In the ongoing debate in neuroscience between those who see consciousness being in the back part of the brain, among the sensory processing regions, or in the front of the brain, in the cognitive action planning regions, there are issues confounding the evidence. Most experiments testing for conscious perception depend on self report from the test subjects, but this causes a problem since the frontal lobes are necessary for any method of self report (speech production, pressing a button, etc), so when those frontal lobes light up in brain scans in correlation with conscious perceptions, the possibility exists that they only light up due to the self report requirement.
So, an experimental protocol was developed: the no-report paradigm. One group of subjects are given a stimulus and asked to report if they consciously perceive it while their brains are being scanned. Another group are given the same stimulus that led the first group to report conscious awareness, but the second group is not required to self report, also while being scanned. The scans of the groups are compared to see if the frontal lobes still light up in the second group. Generally, although there is variation, the frontal lobes do still light up, implicating frontal regions in conscious perception.
However, Ned Block, a philosopher who thinks it likely that phenomenal consciousness “overflows” the self report from access consciousness, sees an issue that he describes in a paper in the journal, Trends in Cognitive Sciences. (Warning: paywall) Block points out that potential confounds remain, because we can’t rule out that the test subject isn’t thinking about reporting their perception, or cognitively processing the perception in some manner, causing the frontal lobes to light up for reasons other than the conscious perception itself.
Block points out that the real fundamental distinction here is between those who see cognition (in the frontal lobes) as necessary for consciousness versus those who see perceptual processing (in the back regions) as sufficient. Global workspace and higher order thought theories are cognitive accounts, while integrated information and local recurrent loop theories are more sensory oriented.
Block argues that the no-report paradigm needs to be replaced with a no-cognition paradigm, or to avoid begging the question against cognitive accounts, a “no-post-perceptual cognition” paradigm. But how can cognition be eliminated from subjects who have perceptions? Short of selectively anesthetizing the frontal lobes (which would be invasive, risky, and unlikely to get past IRBs), is this even possible?
Block focuses on a study of binocular rivalry, by Jan Brascamp and colleagues, as a possible solution. Binocular rivalry is the phenomenon that, when the eyes are shown very different images, conscious visual perception alternates between the two images, rather than blending them together. (Blending can happen, but only if the images are similar.) The goal of Brascamp’s study is to determine whether the selection between the rival images happens in the back or front of the brain.
To do this, the study constructs rival images of random dots such that, although they are different enough to lead to binocular rivalry (the dots in one image move left vs moving right in the other image), they are similar enough that the subject’s attention isn’t called to the switching between the images and so can’t report it.
For subjects who aren’t required to report what they’re seeing, brain scans show variations correlated with the image switching in the back of the brain, but not in the front. In other words, the study shows that the selection of which image to momentarily “win” in the binocular rivalry happens in the back of the brain.
Block sees the methodology here as an example of the “no-post-perceptual cognition” paradigm, and the specific results as indicating that the frontal lobes aren’t necessarily involved in conscious perception of the images. He focuses on the fact that subjects could, if queried, identify whether the dots were moving left or right, indicating that they were conscious of the specific image at the moment.
I think there are problems with this interpretation. By Block’s own description, the subjects didn’t notice and couldn’t self report the oscillations between the rival images, so we shouldn’t expect to see correlated changes in the frontal lobes for those changes. The subjects may have become conscious of some details in the images when asked to report, but when they weren’t asked to report, it seems more likely they were only conscious of an overall “gist” of what was there, a gist that worked for both images, and so didn’t need to oscillate with them.
The Brascamp et al. study is hard core functional neuroscience, aimed at narrowing the location of a specific function in the brain. They succeed at establishing that the selection happens in the back of the brain. But I don’t think a “frontalist” (as Block labels them) should be concerned about this. A pre-conscious selection happening in the back of the brain doesn’t really seem to challenge their view.
And Brascamp et al. actually seem to come to a different conclusion than Block. From the final paragraph in their discussion section:
A parsimonious conceptualization of these results frames awareness of sensory input as intimately related to the planning of motor actions, regardless of whether those actions are, in fact, executed. In this view a perceptual change of which the observer is aware might be one that alters candidate motor plans or sensorimotor contingencies. This view also marries the present evidence against a driving role of fronto-parietal regions in perceptual switches to the notion that these regions do play a central role in visual awareness when viewing a conflicting or ambiguous stimulus, a switch in perception may arise within the visual system, but noticing the change may rely on brain regions dedicated to behavioral responses.
So, while the study succeeded in its aims, I can’t see that that the results mean what Block takes them to mean, or that the methodology accomplishes the no-post-perceptual cognition paradigm he’s looking for. That doesn’t necessarily mean that sensory consciousness isn’t a back of the brain phenomenon. It just means getting evidence for it is very tricky.
This front vs back debate is a major issue in the neuroscience of consciousness. One I’m hoping that Templeton contest does succeed in shedding some light on. Myself, I suspect the frontalists are right, but wouldn’t be surprised if it’s a mix, with maybe sensory consciousness in the back, but emotional and introspective consciousness in the front, with our overall experience being a conjunction of all of them.
What do you think? Is consciousness a cognitive phenomenon? Or is perceptual awareness independent of cognition? Or in a system where the components evolved to work closely together, is this even a well posed question?