Eliciting dual-frequency SSVEP using a hybrid SSVEP-P۳۰۰ BCI

Background: Steady-state visual-evoked potential (SSVEP)-based brain–computer interfaces (BCIs) generate weak SSVEP with a monitor and cannot use harmonic frequencies, whereas P۳۰۰-based BCIs needmultiple stimulation sequences. These issues can decrease the information transfer rate (ITR).New method: In this paper, we introduce a novel hybrid SSVEP-P۳۰۰ speller that generates dual-frequencySSVEP, allowing itto overcome the abovementioned limitations and improve the performance. The hybridspeller consists ofninepanelsflickering atdifferentfrequencies. Eachpanel contains fourdifferent characters that appear in a random sequence. The flickering panel and the periodically updating character evokethe dual-frequency SSVEP, while the oddball stimulus of the target character evokes the P۳۰۰. A canonical correlation analysis (CCA) and a step-wise linear discriminant analysis (SWLDA) classified SSVEP andP۳۰۰, respectively. Ten subjects participated in offline and online experiments, in which accuracy andITR were compared with those of conventional SSVEP and P۳۰۰ spellers.Results: The offline analysis revealed not only the P۳۰۰ potential but also SSVEP with peaks at subharmonic frequencies, demonstrating that the proposed speller elicited dual-frequency SSVEP. Thisdual-frequency stimulation improved SSVEP recognition, increased the number of targets by employing harmonic frequencies, reduced the stimulation time for P۳۰۰, and consequently improved ITR ascompared to the conventional spellers.Comparison with existing methods: The new method reduces the stimulation time and allows harmonicfrequencies to be employed for different stimuli.Conclusions: The results indicate that this study provides a promising approach to make the BCI spellermore reliable and efficient.© ۲۰۱۵ The Authors. Publi