Thursday, June 26, 2008

The last enigma in mind-brain problem

The reader might accept all this but could well complain that I have talked all around the topic of consciousness, with more speculation than hard facts, and have avoided what, in the long run, is the most puzzling problem of all. I have said almost nothing about qualia--the redness of red--except to brush it to one side and hope for the best.

Francis Crick in The Astonishing Hypothesis

5-1 The last enigma in mind-brain problem

As I described in the prologue, the most profound enigma in considering the relation between the mind and the brain is that of qualia, the subjective sensory qualities. The redness of red, the "fluffy" feeling of the hairs of a kitten, the sensation you feel as you sit on a chair. The individual, very unique characters that accompany these sensations are so hard to understand, to be embed in the scientific world view. Compared to the problem of qualia, the rest are just details.
In the discussions from Chapters 1 to 4, I have avoided alluding to the problem of qualia directly. This might seem to be odd given the importance of qualia in the mind and brain problem and the refinement of our world view in general. There are two reasons for this particular treatment.
Firstly, there is no definite prescription for the solution of the enigma of qualia at present. If there is one nontrivial thing that we can be said about the neural origin of qualia, it is perhaps the principle of the "a priori correspondence of qualia", that we will describe later in 5-11. This is a kind of "meta-principle" which shows us how to investigate the neural basis of qualia, but still do not pin down the natures of specific qualia, such as the redness of red, or the hotness of the chili sauce.
Secondly, it was necessary for us to arm ourselves with some fundamental principles about the neural basis of conscious and unconscious perception in order to say something meaningful about qualia. We have been considering some aspects of the foundations of the neural basis of perception through chapters 1 to 4. These considerations were in a sense preparations to discuss the problem of qualia. Most importantly, now we have realized that the concept of response selectivity in analyzing neural activities and statistical approaches in general are inadequate for elucidating the neural basis of conscious perception. We have seen in chapter 2 that the de fact central dogma of response selectivity in neurophysiology today is based on a very fragile logical foundation indeed. In chapter 3, I argued that the statistical approach, which is based on the idea of an ensemble, should not be included in the foundation of the neural basis of perception. We therefore defined a percept (element of conscious perception) as an interaction-connected cluster of firing neurons. This definition of the percept is almost the only one which satisfies Mach's principle in perception. Then we went on to study the principle of interaction simultaneity, which is deeply related to the idea that our perception should be based on the interaction between neurons, and not on the statistical properties of an ensemble of neural firings.
Thus, by expelling the notion of response selectivity and other concepts based on statistics, we are at last ready to discuss the neural basis of qualia from the first principles. The essence of qualia can never be approached as long as we take the statistical picture. Under the statistical picture, there is no necessity to take a quale as an integral gradient of our perceptual processes (which it evidently is from our experience). Under the interaction picture, when we define the percept as interaction-connected cluster of neural firings, it becomes necessary to take qualia into the discussions of the very foundations of perception.
At the end of the day, the enigma of qualia is a very deep one. As Francis Crick remarked in his book "The Astonishing Hypothesis", the best attitude often seems to be "to brush it to one side and hope for the best". However, if we take the view that a scientific investigation of qualia is possible (which is indeed the view I take in this book) we need to analyze carefully what we can reasonably say about the neural basis of qualia at present, based on the empirical evidences, and following a strict logic.

Translated excerpt of Ken Mogi "Qualia and the Brain" (Nikkei Science, 1997). Translation of the original Japanese text by the author