What are you: an introvert or an extrovert? Russell Kane is a comedian, so he has always assumed he's a textbook loud-mouthed extrovert. But now he's not so sure.

Across this series of interviews, Russell explores exactly what we mean by the terms "introvert" and "extrovert". He questions whether it is useful to define people in this way and whether we have a cultural bias towards one personality type over the other.

In this first of three parts, Russell asks psychotherapist and author Mark Vernon about the origins of the terms "introvert" and "extrovert" as coined by psychoanalyst Carl Jung in 1921. How have Jung's definitions been interpreted over the last 100 years? And can his theories help us better understand ourselves?

Producer: Becky Ripley