Time-frequency joint coding method for boosting information transfer rate in an SSVEP based BCI system

Area of Science:

• Neuroscience
• Biomedical Engineering
• Signal Processing

Background:

• Steady-State Visual Evoked Potential (SSVEP) Brain-Computer Interface (BCI) systems offer ease of use and high Information Transfer Rate (ITR).
• Traditional SSVEP BCIs utilize Frequency Division Multiple Access (FDMA), while Time Division Multiple Access (TDMA) has been explored for performance enhancement.
• There is a need for advanced coding methods to further improve SSVEP BCI efficiency.

Purpose of the Study:

• To design and evaluate a novel time-frequency joint coding method for SSVEP-based BCIs.
• To compare the performance of TDMA in Different Frequency (DF) and Same Frequency (SF) modes against traditional FDMA.
• To assess the system's accuracy, ITR, and typing speed in both offline and online experiments.

Main Methods:

• A new time-frequency joint coding strategy was developed, integrating information from both temporal and frequency domains.
• Offline experiments compared TDMA-DF and TDMA-SF modes with FDMA.
• Online experiments evaluated the proposed method's effectiveness in a word-copy spelling task.

Main Results:

• The TDMA-DF mode demonstrated superior performance compared to TDMA-SF and FDMA in offline tests.
• Online experiments achieved high accuracy (83.3%-92.0%) and ITR (130.3-136.6 bits/min) across different trial times (1.25s and 1.5s).
• The system supported average typing speeds of 14.9 cpm (1.25s trial time) and 14.8 cpm (1.5s trial time).

Conclusions:

• The proposed time-frequency joint coding method is feasible and offers significant advantages for SSVEP-based BCIs.
• The TDMA-DF mode represents a promising advancement for enhancing BCI communication efficiency.
• This approach holds potential for improving user experience and practical applications of BCIs.