There's a theory that they see more of lay lines where 'energy' remains - i.e. what some folk describe as spirits or ghosts. The lay line also can explain why only one person in a room of three sees a ghost, it depends on the angle that you are at to the line.
How true all of this who knows, but then there may be energy forms out there that we do not know of. Scientists should remain open in their thinking......after all, folk in the 16thC knew about St Elmo's fire but couldn't explain it....