A mammal does a million things at once. She sniffs the air. She moves her head and eyes. (She has and maintains a head and eyes.) She absorbs photons of different wavelengths and registers them differently. She metabolizes glucose. She increases entropy. She gets curious about sounds. She forms beliefs and desires. She also computes.
Why seize on the last fact and say “aha, here is where all mental aspects lie!” Why that fact to the exclusion of all others? It just looks arbitrary.
It’s worth distinguishing between computationalism and functionalism. As David Lewis’s classic version of functionalism maintained, mental states are identified by their relations to each other and to observations by, and behaviors of, the organism in question. Or as Gualtiero Piccinini (PDF) puts the functionalist thesis, “the mind is (an aspect of) the functional organization of the organ of cognition.” Meanwhile, computing mechanisms “are those mechanisms whose teleological function is manipulating medium-independent vehicles in accordance with a rule.” On Piccinini’s definitions, computationalism is a specific version of functionalism – and Piccinini advocates non-computational functionalism.
As I noted in my post Only Two Cheers for Functionalism, functionalism makes good sense for cognition and (Searle to the contrary notwithstanding) for intentionality. But I don’t see computationalism as adequate even in those domains. And in my view not even functionalism looks promising for distinguishing various aspects of phenomenal consciousness.
Philosophers have a common definition of “computation” which Piccinini rightly criticizes in another article :
If there are two descriptions of a system, a physical description and a computational description, and if the computational description maps onto the physical description, then the system is a physical implementation of the computational description and the computational description is the system‘s software. The problem with this view is that it turns everything into a computer. (p. 14)
Let’s not accept panpsychism on the basis that everything is a computer and computation is mindfulness. Piccinini suggests a different definition of computation:
program execution is understood informally as a special kind of activity pertaining to special mechanisms (cf. Fodor 1968b, 1975; Pylyshyn 1984). Computers are among the few systems whose behavior we normally explain by invoking the programs they execute. (p. 19)
The definition of “function” is also potentially problematic for the functionalism / computationalism distinction. Piccinini has a plausible approach to defining functions (pp. 23ff) that I won’t recap here.
One more worry about computationalism. This thought is inspired by Scott Aaronson in conversation. Computation is normally understood as a causal process spread over time. But computer science is a branch of mathematics, and it’s easy to see that the same mathematical relationships could be realized over a spatially extended structure. Who needs time? Time is a prerequisite for causality, but who needs causality?
But then, who needs space, or matter, or energy? Arguably, mathematical structures like the proof of Fermat’s last theorem exist regardless of whether anyone discovers them or writes them down. (Are there numbers between 6 and 9? Then there are numbers.) If my conscious life is a complex computation, I as a physical being may be redundant – depending on one’s philosophy of mathematics.
No ghost, no machine, only human 