Oh, and one more thing... I'm reminded of the study Adam Grant of the Wharton School has done in this area. See this link on his use of the term, "ambivert": http://www.forbes.com/sites/daviddisalvo/2013/04/10/move-over-extroverts-here-come-the-ambiverts/

Adam also wrote "GIve and Take: A Revolutionary Approach to Success."