If are introverted and choose either, you will learn what extra-introverted means.
(You see, it is a certain science of being introverted until you get to know people, and are extroverted around those people. A good example of being extroverted around others is are your parents. You are trusting of them, and are able to talk to them without causing a windows 98 crash in your system. (I say this to be funny.))