Spontaneous EEG Activity and Biases in Perception of Supra-Threshold Stimuli

Human perception of oriented visual stimuli is biased: some orientations are seen more often than others. We studied how the orientation bias is represented in the electrical brain activity that preceded presentation of ambiguous supra-threshold visual stimuli. We examined scalp EEG over the parieto-occipital regions during 1 sec before stimulus presentation. The alpha activity of pre-stimulus EEG was associated with the orientation bias: the preference for vertical orientation in most observers corresponded to low pre-stimulus alpha power. The results indicate that the orientation bias is encoded in intrinsic properties of ongoing cortical dynamics, forming spontaneous orientation-specific patterns of activity.status: publishe