Steady-State Visual Evoked Potentials (SSVEP) are widely adopted in brain-computer interface (BCI) applications. To increase the number of selectable targets, joint frequency- and phase-coding is sometimes used but it has only been tested in offline settings. In this study, we report on an online, hierarchical SSVEP spelling application that relies on joint frequency-phase coded targets, and, in addition, propose a new decoding scheme based on spatiotemporal beamforming combined with time-domain EEG analysis. Experiments on 17 healthy subjects confirm that with our new decoding scheme, accurate spelling can be performed in an online setting, even when using short stimulation lengths (1 sec) and closely separated stimulation frequencies (1 Hz).
['Benjamin Wittevrongel', 'Marc M. Van Hulle']
Hierarchical online SSVEP spelling achieved with spatiotemporal beamforming