The effect of high and low frequencies in c-VEP BCI

Broadband code modulated visual evoked potential (BBVEP, c-VEP) is the basis of one of the fastest braincomputer interface (BCI) paradigms. Unlike other systems, like those based on steady-state visual evoked potential (SSVEP, f-VEP), the stimulus specificity of c-VEP has not been thoroughly studied yet. One of the important stimulus characteristics that can influence both performance and user comfort is the frequency (the bit clock or frame rate). In this study, we evaluated the effect of stimuli presented at various frame rates (40, 60, 90 and 120 Hz) on c-VEP using LED lights. Accuracy and ITR were used to assess the performance and a questionnaire was used to evaluate the visual comfort. No significant differences in the performance of different frequencies were found, so comfort can be the main factor in the design decision. However, there is a trend for the frame rates of 40 and 90 Hz to yield a higher accuracy as compared to 60 and 120 Hz.