Hierarchical Codebook Visually Evoked Potentials for fast and flexible BCIs

Brain-Computer Interfaces provide a direct communication channel from the brain to a technical device. One major problem in state-of-the-art BCIs is their low communication speed. BCIs based on Codebook Visually Evoked Potentials (cVEP) outperform all other non-invasive approaches in terms of information transfer rate. Used only in spelling tasks so far, more flexibility with respect to stimulus structure and properties is needed. We propose using hierarchical codebook vectors together with varying color schemes to increase the stimulus flexibility. An off-line study showed that our novel hcVEP approach is capable of discriminating groups of targets after only 250ms of stimulus flickering and the final target within the group after 1s. The accuracies are 81% and 67%, respectively. Different color schemes (black/white and green/red) are equally effective.