This study focused on stimulus design for brain-computer interfaces (BCIs) using code-modulated visual evoked potentials (c-VEPs) to investigate how changing the direction of visual-stimuli luminance affects EEG response characteristics and classification performance. While c-VEP BCIs enable high recognition performance with short calibration times, increasing the stimulus sequence to increase the number of inputs can lead to prolonged calibration times. In this study, we designed two stimulus sequences that differed only in the direction of the luminance change, luminance-increasing and luminance-decreasing, based on the same m-sequence series, and verified their EEG response characteristics. We measured EEG responses across multiple stimulus frequencies and evaluated them using the amplitude of the stimulus-frequency component, extracted in synchronization with the stimulus presentation timing based on the luminance-change direction. The results revealed characteristic response differences dependent on the luminance-change direction under specific stimulus-frequency conditions, indicating that luminance-change direction may influence EEG response metrics. These findings provide new guidelines for c-VEP BCI stimulus design, offering insights that contribute to input nunber expansion without increasing calibration time.
Ogura et al. (Thu,) studied this question.