Occipital EEG correlates of conscious awareness when subjective target shine-through and effective visual masking are compared: bifocal early increase in gamma power and speed-up of P1.

Neural correlates of conscious awareness can be comfortably studied when awareness of the target stimuli is a varying dependent variable in the experimental conditions where the key independent variables are kept invariant. We presented vernier targets backward masked by an invariant grating with invariant SOA. EEG data recorded from occipital and parietal electrodes was analyzed for ERPs and time-frequency functions of oscillatory responses. Comparison of data from correct aware trials with data from correct unaware trials showed that conscious awareness of targets was associated with decrease in the latency of ERP/P1, increase in the amplitude of P300, and increase in the power of 70-Hz and 30-Hz gamma band oscillations from 50 ms before target onset up to 100 ms after target onset. Results are interpreted in the context of the well-known views about the role of brain-activity oscillations in conscious awareness and as related to the perceptual retouch theory.