Speaking helps thinking: Embodied or Extended Cognition?

A 12/28/09 Scientific American 60 Second Science story here.

The comment that interests me the most comes near the end (at about 1:00), when Hopkin notes that "how these sketches and monologues help remains a statement waiting for a proof".  What I take this to mean, however, is that we don't know how the sketches and monologues help improve performance.  That, however, suggests to me that even if we say, "Ah, this is extended cognition," we still do not know how the sketches and monologues help improve performance.