Thanks to Levi Bryant I've now been able to read Andy Clark's and David Chalmers's essay “The Extended Mind.” I must say the argument is remarkably akin to some implications of Derrida's essay “Plato's Pharmacy.”
Not that Derrida spells them out—he studiously avoids talking about what is, a sin of omission if you ask me. But he does argue that there's no sense in which some notional internal memory can be said to be better than external devices such as wax tablets and flash drives. Or more real, or more intrinsic to “what it means to be human,” and so on.
Clark and Chalmers seem to echo this when they argue that the idea that cognition happens “inside” the brain is only a prejudice.
The best parts of deconstruction, for me, are those parts that refute relationism. Yes that's right. For me, it's structuralism that is purely relationist. Deconstruction constantly points out that meaningfulness depends upon 1+n entities that are excluded from the system, yet included by being excluded, thus undermining the system's coherence. These entities can include wax tablets, ink and paper. Whether or not they are “signifiers” is precisely at issue.
Meaning arises from the meaningless, in other words. It's not relations all the way down.
There is no such thing as meaning in a void, which is why I prefer Derrida's re-mark to Spencer-Brown's roughly contemporaneous Mark. There must already be an inscribable surface on which the mark appears. This is the preferred sense in which I take the term arche-writing. Not “everything is signs all the way down”—but everything isn't.