In response to a previous thread, Jonathan Livengood asked some very good questions about, roughly, what should count as information processing and computation in physical systems. Perhaps it will help to take a step back.
In my early work on computation, I argued that, roughly, only physical processes that take strings of digits as inputs and return strings of digits as outputs by following a rule defined over the inputs (and possibly internal states) count as computing systems . My reason had to do with the centrality of the formalisms of computability theory to the notion of computation. As to analog computers, which do not manipulate strings of digits but are still called computers, I argued that they are “computational” only by courtesy and for contingent historical reasons .
I later realized that, although there was something right about my early purism about computation, it was unhelpful to try to restrict the notion of computation to digital computation in the face of important yet broader uses of the term “computation” in many sciences, including neuroscience. (BTW, I had this realization in time to dodge Ken Aizawa’s criticism that I was insufficiently pluralistic; Ken’s criticism does apply to my former self, though.).
After that, I needed to characterize a notion of computation more general than that of digital computation (without appealing to representation, of course, otherwise I would have gone against one of my core views about computation ).
What came to my rescue is the notion of medium independence. Medium independence was introduced by Justin Garson in his 2003 MA thesis, part of which was published in a beautiful and underappreciated article in Philosophy of Science on “The Introduction of Information in Neurobiology “.
Justin pointed out that the first person to talk about neural systems transmitting information was Edgar Adrian (1928), on the grounds of his groundbreaking discovery of some crucial properties of neural signals (“all or none”, “rate coding”, and “adaptation”). Justin reconstructed Adrian’s notion of information as involving medium independence:
“Medium independence: The structure S–for example, the structure relation that obtains between the units of a sequence of action potentials–can be instantiated across a wide range of physical mechanisms.” (Garson 2003, p. 927)
While Justin’s medium independence is not necessary for carrying (natural) information in the usual sense, a slightly modified version of it seems well suited for characterizing the general notion of computation. So in my we’ve been discussing. If Jonathan insists in calling this type of thing information processing, so be it. But information processing can also be done in a medium independent way, and IMO that’s what most people mean when they talk about information processing. In any case, if you care about what does and does not compute it’s important to notice the difference between the two cases, because medium-dependent information processing does not entail computation whereas medium-independent information processing does entail computation.