(warning: neuroscience weeds)
Okay, switching back to the other major debate in neuroscience: whether conscious perception happens in the back or front of the brain. A new study presents evidence that seems to bolster the frontal view: Neural Correlates of the Conscious Perception of Visual Location Lie Outside Visual Cortex (warning: paywall):
When perception differs from the physical stimulus, as it does for visual illusions and binocular rivalry, the opportunity arises to localize where perception emerges in the visual processing hierarchy. Representations prior to that stage differ from the eventual conscious percept even though they provide input to it. Here, we investigate where and how a remarkable misperception of position emerges in the brain. This “double-drift” illusion causes a dramatic mismatch between retinal and perceived location, producing a perceived motion path that can differ from its physical path by 45° or more. The deviations in the perceived trajectory can accumulate over at least a second, whereas other motion-induced position shifts accumulate over 80–100 ms before saturating. Using fMRI and multivariate pattern analysis, we find that the illusory path does not share activity patterns with a matched physical path in any early visual areas. In contrast, a whole-brain searchlight analysis reveals a shared representation in anterior regions of the brain. These higher-order areas would have the longer time constants required to accumulate the small moment-to-moment position offsets that presumably originate in early visual cortical areas and then transform these sensory inputs into a final conscious percept. The dissociation between perception and the activity in early sensory cortex suggests that consciously perceived position does not emerge in what is traditionally regarded as the visual system but instead emerges at a higher level.
Subjects were shown a visual stimulus that led to a perceptual illusion. But the illusion correlated more with activity in the frontal lobes than in the visual cortex in the back of the brain. Activity in the visual cortex correlated with the actual visual stimuli rather than the illusion.
And, from the Discussion section of the paper:
Interestingly, the significant cross-classification clusters found in our searchlight analyses were primarily in anterior parts of the brain, such as the lateral prefrontal cortex (LPFC), dACC (the cingulo-opercular control network), and medial prefrontal cortex (MPFC), that are known to be involved in executive control [18, 19, 20, 21, 22] and working-memory-related processing [23, 24, 25, 26]
This seems pretty much in line with predictions from both global workspace (GWT) and higher order theories (HOT) of consciousness. And it seems like a strike against integrated information (IIT) and local first order theories. At least if the results hold up. I imagine the proponents of posterior consciousness theories will be combing through the methodology to see if there are any cracks.
This is actually a stronger result than I would have expected. I was open to the possibility that conscious visual perception happened in the posterior regions, but that the full package, including associated affects, adding the felt quality of the experience, didn’t get integrated until the information reached the frontal lobes. But it’s looking like the frontal lobes might have it all as far as conscious perception.
It’ll be interesting to see if the Templeton funded competition comes to the same conclusion, and if not, what differences in the data lead to the discrepancy. But right now PFC centered theories seem to have a head start.