For the philosophically inclined: http://consc.net/papers/extended.html (the famous "The Extended Mind" paper from Clark/Chalmers)
(And http://philpapers.org/browse/the-extended-mind for in-depth information)
(And http://philpapers.org/browse/the-extended-mind for in-depth information)
I recall reading about other mechanical devices like the steering wheel and computer mice being extensions of the human body. Does anyone know what it's called?