Dependence of EEG response to flicker stimuli on stimulus parameters

Elucidating the spatiotemporal dynamics of the EEG is crucial for applying the EEG to clinical and welfare engineering fields (e.g., a brain-computer interface (BCI) for physically disabilities). The present study focused on the EEG synchronized with flicker stimuli (steady-state visually evoked potential, SSVEP) and investigated the dependence of spatiotemporal characteristics of the SSVEP on the stimulus conditions. The SSVEP was measured from 16 subjects under the conditions of the stimulus intensity I_s and stimulus frequency f_s in the ranges 5 les I_s les 300 (lx) and 7 les f_s les 16 (Hz), respectively. Spatial phase relationship of the SSVEP from the frontal to occipital lobes showed a property of standing wave under the most of the stimulus conditions. However, the spatial phase property tended to shift to a traveling wave-type under the condition of 70 < I_s < 110 (lx), indicating that the SSVEP elicited was spatially localized. This result suggests the parametric dependence of generators which are responsible for the SSVEP. Moreover, the spatial phase characteristics can be applied to discriminate between the SSVEP and various environmental noise/artifact in the BCI.