Bergmann, J. , McGruer, F. , Morgan, A. T. , Petro, L. S. & Muckli, L.
Institute of Neuroscience and Psychology, University of Glasgow, United Kingdom
The question of whether neural modulation in primary visual cortex (V1) is reflective of fluctuations in visual awareness has been under long-time debate. An elegant way to approach this question are illusions in which the conscious percept fluctuates, while the physical stimulation remains the same.
Motion-Induced Blindness (MIB) is one such illusion: here, a global motion field causes a salient target to fall in and out of conscious perception even though it remains physically present. It is unclear whether a target?s representation in V1 is modulated by conscious awareness during MIB, or remains unaffected by the conscious state.
Using 3T-fMRI and information mapping with healthy adults, we find that target orientation is differentiable in V1 when the target is visible and when it is when subjectively invisible.
This suggests that V1 processing does not reflect whether a stimulus is consciously perceived or not. However, it is also possible that there are differences that are overlooked with the standard fMRI methodology. More specifically, it is likely that conscious perception depends on the availability of predictive feedback. This feedback arrives in different layers than feedforward input from the retina. As a consequence, conscious awareness and unawareness could have distinct layer-wise information profiles.
To examine this question, we next used high-resolution layer-specific 7T-fMRI. As hypothesized, we find that target information during MIB is only present in V1 mid-layers, where feedforward projections from the retina arrive. In contrast, when the target is visible, information is also present in feedback layers.
Our results add a twist to the long-standing question of whether V1 is reflective of conscious awareness. The answer is - it depends on the layers. While V1 mid-layers seem to retain stimulus information irrespective of conscious state, the availability of information in feedback layers is linked to whether the stimulus is consciously perceived.