A calibration-free c-VEP based BCI employing narrow-band random sequences.

OBJECTIVE: 
Code-modulated visual evoked potential (c-VEP) based brain-computer interfaces (BCIs) exhibit high encodingefficiency. Nevertheless, the majority of c-VEP based BCIs necessitate an initial training or calibration session, particularlywhen the number of targets expands, which impedes the practicality. To address this predicament, this study introduces a calibration-free c-VEP based BCI employing narrow-band random sequences.

APPROACH: For the encoding method, a series of random sequences were generated within a specific frequency band. The c-VEP signals were subsequently elicited through the application of on-type grid flashes that were modulated by these sequences. For the calibration-free decoding algorithm, filter-bank canonical correlation analysis (FBCCA) was utilized with the reference templates generated from the original sequences. Thirty-five subjects participated into an online BCI experiment. The performances of c-VEP based BCIs utilizing narrow-band random sequences with frequency bands of 15~25 Hz (NBRS-15) and 8~16 Hz (NBRS-8) were compared with that of a steady-state visual evoked potential (SSVEP) based BCI within a frequency range of 8~15.8 Hz.
Main results.
The offline analysis results demonstrated a substantial correlation between the c-VEPs and the original narrow-band random sequences. After parameter optimization, the calibration-free system employing the NBRS 15 frequency band achieved an-average information transfer rate (ITR) of 78.56 ± 37.03 bits/min, which exhibited no significant difference compared to the performance of the SSVEP based system when utilizing FBCCA. The proposed system achieved an average ITR of 104.2 ± 67.18 bits/min in a simulation of a 1000-target BCI system.

SIGNIFICANCE: This study introduces a novel calibration-free c-VEP based BCI system employing narrow-band random sequences and shows great potential of the proposed system in achieving a large number of targets and high ITR.&#xD.