An electrophysiological correlate of human visual awareness.

In order to shed more light on the neural correlates of human visual awareness, event-related potentials (ERPs) were recorded in a perceptual threshold experiment. The masked stimuli (line-drawings of coherent, familiar objects and scrambled, meaningless non-objects) were presented below, near, and above the subjective perceptual threshold. A prominent negative ERP deflection, peaking around 260-270 ms from stimulus onset, was observed only for the stimuli reaching subjective visual awareness. The results indicate a direct relationship between the crossing of the subjective threshold and this negative ERP deflection. A similar ERP response called 'visual awareness negativity' (VAN) has been observed in recent studies, using completely different stimulus manipulations (change blindness, reduced contrast stimuli). Hence, VAN appears to be a general electrophysiological correlate of visual awareness, observed in any experimental design that contrasts consciously perceived vs. unperceived visual stimuli.