It’s easy to be unaware of the fact that notions similar to, if not identical with, the concept of the “extended mind” were in circulation before, say, 1998. Yet there were writers advocating active (as opposed to philosophical) externalism before that date. I have noted before that Tuomela 1989 is one such source:
“The main arguments in [this] paper are directed against the latter thesis, according to which internal (or autonomous or narrow) psychological states as opposed to noninternal ones suffice for explanation in psychology. Especially, feedback-based actions are argued to require indispensable reference to noninternal explanantia, often to explanatory common causes.” — Methodological Solipsism and Explanation in Psychology, Raimo Tuomela, Philosophy of Science Vol. 56, No. 1 (Mar., 1989) , pp. 23-47.