchronous dynamic random access memory module;
the PC end graphical user interface is used for inputting customized graphs and adjusting different stimulation frequencies;
the main control module receives a user-defined graph and stimulation frequency transmitted by a graphical user interface of a PC (personal computer) end through a serial port;
the static memory control module receives the user-defined graph and the stimulation frequency transmitted by the main control module through a bus;
and the synchronous dynamic random storage module receives the self-defined graph and the stimulation frequency for storage and transmission.
Furthermore, a mode register is used in the synchronous dynamic random access memory module to provide control parameters, and initialization operation is performed when the synchronous dynamic random access memory module is started up each time;
the control parameters are acquired according to digital signals provided by the address lines, so that the mode register is set;
after the initialization of the mode register is completed, the addressing of the logic bank is carried out, thereby determining the rows firstly and then determining the rows and the columns
And the read-write command of the mode register is controlled by the writable state of the synchronous dynamic random access memory module.
A stimulation method of an SSVEP visual stimulator, comprising:
inputting a user-defined graph and visual stimulation frequency to be adjusted;
sampling the sinusoidal signal of the visual stimulation frequency by taking the refresh frequency as the sampling frequency, calculating the sampled data, and storing the amplitude values and gray values corresponding to different visual stimulation frequencies obtained by calculation;
generating a line synchronizing signal, a field synchronizing signal and a digital signal type of graphic stimulation signal;
reading the amplitude and the gray value corresponding to the visual stimulation frequency through the received visual stimulation frequency, and generating an RGB signal and a visual stimulation frequency control signal through the amplitude and the gray value;
transmitting the graphic stimulation signal, the RGB signal and the visual stimulation frequency control signal;
generating parameter information of the size, shape and quantity of the graph according to the received custom graph and transmitting the parameter information;
and displaying and flashing visual stimulation graphs through the received graph stimulation signals, RGB signals, visual stimulation frequency control signals and parameter information.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. according to the SSVEP visual stimulator, the VGA is controlled by the FPGA platform to drive and display the graphic stimulation, the stimulation frequency is obtained without frequency division, and the flicker stability and the accuracy of the stimulation graphic generated by the visual stimulator are good.
2. According to the SSVEP visual stimulator disclosed by the invention, the data of the visual stimulator is directly displayed through the VGA interface, the limitation of a frequency refresh rate is avoided, and the number of the visual stimulation frequencies which can be set is more.
3. The invention relates to an SSVEP visual stimulator, which adjusts parameters of a visual stimulation graph through a graph user interface and can realize different function definitions of the visual stimulator through a user-defined graph. The problem that the traditional visual stimulator is difficult to modify is solved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is an overall block diagram of the present invention;
FIG. 2 is a block diagram of the circuit designed in the FPGA of the present invention;
fig. 3 is a schematic diagram of an application of an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1
As shown in fig. 1, an SSVEP visual stimulator includes a VGA control module, a stimulation frequency generation module, a storage module and an image transmission module;
the VGA control module comprises a scanning time sequence generation module and an image description module;
the image transmission module: transmitting the input user-defined graph and the visual stimulation frequency to be adjusted to the VGA control module;
the frequency generation module: sampling a sinusoidal signal of the visual stimulation frequency, calculating sampled data, and loading amplitude values and gray values corresponding to different visual stimulation frequencies, which are calculated by the frequency generation module, into a storage module;
the scan timing generation module: generating a line synchronizing signal, a field synchronizing signal and a digital signal type of graphic stimulation signal;
the image description module: reading the amplitude and the gray value corresponding to the visual stimulation frequency from the frequency generation module, generating RGB signals and visual stimulation frequency control signals through the amplitude and the gray value, generating parameter information of the size, the shape and the quantity of the graph according to the received user-defined graph, and transmitting the parameter information to the interface control display module;
the interface control module: and displaying and flashing visual stimulation graphs through the graph stimulation signals, the RGB signals, the visual stimulation frequency control signals and the parameter information.
The working principle of the stimulation frequency generation module comprises:
the stimulation frequency generation module samples a sinusoidal signal of the visual stimulation frequency, and the sampling frequency is the refresh frequency of the display;
the stimulation frequency generation module calculates the sampled sinusoidal signals to obtain stimulation sequences corresponding to the corresponding frequencies and amplitudes of the sinusoidal signals;
the stimulation frequency generation module adjusts the gray value corresponding to each frame of the stimulation sequence according to a sine wave form;
and the stimulation frequency generation module outputs the data generated after the stimulation sequence is processed in a file form and loads the data into the storage module.
The working principle of the VGA control module comprises the following steps:
when each frame of a field synchronizing signal generated by the scanning time sequence generating module starts, the field synchronizing signal can generate a high pulse with a fixed width;
when each line of the line synchronizing signal generated by the scanning time sequence generating module starts, the line synchronizing signal can generate a high pulse with a fixed width;
the VGA time sequence of the scanning time sequence generation module sequentially carries out synchronous pulse, back porch pulse, display pulse and front porch pulse according to a reference driving clock, and scans the line synchronous signal in the effective pulse of the field synchronous signal;
the image description module generates parameter information of the size, shape and quantity of the graph according to the received custom graph and transmits the parameter information to the interface control display module;
the image description module reads corresponding amplitude and gray value from a stimulation sequence corresponding to the stimulation frequency of the stimulation frequency generation module according to the stimulation frequency, and generates RGB signals and stimulation frequency control signals through the amplitude and gray value;
and the VGA control module transmits the graphic stimulation signal, the RGB signal and the visual stimulation frequency control signal to the interface control module.
The interface control display module comprises VGA interface drive display equipment and a display;
the VGA interface drives display equipment to transmit the received graphic stimulation signal, the received RGB signal, the received stimulation frequency control signal and the received parameter information to a display;
and the displayer displays the received graphic stimulation signal, the RGB signal, the stimulation frequency control signal and the parameter information which are output by the VGA interface driving equipment, so as to stimulate the graphic.
The image transmission module comprises a PC end graphical user interface, a main control module, a static memory control module and a synchronous dynamic random storage module;
the PC end graphical user interface is used for inputting customized graphs and adjusting different stimulation frequencies;
the main control module receives a user-defined graph and stimulation frequency transmitted by a graphical user interface of a PC (personal computer) end through a serial port;
the static memory control module receives the user-defined graph and the stimulation frequency transmitted by the main control module through a bus;
and the synchronous dynamic random storage module receives the self-defined graph and the stimulation frequency for storage.
The synchronous dynamic random access memory module uses a mode register to provide control parameters, and initialization operation is carried out when the synchronous dynamic random access memory module is started up each time;
the control parameters are acquired according to digital signals provided by the address lines, so that the mode register is set;
after the initialization of the mode register is completed, the addressing of the logic bank is carried out, thereby determining the rows firstly and then determining the rows and the columns
And the read-write command of the mode register is controlled by the writable state of the synchronous dynamic random access memory module.
A stimulation method of an SSVEP visual stimulator, comprising:
inputting a user-defined graph and visual stimulation frequency to be adjusted;
sampling the sinusoidal signal of the visual stimulation frequency by taking the refresh frequency as the sampling frequency, calculating the sampled data, and storing the amplitude values and gray values corresponding to different visual stimulation frequencies obtained by calculation;
generating a line synchronizing signal, a field synchronizing signal and a digital signal type of graphic stimulation signal;
reading the amplitude and the gray value corresponding to the visual stimulation frequency through the received visual stimulation frequency, and generating an RGB signal and a visual stimulation frequency control signal through the amplitude and the gray value;
transmitting the graphic stimulation signal, the RGB signal and the visual stimulation frequency control signal;
generating parameter information of the size, shape and quantity of the graph according to the received custom graph and transmitting the parameter information;
and displaying and flashing visual stimulation graphs through the received graph stimulation signals, RGB signals, visual stimulation frequency control signals and parameter information.
Example 2
On the basis of the embodiment 1, an image transmission module, a stimulation frequency generation module and a VGA control module which are designed and realized on the FPGA are shown in fig. 2;
the visual stimulus frequency used in this example was 261 frequencies spaced 0.1Hz apart between 4Hz and 30 Hz. The VGA driver used in this example has a screen refresh rate of 60Hz and a resolution of 1024 x 768.
The working principle of the stimulation frequency generation module comprises:
the stimulation frequency generation module samples sinusoidal signals of visual stimulation frequency which is spaced between 4Hz and 30Hz by 0.1Hz in MATLAB, and the sampling frequency is 60 Hz;
the stimulation frequency generation module calculates a sampled sinusoidal signal to obtain a stimulation sequence corresponding to the sinusoidal signal with the corresponding frequency f and the amplitude A;
the stimulation frequency generation module adjusts the gray value corresponding to each frame of the stimulation sequence according to a sine wave form, wherein 0 is black, 255 is white, and 256 levels are provided, so that the brightness change of the gray value is sine wave change;
and the stimulation frequency generation module outputs the data generated after the stimulation sequence is processed in an MIF mode and loads the data into a ROM.
The reference clock frequency of the embodiment is 65MHz, the frequency is generated by PLL, an integrated IP core is available in FPGA, stable clock frequency can be generated, and the FPGA is connected to a VGA control module to provide the reference clock frequency for the module. In this embodiment, in order to generate contrast, two rectangular boxes are designed as custom graphics. The method is directly described according to the pixel coordinates of a graph, the graph is a rectangular block diagram, the specific pixels are 256 × 256, the color is white, and the visual stimulation frequency is 20 Hz.
The working principle of the VGA control module comprises the following steps:
when each frame of a field synchronizing signal generated by the scanning time sequence generating module starts, the field synchronizing signal can generate a high pulse with a fixed width;
when each line of the line synchronizing signal generated by the scanning time sequence generating module starts, the line synchronizing signal can generate a high pulse with a fixed width;
the VGA time sequence of the scanning time sequence generation module sequentially carries out synchronous pulse, back porch pulse, display pulse and front porch pulse according to a reference driving clock of 65MHz, and scans the line synchronous signal in the effective pulse of the field synchronous signal;
the image description module generates 2 pieces of parameter information with specific pixels of 256 × 256 according to the two received rectangular frames, and transmits the parameter information to the interface control display module;
the image description module reads the corresponding amplitude A from the 20Hz corresponding stimulation sequence of the stimulation frequency generation module according to 20Hz1And gray value, and through the amplitude value and gray value to generate RGB signal and stimulation frequency control signal;
and the VGA control module transmits the graphic stimulation signal, the RGB signal and the visual stimulation frequency control signal to the interface control module.
The interface control display module comprises VGA interface drive display equipment and a display;
the VGA interface drives display equipment to transmit the received graphic stimulation signal, the received RGB signal, the received stimulation frequency control signal and the received parameter information to a display;
and the displayer displays the received graphic stimulation signal, the RGB signal, the stimulation frequency control signal and the parameter information which are output by the VGA interface driving equipment, so as to stimulate the graphic.
The image transmission module comprises a PC end graphical user interface, a main control module, a static memory control module and a synchronous dynamic random storage module;
the PC side graphical user interface is used for inputting a rectangular frame and 20 Hz;
the STM32 receives a rectangular frame and 20Hz transmitted by a graphical user interface of a PC end through a serial port;
the FPGA receives the rectangular frame and 20Hz transmitted by the STM32 through a bus;
the SDRAM receives the rectangular frame and 20Hz for storage.
A mode register is used in the SDRAM to provide control parameters, and initialization operation is carried out when the SDRAM is started up every time;
the control parameters are acquired according to digital signals provided by the address lines, so that the mode register is set;
after the initialization of the mode register is completed, the addressing of the logic bank is carried out, thereby determining the rows firstly and then determining the rows and the columns
And the read-write command of the mode register is controlled by the writable state of the synchronous dynamic random access memory module.
A stimulation method of an SSVEP visual stimulator, comprising:
inputting a rectangular frame and 20 Hz;
sampling a sinusoidal signal of a visual stimulation frequency by taking a refresh frequency of 60Hz as a sampling frequency, calculating data obtained by sampling, and storing amplitude values and gray values corresponding to different visual stimulation frequencies obtained by calculation;
generating a line synchronizing signal, a field synchronizing signal and a digital signal type of graphic stimulation signal;
reading the amplitude value and the gray value corresponding to 20Hz through the received 20Hz, and generating an RGB signal and a visual stimulation frequency control signal through the amplitude value and the gray value;
transmitting the graphic stimulation signal, the RGB signal and the visual stimulation frequency control signal;
generating 2 pieces of parameter information with specific pixels of 256 x 256 according to the received custom graph and transmitting the parameter information;
and displaying and flashing visual stimulation graphs through the received graph stimulation signals, RGB signals, visual stimulation frequency control signals and parameter information.
As shown in fig. 3, the visual stimulation graph and the user-defined transmission picture are simultaneously displayed, when a start command is sent, the user enters a preparation state, visual stimulation is carried out after a delay of several seconds, and simultaneously a synchronous signal is sent to the electroencephalogram signal acquisition system to start acquiring electroencephalogram signals.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. An SSVEP visual stimulator is characterized by comprising a VGA control module, a stimulation frequency generation module, a storage module and an image transmission module;
the VGA control module comprises a scanning time sequence generation module and an image description module;
the image transmission module: transmitting the input user-defined graph and the visual stimulation frequency to be adjusted to the VGA control module;
the stimulation frequency generation module: sampling a sinusoidal signal of a visual stimulation frequency, calculating sampled data, and loading amplitude values and gray values corresponding to different visual stimulation frequencies calculated by the stimulation frequency generation module into a storage module;
the scan timing generation module: generating a line synchronizing signal, a field synchronizing signal and a digital signal type of graphic stimulation signal;
the image description module: reading the amplitude and the gray value corresponding to the visual stimulation frequency from the stimulation frequency generation module, generating RGB signals and visual stimulation frequency control signals through the amplitude and the gray value, generating parameter information of the size, the shape and the quantity of the graph according to the received user-defined graph, and transmitting the parameter information to the interface control display module;
the interface control module: and displaying and flashing visual stimulation graphs through the graph stimulation signals, the RGB signals, the visual stimulation frequency control signals and the parameter information.
2. The SSVEP visual stimulator of claim 1, wherein the stimulation frequency generation module operates on the principle of:
the stimulation frequency generation module samples a sinusoidal signal of the visual stimulation frequency, and the sampling frequency is the refresh frequency of the display;
the stimulation frequency generation module calculates the sampled sinusoidal signals to obtain stimulation sequences corresponding to the corresponding frequencies and amplitudes of the sinusoidal signals;
the stimulation frequency generation module adjusts the gray value corresponding to each frame of the stimulation sequence according to a sine wave form;
and the stimulation frequency generation module outputs the data generated after the stimulation sequence is processed in a file form and loads the data into the storage module.
3. The SSVEP visual stimulator of claim 1, wherein the VGA control module operates on the principle of:
when each frame of a field synchronizing signal generated by the scanning time sequence generating module starts, the field synchronizing signal can generate a high pulse with a fixed width;
when each line of the line synchronizing signal generated by the scanning time sequence generating module starts, the line synchronizing signal can generate a high pulse with a fixed width;
the VGA time sequence of the scanning time sequence generation module sequentially carries out synchronous pulse, back porch pulse, display pulse and front porch pulse according to a reference driving clock, and scans the line synchronous signal in the effective pulse of the field synchronous signal;
the image description module generates parameter information of the size, shape and quantity of the graph according to the received custom graph and transmits the parameter information to the interface control display module;
the image description module reads corresponding amplitude and gray value from a stimulation sequence corresponding to the stimulation frequency of the stimulation frequency generation module according to the stimulation frequency, and generates RGB signals and stimulation frequency control signals through the amplitude and gray value;
and the VGA control module transmits the graphic stimulation signal, the RGB signal and the visual stimulation frequency control signal to the interface control module.
4. The SSVEP visual stimulator of claim 1, wherein the interface control display module comprises a VGA interface driving display device and a display;
the VGA interface drives display equipment to transmit the received graphic stimulation signal, the received RGB signal, the received stimulation frequency control signal and the received parameter information to a display;
and the displayer displays the received graphic stimulation signal, the RGB signal, the stimulation frequency control signal and the parameter information which are output by the VGA interface driving equipment, so as to stimulate the graphic.
5. The SSVEP visual stimulator of claim 1, wherein the image transmission module comprises a PC-side graphical user interface, a main control module, a static memory control module and a synchronous dynamic random access memory module;
the PC end graphical user interface is used for inputting customized graphs and adjusting different stimulation frequencies;
the main control module receives a user-defined graph and stimulation frequency transmitted by a graphical user interface of a PC (personal computer) end through a serial port;
the static memory control module receives the user-defined graph and the stimulation frequency transmitted by the main control module through a bus;
and the synchronous dynamic random storage module receives the self-defined graph and the stimulation frequency for storage and transmission.
6. The SSVEP visual stimulator of claim 5, wherein the synchronous DRAM module uses a mode register to provide control parameters for initialization operations at each power-on;
the control parameters are acquired according to digital signals provided by the address lines, so that the mode register is set;
after the initialization of the mode register is completed, the addressing of the logic bank is carried out, thereby determining the rows firstly and then determining the rows and the columns
And the read-write command of the mode register is controlled by the writable state of the synchronous dynamic random access memory module.
7. A stimulation method of an SSVEP visual stimulator, comprising:
inputting a user-defined graph and visual stimulation frequency to be adjusted;
sampling the sinusoidal signal of the visual stimulation frequency by taking the refresh frequency as the sampling frequency, calculating the sampled data, and storing the amplitude values and gray values corresponding to different visual stimulation frequencies obtained by calculation;
generating a line synchronizing signal, a field synchronizing signal and a digital signal type of graphic stimulation signal;
reading the amplitude and the gray value corresponding to the visual stimulation frequency through the received visual stimulation frequency, and generating an RGB signal and a visual stimulation frequency control signal through the amplitude and the gray value;
transmitting the graphic stimulation signal, the RGB signal and the visual stimulation frequency control signal;
generating parameter information of the size, shape and quantity of the graph according to the received custom graph and transmitting the parameter information;
and displaying and flashing visual stimulation graphs through the received graph stimulation signals, RGB signals, visual stimulation frequency control signals and parameter information.
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