In this paper, the brain function in relation with human’s visual attention was investigated by means of coherence and bicoherence methods. Throughout experimentation with attentional visual stimulus ERP (Event Related Potential) data and synthesized simulated data with different combinations of parameters, it is demonstrated that bicoherence and coherence can be useful to reveal the phase synchronies between different frequency bands at fixed scalp location, and between different scalp locations at fixed frequency band, respectively. Both methods are also affected by time interval from the onset, and the level of white noise added. The phase coupled relationships among θ, δ, and α bands, and between frontal and central lobes were observed for attentional tasks, while those were little observable for inattentional tasks, which can show brain’s functional spatio-spectral differences associated with human’s attention.