It's nice to see an introvert/extrovert discussion on an AS site - since i'm one who doesn't think introverts & AS people are all that far apart on the spectrum. Sometimes they're one and the same.
The introvert/extrovert terms were coined by Carl Jung. He said you have four parts to your psyche -feeling/thinking/sensation/intuition - You can be an introvert in one & an extrovert in the other - I, for example, am 3 parts introvert, but (and it was a surprise to me to recognize it) an extrovert in intuition - that means my intuition is more interested in things like trees, fish, galaxies, and what is going on with them, than in things like religous experience (ie, in the world outside me - i'm even interested in people, but i still have to avoid them).
If you really want to dig into that, get Jung's book [Psychological Types] - it's just packed with ideas, examples, etc
AC