Pasadena, March 18, 1996
 
Reply to Dancing Qualia in a Synthetic Brain,
in The Puzzle of Conscious Experience,
by D. J. Chalmers
Sci. Am. Dec. 1995 p.86
 
by Alex Backer
California Institute of Technology 139-74
Pasadena, CA 91125
 
David Chalmer's conclusion that systems with the same organization have the same 
conscious experience appears to be based upon the assumption that a person's 
behavior has a unique and unchangeable relationship with what the person 
consciously experiences. Evidence from neurological patients, however, suggests 
that dissociations exist between different brain processes that seemed a priori 
unseparable and that the actions of a primate are subject to manipulation (see 
Newsome et al., for example). For example, a hemiplegic patient can experience the 
desire to move his paralyzed leg, and yet he cannot move it. Thus, if we were to 
judge his conscious experience by his motor response alone, we would erroneously 
interpret he has the same conscious experience as a normal man who does not wish 
to move his leg. Also, if we electrically stimulate the neurons or muscle cells 
controlling tongue and mouth movements, we could presumably produce any verbal 
output, and yet not produce any sensation.
 
In the same way, if we replace a part of a human brain that is at least 
partly responsible for a conscious experience with an analogous part of a 
system with no (or different) conscious experience that provides the same 
output to other areas (as Chalmer's thought experiment suggests), the 
other parts of the brain (including the cells controlling speech) will have no 
way of knowing any difference, and yet the conscious experience will have 
vanished or changed. Even if we switch back and forth between the brain part 
and its analog, if its outputs are the same, the rest of the brain will have no 
way of knowing, even if the experiences do vary between the switches. Thus, 
the statement "You will hold that you are seeing red and have seen nothing 
but red -even though the two colors are dancing before your eyes. This 
conclusion is so unreasonable that it is best taken as a reduction ad 
absurdum..." does not appear justifiable.
 
The phrase "...a silicon-based system in which the chips are organized 
and function in the same way as the neurons in your brain" seems 
ambiguous, if not contradictory. The analogy must assume a difference at 
some level, or it would not employ silicon; if the silicon chips are assumed to 
have ALL properties equal to the (carbon-based) brain, the question asked is 
trivial, by definition. The same is true if the statement is meant as 
"in the same ways in all properties relevant to consciousness". Thus, 
some levels of similarity must be assumed, leaving room for differences. 
The crucial question, precisely, is where that line must be drawn: what 
is the essence or defining elements of consciousness (and what is not).
It appears arbitrary at this point to say that consciousness only 
depends on the properties above some level, e.g. the cellular level. We 
have no evidence that subcellular mechanisms are not relevant, or that 
the similarity could not be at a higher level and yet entail equal 
consciousness.