Steady state visual evoked potentials by dual sine waves

The sum of sine waves was used to evoke Steady State Visual Evoked Potentials (SSVEP). The SSVEP responses were elicited by visual stimuli in the form of a flickering light emitting diode (LED). We recorded EEG responses to these stimuli and analyzed the observed spectral differences due to square waves, triangle waves and sine waves. We showed that the resolution of the dual stimuli, which is defined as the difference between two frequencies, is essential to SSVEP experiments. Reliable dual SSVEP spikes from EEG signals can only be acquired if the dual stimuli are at least 4Hz apart. We also tested tri-stimuli and showed that consistent EEG responses are not achievable, even though the stimuli were 4Hz apart. The essence of these experiments is to demonstrate the resolutions under which dual sine waves can generate consistent SSVEP responses.