A brain-computer interface using binary phase-shift keying visual stimuli

Steady-state visual evoked potentials (SSVEPs) enable brain-computer interfaces to achieve efficient performance in command detection accuracy and information transfer rate (ITR). However, a limited bandwidth of SSVEPs causes a limited number of possible command in BCIs. Moreover since the amplitude of SSVEP at a particular frequency depends on users, some BCI commands could be executed easily (higher accuracy) and the others hardly (lower accuracy). To solve these problems, the present paper proposes a paradigm of BCI using phase-modulated visual stimuli. The commands of BCI are represented by a combination of binary codes. Two different phases of flickering stimuli correspond to binary codes. A command is determined by the sequence of binary codes which is demodulated from the phases of SSVEP. This protocol can be analogues of binary phase-shift keying (BPSK) in digital communications. Experimental results show that the proposed paradigm achieves even probabilities of command execution, although only a single electrode was used for SSVEP detection.