Now consider Otto. Otto suffers from Alzheimer's disease, and like many Alzheimer's patients, he relies on information in the environment to help structure his life. Otto carries a notebook around with him everywhere he goes. When he learns new information, he writes it down. When he needs some old information, he looks it up. For Otto, his notebook plays the role usually played by a biological memory. Today, Otto hears about the exhibition at the Museum of Modern Art, and decides to go see it. He consults the notebook, which says that the museum is on 53rd Street, so he walks to 53rd Street and goes into the museum. 
It's far from clear whether Alzheimer's patients, who have trouble tying their shoe laces and finding their way home in neighborhoods they have lived all their lives, could perform such complicated actions as recording relevant notes and retrieving them at relevant times—or so it would seem to me. Perhaps something like this is possible during early stages of the disease, but I don't know. In any case, the whole thing reads too much like the thought experiments some philosophers are overly fon of. I would be more interested in empirical research concerning this.
Now there is a book by Andy Clark, Supersizing the Mind: Embodiment, Action and Cognitive Extension. It is reviewed by Jerry Fodor in the London Review of Books. At one point he finds some of the examples "pretty impressionistic," but then notes that unless [he has] missed it, there isn’t an exposition of EMT [Extended Mind Thesis] that is markedly less metaphorical in the book". Too bad ... if true.
1. Another thing that bothers me in the article is that there is no reference to the work of Donald and others, who proposed this view long before they did.