Observing the steady-state visual evoked potentials with a compact quad-channel spin exchange relaxation-free magnetometer

Du Peng-Cheng^{1, 3}, Li Jian-Jun^{1, 3}, Yang Si-Jia^{2, 4, 6}, Wang Xu-Tong¹, Zhuo Yan^{2, 4, 6}, Wang Fan^{2, 4, 5, 6, ‡}, Wang Ru-Quan^{1, 3, §}

SSVEP stimulus: black and white squares appearing on the screen interchangeably, flickering at a fixed frequency. The OPM is attached to the scalp area over the occipital cortex (red area).