Chalmers and Extended Mind

There seems to be a possible disanalogy in Professor David Chalmers' paper("Extended Mind", Issues in the Philosophy of Mind, The 22nd World Congress of Philosophy, Seoul, 2008), a disanalogy between stories of Eileen and Otto. One may ask them by saying "are you sure that the museum is on the 52nd street?" Eileen may promptly respond to the question by answering "yes, I am sure of my belief because I checked it yesterday". But Otto may take a few seconds of time to ponder how to formulate his position in connection to the question. Being a considerate man and/or being handicapped of memory trouble, Otto would say "If my notebook is reliable I may be certain of my belief to that extent".

The disanalogy between the two appears to be this: Whereas Eileen herself is authoritative as to what she believes, Otto ascribes the authority of his belief to his notebook. Anybody can question Otto by asking how he can appeal to the authority of a written text?

One of the further implications of this disanalogy is that Eileen and the questioner may come to share some personal relationship whereas Otto and the questioner are limited to having an informational relationship.