不同刺激光源面积对SSVEP共振频率的影响研究

稳态视觉诱发电位(steady-state visual evoked potentials,SSVEP)的共振频率为诱发最大SSVEP响应对应的刺激频率,对其研究在临床神经科学和脑机接口技术领域均具有很好的应用前景。刺激光源面积是影响SSVEP共振频率的一个要素,但目前对共振频率随光源面积变化规律知之甚少。本文首先进行的理论研究结果表明周期性视觉刺激光源面积变化和SSVEP性能变化密切相关;然后侧重实验研究不同LED光源刺激面积变化对SSVEP共振频率的影响规律:首先采集不同光源面积刺激下的SSVEP信号,对其依次进行50 Hz陷波、带通滤波(带宽为3~35 Hz)去噪、去趋势与眼电等预处理;然后基于快速傅里叶变换进行频谱分析,计算不同刺激频率下的SSVEP平均归一化基波功率,以确定SSVEP的共振频率。结果表明:当光源半径和刺激频率分别在5~9 mm和6~20 Hz取值时,SSVEP共振频率随光源面积变化的规律是:当光源面积小于某阈值时,共振频率与光源面积正相关;而超出这个阈值时,共振频率与光源面积负相关。此外本文用闪光LED作为刺激源,可有效解决以屏幕闪光为刺激源时存在的频率选择受限于屏幕刷新率的问题。本文研究结果可为神经系统疾病的预测或诊断和SSVEP在脑机接口领域的有效应用提供有意义的理论和实验依据。

Study on the effect of different stimulating light source area on SSVEP resonance frequency

Abstract: The resonance frequency of steady-state visual evoked potential was the stimulation frequency corresponding to the maximum visual steady-state response, and the research of SSVEP had a good application prospect in clinical neuroscience and brain computer interface technology. The area of stimulus light source was a factor affecting SSVEP resonance frequency, but little was known about the variation of resonance frequency with the area of light source. In this article, the theoretical research results showed that the change of the area of periodic visual stimulation light source was closely related to the change of SSVEP, and the influence of the stimulation area of different LED sources on SSVEP resonance frequency was studied experimentally. First, SSVEP signals under the stimulus of different light sources were collected and preprocessed by 50 Hz notch, band-pass filter (bandwidth 3-35 Hz) de-noising, de-trending and de-eye-electricity. Then, the average normalized fundamental power of SSVEP under different stimulation frequencies was calculated based on the spectrum analysis of FFT to determine the SSVEP resonance frequency. The results showed that when the light source radius was 5-9 mm and the stimulation frequency was 6-20 Hz, the law of SSVEP resonance frequency changing with the light source area was that when the light source area was less than a certain threshold, the resonance frequency was positively correlated with the light source area. when the threshold was exceeded, the resonance frequency was negatively correlated with the light source area. In addition, this article used flash LED as stimulation source, which could effectively solve the problem that the frequency selection was limited by the screen refresh rate when screen flash was used as stimulation source. The results of this study can provide significant theoretical and experimental basis for the prediction or diagnosis of nervous system diseases and the application of SSVEP in BCI.