CN-121996069-A - Method, system and storage medium for improving stimulation stability of brain-computer interface local SSMVEP based on fixation area switching

CN121996069ACN 121996069 ACN121996069 ACN 121996069ACN-121996069-A

Abstract

The invention provides a method, a system and a storage medium for improving the stimulation stability of a brain-computer interface local SSMVEP based on fixation area switching, wherein the method comprises the steps of tracking eye movement information of a user in real time and judging a fixation screen area; when the gazing area is switched, a smooth switching control flow is executed, SSMVEP stimulation leaving the area and/or SSMVEP stimulation entering the area are faded in gradually, a switching protection window is started during execution of the smooth switching control flow, the synchronously acquired electroencephalogram data is processed by adopting a preset protective decoding strategy within the duration of the protection window, and finally, a control instruction for driving external equipment or switching interaction interface is generated based on the processed electroencephalogram signal decoding. The method and the device effectively solve the problems of local stimulus mutation and signal-to-noise ratio reduction of the induced signals caused by the movement of the fixation point, and remarkably improve the decoding stability and the user experience of the system.

Inventors

HE YONGZHENG
LI XIN
Shi Yunchuan
SONG AIXIA
WANG PENGGANG

Assignees

河南翔宇医疗设备股份有限公司

Dates

Publication Date: 20260508
Application Date: 20260119

Claims (10)

1. A method for improving the stability of stimulation of a brain-computer interface local SSMVEP based on gaze area switching, applied to a brain-computer interface system that is divided into at least two predefined areas on the same display interface and activates SSMVEP stimulation in a certain area only when it is detected that the user is gazing at that area, characterized in that it comprises the steps of: s1, tracking eye movement information of a user in real time, and acquiring a fixation point position; s2, determining a predefined screen area where the user looks at currently according to the fixation point position; s3, when judging that the gazing area of the user is switched, executing a smooth switching control flow to control SSMVEP stimulus fade-out of the leaving area and/or SSMVEP stimulus fade-in of the entering area, wherein the smooth switching control flow comprises gradual change control of stimulus amplitude; S4, starting a switching protection window during the execution of the smooth switching control flow, wherein the switching protection window lasts for a preset time length; S5, processing the synchronously acquired brain electrical data by adopting a preset protective decoding strategy within the duration time of the switching protection window; S6, decoding based on the electroencephalogram signals processed in the step S5, and generating a control instruction, wherein the control instruction is used for driving external equipment or controlling switching of an interactive interface.
2. The method for improving the stability of brain-computer interface local SSMVEP stimulation based on gaze area switching of claim 1, wherein in step S5, the protective decoding strategy is "ignore strategy", in which the electroencephalogram decoder pauses outputting new classification instructions based on electroencephalogram data during the switching protection window and maintains the state of the previous instruction or outputs a neutral state.
3. The method for improving the stimulation stability of a brain-computer interface local SSMVEP based on gaze area switching according to claim 1, wherein in step S5 the protective decoding strategy is a "weighted decay strategy", wherein in the switching protection window the brain electrolysis encoder assigns a time-varying weight w (t) to brain electrical data samples in the time period, wherein the weight at the start of the protection window is lower than the weight at the end of the protection window, and then uses the weighted data for classification.
4. The method for improving the stimulation stability of the brain-computer interface local SSMVEP based on gaze area switching according to claim 1, wherein in step S3, when it is determined that the user' S gaze area is switched, it means that the duration of the gaze point in the newly entered predefined screen area exceeds a first preset threshold, and the gaze point confidence level output by the eye tracking system exceeds a second preset threshold.
5. The method for improving the stimulation stability of the brain-computer interface local SSMVEP based on the gaze area switching according to claim 1, wherein in step S3, the "gradual control of the stimulation amplitude" refers to a process of changing the visual intensity parameter of the stimulation from an initial value to a target value over time, the changing process lasts for a preset gradual time t_ramp, where 50ms is less than or equal to t_ramp is less than or equal to 500ms, and the gradual control modulates the stimulation amplitude with at least one of a linear function, a cosine window function, or an exponential function.
6. The method for improving the stability of stimulation of a brain-computer interface local SSMVEP based on gaze area switching according to any one of claims 1-5, wherein in step S3, the smooth switching control flow further includes a phase continuity process of setting an initial phase Φnew for SSMVEP stimulation of the entry area, which is calculated by the following formula: where phi_prev is the reference phase, f is the target frequency of SSMVEP stimulation of the entry region, and Δt is the time interval from the failure of stimulation of the exit region to the beginning of fade-in of stimulation of the entry region.
7. The method for improving the local SSMVEP stimulation stability of a brain-computer interface based on gaze area switching according to any one of claims 1-5, wherein in step S3, the smooth switching control procedure uses a cross-fade approach to control the stimulus fade out of the exit area to overlap in time with the stimulus fade in of the entry area.
8. The method for improving the stability of stimulation of a brain-computer interface local SSMVEP based on gaze area switching according to any one of claims 1-5, characterized in that the motor imagery cues corresponding to the area are triggered synchronously during or after a predetermined amplitude of stimulation of SSMVEP of the entering area.
9. A system for improving stimulation stability of brain-computer interface sites SSMVEP based on gaze area switching, comprising: The eye movement tracking module is used for acquiring the fixation point position of the user in real time; The area judging module is used for judging a predefined screen area where the user looks at currently according to the fixation point position; The device comprises a display interface, a stimulus presentation and control module, a smooth switching control logic and a control module, wherein the stimulus presentation and control module is used for presenting SSMVEP stimulus on the display interface, and is configured to execute the smooth switching control logic to control SSMVEP stimulus leaving the region and/or SSMVEP stimulus entering the region when the output of the region judgment module indicates that the gazing region is switched; And the signal processing and decoding module is configured to start a switching protection window during the execution of the smooth switching control logic, process the synchronously acquired electroencephalogram data by adopting a preset protective decoding strategy within the duration of the switching protection window, and generate a control instruction based on a processing result.
10. The system for improving stimulation stability of brain-computer interface local SSMVEP based on gaze area switching of claim 9, wherein the stimulation presentation and control module is further configured to trigger a motor imagery prompt corresponding to the area synchronously during or after a predetermined magnitude of stimulation fade-in of SSMVEP into the area.

Description

Method, system and storage medium for improving stimulation stability of brain-computer interface local SSMVEP based on fixation area switching Technical Field The invention relates to the technical field of brain-computer interfaces, in particular to a method, a system and a storage medium for improving stimulation stability of a brain-computer interface local SSMVEP based on fixation area switching Background Steady State Visual Evoked Potential (SSVEP) and its motion variants (SSMVEP) are common paradigms in brain-computer interfaces that are of great interest due to their stable signals and high recognition accuracy. In applications such as rehabilitation training or assisted control, motor Imagery (MI) is often combined to enhance activation of the motor cortex, thereby developing a multi-modal fusion brain-machine interface. The system design thought for reducing visual disturbance and improving fusion effect is to adopt a 'fixation region switching' mode, namely dividing a plurality of predefined regions (such as left, middle and right) on the same display interface, and integrating SSMVEP stimulation and MI prompt into the interface. The system sets rules-only when it is detected by eye tracking that the user's gaze point falls steadily within a certain region, activates SSMVEP the stimulus within that region and synchronizes presentation of the corresponding MI cues within the interface while maintaining the stimulus silence or low-disturbance state in other non-gaze regions. The design concept can effectively reduce visual fatigue and cross-target interference caused by ineffective flicker. However, when the system adopts the "gazing area switching" mode, a new technical problem is introduced, which is not fully solved, because the movement of the gazing point of the user is dynamic and possibly unstable, and the local visual stimulus is frequently started and stopped along with the switching of the gazing area. The sudden opening or closing of the stimulus based on the fixation event not only causes visual discomfort, but also introduces significant transient artifacts in the electroencephalogram signal, destroying the steady state characteristics of the SSMVEP signal. Such corruption causes the spectrum of the induced signal to become impure, degrading the signal-to-noise ratio (SNR), ultimately severely affecting the accuracy of frequency identification-based decoding and the control stability of the overall system. In the prior art, although SSVEP research based on gaze triggering (size-contingent) is performed, most focus is on implementation of gaze triggering logic or application of the gaze triggering logic in control, and a systematic and targeted signal quality guarantee scheme is lacking for the problem of SSMVEP signal instability caused by a specific dynamic process of gaze switching. In particular, how to maintain the visual smoothness of local SSMVEP stimulation and the spectral continuity of evoked electroencephalogram signals in the dynamic process of gaze area switching through precise time sequence control, stimulation parameter modulation and signal processing strategies is a technical problem to be solved in the field. Therefore, a method for effectively improving the stability and the recognizability of local SSMVEP stimulation, which is specially used for 'gazing region switching' application scenes, is urgently needed. Disclosure of Invention The primary purpose of the invention is to overcome the problems of unstable evoked signals and reduced signal-to-noise ratio caused by sudden start and stop of local SSMVEP stimulus due to movement of a gaze point in a brain-computer interface system adopting a gaze area switching mode in the prior art. Specifically, the invention provides a method and a system, which are characterized in that a set of fine-controlled 'instant start-stop and smooth switching mechanism' and a matched 'switching protection window' mechanism are introduced in the start-stop process of stimulation, so that the fact that the local SSMVEP stimulation can still induce stable and high signal-to-noise ratio electroencephalogram signals under the dynamic fixation condition is ensured, thereby laying a foundation for generating accurate and stable control instructions (used for driving external equipment or switching an interactive interface) and improving the decoding robustness and practicability of the whole brain-computer interface system. The technical scheme of the invention is as follows: According to a first aspect of the present invention, a method for improving the stimulation stability of a brain-computer interface local SSMVEP based on gaze area switching is disclosed, which is applied to a brain-computer interface system, which is divided into at least two predefined areas on the same display interface, and activates SSMVEP stimulation in a certain area only when it is detected that the user is gazing at that area, the method comprising the steps of