IEEE Trans Neural Syst Rehabil Eng. 2013 Sep;21(5):697-703. doi: 10.1109/TNSRE.2013.2265308. Epub 2013 Jun 4.
This study aims to design a steady state visual evoked potentials (SSVEP) based brain-computer interface (BCI) system with only three electrodes. It is known that low frequency flickering induces more intensive SSVEP, but might cause users feel uncomfortable and easily tired. Therefore, this paper proposes a novel middle/high frequency flickering stimulus. However, users show different SSVEP responses when gazing at the same stimuli. It is improper to design fixed frequency flickering stimuli for all users. This study firstly proposes a strategy to adjust the stimuli frequency for each user that could cause better SSVEP. Moreover, to further enhance the SSVEP, this study incorporates flickering duty-cycle for stimuli design, which has been discussed less for SSVEP-based BCI systems. The proposed system consists of two modes, flicker frequency/duty-cycle selection mode and application mode. The flicker frequency/duty-cycle selection mode obtains two best frequencies between 24 and 36 Hz with their related optimal duty-cycle. Then the system goes into the application mode to control the devices. A new fact that has been found is that the optimal flicker frequency and duty-cycle do not vary with time. It means once the optical flicker frequency and duty-cycle is determined the first time, flicker frequency/duty-cycle selection mode does not need to operate the next time. Furthermore, the phase coding technology is used to extend the one command/one frequency to multi command/one frequency. Experimental results show the proposed system has good performance with average accuracy 95% and average command transfer interval 4.4925 s per command.
本研究旨在设计一种仅使用三个电极的稳态视觉诱发电位（SSVEP）脑-机接口（BCI）系统。已知低频闪烁会引起更强烈的 SSVEP，但可能会使用户感到不适和容易疲劳。因此，本文提出了一种新的中/高频闪烁刺激。然而，当用户注视相同的刺激时，会表现出不同的 SSVEP 响应。为所有用户设计固定频率的闪烁刺激是不合适的。本研究首先提出了一种为每个用户调整刺激频率的策略，该策略可以产生更好的 SSVEP。此外，为了进一步增强 SSVEP，本研究将闪烁占空比纳入刺激设计中，这在基于 SSVEP 的 BCI 系统中讨论较少。所提出的系统由两个模式组成，即闪烁频率/占空比选择模式和应用模式。闪烁频率/占空比选择模式在 24 到 36 Hz 之间获得两个最佳频率及其相关的最佳占空比。然后，系统进入应用模式以控制设备。一个新的事实是，最佳闪烁频率和占空比不会随时间变化。这意味着一旦第一次确定了光学闪烁频率和占空比，闪烁频率/占空比选择模式就不需要在下一次操作。此外，相位编码技术用于将一个命令/一个频率扩展到多个命令/一个频率。实验结果表明，所提出的系统具有良好的性能，平均准确率为 95%，平均命令传输间隔为每个命令 4.4925 秒。
