Modular Time-Frequency Joint Coding for a Virtual Keyboard Speller Using an SSVEP-Based Brain-Computer Interface

This paper presents the design of a modular time-frequency joint coding method for steady-state visual evoked potential, in which the stimulus consists of two stages: module flashing and individual flashing. In the first stage, targets are grouped into six-target modules. The modules flash at different frequencies and phases, whereas all targets within the module flash at the same frequency and phase. In the second stage, each target in the module flashes at different frequencies and phases. This coding method is compared with the control method in experiments. The results show that the proposed experimental paradigm performed better; the average accuracy and information transfer rate are higher than those of the control. Specifically, average accuracy is 89.6 ± 8.8%, which is 12.9% higher than that of the control experiment. These results prove the feasibility and superiority of the designed modular time-frequency joint coding method.