Sceptic
From Tardis Wiki, the free Doctor Who reference
A sceptic was an individual who did not believe something. In paranormal terminology, a sceptic was an individual who did not believe in the existence of ghosts.
Preston Gilchrist was a self-proclaimed sceptic, and embarrased Dennis Bridger during a live broadcast of Scared Stiff by exposing the techniques used in his medium routine. (PROSE: Scared Stiff)