Psychophysical Parallelism: Structural Coherence
Chalmers offers a principle of psychophysical parallelism that he calls the principle of structural coherence. It involves awareness, in his technical nonexperiential sense. Awareness is normally thought of as more or less synonymous with experience. However, as we have seen, Chalmers thinks differently about consciousness, and this shows up in how he defines awareness as functionalist information processing. For Chalmers, to explain awareness is to explain one of the easy problems of consciousness—it is essentially a job for traditional information-processing cognitive science. The nonconscious zombies of World Two mentioned in section “David Chalmers on Consciousness” are aware of the world around them, as informationprocessing robots.
Structural coherence is easy to grasp with an example. Imagine looking at a Christmas tree. How does it get into your experience? Light is reflected from the tree and hits your retinas, then signals continue through the optic nerve to the lateral geniculate nucleus and go on to the primary visual cortex, then through the dorsal and ventral streams for higher-level information processing. In Chalmers’s view, at some point in the visual processing, your brain becomes aware (in his nonconscious sense) of the tree as an information structure. This structure then gives rise to a conscious experience through the principle of structural coherence. Again, it is unclear what “gives rise” means here; we cannot read it as simply “causes.” Chalmers believes that what goes for this sort of example applies to all conscious experiences. There is a psychophysical parallelism between the information structures in your brain and your experiences. The way that a system functions to process information must cohere with experience through isomorphic relations. The parallelism between information processing and experience has the consequence that the same information processing will be associated with the same experiences. So if a robot, a cyborg, a computer, or some other system X does the same information processing as you, then it will have type-identical experiences. The key to understanding consciousness is information processing, as conceived by Shannon and on through the history of artificial intelligence, and up to modern-day computational cognitive science:
I suggest that the primary psychophysical laws may centrally involve the concept of information. The abstract notion of information, as put forward in the 1940s by Claude E. Shannon of the Massachusetts Institute of Technology, is that of a set of separate states with a basic structure of similarities and differences between them. We can think of a 10-bit binary code as an information state, for example. Such information states can be embodied in the physical world. This happens whenever they correspond to physical states (voltages, say); the differences between them can be transmitted along some pathway, such as a telephone line. (Chalmers 1995b, p. 85)
The information-processing approach is on the right track with regard to cognition and consciousness. Conscious experience, Chalmers speculates, is information from the inside. On the one hand, we can think of information systems as being implemented in physical or abstract structures. On the other hand, we can think of information as being experienced. There are two aspects of information: structural and experiential.
On his dual-aspect theory of information, everything that processes information would have to be conscious. This suggests that calculators and even thermostats are conscious:
Where there is simple information processing, there is simple experience, and where there is complex information processing, there is complex experience. A mouse has a simpler information-processing structure than a human, and has correspondingly simpler experience; perhaps a thermostat, a maximally simple information-processing structure, might have maximally simple experience? (Chalmers 1995b, p. 86)
It is not easy to say what things would not be conscious according to Chalmers’s account, for you can interpret anything as processing information. Chalmers also makes wider connections with late metaphysical theorizing about the universe as operating according to laws of information processing:
The idea is at least compatible with several others, such as physicist John A. Wheeler’s suggestion that information is fundamental to the physics of the universe. The laws of physics might ultimately be cast in informational terms, in which case we would have a satisfying congruence between the constructs in both physical and psychophysical laws. It may even be that a theory of physics and a theory of consciousness could eventually be consolidated into a single grander theory of information. (Chalmers 1995b, p. 85)
There are those who claim that the universe as a whole can be seen under the aspect of information as well as under the aspect of matter, such as the physicist John A. Wheeler, whom Chalmers cites. Wheeler sees the universe as a dynamic information structure—the mother of all computers—that is moving from one state to the next.
Chalmers suggests a picture of an information-processing universe, where both consciousness and physics can be understood in terms of information. Chalmers’s account is a combination of property dualism, pancomputationalism, and panpsychism (the view that consciousness is everywhere in nature). In such a view, the brain is no more important than any other thing in the universe for understanding consciousness. It is a particularly complex information-processing machine, so it is special in this sense and, in Chalmers’s view, it is supposedly capable of sustaining a rich form of consciousness.