I was re-reading Dennett and Cohen’s recent paper in Trends in Cognitive Science, “Consciousness Cannot be Separated from Function” and I am now puzzled by their view (before I go on, I would like to note that this issue of TICS also has Joe LeDoux’s paper where he mentions the Qualia Fest, and Lau & Rosenthal’s paper…all in all a great issue!).
Cohen and Dennett want to argue against phenomenological overflow, which is a debate I am currently in the middle of myself, by showing that it is essentially an unscientific view. To do this they introduce what they call the ‘perfect experiment’. They imagine that the area of the brain that is responsible for processing color is somehow allowed to function but is isolated in such a way that it cannot be accessed. The subject in this experiment is shown a blue cup, say, and will deny that they see the color even though the isolated brain area is doing what it normally does. They say,
In spite of this frank denial by subjects, theories that posit dissociation between consciousness and function would necessarily assume that participants of the ‘perfect experiment’ are conscious of the apple’s color but simply cannot access that experience. After all, the conditions these theories stipulate for phenomenal consciousness of color are all met, so this experiment does not disprove the existence of isolated consciousness; it merely provides another particularly crisp example of consciousness with- out access.
However, there is a crucial problem with this logic. If this ‘perfect experiment’ could not definitively disprove [overflow theories] theories, then what could? The subject man- ifests all the functional criteria for not being conscious of color so what would ground the claim that the subject nevertheless enjoys a special kind of consciousness: phenomenal consciousness without access consciousness
I think it is interesting to note that this kind of argument against overflow has been around for a long time. Here is a passage from Huxley’s On the Hypothesis that Animals are Automata, and Its History (from 1874),
If the spinal cord is divided in the middle of the back, for example, the skin of the feet may be cut, or pinched, or burned, or wetted with vitrol, without any sensation of touch, or of pain, arising in consciousness. So far as the man is concerned, therefore, the part of the central nervous system which lies beyond the injury is cut off from consciousness. It must be admitted, that, if any one think fit to maintain that the spinal cord below the injury is conscious, but that it is cut off from any means of making its consciousness known to the other consciousness in the brain, there is no means of driving him from his position by logic. But assuredly there is no way of proving it, and in the matter of consciousness, if anything, we may hold the rule, “De non apparentibus et de non existentibus eadem est ratio.”
The latin phrase there means something like “things that can’t be detected don’t exist.” As Huxley himself points out in the matter of consciousness, if anything, this seems correct. What sense can we make of a phenomenally conscious state that one is in no way aware of?
But it seems to me that these kinds of arguments need to deal with the mesh argument that Block defends. If the mesh argument works (I don’t think it does, at least not in favor of overflow), then we have an answer to the perfect experiment. We say that there is unaccessed consciousness in the isolated brain region because that is the (allegedly) the best over-all interpretation of the data coming in from neuroscience and psychology. Just to repeat, I DO NOT think that there is overflow but I do think that the above kinds of arguments need to deal with the mesh argument directly so I don’t find Cohen and Dnnett’s paper to advance the debate.