Departament de Psicobiologia, Facultat de Psicologia, Universitat de València, 46010 València, Spain.
Instituto de Automática e Informática Industrial, Universitat Politècnica de València, 46022 València, Spain.
Sensors (Basel). 2020 Dec 27;21(1):117. doi: 10.3390/s21010117.
Brain-computer interfaces (BCI) can extract information about the subject's intentions by registering and processing electroencephalographic (EEG) signals to generate actions on physical systems. Steady-state visual-evoked potentials (SSVEP) are produced when the subject stares at flashing visual stimuli. By means of spectral analysis and by measuring the signal-to-noise ratio (SNR) of its harmonic contents, the observed stimulus can be identified. Stimulus color matters, and some authors have proposed red because of its ability to capture attention, while others refuse it because it might induce epileptic seizures. Green has also been proposed and it is claimed that white may generate the best signals. Regarding frequency, middle frequencies are claimed to produce the best SNR, although high frequencies have not been thoroughly studied, and might be advantageous due to the lower spontaneous cerebral activity in this frequency band. Here, we show white, red, and green stimuli, at three frequencies: 5 (low), 12 (middle), and 30 (high) Hz to 42 subjects, and compare them in order to find which one can produce the best SNR. We aim to know if the response to white is as strong as the one to red, and also if the response to high frequency is as strong as the one triggered by lower frequencies. Attention has been measured with the Conner's Continuous Performance Task version 2 (CPT-II) task, in order to search for a potential relationship between attentional capacity and the SNR previously obtained. An analysis of variance (ANOVA) shows the best SNR with the middle frequency, followed by the low, and finally the high one. White gives as good an SNR as red at 12 Hz and so does green at 5 Hz, with no differences at 30 Hz. These results suggest that middle frequencies are preferable and that using the red color can be avoided. Correlation analysis also show a correlation between attention and the SNR at low frequency, so suggesting that for the low frequencies, more attentional capacity leads to better results.
脑-机接口（BCI）可以通过记录和处理脑电图（EEG）信号来提取关于主体意图的信息，从而在物理系统上生成动作。当主体注视闪烁的视觉刺激时，会产生稳态视觉诱发电位（SSVEP）。通过频谱分析和测量其谐波含量的信噪比（SNR），可以识别观察到的刺激。刺激颜色很重要，一些作者提出使用红色，因为它能够吸引注意力，而另一些作者则拒绝使用红色，因为它可能会引发癫痫发作。也有人提出使用绿色，并且声称白色可能会产生最佳信号。关于频率，中频被认为可以产生最佳 SNR，尽管高频尚未得到彻底研究，但由于该频段的自发脑活动较低，因此可能具有优势。在这里，我们向 42 名受试者展示了三种频率（低、中、高）的白色、红色和绿色刺激，并对它们进行了比较，以找出哪种刺激可以产生最佳 SNR。我们旨在了解白色刺激的反应是否与红色刺激一样强烈，以及高频刺激的反应是否与低频触发的反应一样强烈。我们使用康纳连续性能任务版本 2（CPT-II）任务来测量注意力，以寻找注意力能力与之前获得的 SNR 之间的潜在关系。方差分析（ANOVA）显示中频具有最佳 SNR，其次是低频，最后是高频。在 12 Hz 时，白色和红色的 SNR 一样好，在 5 Hz 时，绿色和红色的 SNR 一样好，而在 30 Hz 时则没有差异。这些结果表明中频更可取，并且可以避免使用红色。相关分析还显示了注意力与低频 SNR 之间的相关性，因此表明在低频时，更多的注意力能力会导致更好的结果。
