I've set out to read Clark's Supersizing the Mind. Not that it pleases me, mind you, but it's hard to be credible if you write in the extended mind without having read Clark seriously. Sure, I read his infamous 1998 paper, but this paper is somewhat programmatic, filled with loose threads, and what positive thesis it defends—the Parity Principle—is more of an eye-opener, or an "intuition pump", than an actual draft towards a theory of the mind or the cognitive. (By the way, I've never understood why commentators make so much fuss about it... it feels like the old joke: C&C are pointing towards the sky, and people are looking at the finger.)
The first part of Supersizing the Mind is not a very exciting reading. The idea, it seems, is to lay out some background knowledge in order for it to be picked up in the discussions featured in the two following parts of the book (although, honestly, I'm in the process of reading them, so I can't say for sure). In fact, it feels like reading Aristotle for the first time: it seems purely encyclopedical, there doesn't seem to be any thread holding everything together in a narrative.
Take this, for instance: in the end of the first chapter, he talks about the Dynamic Systems Theory, first to mention how its holistic approach enables us to understand phenomena which would otherwise be incomprehensible, and then pointing out that, despite Van Gelder's optimism, it fails to be appropriate for many problems, such as those involving "independant variable causally interacting substates". There are parts in systems, and sometimes it's worth examining the parts to understand them. Thus, he proposes a hybrid approach, which, he claims, is already being used by cognitive scientists: he sees "computational, representational, information-theoretic and dynamic approaches as deeply complimentary".
This might tip you in a direction: sure, the traditional information-theoretic approach commits you to a parts-relation ontology, but it's insufficient to account for the mind or the cognitive system. You need the "flow" from the dynamic approach. But then, section 4.7: EC is about vehicules, not content. He even describes how the vehicule is a part of the content-generating system, thus excluding content-generating mecanisms which are not representation (in Clark's sense) vehicules from what could count as mind. It's hard not to make the link of this part-whole distinction with the part-whole distinction that was at play when he talked about the dynamic approaches. In fact, it's probably valid: you need a holistic, probably dynamic approach to make sense of content, and yet something which is hopefully localized and which holds information in a way that can be understood by information-theoretic approaches counts as the vehicule. But then, if EC is vehicular, why is the dynamic/holistic approach so important?
Well, Clark talks a lot about recruitment. The agent, he says, is constantly renegotiating his boundaries—and to illustrate this, he talks about how tools become integrated in our activities when they become "transparent", about how our brain begins to think of space as if they were part of our body, etc. That would be the cyborg argument, and the underlying intuition behind this conception of an agent would not be the conscious, theory-ladden ones we usually see in cognitive science, but rather the one that would be implicit in our problem-solving and in our actions—in our "body schema", he mentions, to use Gallagher's terminology. The dynamic/holistic approach is just a way to study this scientifically.
I think even Rupert, as careful as he is, fails to appreciate the cyborg argument. It's not cognitive systems made on the fly, it's an agent renegotiating itself. The tool has to become familiar before it becomes transparent. You have to work for this recharacterization, but it gets done.