Novel AR Stereo Visual Stimulus Paradigm Incorporating Mixed Colors and Dynamic Targets for SSVEP-BCI

Steady-state visual evoked potentials (SSVEPs) are widely used in brain-computer interfaces (BCIs) because of their simplicity of application and high information transfer rate (ITR). However, SSVEP-BCI systems based on augmented reality still face the challenges of insufficient stability of the stimulus paradigm and poor quality of the acquired signals. To address these problems, We proposed a stereo visual stimulus paradigm incorporating mixed colors and dynamic targets suitable for SSVEP signal acquisition in AR environments. Mixed colors corresponding to four designed frequencies (i.e., 10 Hz, 11 Hz, 12 Hz, and 13 Hz) were introduced to enhance the stability of visual stimuli. Furthermore, dynamic targets were designed to further improve visual attention and to alleviate visual fatigue caused by low-frequency flickering. The proposed new stimulus paradigm was established by incorporating mixed colors and dynamic targets into the traditional stereo stimulus paradigm. To validate its stability and effectiveness, we set up two control groups employing a single color or stationary targets, and conducted comparative experiments with a variety of visualization tools and feature classification methods. By comparing the mean spectrograms and brain topographic maps of SSVEP signals induced by different stimulus paradigms, it was found that the proposed paradigm induced higher SSVEP harmonic amplitudes and stronger brain responses than the control groups. To further validate the effectiveness of mixed colors and dynamic targets, feature classification of EEG signals was performed using shallow ConvNet. The results showed that the highest average accuracy and maximum ITR of the proposed paradigm could reach up to 87.08% and 59.59 bits/min. It was 6.60% and 9.74 bits/min higher than the control group using a single color, as well as 4.46 % and 4.21 bits/min higher than the one using stationary targets. This paper proposed a novel AR-based stereo visual stimulus paradigm, which will be benefit for SSVEP-BCI application.