The steady-state visually evoked potential (SSVEP) is an important type of BCI that has various potential applications, including in virtual environments using virtual reality (VR). However, compared to VR research, the majority of visual stimuli used in the SSVEP-BCI are plane stimulation targets (PSTs), with only a few studies using stereo stimulation targets (SSTs). To explore the parameter optimization of the SSVEP-BCI virtual SSTs, this paper presents a parameter knowledge graph. First, an online VR stereoscopic stimulation SSVEP-BCI system is built, and a parameter dictionary for VR stereoscopic stimulation parameters (shape, color, and frequency) is established. The online experimental results of 10 subjects under different parameter combinations were collected, and a knowledge graph was constructed to optimize the SST parameters. The best classification performances of the shape, color, and frequency parameters were sphere (91.85%), blue (94.26%), and 13Hz (95.93%). With various combinations of virtual reality stereo stimulation parameters, the performance of the SSVEP-BCI varies. Using the knowledge graph of the stimulus parameters can help intuitively and effectively select appropriate SST parameters. The knowledge graph of the stereo target stimulation parameters presented in this work is expected to offer a way to convert the application of the SSVEP-BCI and VR.

This study objectively evaluated the effects of Virtual Reality Visual Cues (VRVCs) and Traditional Plane Visual Cues (TPVCs) on motor imagery (MI) subjects and Brain-Computer Interface (BCI) performance when building a classification model for MI-BCIs. Four metrics, namely, imagery stability, brain activation and connectivity, classification accuracy, and fatigue level, were used to evaluate the effects of TPVCs and VRVCs on subjects and MI-BCI performance. Nine male subjects performed four types of MI (left/right-hand grip strength) under VRVCs and TPVCs while EEG and fNIRS signals were acquired. FBCSP and HFD were used to extract features, and KNN was used to evaluate MI-BCI accuracy. Rt-DTW was used to evaluate MI stability. PSD topography and the brain functional network were used to assess brain activation and connectivity. Cognitive load and fNIRS mean features were used to evaluate fatigue. The mean classification accuracies of the four types of MI under TPVCs and VRVCs were 50.83% and 51.32%, respectively. However, MI was more stable under TPVCs. VRVCs enhanced the connectivity of the brain functional network during MI and increased the subjects’ fatigue level. This study’s head-mounted VRVCs increased the subjects’ cognitive load and fatigue level. By comparing the performance of an MI-BCI under VRVCs and TPVCs using multiple metrics, this study provides insights for the future integration of MI-BCIs with VR.