Dataset: Influence of spatial frequency in visual stimuli for cVEP-based BCIs: evaluation of performance and user experience

Code-modulated visual evoked potentials (c-VEPs) are an innovative control signal utilized in brain-computer interfaces (BCIs) with promising performance. Prior studies on steady-state visual evoked potentials (SSVEPs) have indicated that the spatial frequency of checkerboard-like stimuli influences both performance and user experience. Spatial frequency refers to the dimensions of the individual squares comprising the visual stimulus, quantified in cycles (i.e., number of black-white squares pairs) per degree of visual angle. However, the specific effects of this parameter on c-VEP-based BCIs remained unexplored. In this dataset, a total of 16 healthy participants engaged in BCI spelling tasks using eight different conditions with varying spatial frequencies: C001 (0 c/°, 1×1 squares), C002 (0.15 c/°, 2×2 squares), C004 (0.3 c/°, 4×4 squares), C008 (0.6 c/°, 8×8 squares), C016 (1.2 c/°, 16×16 squares), C032 (2.4 c/°, 32×32 squares), C064 (4.79 c/°, 64×64 squares), and C128 (9.58 c/°, 128×128 squares). The system employed a binary m-sequence of 63 bits displayed at a 120 Hz rate using a black-background checkerboard (BB-CB) pattern; i.e. event “1” was encoded with a checkerboard pattern and “0” with a black flash. Each participant completed a single session that included a calibration phase consisting of 240 cycles (repetitions of the m-sequence), followed by an online spelling task of 18 trials (with 8 cycles per trial) for each condition. Online selections were made using a 3x3 command matrix (chance level of 11.11%).