Focusing of attention on a repetitive visual stimulation (RVS) at a constant frequency, elicits the so called steady-state visual evoked potential (SSVEP). This effect can be advantageously utilized in brain-computer interfaces (BCIs). SSVEP based BCIs can offer higher bitrates and require shorter training time as compared to other BCI modalities. Detection of the SSVEP from the EEG can be facilitated through spatial filtering (linear combination of the signals recorded at several electrodes). Literature offers several options to perform this. In this paper we propose a taxonomy to categorize these methods and we extensively evaluate them using 22 stimulation frequencies. We suggest improvements to existing methods to increase the SSVEP detection performance. We also consider practical aspects in the discussion of results.
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