Responsive EEG-based communication systems have been implemented with brain-computer interfaces (BCIs) based on code-modulated visual evoked potentials (c-VEPs). The BCI targets are typically encoded with binary m-sequences because of their autocorrelation property; the digits one and zero correspond to different target colours (usually black and white), which are updated every frame according to the code. While binary flickering patterns enable high communication speeds, they are perceived as annoying by many users. Quintary (base 5) m-sequences, where the five digits correspond to different shades of grey, may yield a more subtle visual stimulation. This study explores two approaches to reduce the flickering sensation: (1) adjusting the flickering speed via refresh rates and (2) applying quintary codes. In this respect, six flickering modalities are tested using an eight-target spelling application: binary patterns and quintary patterns generated with 60, 120, and 240 Hz refresh rates. This study was conducted with 18 nondisabled participants. For all six flickering modalities, a copy-spelling task was conducted. According to questionnaire results, most users favoured the proposed quintary over the binary pattern while achieving similar performance to it (no statistical differences between the patterns were found). Mean accuracies across participants were above 95%, and information transfer rates were above 55 bits/min for all patterns and flickering speeds.

中文翻译：

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灰色的五种阴影：探索五次m序列以获得更多基于c-VEP的用户友好型BCI

基于脑电接口（BCI）的基于脑电接口的响应式通信系统已基于代码调制的视觉诱发电位（c-VEP）。由于BCI目标具有自相关特性，因此通常使用二进制m序列进行编码。数字1和0对应于不同的目标颜色（通常是黑色和白色），它们根据代码在每一帧进行更新。尽管二进制闪烁模式可实现较高的通信速度，但许多用户认为它们很烦人。五进制（以5为基数）m-五个数字分别对应于不同灰度阴影的序列可能会产生更细微的视觉刺激。这项研究探索了两种减少闪烁感的方法：（1）通过刷新率调整闪烁速度；（2）应用五进制编码。在这方面，使用八目标拼写应用程序测试了六个闪烁模式：以60、120和240 Hz刷新率生成的二进制模式和五进制模式。这项研究是在18位非残障人士中进行的。对于所有六个闪烁方式，都执行了复制拼写任务。根据调查表的结果，大多数用户在与二进制模式相比时都更喜欢拟议的五进制，同时实现了与之类似的性能（未发现模式之间的统计差异）。参与者的平均准确度超过95％，