Negativity of ERP has been often related to up-state and (the concomitant) awareness (He & Raichle; Bachmann, 1994 book; VAN in Revonsuo et al., Uttal & Cook on sleep vs awake ERPs to auditory signals, etc). At the same time, from my years of long experience in the perception and NCC lab, I can tell that introspecting on what goes on after stimulus presentation and up to the report (this interval lasting from about 1 to about several seconds) does not cause the awareness of the stimulus to disappear abruptly, but continues for some time in a vague, "shadowy" form. Essentially, this is the basis for our reports in experiments. If negativity lasts after the first standard P1, N1, P300 components and coincides in time with this introspection, it could really be a correlate of conscious perceptual contents.
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can you' wil'l the stimulus shadow to disappear, and then see a change in the EEG ?
Hi Talis, I'm not sure I understand your comment completely. The duration of the ERP in the visible trials can be found in figure 4D, and lasted up to 250 ms (electrode Oz). This is a CSD though, so it might be slightly more focal than the raw ERP. However, a trial contained a stimulus sequence that repeated four times in order to maximize power in the fMRI design (see Supplementary Figure 1A for details of the stimulus sequence). Because the stimulus is repeated in the rest of the sequence, we only show the first 250 ms of the ERP. After 250 ms you would see a second ERP due to stimulus repetition. Interestingly, the gamma band activity only occurs after about 400 ms, and is largely unrelated to the ERP because it is an 'induced' response, meaning that the ERP portion of the signal was subtracted out before calculating changes in the power spectrum (see page 5, second paragraph of the manuscript). Does this answer you question?
Thanks, Johannes, for clarifying this. I overlooked some of the experimental details so perhaps at present my question cannot be answered in substance because it has no real empirical foundation for it in your experiment.
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