Impact of electrode positions and harmonic frequency components in SSVEP-based BCIs

Steady state visual evoked potential (SSVEP) based brain computer interfaces (BCIs) have been recognised as having major potential to be used practically in everyday daily life as they typically outperform more traditional BCIs in terms of detection accuracy and information transfer rates. It is also essential to improve the ease of use such as reducing the number of necessary electrodes without decreasing speed or accuracy. This study investigated the extent to which electrode positions, derivation methods, and harmonics will affect the performance of a SSVEP-based BCI. A pilot study was carried out on a 4-class SSVEP-based BCI with six healthy subjects. Detection accuracy increased from 63.75 ± 5.62% (mean ± SD) with monopolar derivation to 89.42 ± 5.58% with two-channel bipolar derivation using only harmonic H1. The significantly improved detection accuracy with two electrodes implies that it is possible to achieve high classification accuracy with a very low number of electrodes.