Seeing Invisible Motion: A Human fMRI Study

SummaryA common view about visual consciousness is that it could arise when and where activity reaches some higher level of processing along the cortical hierarchy. Reports showing that activity in striate cortex can be dissociated from awareness 1 and 2, whereas the latter modulates activity in higher areas 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 and 16, point in this direction. In the specific case of visual motion, a central, “perceptual” role has been assigned to area V5: several human 5, 6, 7, 8, 9, 10 and 11 and monkey 12, 13, 14, 15 and 16 studies have shown V5 activity to correlate with the motion percept. Here we show that activity in this and other higher cortical areas can be also dissociated from perception and follow the physical stimulus instead. The motion information in a peripheral grating modulated fMRI responses, despite being invisible to human volunteers: under crowding conditions [17], areas V3A, V5, and parietal cortex still showed increased activity when the grating was moving compared to when it was flickering. We conclude that stimulus-specific activation of higher cortical areas does not necessarily result in awareness of the underlying stimulus.