Optimizing Spatial Contrast of a New Checkerboard Stimulus for Eliciting Robust SSVEPs

Most existing steady-state visual evoked potential (SSVEP)-based brain-computer interfaces (BCIs) adopted low- or medium-frequency stimuli towards high information transfer rates (ITRs). However, the intense flashes will deteriorate the user experience. With the increase of stimulation frequency, the discomfort caused by flickering stimuli can be significantly reduced, but the amplitude of SSVEP is also decreased, which greatly increases the difficulty of SSVEP detection. To cope with the tradeoff between SSVEP intensity and user experience, this study proposed a new checkerboard stimulus scheme with spatially alternated flickering and background squares. This study compared black-white, black, and white-background checkerboard stimuli, together with a traditional single flickering stimulus in eliciting SSVEPs at different frequencies. The data analysis results showed that the signal-to-noise ratio (SNR) of SSVEP for the black-background checkerboard stimulus was comparable to the single flickering stimulus, both of which were significantly higher than the other two checkerboard stimuli in the high-frequency range (40 Hz and 60 Hz). Additionally, with a consensus of reduction in subjective visual irritation, the black-background checkerboard stimulus can lead to improved user experience of the SSVEP-based BCIs.