面向高频稳态非对称视觉诱发电位特征增强的相位调制研究

Research on phase modulation to enhance the feature of high-frequency steady-state asymmetric visual evoked potentials

高频稳态非对称视觉诱发电位(SSaVEP)为设计舒适、实用化的脑-机接口(BCI)系统提供了一种新的范式,但是高频信号幅值弱、噪声强,研究如何增强其信号特征具有重要意义。本研究采用30 Hz高频视觉刺激,将周围视野标准等分为八个环形扇区,基于视觉空间到初级视觉皮层(V1)的映射关系选择八种环形扇区对,并为每种环形扇区对设计三种相位(同相[0°,0°]、反相[0°,180°]、反相[180°,0°]),探究相位调制下SSaVEP的响应强度和信噪比两类特征。本文共招募八名健康受试者参与试验,结果表明,30 Hz高频刺激下,有三种环形扇区对在相位调制下SSaVEP特征的差异较大,且空间特征表现为下侧视野环形扇区对的两类特征值明显高于上侧视野环形扇区对。研究进一步采用滤波器组集成任务相关成分分析计算环形扇区对在三种相位调制下的分类精度,平均分类精度最高可达91.5%,证明了相位调制的SSaVEP特征可用于编码高频SSaVEP。综上,本研究结果为增强高频SSaVEP信号特征,拓展传统稳态视觉诱发电位范式指令集提供了新思路。

High-frequency steady-state asymmetric visual evoked potential(SSaVEP)provides a new paradigm for designing comfortable and practical brain-computer interface(BCI)systems.However,due to the weak amplitude and strong noise of high-frequency signals,it is of great significance to study how to enhance their signal features.In this study,a 30 Hz high-frequency visual stimulus was used,and the peripheral visual field was equally divided into eight annular sectors.Eight kinds of annular sector pairs were selected based on the mapping relationship of visual space onto the primary visual cortex(V1),and three phases(in-phase[0°,0°],anti-phase[0°,180°],and anti-phase[180°,0°])were designed for each annular sector pair to explore response intensity and signal-to-noise ratio under phase modulation.A total of 8 healthy subjects were recruited in the experiment.The results showed that three annular sector pairs exhibited significant differences in SSaVEP features under phase modulation at 30 Hz high-frequency stimulation.And the spatial feature analysis showed that the two types of features of the annular sector pair in the lower visual field were significantly higher than those in the upper visual field.This study further used the filter bank and ensemble task-related component analysis to calculate the classification accuracy of annular sector pairs under three-phase modulations,and the average accuracy was up to 91.5%,which proved that the phase-modulated SSaVEP features could be used to encode high-frequency SSaVEP.In summary,the results of this study provide new ideas for enhancing the features of high-frequency SSaVEP signals and expanding the instruction set of the traditional steady state visual evoked potential paradigm.