Figure 1a from a new paper in Nature Neuroscience, Heirarchy of cortical responses underlying binocular rivalry, from Heeger and others. They performed an interesting fMRI study of binocular rivalry (when a different visual stimulus is presented to each eye, you don’t see a fusion of the two stimuli, but a kind of waffling between the two stimuli: it is a useful experimental dissociation of stimulus and percept).
When the percept switches between stimuli, it is not an instantaneous switch, but the new percept gradually appears like a travelling wave in your visual field. It has been found that travelling waves occur in V1 during such shifts with similar temporal dynamics to the shift in the percept. Interesting, and suggests that rivalry may just reflect what is happening in V1 rather than anything specific to consciousness (that is, if we assume V1 is not part of the sufficient NCC).
In the present experiment subjects performed a difficult task in the center of the visual field while rivalrous stimuli were presented to the two eyes. Subjects were unaware of any perceptual shifts in the periphery, while the fMRI showed that V1 still displayed the same travelling waves. At the same time, the usual mirroring of this wave in higher visual areas (V2 etc) was absent!
These results suggest that the contents of consciousness are not driven bottom-up solely by what is happening in V1, but that attention acts as a gate between what is happening in V1 and what is sent up to higher visual areas for conscious processing.