In his tract called The Secret Commonwealth of Elves, Fauns and Fairies written in 1691, Robert Kirk speaks of those who have the Second Sight which enables them to see the folk who live underground. He says that he has been told by some of these with the Second Sight that "they have seen a Doubleman, or the shape of some man in two places, perfectly resembling one another in all points". He also says that in spite of the two apparently being identical those with the Second Sight can easily tell which is the 'above ground' man and which is the 'subterranean man'. He affirms that "They call this reflex-man a 'Co-Walker', every way like the man as a twin brother and companion, haunting him as his shadow ...."
"This copy, echo, or living picture goes at last to his own herd. It accompanies the person so long and frequently for ends best known to itself, whether to guard him from the secret assaults of some of its own folks, or only as a sportful ape to counterfeit all his actions."
The doppleganger or other self is well known as a psychic phenomenon, but is interestingly here seen as a consequence of 'haunting' by the faerie folk.