Use of Phase in Brain–Computer Interfaces based on Steady-State Visual Evoked Potentials

Brain–computer interfaces based on steady-state visual evoked potentials (SSVEP-BCIs) extract the amplitude of these potentials for classification. The use of the phase has not yet been widely used in on-line classification, since it requires a very accurate real time system that keeps synchronized the stimulation, recording and processing. In this paper, it has been presented an experiment, based on the AM modulation of flickering stimuli, that demonstrates that first, the phase shifts of different stimuli can be recovered from that of the corresponding SSVEPs without the need of a real time system; second, this information can be used efficiently to develop a BCI based on the classification of the phase shifts of the SSVEPs. Since the phase is statistically independent of the amplitude, the joint use in classification of both would improve the performance of this type of BCI.